Vietnam Oil and Gas Journal Vol 10/2019 with the situation of Vietnam Oil and Gas industry, domestic and international cooperation of the petroleum industry in June 2019. With posts: CO2 removal optimisation for the BR-E membrane system by data analysis and modeling; orientations for efficient treatment and processing of high CO2 content natural gas resources in Vietnam; study on preparation of advanced Ni-Ga based catalysts for converting CO2 to methanol.
Petro ietnam An Official Publication of the Vietnam National Oil and Gas Group Vol 10 - 2019 ISSN-0866-854X PETROVIETNAM JOURNAL IS PUBLISHED MONTHLY BY VIETNAM NATIONAL OIL AND GAS GROUP Petro ietnam An Official Publication of the Vietnam National Oil and Gas Group Vol 10 - 2019 ISSN-0866-854X EDITOR-IN-CHIEF Dr Nguyen Quoc Thap DEPUTY EDITOR-IN-CHIEF Dr Le Manh Hung Dr Phan Ngoc Trung EDITORIAL BOARD MEMBERS Dr Trinh Xuan Cuong Dr Nguyen Minh Dao BSc Vu Khanh Dong Dr Nguyen Anh Duc MSc Nguyen Ngoc Hoan MSc Le Ngoc Son Eng Cao Tung Son Eng Le Hong Thai MSc Bui Minh Tien MSc Nguyen Van Tuan Dr Phan Tien Vien Dr Tran Quoc Viet Dr Nguyen Tien Vinh SECRETARY MSc Le Van Khoa M.A Nguyen Thi Viet Ha DESIGNED BY Le Hong Van MANAGEMENT Vietnam Petroleum Institute CONTACT ADDRESS Floor M2, VPI Tower, Trung Kinh street, Yen Hoa ward, Cau Giay district, Ha Noi Tel: (+84-24) 37727108 * Fax: (+84-24) 37727107 * Email: tcdk@pvn.vn/pvj@pvn.vn Mobile: 0982288671 Cover photo: What should we make with CO2 and how can we make It? Joule 2018; 2(5) Publishing Licence No 100/GP-BTTTT dated 15 April 2013 issued by Ministry of Information and Communications PETROLEUM PROCESSING PETROLEUM EXPLORATION & PRODUCTION PETROVIETNAM JOURNAL PETROVIETNAM JOURNAL Vol 10, p 14 - 20, 2019 ISSN-0866-854X Vol 10, p - 13, 2019 ISSN-0866-854X Orientations for efficient treatment and processing of high CO2 content natural gas resources in Vietnam CO2 removal optimisation for the BR-E membrane system by data analysis and modelling Nguyen Huu Luong Vietnam Petroleum Institute Email: luongnh@vpi.pvn.vn Nguyen Hai An Petrovietnam Exploration and Production Corporation Email: annh1@pvep.com.vn Summary Summary CO2-rich natural gas sources are popular in Vietnam, with their CO2 contents in the range of 10 - 60 mol% Based on various CO2 contents of natural gas sources, certain technologies are recommended for their wise uses If the gas contains less than 10 mol% of CO2, it can be used for urea production In the case for its CO2 content of up to 25 mol%, methanol and dimethyl ether (DME) production could be considered The gas having the CO2 content of up to 50 mol% could be a good feedstock for carbon nanotube (CNT) production On the other hand, if the gas contains more than 50 mol% of CO2, CO2 removal should be an option, and separated CO2 could be used as feedstock for the production of various products, including methanol, DME, and CNTs Development of offshore high carbon dioxide (CO2) gas fields will indisputably pose significant new challenges for all E&P companies in the world Acid gas removal from natural gas is an indispensable treatment process that is required to boost the produced gas quality prior to its utilisation The use of membrane units has increased in natural gas treatment plants, particularly for acid gas removal Such technology shows tremendous advantages over other conventional methods in terms of removal efficiency, compactness, and environmental friendliness BR-E CO2 removal facility using membrane technology has been utilised for more than 10 years As new acid gas fields require increasingly high gas volumes (more than 700 MMscfd production) and have very high CO2 content (above 50%), existing membrane performance is no longer economical for such new field development Key words: CNTs, CO2-rich natural gas, DME, methanol, urea In this paper, a data analysis model for membrane separation has been incorporated with HYSYS as a user defined unit operation in order to optimise performance and redesign the membrane system for CO2 separation from natural gas Parameter sensitivities have been studied for different crude gas flow and CO2 contained in gas Introduction to CO2-rich natural gas sources in Vietnam Vietnam is in the region of CO2-rich gas fields It currently holds 700 billion cubic meters of proved natural gas reserves [1] A number of gas fields have been discovered with high reserves but their gas composition contains a significant amount of CO2, ranging in 10 - 60 mol% In 2011, the biggest gas field, Ca Voi Xanh, was discovered with the reserves of more than 150 billion cubic meters of natural gas [2] However, its composition owns high contents of impurities, especially CO2 Table shows its hydrocarbon and non-hydrocarbon composition Key words: Petroleum system modelling, a prospect, drainage area, hydrocarbon migration and accumulation, Block 09-3/12 Introduction Membrane systems are modular and can easily cope with the increase of feed flow rate An increase in feed flow rate requires a proportional increase in membrane area requirements If the membrane area is fixed, an increase in feed flow will result in an increase of CO2 in the produced gas Next to the changes in feed-gas conditions (flow and composition), normal membrane aging can result in a CO2 concentration increase in the sales gas Membranes are subjected to a lifetime that varies with feed-gas conditions, membrane pre-treatment design, and operator skills The BR-E gas plant has shown excellent performance with the membrane lifetime of more than 10 years The design of a membrane system takes into account the natural performance decline (membrane aging) by sizing the system for end-of-life conditions so that the Date of receipt: 5/11/2019 Date of review and editing: - 11/11/2019 Date of approval: 11/11/2019 system will always reach the required specifications During the lifetime of the membrane, the system will require minor operational adjustments as the membrane properties (selectivity and permeability) vary The research will further describe how the BR-E gas plant has been optimised as feed-gas conditions changed and as membranes aged, the objectives of producing gas with acceptable CO2 content while minimising hydrocarbon losses that transpose directly in sales gas volume and revenue Besides Ca Voi Xanh, other gas fields and wells have been also found with high contents of CO2, including Block B, Ca Ngu Vi Dai, Ca Map Trang, and some wells Table Composition of Ca Voi Xanh gas [2] Removal of CO2 with membranes Component N2 CO2 H2 S C1 C2 C3 C4 2.1 Membrane general The most common membranes for gas sweetening processes are cellulose acetate (CA) membranes [1] Recently, fixed site carrier membranes showed a great potential for removal of CO2 A simple membrane process can be schematically represented as shown in Figure Date of receipt: 25/4/2019 Date of review and editing: 25 - 28/4/2019 Date of approval: 30/9/2019 Membrane based gas separation process depends on the gas components, membrane material and the process PETROVIETNAM - JOURNAL VOL 10/2019 Composition (mol%) 9.88 30.26 0.21 57.77 0.92 0.31 0.18 14 PETROVIETNAM - JOURNAL VOL 10/2019 in the southern Song Hong basin The presence of CO2 in gas composition decreases its quality due to its low heat value and related issues during its storage, transfer and processing In Vietnam, currently, more than 80% of natural gas is used for power production It can be seen that these CO2-rich gas sources are not ideal for this usage because CO2 is a zero-heat-value component However, CO2 consists of carbon and oxygen elements that are present in the composition of chemicals used in industries and civil life In fact, CO2 should be considered a resource rather than a waste Therefore, it is interesting and important to determine suitable ways for efficient use of these gases via technologies that can process both hydrocarbons and CO2 into high-value products In this paper, suitable technologies for natural gas processing in relation to its CO2 contents are recommended Their maturity is also pointed out Natural gas with its CO2 content up to 10 mol% - A feedstock for urea production Urea (NH2CONH2) is of great nutrition to soil as a nitrogen-rich fertiliser Natural gas is one of the important feedstocks to produce hydrogen that is used for ammonia synthesis in urea production Transformation of natural gas with methane as a representative component into urea is described by Equations - CH4 + H2O ⇌ CO + 3H2 (1) 14 SCIENTIFIC RESEARCH PETROLEUM EXPLORATION & PRODUCTION PETROLEUM PROCESSING CO2 removal optimisation for the 14 Orientations for efficient BR-E membrane system by data analysis and modelling treatment and processing of high CO2 content natural gas resources in Vietnam 21 Progress in catalysts of reforming methane process - A potential solution for effective use of CO2 - rich natural gas sources 34 Study on preparation of advanced Ni-Ga based catalysts for converting CO2 to methanol 55 Impact of high CO2 content in natural gas 59 Advanced technology utilising CO2-containing methane for production of CNTs and graphene and their applications CONTENTS PETROVIETNAM PETROVIETNAM JOURNAL Vol 10, p 21 - 33, 2019 ISSN-0866-854X Progress in catalysts of reforming methane process - A potential solution for effective use of CO2 - rich natural gas sources Luu Cam Loc, Phan Hong Phuong University of Technology Email: luucamloc@hcmut.edu.vn Summary The rapid increase in emissions of major greenhouse gases such as CO2 and CH4 in the last decade has seriously affected the climate change and the living environment in the world in general and in Vietnam in particular In addition, the demand for effective use of CO2rich natural gas has promoted studies to find new, highly active and stable catalysts for the methane reforming process NiO has proven to be the most suitable catalyst for industrial application of the reforming process To overcome the disadvantages of NiO-based catalysts such as coke formation and sintering at high reaction temperatures, many diverse researches from using new carriers to supporting catalyst by alkali, alkaline earth metals and other metal oxides to improve the catalyst synthesis method have been conducted As a result, highly efficient catalysts were created, partly thanks to the reduction of the reaction temperature from 800oC to 700oC, the coke formation significantly decreased and the stable working time of the catalyst increased to over 600 hours Key words: CO2-rich natural gas, dry reforming, bi-reforming, catalyst Greenhouse gas emissions causing global warming and climate change has been the issue of concern all over the world The concentration of CO2 in the atmosphere increases about 1.5ppm/year in the period 2001 - 2011 [1], ppm/year in the period 2011 - 2015 [2] and it is predicted to reach 661ppm by the end of the 21st century [3] This led to an increase in the global temperature of 0.8oC in the 20th century and an increase of 1.4 - 5.8oC in the 21st century [4] CO2 and CH4 account for 76% and 16% respectively in total greenhouse gas emission while CH4 is 21 times more potent to the environment than CO2 [5] Currently, the “average mixing ratio” of CH4 in the troposphere reaches 1.74ppmV, which doubles the pre-industrial period value (0.8ppmV) [6] For Vietnam, this issue has become more serious and urgent because of rapid industrialisation According to Vietnam’s first report for the United Nations Framework Convention on Climate Change, implemented by the Ministry of Natural Resources and Environment in 2014, in the period 1994 - 2010 total greenhouse gas emissions in Vietnam increased rapidly from 103.8 million metric tons of carbon dioxide equivalent (MMTCDE) to Date of receipt: 1/5/2019 Date of review and editing: 2/5 - 10/6/2019 Date of approval: 11/11/2019 246.8 MMTCDE Greenhouse gas emissions in the energy sector increased from 25.6 MMTCDE to 141.1 MMTCDE, making the sector the fastest and the largest emitter in 2010 In Vietnam, total proven natural gas reserves in 2016 were around 207 billion standard m3, and marketed production of natural gas was 9,297 million standard m3 [7] Besides the qualified reservoirs, some reservoirs with high content of CO2 have been discovered in recent years Typically, Lot B - O Mon gas field has a gas capacity of about 107 billion m3 and the Ca Voi Xanh gas field is estimated at approximately 150 billion m3, which is times of Lan Tay and Lan Do fields in the Nam Con Son Gas Project [8] The natural gas extracted from Lot B - O Mon and Ca Voi Xanh gas field contains high amount of CO2, around 20% and 30%, respectively In addition, a number of other gas fields also have high concentration of CO2, such as Song Hong, Phu Khanh, Nam Con Son, Cuu Long, Ma Lay-Tho Chu, and Tu Chinh Region, with proved gas reserves from 2,100 up to 2,800 billion m3 More specifically, Song Hong field has CO2 content ranging from 27% to 90% and even 98% In Ma Lay-Tho Chu basin, CO2 content is from a little to 80% [8] The presence of CO2 with high content in natural gas causes difficulties in exploration and transportation, and that may lead to a huge amount of CO2 released into the PETROVIETNAM - JOURNAL VOL 10/2019 21 Ni-Ga Ni-Ga/oxide Ni-Ga/mesosilica Mesosilica 21 Intensity (a.u.) Introduction 38 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 2Theta PETROLEUM EXPLORATION & PRODUCTION PETROVIETNAM JOURNAL Volume 10/2019, p - 13 ISSN-0866-854X CO2 removal optimisation for the BR-E membrane system by data analysis and modelling Nguyen Hai An Petrovietnam Exploration and Production Corporation Email: annh1@pvep.com.vn Summary Development of offshore high carbon dioxide (CO2) gas fields will indisputably pose significant new challenges for all E&P companies in the world Acid gas removal from natural gas is an indispensable treatment process that is required to boost the produced gas quality prior to its utilisation The use of membrane units has increased in natural gas treatment plants, particularly for acid gas removal Such technology shows tremendous advantages over other conventional methods in terms of removal efficiency, compactness, and environmental friendliness BR-E CO2 removal facility using membrane technology has been utilised for more than 10 years As new acid gas fields require increasingly high gas volumes (more than 700 MMscfd production) and have very high CO2 content (above 50%), existing membrane performance is no longer economical for such new field development In this paper, a data analysis model for membrane separation has been incorporated with HYSYS as a user defined unit operation in order to optimise performance and redesign the membrane system for CO2 separation from natural gas Parameter sensitivities have been studied for different crude gas flow and CO2 contained in gas Key words: Petroleum system modelling, a prospect, drainage area, hydrocarbon migration and accumulation, Block 09-3/12 Introduction Membrane systems are modular and can easily cope with the increase of feed flow rate An increase in feed flow rate requires a proportional increase in membrane area requirements If the membrane area is fixed, an increase in feed flow will result in an increase of CO2 in the produced gas Next to the changes in feed-gas conditions (flow and composition), normal membrane aging can result in a CO2 concentration increase in the sales gas Membranes are subjected to a lifetime that varies with feed-gas conditions, membrane pre-treatment design, and operator skills The BR-E gas plant has shown excellent performance with the membrane lifetime of more than 10 years The design of a membrane system takes into account the natural performance decline (membrane aging) by sizing the system for end-of-life conditions so that the Date of receipt: 5/11/2019 Date of review and editing: - 11/11/2019 Date of approval: 11/11/2019 PETROVIETNAM - JOURNAL VOL 10/2019 system will always reach the required specifications During the lifetime of the membrane, the system will require minor operational adjustments as the membrane properties (selectivity and permeability) vary The research will further describe how the BR-E gas plant has been optimised as feed-gas conditions changed and as membranes aged, the objectives of producing gas with acceptable CO2 content while minimising hydrocarbon losses that transpose directly in sales gas volume and revenue Removal of CO2 with membranes 2.1 Membrane general The most common membranes for gas sweetening processes are cellulose acetate (CA) membranes [1] Recently, fixed site carrier membranes showed a great potential for removal of CO2 A simple membrane process can be schematically represented as shown in Figure Membrane based gas separation process depends on the gas components, membrane material and the process PETROVIETNAM conditions The governing flux equation (Equation 1) is given by Fick’s law of diffusion where the driving force is the partial pressure difference over the membrane , = , = = ( − ) (1) Where J (m3(STP)/m2 h) is the flux of gas component i, qp is the volume of the permeating gas (i) (m3(STP)/h), Pi is the permeability of gas component i ((m3(STP)/m2 h bar), ph and pl are feed and permeate side pressures (bar), xi and yi are the fractions of component i on the feed and permeate sides and Am (m2) is the membrane area required for the permeation The permeability (P) can be expressed as (2) P = DAB × S Where DAB (m2/s) is the diffusivity and S (m3(STP)/m3 bar) is the solubility coefficient for the gas in the membrane The ratio of pure gas permeabilities (PA, PB) gives the separation factor or membrane selectivity, α = PA/PB Permeate G yi Membrane F xi Feed R ri Retentate Figure Schematic illustration of membrane separation process It is important to mention here that Equation can be used to accurately and predictably rationalise the properties of gas permeation membranes 2.2 Membrane modules In order to make a membrane module for industrial application [2, 3] that consists of cellulose acetate membrane sheets that are bound onto a woven cloth support A membrane sheet has two layers: a relatively thick microporous layer that is in contact with the cloth support and a thin active layer on top of the microporous layer A membrane element is a spiral wound assembly with a perforated permeate tube at its centre (Figure 2) One or more membrane leaves are wrapped around the permeate tube Each leaf contains two membrane-cloth composite layers that are separated by a rigid, porous, fluid-conductive permeate channel spacer These leaves are separated from each other by a high-pressure channel spacer The membrane leaves are sealed with an adhesive on three sides; the fourth side is open to the permeate tube As the feed gas passes through the membrane tubes, the gas is separated into a *Two membrane sheets with permeate spacer between: leaves are separated by feed spacers and wrapped around a permeate tube facing it with three open ends Figure Spiral-wound membrane elements [3] PETROVIETNAM - JOURNAL VOL 10/2019 PETROLEUM EXPLORATION & PRODUCTION high-pressure methane rich gas (residual), and a lowpressure gas stream concentrated in carbon dioxide (permeate) The first membrane stage is designed to produce a residual gas (sales gas) with low CO2 concentration, which is supplied to the export compressors for gas metering The permeate gas containing high CO2 %mol is compressed through the permeate compressor and then directed to the second stage membrane package The second membrane stage is designed to recover most of the hydrocarbons from the first-stage permeate gas The second membrane stage residual gas is recycled back to the first membrane stage The second stage permeate gas containing the high concentration of CO2 is flared 2.3 Membrane system configurations A single-stage membrane configuration consists of one permeation unit or more than one unit, but all are arranged in a barrel setup and have the same feed composition This configuration is the simplest and corresponds to the lowest capital investment The single-stage configuration is schematically shown in Figure The crude natural gas flows over the feed side of the membrane Along the way, CO2 permeates through the membrane to the permeate side The retentate leaves the membrane with nearly the same pressure as the feed On the permeate side, a permeate stream enriched with CO2 leaves the membrane As seen in many industrial applications [3], the single-stage membrane separation has limitation in achieving high quality permeate or retentate while typically the objective of separation is either of these As such, more stages are required in order to accomplish the desired product quality and recovery ratio Figure illustrates a simplified flow scheme of a two-stage cascade membrane system A multistage configuration reduces the hydrocarbon losses to a minimum, however, those plants have higher investment costs than single stage configurations The permeate stream of the first membrane serves as feed for the second membrane Therefore, the permeate stream needs to be recompressed and cooled The retentate stream of the second membrane stage is recompressed, cooled and recycled as feed PETROVIETNAM - JOURNAL VOL 10/2019 to the first stage The retentate stream from the first stage is collected as the product gas BR-E CO2 removal facility The BR-E CO2 removal facility is 370km from Ca Mau terminal The platform processes gas condensate from northern fields complex, and associated gas from the southern oil fields The project produces about 350MMscfd (max) of export gas at an export pressure of 101 bars and 3,700stb of stabilised condensate The BR-E platform has been in operation since in Q1, 2007 with the main function to process high CO2 production gas to meet the sale gas specification of 8% mol CO2 The flow diagram of the BR-E gas facility (Figure 5) shows gas flowing from the complexes into the system First it enters a two-phase feed gas separator where the main condensategas separation takes place Gas from the separator goes to the Coalescing Unit for liquid and mist elimination to reduce overall plant pressure drop Then it flows to the Membranes System, which consists of a temperature swing adsorption (TSA) regenerable beds for the simultaneous removal of aromatics, water and other contaminants (e.g., mercury) The retentate stream of the second membrane stage is recycled as feed to the first stage This combined stream has a design CO2 content of 40 - 45% mol and is the feed gas to the first-stage membrane skids The retentate stream from the first stage is collected as product gas Condensate collected from the various processing steps moves to stabilisation before Residue (CO2 Reduced) Feed Membrane Unit Permeate (CO2 Enriched) Figure Single-stage flow scheme Residue Feed Permeate Figure Dual-stage flow scheme PETROVIETNAM Export Gas to BRA Coalescer filter A/B Regeneration Gas System Feed gas Separator Gas from Northern fields Gas from Southern fields MEMGUARD Adsorber A - F Particle Filter A/B Lean CO2 Gas Retrigeration Sys Separator CW Membrane Pre-hearers Residue Gas @ Sales Gas Specifications CO2 to Vent CO2 to Vent Stabilised Condensate BRA Condensate Stabilisation System Primary Membrane A - F Retrigeration Sys Secondary Membrane A - B Produced water Overboard Stage Permeate Compressor A/B/C 700 46 600 44 42 500 40 400 38 300 36 200 CO2 content (%) Gas flowrate (MMscfd) Figure Flow diagram for CO2 removal on BR-E platform [4] 34 100 32 Feed Flowrate Process % CO2 30 201X Dec Nov Oct Sep Aug Jul Jun May Apr Mar Feb Jan Dec Nov Oct Sep Aug Jul Jun May Apr Mar Feb Jan 201Y Figure Gas process behaviour being stored in the three storage tanks The stabiliser tower removes the light hydrocarbons to avoid release in the tanks and to achieve the rvp specification After heating to required temperature, the gas enters the gas-sweetening system (dual-stage membrane package) to reduce CO2 in the export gas The final step is to export the gas via the export compressors 3.1 Operation performance Throughout the operating period of two years, changes were daily made in the feed gas rate and the CO2 concentration Figure gives information about the behavior of feed gas flowrate, retentate (“process gas”), for two different levels of CO2 concentration in the feed gas In fact, the CO2 concentration in the retentate product PETROVIETNAM - JOURNAL VOL 10/2019 PETROLEUM EXPLORATION & PRODUCTION 0.7 0.65 0.6 Stage cut 0.55 0.5 CO2 > 40% 0.45 CO2 < 40% 0.4 0.35 0.3 30 80 130 180 230 280 330 380 430 Feed gas rate (MMscfd) Figure Total gas stage cut for BR-E membranes system remained below the pipeline specification throughout the measurement These results show that, even with a CO2 concentration of over 40% mol in the feed, it was possible to meet the pipeline specification of 8% mol CO2 Figure shows the “total gas stage cut” for different CO2 components of natural gas as a function of feed gas rate for membranes The “stage cut” is generally defined as the fraction of the feed stream allowed to permeate through the membrane, i.e the permeate/feed ratio In the measurement period, it was found necessary to “force” the CO2 balances for some surveys to obtain a good data fit, especially the data for high CO2 concentrations in the feed The field staff observed that the CO2 concentration in the “sour” gas from the well typically varied by about 5% mol out of an average concentration of about 40% mol This meant that the CO2 stage cut for feed gases with high CO2 content could vary by as much as 10% For consistency, the CH4 balances were also forced as necessary, but there was much less variability in these data because of the relatively high concentration of CH4 in all streams PETROVIETNAM - JOURNAL VOL 10/2019 The parameters of feed flow rate and CO2 concentration in the feed are arbitrarily grouped in Figure into ranges denoted as “CO2 < 40%” and “CO2 > 40%” As can be seen from this figure, the data are generally consistent in that the stage cuts decrease with increasing feed flow rate The scatter in the data is not unusual for field test conditions It was not possible to obtain data at higher feed flow rates with medium-to-high CO2 concentrations in the feed without exceeding the pipeline-specified limit of 8% mol CO2 in the retentate Therefore, the data are generally limited to lower feed flow rates and lower CO2 concentrations There was no indication of membrane deterioration with time, based on the field test data In general, the stage cuts for the membrane system followed the same general dependence on feed flow rate and CO2 concentration in the feed High CO2 stage cuts were necessary to reduce the CO2 concentration in the retentate product to the pipeline specification of 8% mol, however the outlet gas rate was decreased accordingly While this results in a better CO2 removal, it also increases the losses of CH4 and higher hydrocarbons in the permeate PETROVIETNAM 3.2 Process simulation 0.7 0.7 0.65 0.65 0.6 0.6 0.55 0.55 0.5 0.5 0.45 0.45 0.4 0.4 0.35 0.35 0.3 0.3 30 30 32 32 34 34 36 36 38 40 42 44 38 40 42 44 CO2 concentrationof feed gas (%) CO2 concentrationof feed gas (%) 46 46 48 48 50 50 0.7 0.7 0.65 0.65 Stage cut Stage cut 0.6 0.6 0.55 0.55 0.5 0.5 0.45 0.45 0.4 0.4 0.35 0.35 0.3 0.3 30 30 80 80 130 130 180 230 280 180 Outlet 230 280 gas (MMscfd) Outlet gas (MMscfd) 330 330 380 380 430 430 Figure Depends of outlet gas on CO2 concentration of feed gas (vent) stream The component stage cuts also increase, as expected, with increasing pressure, because the partial pressures of the components increase It should be pointed out that the actual field surveyed flow rates were generally much lower than the design rate since the purpose of the tests was to obtain operating data over a wide range of conditions Therefore, back-diffusion and perfect mixing were possible, and the methane loss in the permeate was generally higher than desired in commercial operation The numerous material balances that need to be resolved simultaneously within a multistage membrane unit make the prediction of unit’s performance using conventional mathematical solvers (e.g spreadsheet) challenging Further, the struggle to solve the indicated balances obstructs any intended process optimisation Hence, the development of a flexible, efficient, and userfriendly model is crucial to simulate, evaluate and optimise such processes The membrane separation process is modelled based on the solution-diffusion mechanism, which is governed by the following mass transfer equation Detailed modelling of the CO2 removal BR-E facility was performed with the confirmation of the capability of this equipment to process the design cases Stream data for the boundaries of the model were provided, for the high and low CO2 cases The new process configuration and updated production data were incorporated into the HYSYS model, which has been further amended to align with the two design cases for CO2 concentration In order to align with the models of design cases, it was necessary to match streams at the interface with the boundary stream data provided As these design cases represent different production rates for modelling, it was necessary to adjust flows from wellhead platforms to the processing facilities PETROVIETNAM - JOURNAL VOL 10/2019 PETROLEUM PROCESSING Urea product Urea prilling Urea synthesis Process air Feed (High CO2) Reforming Shift CO2 removal Methanation Ammonia synthesis Ammonia product Feed Energy Figure Ammonia to urea with addition of hydrogen The optimum content of CO2 in the feedstock for an ammonia/urea plant is depending on the composition of the natural gas If it is lean gas then it is good to have a few percent, say up to 5% of CO2 Whereas, if the gas is heavy, it is desirable not to have CO2 at all in the gas It is about balancing carbon and hydrogen in the syngas production When there is a very high CO2 content in the gas, it is still practical to balance it with hydrogen produced from electrolysis However, in order not to make too big changes to the existing plant, up to 10% of the hydrogen could come from electrolysis An estimate of maximum CO2 content would be around 20% depending on what the plant is initially designed for There is no doubt about water electrolysis being the future reforming Presently, in many regions the power from a reliable grid is still more expensive than the equivalent energy from natural gas There will be a lot of factors for the given plant, influencing at what cost the power should be available before revamp with electrolysis is economical feasible A good rule of thumb is when the price ratio is one between gas and power In Asia, the production cost of renewable power is lower than the cost of natural gas Methanol production Together with CO and hydrogen, CO2 is one of the reactants for methanol production This means it can be an advantage to have a high CO2 content in the natural gas feedstock The below equations show the optimal amount of CO2 content can be up to 25% for methanol production 3CH4 + CO2 + 2H2O = 4CH3OH M = 56 PETROVIETNAM - JOURNAL VOL 10/2019 3C2H6 + CO2 + 5H2O = 7CH3OH M = For syngas production from natural gas reforming, we typically distinguish between three different designs of reforming - One step reforming is the simplest as only a fired tubular reformer is required For a low CO2 containing feed gas, this will typically give a syngas being overstoichiometric in hydrogen, which gives a high purge rate from the loop This purging results in having a fuel gas to the reformer being rich in hydrogen The syngas is less reactive due to high CO2 to CO ratio - Two-step reforming consists of a primary reformer and an oxygen fired secondary reformer With this design, the syngas composition can be adjusted by steam-tocarbon ratio and oxygen amount to give a stoichiometric syngas having a module of 2.0 The reactivity of the syngas is higher than that for one step reforming, resulting in smaller methanol reactors and typically lower specific energy consumption - Autothermal reforming (ATR), or with Topsoe terminology SynCOR™, is without a primary reformer and consists of only an oxygen fired reactor, giving typically a slight under-stoichiometric syngas composition This requires recovery of hydrogen from the loop purge gas in order to make a stoichiometric syngas in the loop This design gives the highest reactivity of the syngas because the CO to CO2 ratio is the highest The Table summarises the syngas module for the three different reforming designs and if they are suitable for either CO2 import for injection or simply high CO2 content in the feedstock PETROVIETNAM Table Comparison of reforming designs for methanol production Reforming Syngas Module Suitability for CO2 import Capacity gain CO2 import One-step Over stoichiometric Very 10 - 20% Two-step Ideal module NA NA ATR Sub stoichiometric NA NA Figure IMAP ammonia+TM process design As it can be seen, the one-step reforming is very suitable for feedstock with high CO2 content to compensate for the typical over-stoichiometric syngas module IMAPTM Today, Topsoe’s IMAPTM (integrated methanol & ammonia process) portfolio consists of different process solutions: IMAP ammonia+TM, IMAP methanol+TM and IMAP urea+TM IMAP ammonia+TM is an ammonia plant with an in-line methanol synthesis, where the methanol capacity can vary from - 35% IMAP methanol+TM is a methanol plant having an ammonia synthesis downstream operating at similar pressure as the methanol synthesis This is a very cost-effective co-production plant because it is the simplest process with very limited flexibility on product split being around 80/20 methanol/ammonia IMAP urea+TM is the most flexible product split on three products: ammonia/urea/methanol It can be designed with the required product split flexibility, and it will typically require higher investment compared to the other two IMAP solutions In the following, the process solution of an IMAP ammonia+TM plant will be described The technology is equally suitable for grassroots plants as well as revamps, where a methanol synthesis unit is added to an existing ammonia plant The IMAP ammonia+TM solution is typically configured to provide a product flexibility ranging from 100% ammonia and up to 35% of the capacity being substituted by methanol If only ammonia is needed, the methanol unit is simply by-passed The block diagram in Figure summarises the different process steps to co-produce ammonia and methanol for downstream granulated urea 3.1 Advantages of IMAPTM co-production The choice of the ammonia and methanol co-production concept can be an important strategic decision providing added value to plant owners It should be considered in cases where opportunities exist, such as import substitution or local off-takers of methanol and/or UFC-85 A urea granulation plant requires UFC-85 as coating material for granulated urea The co-production process is a convenient way to supply the UFC-85 plant with methanol produced locally Specific opportunities exist in remote areas or cold sites where, due to high viscosity of PETROVIETNAM - JOURNAL VOL 10/2019 57 PETROLEUM PROCESSING By powering the water electrolysis unit with renewable energy, a partial energy substitution is made for natural gas by renewable energy Overall the CO2 emissions will be reduced because less fuel firing will be required for the primary reformer ($/MT) 700 600 400 3.2 Estimated savings for IMAP 700 The below table is showing a comparison of CAPEX for IMAP ammonia+TM The specific energy consumption per ton of products is very similar for IMAP as for stand-alone plants 300 200 Conclusions 100 Mar11 Mar12 Mar13 Mar14 Mar15 Mar16 Figure Market product price Table CAPEX comparison #reforming units #syngas compressors NG consumption index Relative investment cost index Two stand-alone units Ammonia+TM 2 102 100 115 - 125 100 UFC-85, it is difficult to procure and transport UFC-85 or methanol as an imported chemical As an alternative to two stand-alone ammonia and methanol plants, an IMAPTM co-production facility offers the advantage to produce multiple products without the often prohibitive cost of installing and operating a second plant Diversifying the product portfolio offers plant owners the possibility to maximise their profits by meeting changing market needs as they arise and as prices fluctuate, as seen in Figure At a point, when having high CO2 content in the natural gas feedstock for IMAP plants, it would be beneficial to have an electrolysis unit to compensate for less hydrogen production from the reforming to keep the full flexibility of the plant 58 PETROVIETNAM - JOURNAL VOL 10/2019 High CO2 content in natural gas feedstock can impact negatively on existing ammonia and methanol plants resulting in capacity reduction or higher energy consumption For existing plants as well as for new plants, the high CO2 content can be addressed for all technologies discussed above and will always depend on the given case In Topsoe, we have a long tradition designing for all kinds of natural gas composition, and for revamping existing plants to handle major changes in the feedstock composition One of the latest design options is the use of renewable energy for substitution of natural gas via introduction of electrolysis This will reduce the overall CO2 footprint of the ammonia and methanol as well as for IMAP plants The most mature electrolysis technology is the alkaline electrolysis and has been proven for approximately 100 years It provides hydrogen and oxygen purity suitable for use in ammonia and methanol production Topsoe’s way of utilising electrolysis in the process for ammonia and methanol plants is patent pending PETROVIETNAM PETROVIETNAM JOURNAL Vol 10, p 59 - 70, 2019 ISSN-0866-854X Advanced technology utilising CO2-containing methane for production of CNTs and graphene and their applications Cattien V Nguyen NTherma Corporation Email: cattien.nguyen@ntherma.com Summary Nanotechnology in particular carbon nanomaterials, such as carbon nanotubes (CNTs) and graphene, is both technologically and commercially important This is clearly seen from the amount of scientific and production activities in the last two decades Carbon nanomaterials have been portrayed as the materials of the 21st century, in a similar manner that Si technology/information technology and petrochemicals have significantly contributed to the worldwide development in the last century Such enthusiastic outlook with carbon nanomaterials comes from the extraordinary chemical and physical characteristics of the materials, which have inherent high chemical/thermal stability (700oC in air), high surface area (100m2/g to greater than 2000m2/g), high thermal conductivity (as high as 3000W/mK), high electrical conductivity (as high as 107S/m), and exceptional mechanical properties (Young’s Modulus at about 1000GPa) More importantly, many applications utilising these carbon nanomaterials have been widely demonstrated at university labs and by commercial entities This paper will first outline the method for industrial-scale production of the carbon nanomaterials, CNTs and graphene, including new production methods for CNTs and graphene developed by NTherma Corporation We will include previous examples for the utilisation of methane gas containing high CO2 as a feedstock for the production of CNTs We will discuss a number of applications, including nanocoatings, information technology, and energy Specific applications in lubricant, anti-corrosive oil pipeline coatings, and Li-ion batteries will be discussed in greater details Key words: CNTs, graphene Introduction Carbon nanotubes (CNTs) and graphene are allotropes of carbon with C-C bonds between a single bond and a double bond Graphene comprises of Sp2 carbon atoms arranged in a 2D regular array of hexagonal structure as seen in Figure Graphene has a single-atom thickness in the Z-direction In comparison, CNTs have a tube structure derived from the rolling up of a graphene molecule When the tube structure is formed by rolling up a single-layer graphene, the CNT is characterised as a single-walled CNT (SWCNT) as seen in Figure 2, with diameter ranging from less than 1nm to 2nm Another type of CNTs is characterised as multi-walled CNTs (MWCNTs) when the tube structure is formed by rolling up of a multi-layer graphene The diameter of MWNTs has a range between a few nm to as large as 100nm CNTs have lengths ranging Date of receipt: 6/5/2019 Date of review and editing: - 11/5/2019 Date of approval: 11/11/2019 from a few micrometres to as long as centimetre and as such the high aspect ratio structure of CNTs exhibits 1D characteristic behaviours For over the last two decades, much research and development have contributed to the basic understanding as well as demonstrating the commercialisation potential of these carbon nanomaterials in many applications The interesting properties of both CNTs and graphene are derived fundamentally from the structure in the hexagonal arrangement of the Sp2 carbons The C-C bonds of the Sp2 carbons in carbon nanomaterials are between a single and a double bond and are called graphitic carbons The bond dissociating energy of graphitic carbon is about 500 KJ/mol, as compared to 346 KJ/mol for a C-C single bond and 602 KJ/mol for a C=C double bond As a result, the C-C bonds in graphene and CNTs are very stable as compared to typical C-C bonds in organic and polymeric molecules These carbon nanomaterials are less chemically reactive and have high thermal stability with a decomposition temperature PETROVIETNAM - JOURNAL VOL 10/2019 59 PETROLEUM PROCESSING Figure Diagrams representing the structure of 2D graphene and some of their structure and physical characteristics Graphene Graphene (a) (b) SWCNT MWCNT Figure Structures and TEM images of (a) single-walled carbon nanotube (SWCNT) and (b) multi-walled carbon nanotube (MWCNT) as schematic representation from the rolling up of a single-layer and multi-layer graphene, respectively Scale bars in TEM micrographs are 5nm greater than 700oC The graphitic bonding structure also imparts exceptional mechanical properties For example, the Young’s Modulus of CNTs is higher than 1000Gpa which is about 5X higher than the Young’s Modulus of steel These outstanding mechanical properties and chemical and thermal stability have led to many applications for structural reinforcement such as polymer composites and metal matrix composites The fact that these materials are a single- or a fewatomic layer thickness, the specific surface area (SSA) of both CNTs and graphene are very high The SSA for a perfectly flat single layer graphene is 2630m2/g, while 60 PETROVIETNAM - JOURNAL VOL 10/2019 those of SWCNT and MWCNT can be as high as 900m2/g and 400m2/g, respectively, depending on the diameters of the tubes of the CNTs (Table 1) In addition, the pi-electrons of the Sp2 carbons in CNTs and graphene are delocalised and thus they give these carbon nanomaterials high electrical conductivity, with values as high as 107σ (S/m) for nondefective CNT and graphene structures Furthermore, the high ordered C-C bonds in both graphene and CNTs also lead to high thermal conductivity with values as high as 3000W/mK for perfect graphitic carbon structures In combination, the high SSA and thermal and electrical properties of CNTs and graphene have enabled the PETROVIETNAM Table Physical characteristics of CNTs and graphene in comparison to those of steel Material Young’s modulus (Gpa) Tensile strength (Gpa) Density (g/cm3) Thermal conductivity (W/mK) Electrical conductivity σ (S/m) Thermal stability in air ( oC) Specific surface area (m 2/g) 1200 150 2.6 3,000 Graphene parallel to surface 1000 2.2 3,000 Graphene perpendicular N/A N/A 2.2 105 - 107 105 – 107 107 102 × 106 >700 400 - 900 >700 200 - 400 >700 2630 >700 N/A 800 N/A SWCNT MWCNT 1054 150 ~2 3,000 Steel 208 0.4 7.8 50.2 2.1 Carbon nanomaterials from graphite starting materials Cathode deposit Sheath Sheath Plasma Anode Nanotubes Ni + C + Y Helium filled Chamber Cathode Figure Schematic representation of a chamber for the production of CNTs by an arc discharge method development of these materials for coating applications For example, a polymeric-CNT composite coating on airplane wing can be applied for de-icing by current induced melting of ice formation on airplane structural surface Production methods for CNTs and graphene There are many methods for the production of CNTs and graphene that developed over the last decade or two These methods can be classified based on the two types of starting materials utilised in the production of these nanomaterials: - Graphite as the source of starting materials; - Hydrocarbon feedstock as the source of carbon for chemical vapour deposition method The production of CNTs from graphite requires a high energy source for the formation of CNTs The two methods which originally developed in laboratories and produced CNTs for laboratory usage are 1) arc discharge and 2) laser ablation Arc discharge method is currently being used for the production of small volume of both SWCNTs and MWCNTs (Figure 3) This production method gives amorphous carbons as a side product and requires a purification process In contrast, the current production technique for graphene relies exclusively on graphite as the starting material (Figure 4) Here layers of graphene in the graphite are the first chemically oxidised to form graphite oxides (GO), which are then exfoliated to one or more layers of GO by ultrasonication Other techniques for delamination of GO have also been reported, including the use of microwave to separate graphite into layers of GO Many companies worldwide are claiming to have the capability for producing large quantities of graphene by the tons with this method The current price for graphene significantly increases with a fewer number of layers, an indication of the difficulty and cost associated with producing graphene with a few layers of graphite As an example, graphene with 15 layers or more is about USD 1,500 per kg, whereas graphene with one and up to five layers are about USD 50,000 per kg The challenges of this graphite exfoliation production method come from the lack of control of the graphite oxidation process in order to get uniform and consistent GO and reduced GO (rGO) end product This lack of control of a number of layers as well as the size and shape of graphene is due mostly to the inherent non-uniformity in the size and shape of the starting graphite materials, which are a product from mining It should also be pointed out that graphene from PETROVIETNAM - JOURNAL VOL 10/2019 61 PETROLEUM PROCESSING Graphite Oxidation Oxidative Exfoliation Delamination Graphite Oxide Graphene Oxide (GO) Chemical Reduction CR-GO Thermal reduction Electrochemical Reduction TR-GO Reduced Graphene Oxide – r(GO) ER-GO (b) (a) Figure (a) Digital images of two graphite lumps showing dissimilarity in sizes and shapes of the mined materials and (b) Schematic representation of production process for graphene from the graphite starting material Note that the graphene oxide (GO) can be reduced to rGO in the final step by a number of techniques Growth stops CxHy C CxHy C CxHy Metal Substrate (ii) (i) (iii) (a) CxHy CxHy CxHy CxHy CxHy CxHy Metal Substrate (i) (ii) (b) Figure Schematic representation of the two growth mechanisms for the CVD production of MWCNTs utilising hydrocarbon feedstock: (a) Tip growth mechanism with catalyst metal particle lifted from the substrate and (b) Base growth mechanism where the catalyst remained attached to the surface of the substrate 62 PETROVIETNAM - JOURNAL VOL 10/2019 PETROVIETNAM this production method also has impurities as a result of the impurities naturally present in graphite Therefore, high purity graphene needs additional purification step and this also adds to the production cost Furthermore, it is important to note that the rGO is not absolutely like perfect and pristine graphene in that the rGO very likely has defects in structure and thus some physical properties are compromised 2.2 Carbon nanomaterials from gaseous starting materials by chemical vapour deposition Figure Diagram of a fluidised bed reactor with the CVD growth of CNTs in the gas phase Amorphous carbons and CNTs of various lengths are the products of this production process The main method for industrial scale production of CNTs is not derived from graphite starting materials as described above for graphene, instead most of the CNTs are produced by chemical vapour deposition (CVD) with hydrocarbons as the starting materials CVD method of production is preferred due to high volume and high throughput capability Figure shows a schematic representation of the CVD growth mechanism of MWCNTs, where hydrocarbon gaseous molecules, CXHY, are broken by either a high temperature or a high energy plasma source in the presence of metal catalyst particles, as seen Figure LG chemical plant for the production of CNTs in South Korea The cost of the facility was reported to be USD 20M PETROVIETNAM - JOURNAL VOL 10/2019 63 PETROLEUM PROCESSING Figure Digital photographs of the NTherma CNT production tool and a roll-to-roll metal foils, coated with CNTs, exiting the production tool in step (i) in Figure The activated carbon species, derived from the breakdown process of the CXHY gas, are then diffused into the metal catalyst particles on the surface of a substrate in the CVD chamber At this stage when the metal catalyst particles are saturated with the activated carbon species, the CNTs begin to grow from the catalyst particles through what has been termed “nucleation and growth” as seen in step (ii) in Figure The hydrocarbon gas molecules can be methane, acetylene, ethylene, and ethanol, just to name a few examples The type of hydrocarbon gas coupled with the type of metal catalyst and the CVD processing conditions are the main determining factors as to the types of CNTs one can produce, whether it is SWCNTs or MWCNTs It is important to note that there are two mechanisms of CNT growth as shown in Figure 5, a tip growth mechanism and a base growth mechanism To a large degree, the type of growth mechanism is determined by the force of interaction between the metal catalyst with the surface material on the substrate The strong adhesive force between the metal particles and the surface of a substrate prevents the metal from physically lifting off the substrate and therefore base growth is the resulting mechanism The tip growth mechanism is, on the other hand, a result of poor adhesive force between the metal particle and the surface material of the substrate The typical substrate for the CVD growth of CNTs is a Si wafer with a thin film of either Al2O3 or SiO2 coating as this was initially developed in many university labs in the 1990s This method of CVD growth using a Si substrate for supporting metal catalyst particles was not widely used for the production of CNTs due to it being limited to only a batch process production and thus only able to produce low volume at a low throughput rate For large industrial 64 PETROVIETNAM - JOURNAL VOL 10/2019 Figure Digital photograph of the continuous extraction process for CNTs grown on the surface of a metal foil The CNTs have greater than 99% purity and will not require any additional purification process scale production, the method of choice is the use of a fluidised bed reactor, as seen in Figure 6, from the initial stage of commercialisation of CNTs Here the formation of the metal catalyst particles and the ‘nucleation and growth’ process is more in the gas phase and not supported on a surface of a substrate It is important to point out that this has been the main method for large industrial scale production of CNTs for more than a decade Even with a great number of efforts in the development of metal catalysts and CVD processing gases and processing conditions over these many years, the inherent issues of impurities and control of structural uniformity such as length remained elusive Because of this reason, high purity CNTs are much more expensive due to the required purification step being very expensive from both equipment and operation terms For example, 95% pure MWCNTs with the length of less than 50 microns are priced at above USD 9K per kg, whereas 60% purity MWCNTs are priced less than USD 400 per kg A typical chemical plant PETROVIETNAM Figure 10 Schematic representation of (a) the chemical unzipping process of CNTs to produce graphene nanoribbons and (b) the chemical mechanism of KMnO4 and H2SO4 reagents in the oxidation of CNTs and unzipping C-C bonds along the length of CNTs for the production of CNTs is shown in Figure and it is reported to cost USD 20M for production volume of tons of CNTs per year 2.3 Carbon nanotubes by NTherma’s new production method In the last few years, NTherma Corporation demonstrated a new approach for the production of 99.5+% purity of CNTs, with absolute control of CNT lengths ranging about 10 microns to 250 microns, and at a much lower production cost This is achieved by having the CVD CNT growth process Graphene Nanoribbons MWCNTs Graphene Nanoplatelets Figure 11 TEM images showing the conversion of MWCNTs to graphene nanoribbons and graphene nanoplatelets by chemical unzipping process PETROVIETNAM - JOURNAL VOL 10/2019 65 PETROLEUM PROCESSING with the metal catalyst on the surface of a moving substrate in a continuous fashion The substrate for supporting metal catalyst particles is a thin stainless-steel metal foil and thus this production method is achieved as a roll-to-roll process for high volume and high throughput production rate Images of NTherma’s equipment for CNT production and rolls of stainless-steel metal foil coated with CNTs exiting the production tool are shown in Figure The nature of the CVD growth of CNTs with metal catalyst particles supported on the physical surface of a substrate affords CNTs of highly uniform lengths This is one technological advantage of this method as compared to the conventional fluidised bed CVD method currently used in production worldwide Another advantage of NTherma's new production method is the ability to produce CNTs with 99+% purity without requiring any costly purification process The CNTs produced in this roll-to-roll method can be completely extracted from the metal substrate by physically scraping with a knife edge or by ultrasonication, also in a continuously automated fashion, as demonstrated by the photograph seen in Figure It should also be pointed out that because a purification process with strong oxidation chemicals is not needed, the structure integrity such as lengths and crystallinity of the as-grown CNTs is maintained, and thus purity higher than 99+% and CNTs longer greater than 50 microns are available only from NTherma production method This type of high quality MWCNTs may offer opportunities for end users to be able to better optimise performances in various applications 2.4 Chemically unzipping CNTs for the production of graphene As discussed above, the oxidative exfoliation of graphite as a method to produce graphene still has many challenges, namely inconsistent quality and high cost for high quality graphene with a fewer number of layers (less than 5) Using NTherma’s high quality CNTs and opening up the CNTs by well demonstrated chemical unzipping process offers a very practical solution to produce high quality graphene at a lower cost The unzipping of CNTs is achieved with the common chemicals, KMnO4 and H2SO4, where the oxidation of CNTs occurred along the length of the CNTs causing the CNTs to open and resulting in the formation of graphene The process is schematically represented in Figure 10, in which the unzipping chemistry introduces oxide groups along the basal plane of the graphene The graphene produced from the unzipping of CNTs can be tailored to two types: graphene nanoribbons and graphene nanoplatelets As the name implied, the nanoribbons are long strips of graphene with a high aspect ratio structure The length of the graphene nanoribbons is predetermined by the length of the starting CNTs, which is controlled by NTherma's unique production method and thus gives the absolute ability T > 900oC T ~ 600oC with CO2 + H2 and CO Catalyst = Ni or Ni/Fe SiO2 film on support Figure 12 CVD growth of CNTs using methane and CO2 TEM images of various carbon nanomaterials, including large diameter double-walled CNTs (top image) and carbon nanofiber (bottom image) 66 PETROVIETNAM - JOURNAL VOL 10/2019 PETROVIETNAM (a) (b) Figure 13 (a) Diagram showing various applications of carbon nanomaterials, with polymer composite currently being the largest users of CNTs, at almost 50%; and (b) A very low weigh bicycle frame fabricated from a carbon nanomaterial composite to produce graphene nanoribbons of any desirable lengths Moreover, the oxidative chemistry for unzipping can be extended to produce graphene nanoplatelets by simply increasing the time or temperature of the reaction and with more oxidising reagents Figure 11 shows the resulting TEM images of both graphene nanoribbons and graphene nanoplatelets as products from the unzipping of MWCNTs under different reaction conditions, wherein the nanoplatelets are produced in reaction conditions that have higher oxidative chemical reagents and at a higher temperature of reaction It is important to note that graphene produced using high purity CNTs is also of high purity since the chemical reagents and the end products are easily dissolved away with water Thermal Gravimetric Analysis data show 100% mass lost with almost 100% attributed to graphitic carbons at decomposition temperature greater than 600oC (data not shown), and specific surface area measurements by BET show more than doubling of values consistent with the opening of CNTs to more surface area graphene 2.5 Utilisation of high CO2-containing methane for production of CNTs by CVD More recently, the utilisation of methane and CO2 mixed gases for the growth of CNTs has successfully demonstrated There are several advantages for this method, the most obvious being the utilisation of CO2, a greenhouse gas, for the production of high value-added carbon nanomaterials Methane gas has been widely used previously for the production of CNTs, mainly for SWCNTs both in the labs and in industrial production Metal catalyst requirements are more stringent and the temperature is higher for thermal CVD in order to produce SWCNTs with methane gas CO2 in a mixture with CH4 has also been demonstrated in the CVD growth of CNTs It has been reported that the temperature required for the CVD process is significantly lower, from greater than 900oC to as low as 600oC Also, Ni or Ni/Fe catalyst was reported to be more efficient in the growth of CNTs with fewer defects Figure 12 shows a reaction involving CH4 and the CVD conditions for growing large diameter double-walled CNTs and carbon nanofibers Clearly, the CVD process for the production of CNTs utilising CO2-containing CH4 gas has been demonstrated and the CNTs can be utilised in various applications It should be pointed out that the chemical unzipping of these CNTs, as briefly discussed in Section 2D, for producing graphene of different structures, will also find uses in applications where the structural requirement of graphene is altogether different from the existing graphene derived from the unzipping of MWCNTs There are still many parameters to be investigated for optimal CNT growth utilising CO2CH4 gas mixture as the feedstock These are exciting opportunities For example, the ability to grow SWCNTs with CO2-CH4 mixed gas feedstock at large industrial scale and low cost is without a doubt a game changer Applications of CNTs and graphene Currently, the amount of CNTs being produced wordwide is valued at more than USD 4.5B and according to a projected market growth of higher than 15%, the size of the market will be close to USD 10B in 2023 In PETROVIETNAM - JOURNAL VOL 10/2019 67 PETROLEUM PROCESSING Graphene Protective Film PISTON CYLINDER WALL (a) (b) Figure 14 (a) Digital photograph comparing motor oil with and without graphene at 25 mg/L concentration; (b) a diagram showing the coating of graphene on the surface of piston and cylinder as the proposed working mechanism of graphene additive to oil comparison, the market size of graphene is smaller due to a later start of development and it is expected to grow by more than 40% per year Even with all the technical and productisation challenges currently faced by these materials, there are clear market opportunities for both CNTs and graphene, particularly for materials with higher quality and lower cost The main reason for such a high rate of market growth for CNTs and graphene is the wide array of applications with high market potential Therefore, it stands to reason why carbons have been considered to be the materials for the 21st century Figure 13 shows a diagram of many applications for CNTs and graphene that have been reported scientifically and in some cases, have been adapted by industries Many of these applications have high economic and technological impacts Currently, the biggest use of CNTs and graphene is for polymer composites mainly in the sport equipment market, such as a lightweight bicycle frame as seen in Figure 13 Other applications in composites are in late stage development with high end applications facing technical problems such as inconsistency in CNT and graphene quality, high prices, lack of availability required structures for high performance, or combination thereof There is a saying that “not all CNTs are the same” and it could be said for graphene as well Moreover, specific applications will require specific sets of physical characteristics from the CNTs or graphene, whether the applications are to exploit the mechanical, chemical, thermal, electrical or high surface area properties of these materials Therefore, each different application will require a different type of CNT and graphene and the ability to tailor the structure of these materials will allow one to optimise for best performance 68 PETROVIETNAM - JOURNAL VOL 10/2019 CNT coating - 3,000 hrs 3.5% salt water exposure CNT coating - 3,000 hrs 3.5% salt water exposure Figure 15 Digital photographs showing CNT coating of metal nut and bolt in preventing oxidation when exposed to high concentration salt water A discussion with all the important details on any one of these applications would be beyond the scope of this paper, instead, we will briefly survey a number of applications related to the oil industry and energy These applications include: 1) graphene oil additive, 2) nanocoating for anti-corrosive oil and gas pipelines, and 3) Li-ion battery 3.1 Graphene as an oil additive The lubricity characteristic of the long chain carbon molecule, i.e oil molecule, is well known and therefore it is not very surprising that graphene and CNTs also exhibit lubricant behaviour Many scientific publications have demonstrated the lowering of the coefficient of friction by SWCNTs and graphene when added to motor oil or mineral oil The key issue for fully realising this application is the ability to form a stable solution of graphene or CNTs in oil, which many university labs and industrial R&D centres have not been fully able to achieve A stable suspension of an oil additive is required to have at least a 6-month shelf-life as a requirement of the oil industry, as seen in Figure 14a We found that by chemically unzipping high purity MWCNTs less than 20 microns in length to produce graphene, the solution stability is achieved with NTherma’s graphene Testing in laboratory under a controlled environment for both physical characteristics PETROVIETNAM Ultrasonic treatment + Graphene Spray drying Active particles: Anode - Si/SiO2 Cathode - NMC or LCO Calcination at 700oC Figure 16 Schematic representation of the wrapping of graphene around active particles in Li-ion battery The results are faster charging, higher cycle life and improve safety as well as testing in a lab engine were done for comparison of oil samples with and without graphene addition Results show great performance characteristics for oil with graphene additive for reduction of coefficient of friction by 50% in a four-ball tribology tester Scar sizes on the balls for tribological testing equipment were also smaller for oil with graphene which indicated an anti-ware characteristic of graphene Figure 14b shows a diagram of graphene coating the metal surfaces of the piston and cylinder wall as the working mechanism of the graphene additive An increase in fuel efficiency of up to 15% was also observed for testing in an engine in the lab It is important to point out that the efficiency is highly dependent on the running conditions of the engine and whether it was under a load In addition, vehicle testing on normal road conditions was also carried out for small passenger cars, buses, and container trucks As compared to vehicles using oil without graphene, there was an increase in fuel efficiency ranging between 5% to 19% with some correlation to the type of vehicles Similar to the data from the lab test, a wide range of data results from the road testing in vehicles can be attributed to driving conditions, engine sizes, the age of vehicles, and the load on vehicles These are extremely promising data and the commercialisation of graphene oil additive is underway 3.2 Anti-corrosive coatings with graphene for oil and gas pipeline Corrosion of metal is a big problem in many industries, particularly for metal that interacts with a corrosive environment such as seawater or crude oil as are the cases for seagoing vessels and oil/gas pipelines, respectively Graphitic carbons such as those in CNTs and graphene have strong resistance to chemical oxidation and therefore it stands to reason that a coating containing graphene or CNTs would have an anti-corrosive characteristic Many examples demonstrating this characteristic for CNTs and graphene have been reported Figure 15 demonstrates the coating of CNT-polymer thin film for anti-corrosive effect on exposure to salt water It is clearly seen that the coating of CNT-containing film protects the metal nut and bolt from oxidation by the salt water Many examples of anti-corrosive data have been reported for both graphene and CNTs coating on steel pipes and other steel surfaces Graphene nanoplateletepoxy composite coating of a metal substrate has been showed to inhibit diffusion of molecules from solution to the metal substrate by EIS (Electrochemical Impedance Spectroscopy) In order to achieve highly reliable anticorrosive protection, consistency in graphene quality and structure is absolutely needed to fully realise the oil pipeline coating application This is a very promising application with high economic impact on the oil industry 3.3 Graphene balls and conductive graphene for improved li-ion battery performance As electric vehicles are becoming more mainstream, there is a real need for better performing batteries Graphene and CNTs are currently used extensively in PETROVIETNAM - JOURNAL VOL 10/2019 69 PETROLEUM PROCESSING batteries as a replacement of carbon blacks in order to improve the electrical conductivity at both the anode and cathode Recent development has now moved beyond just replacement of carbon black but rather actively wrapping active particles with graphene in order to further improve electrical connectivity and conductivity of the active particles on both the anode and cathode Figure 16 shows an example of a method for actively wrapping active particles with graphene nanoplatelets The formation of graphene balls for use in Li-ion batteries for both anode with Si particles and cathode with LiCoO particles have been demonstrated Recently Samsung Electronics has demonstrated the concept of graphene balls for cathodes in Li-ion battery and showed that this improved the rate of charging by 5X while still maintaining high capacity and long cycle life It was also demonstrated that the wrapping of graphene on LiCoO (LCO) active particles for the cathode also increase the safety of Li-ion battery Oxygen gas was not released when the LCO particle was covered by graphene nanoplatelets thus the highly exothermic reaction of 70 PETROVIETNAM - JOURNAL VOL 10/2019 O2 with Li metal was minimal and thermal runaway was prevented The study attributed graphene high thermal conductivity as the mechanism to keep the LCO particles from becoming overheated and thus prevent any release of O2 and hence improve the safety of Li-ion batteries This application of graphene is also economic importance to the EV and battery industry Conclusions Carbon nanomaterials such as CNTs and graphene are an important class of material The application space for both CNTs and graphene is wide and will have high economic impact Applications such as coatings, additive to oil and battery will continue to grow as these industries adapt the new technology The use of CO2-containing CH4 gas for the CVD growth of CNTs has been demonstrated to be feasible This gas mixture combine with the new method for producing high quality CNTs and graphene in a high throughput roll-to-roll fashion has a high chance to be a game changer to CNTs and graphene development in many applications and industries ... nanotubes and nested 20 PETROVIETNAM - JOURNAL VOL 10/2019 26 Stuart Licht Carbon dioxide to carbon nanotube scale-up ww.arxiv.org PETROVIETNAM PETROVIETNAM JOURNAL Volume 10/2019, p 21 - 33 ISSN-0866-854X... UOP LLC 2007 PVEP BR-E CO2 removal process overview PETROVIETNAM - JOURNAL VOL 10/2019 13 PETROLEUM PROCESSING PETROVIETNAM JOURNAL Volume 10/2019, p 14 - 20 ISSN-0866-854X Orientations for efficient... Information and Communications PETROLEUM PROCESSING PETROLEUM EXPLORATION & PRODUCTION PETROVIETNAM JOURNAL PETROVIETNAM JOURNAL Vol 10, p 14 - 20, 2019 ISSN-0866-854X Vol 10, p - 13, 2019 ISSN-0866-854X