Syngas cleaning with nanostructured microporous ion exchange polymers in biomass gasification using a novel downdraft gasifier

Journal of Energy Chemistry 22(2013)426–435 Syngas cleaning with nano-structured micro-porous ion exchange polymers in biomass gasification using a novel downdraft gasifier Galip Akaya∗ , C Andrea Jordanb , Abdulaziz H Mohameda a Process Intensif ication and Miniaturization Centre, School of Chemical Engineering and Advanced Materials, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK; b ITI Energy Limited, Advanced Manufacturing Park, Brunel Way, Rotherham S60 5WG, UK [ Manuscript received November 30, 2012; revised March 14, 2013 ] Abstract Sulphonated nano-structured micro-porous ion exchange polymers, known as sulphonated PolyHIPE Polymers (s-PHPs) were used in syngas cleaning to investigate their impact on tar composition, concentration and dew point depression during the gasification of fuel cane bagasse as a model biomass The results showed that the s-PHPs used as a secondary syngas treatment system, was highly effective at adsorbing and reducing the concentration of all class of tars in syngas by 95%–80% which resulted in tar dew point depression from 90 ◦ C to 73 ◦ C It was shown that tars underwent chemical reactions within s-PHPs, indicating that tar diffusion from syngas was driven by chemical potential It was also observed that s-PHPs also captured ash forming elements from syngas The use of s-PHPs in gasification as well as in an integrated thermochemical biorefinery technology is discussed since the tar loaded s-PHPs can be used as natural herbicides in the form of soil additives to enhance the biomass growth and crop yield Key words biorefinery; biomass; downdraft gasifier; gasification; PolyHIPE Polymer; syngas cleaning; tar removal Introduction 1.1 Integrated bioref inery Biomass (including biomass waste) offers a unique opportunity in the prevention and abatement of global warming since it is the only renewable source which can simultaneously provide chemicals, energy and fuel (CEF) In order to establish CEF generation technologies based on biomass (i.e., biorefinery), the potential energy value, availability, conversion characteristics of feedstock and their environmental impact must be examined to ensure sustainability The availability of energy from biomass waste is some times that of current global energy demand whereas the availability for solar and wind is 100 and 10 fold, respectively However, the physical distribution of these energy sources becomes broader as their energy potential increases Furthermore, unlike solar and wind, unused/waste biomass is environmentally detrimental and a net contributor to global warming due to the generation of methane during its decay While solar and wind resources generate only power, biomass can generate valuable chemicals through the production of syngas, all the essential chemicals can be produced through the establishment of a biorefinery technology to replace existing oil-refineries One of the impacts of global warming and reduced fossil fuel resources is the emergence of food, energy and water shortages (FEWs) Solar and wind energy generation does not have any direct impact on food and water, but any biomass based CEF generation technologies must take into account its impact on food and water production and land availability Therefore, it is necessary to ensure that the biomass based CEF technologies are holistic and integrated with agriculture which consume 80% of water resources and energy used by industry Integration of chemical or biochemical processes within a chemical/biochemical plant is well known as it provides energy efficiency as well as reduction in capital and operating costs However, process integration on a wider scale is not practiced partly because of the nature of chemical/biochemical plants for which the ‘sustainability’ is pro- ∗ Corresponding author Tel: +44-191-2227269; E-mail: Galip.Akay@ncl.ac.uk This work was supported by the EU FP7 Integrated Project (COPIRIDE) Andrea Jordan was supported for her PhD studies by a National Development Scholarship from the Government of Barbados and a research grant from the Barbados Light and Power Company Limited which also supplied fuel cane bagasse for the experiments Abdulaziz Mohamed was supported for his PhD studies by the Libyan Ministry of Higher Education and Scientific Research Copyright©2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences All rights reserved Journal of Energy Chemistry Vol 22 No 2013 vided through the ‘economies of scale’ As a result, oil refineries, power generators and petrochemical plants are very large centralized production platforms consistent with the centralized nature of the feedstock chemicals and intermediates (i.e., fossil fuels) Costs and environmental impact associated with feedstock transport and product distribution from centralized production facilities can be avoided by localized small scale production facilities operating near the feedstock source and product consumption which can be achieved with biomass based CEF technologies However, such production facilities will not benefit from ‘economies of scale’ Therefore, it is necessary to develop a technology which does not have the burden of ‘economies of scale’ This technology is already available in the form of Process Intensification (PI) [1] and is highly suitable for small scale CEF generation The full benefits of PI can only be realized if intensified unit operations are integrated to obtain chemical-biochemical plants Process integration on a global scale can further enhance the sustainability of biorefineries This approach has been recently proposed and exemplified in the form of ammonia production from biomass through integrated intensified processes [2,3] and subsequently extended to biofuel production and power generation [4,5] The critical intensified unit operations of this ammonia technology include gasification, syngas cleaning, gas separation and various reactors for ammonia conversion and steam reforming of syngas The integration of the unit operations and global scale integration with water and food generation technologies require novel processes, catalysts and material particularly polymers, in order to enhance biomass and crop yields and water and fertiliser uptake efficiency by plants [6,7] which can be achieved by nano-structured micro-porous (NSMP) polymers [8,9] These materials are a special class of micro-porous polymers known as PolyHIPE Polymers (PHPs) [8,10] 1.2 Nano-structured micro-porous polymers in process intensif ication and energy Based on the so called ‘confinement phenomenon’ using NSMP-polymers [1], various intensified processes have been discovered in agriculture (A-PI) [6,7,11], biology (BPI) [12,13] Intensified processes have also been observed in chemicals sector (C-PI) [14,15] and energy conversion (EPI) [3] with intensification factor reaching well over 200 fold compared with the current technology In these intensified processes, various types of PHPs have been used and the underlying mechanism of intensification is similar More recently, these materials have been used as ‘intermediate chemicals’ in the manufacture of ammonia from syngas in a catalytic low temperature plasma induced process which operates at atmospheric pressures Here, sulphonated PHPs (s-PHPs) are used as solid acid for ammonia adsorption in a multi-stage process since at each stage only ca 10% conversion takes place This method thus creates ammonium sulphonate within the pores of s-PHP as slow release fertiliser However, am- 427 monia loaded s-PHP is also used as soil additive functioning as synthetic rhizosphere (SRS) to enhance interactions among plant roots, nutrients, water, bacteria and root exudates which result in the enhancement of biomass generation and crop yield; i.e., Agro-Process Intensification [6,7,10] These interactions occur because the plant roots penetrate into the s-PHPs which are also highly hydrophilic As a result of hydrotropism and chemotropism, root penetration into s-PHPs is not random [6,10] 1.3 Tars as natural herbicides Low molecular weight polycyclic aromatic hydrocarbons (PAHs) are found to show some phytoxicity in soil [16–18] However, tars are also used as protection against weeds, harmful insects and rodents and it was suggested that tars such as birch tar oil should be preferable to organic herbicides [18] Therefore, the profile of tars recovered from syngas and process water cleaning can be modified and low molecular tars can be oxidised to achieve non-phytoxicity and herbicidal properties This suggests that some of the PAHs captured by s-PHP during syngas cleaning can therefore be used as herbicides 1.4 Gasif ication and syngas cleaning Gasification has emerged as one of the primary energy conversion technologies for sustainable energy production, particularly from low heating value biomass residues, due to the higher efficiencies of fuel conversion to energy as compared with combustion [19−21] It represents a key technology in the establishment of a thermochemical biorefinery [3] having the lowest environmental impact in energy conversion technologies [21] as concluded through exergy analysis [22,23] During gasification condensable organic compounds known as tars are produced and become entrained in the syngas [24−28] Tars can cause widespread fouling of operating equipment as they can condense on downstream users causing extensive coking of heat exchangers and plugging of valves [29] Consequently in most post gasification applications, including power generation and gas to liquid conversion, tars as well as particulates must be removed to varying degrees [29−31] Biomass fuels which are high in lignin such as fuel cane bagasse (FCB), yield higher concentrations of tar compared with other fuels such as bone meal or municipal solid waste which contain catalytic contaminants useful in tar cracking Tars can be classified into five classes on the basis of their condensation behaviour and water solubility [32] Various tar compounds in each class are available (Tables and in reference [28] Also see reference [32]) In this classification system, the potential for condensation of a given composition of tars is determined by calculating the tar dew point that is defined as the temperature at which the real total partial pressure of tar equals the saturation pressure of tar [25,30] The 428 Galip Akay et al./ Journal of Energy Chemistry Vol 22 No 2013 classification system (Class 1−5) [32] indicates that at very low concentrations of Class and tars, these compounds will condense even at high temperatures while Class and tars condense only at extremely high concentrations and temperatures below ◦ C Tars not only cause fouling of downstream process equipment but can represent as much as 10% of the low heating value of the syngas produced [28,30] which is lost to the syngas if not converted to H2 , CO and CH4 The production of tar therefore lowers the overall conversion efficiency of biomass to syngas and increases the capital operating costs Consequently the reduction and/or removal of tar from syngas is critical to the wide spread development of commercial smallscale biomass gasifier systems Currently, the preferred option for tar reduction is in the gasifier itself through process control and the use of primary measures such as additives (i.e., CaO) and catalysts which modify gasification conditions to produce less tar and more hydrogen [4,30,33,34] However, even by the addition of catalysts, tars are still formed and in certain applications such as syngas-to-liquid conversion or syngas-to-power conversion through fuel cells, tars as well as degraded catalysts need to be captured from syngas Several techniques for this secondary tar removal have been developed [4,35,36] A third method of tar removal is catalytic tar cracking after syngas generation This method combines the advantages of the above methods [26] In this study we investigated the use of nano-structured microporous and highly hydrophilic ion-exchange polymers (s-PHPs) as a secondary measure to remove tars from syngas produced through the gasification of fuel cane bagasse (FCB) waste residues in a novel downdraft gasifier Materials and methods 2.1 Fuel cane bagasse (FCB) Fuel cane, grown at various locations in Barbados (13o 10N, 59o 32 W) and at elevations ranging from 60–90 m was harvested by mechanical harvesters in February during the dry season They were cut approximately 15 cm above ground and the stalk, cane tops and trash were immediately loaded unto trailers and delivered to the Portvale sugar factory where sugar was extracted within 48 h of harvesting To avoid changes in biomass structure caused by complete drying, the produced bagasse was then air dried outdoors in covered areas under ambient conditions (32 ◦ C) to a moisture content of 20−25 wt% After drying, the bagasse was sealed in polypropylene bags and shipped over a two week period to the United Kingdom for use in this study On arrival at the laboratory in the UK, FCB was air dried indoors under laboratoryambient conditions During this time the heaps were mixed every two days to ensure even drying and the moisture content monitored periodically until equilibrium with the ambient at- mosphere (9.4−10 wt%, dry basis) was obtained It was then shredded in a hammer mill and pelletised into mm diameter pellets using a Swedish Power Chippers AB commercial pellet press PP300, the final moisture content of the pellets ranged from 6.0−7.4 wt% (dry basis) The proximate and ultimate analyses of the FCB are presented in Table Table Proximate and ultimate analysis of fuel cane bagasse Ultimate analysis Carbon (wt%) Hydrogen (wt%) Oxygen* (wt%) Nitrogen (wt%) Sulphur (wt%) Chlorine (wt%) High heating value (HHV) (MJ·kg−1 ) Low heating value (LHV) (MJ·kg−1 ) 49.4±0.03 6.3±0.3 43.9±0.5 0.30±0.06 0.07±0.01 0.05±0.01 18.9±0.3 17.6±0.2 Proximate analysis Moisture (wt%) Volatile matter (wt% db) Fixed carbon (wt% db) Ash (wt% db) 9.4±0.8 65±5 31±4 3.6±0.7 Size and bulk density Bagasse type Fibrous bagasse Pelletised bagasse size (mm) 0.09−4.0 D = mm density (kg·m−3 ) 68±5 727±3 * Calculated by difference db—dry basis 2.2 50 kWe air-blown downdraft gasif ier A schematic of the downdraft gasifier system used in this work is shown in Figure Gasification of FCB was carried out at atmospheric pressure in an intensified autothermal airblown 50 kWe throated downdraft gasifier (Figure 1) The reactor has a double wall and heat loss is further reduced by fibreglass lagging which covers the outer shell The basic gasification system was described in reference [4] Briefly, fuel is batch fed manually into the reactor through the hopper at the top; after loading the gasifier the induced draft fan was switched on and the reactor started by manually lighting the air inlet ports with a butane torch Air, the gasifying agent, was sucked into the gasifier through the main air inlet valve at a controlled flowed rate and into the chamber surrounding the throat by the induced draft fan From there the air then flowed into the oxidation zone through a plane of air nozzles The syngas generated in the gasifier was then extracted from the reactor by the suction effect of the induced draft fan As the solid fuel was converted to syngas, this caused the remaining fuel to flow down through the reactor under gravity The ash and char produced during gasification were manually emptied into the ash box by turning the ash box handle periodically during the gasification Thermocouples located at T1 (drying zone), T2 (pyrolysis zone), T3 (oxidation zone) and T4 (reduction zone) continuously monitored the gasification zone temperatures Online syngas sampling and analysis was Journal of Energy Chemistry Vol 22 No 2013 carried out by Agilent HP 6890 gas chromatograph (GC) connected at sampling point S3 whilst syngas samples were col- 429 lected manually in gas tight Tedlar sample bags at sampling Points S2 and S3 These samples were also analysed by GC Figure Newcastle university 50 kWe gasification system 2.3 Gasif ication of fuel cane bagasse Gasification was carried out under optimal operating conditions for FCB [19] Approximately 150 kg FCB was gasified in experimental run The equivalence ratio (ER) was 0.26 and the gasification of pelletised FCB could be sustained without bridging, thus yielding consistent syngas quality FCB with a moisture content of 11.5 wt% was used in these experiments; the typical operating temperatures in the pyrolysis zone was 716±66 ◦ C and in the oxidation zone was 1040±130 ◦ C The typical molar percentage syngas composition (dry basis) was: H2 = 12.1, CO = 17.2, CH4 = 3.6, CO2 = 15.9, O2 = 1.0 with N2 representing the balance and trace amounts of C2 H4 and C2 H6 The low heating value (LHV) was 5.7±0.6 MJ·m−3 n (dry basis) with cold gas efficiency of 82% 2.4 Tar collection and storage The filter box located immediately after the water scrubber was filled with kg s-PHP discs and the discs exposed to a constant flow of 150 Nm3 of syngas from gasification of fuel cane bagasse over a h period The effect of s-PHP on tar concentration and composition in syngas was evaluated by comparison of these parameters before and after the filter box Tar sampling was carried out according to the draft Tar Protocol [37] with some modification Immediately after stabilisation of syngas production, samples of syngas were collected simultaneously at sampling Points S2 and S3 under isothermal conditions and at a constant flow rate for 3.5 h To prevent condensation and/or thermal decomposition of target analytes in the sample line, the line was trace heated to 300 ◦ C for the duration of sample collection The syngas was then bubbled through a heated glass fibre thimble filter at a flow rate of 0.6 Nm3 ·h−1 into a series of three impingers heated to 40 ◦ C and another three contained in a salt and ice bath at −12 ◦ C (standard conditions are defined here according to NIST as 293.15 K and 101.325 kPa) All the impingers contained isopropanol (99.9%) and after flow through the impingers the syngas stream was discharged to the atmosphere On completion of sample collection, the isopropanol in the impingers was mixed, the impingers and tubing were rinsed with additional isopropanol and the rinsate was added into the impinger solutions and stored in an air tight brown bottle at ◦ C until the sample could be analysed 2.5 Tar recovery for analysis The tars contained in the glass fibre thimble filters were extracted by Soxhlet extraction over a period of h using isopropanol After each extraction, 100 mL of the extract was removed and the remainder was added to the stored solution collected from the impingers After Soxhlet extraction the glass fibre filter thimbles were dried in an oven at 105 ◦ C overnight and then cooled in a desiccator The difference in mass between the initial filter used and the extracted filter represents the mass of particulate matter contained in the sampled syngas To determine the mass of gravimetric tar contained in the filters, the 100 mL extract was evaporated at 55 ◦ C and 180 mbar using a rotary evaporator and the mass of the residue was recorded Determination of GC-detectable tar content of the gravimetric tar was carried out by re-dissolving the residue in 25 mL isopropanol which was then stored in a sealed brown bottle at ◦ C until it could be analysed by GC/MS 2.6 Supercritical f luid extraction of tar from sulphonated PolyHIPE Polymers PHP discs which were exposed to syngas containing tars were subjected to extraction in an SFT-100 supercritical fluid 430 Galip Akay et al./ Journal of Energy Chemistry Vol 22 No 2013 extractor using liquid CO2 at 4000 psi and 85 ◦ C Each sample was soaked in supercritical CO2 for 15 min; the extract produced was then released and collected in a separator This was followed by another soaking for 10 min, release of the extract and a further soaking for another 10 after which the extract was released The process of soaking with CO2 was repeated until no further increase in tar extraction was observed The extraction vessel was then vented and the collected tar extract was stored in a brown bottle at ◦ C prior to analysis using GC/MS 2.7.2 Washing and drying of PolyHIPE Polymer The mm thick PHP discs were washed for 30 with deionised water, then rinsed, and the process of washing and rinsing was repeated twice On completion, the discs were air dried overnight in a fume cupboard Dryness was determined qualitatively by visual inspection of the tissue surface on which the discs had been placed, and the dried discs were then sulphonated 2.7 Sulphonated PolyHIPE Polymer Sulphonated PolyHIPE Polymer (s-PHP) was used for the collection and removal of tars from syngas after flow through the water scrubber It was prepared in batches and carried out as described in reference [8] A synopsis of the methodology used is described below 2.7.1 Emulsion preparation Continuous phase (100 mL) and aqueous phase (1 L) were prepared separately 25 mL of continuous phase was poured into a stainless steel mixing vessel and 225 mL of aqueous phase was pumped continuously into the continuous phase for exactly with constant stirring Mixing was done using a cm diameter double blade impeller in which the two blades are positioned cm apart at right angles to each other The base of the impeller was positioned 1cm above the bottom of the vessel and the rotational speed of the impeller was 300 rpm On completion of the dosing period for the aqueous phase, stirring continued for another minute The resulting high internal phase emulsion (HIPE) was then poured into 50 mL plastic tubes (26 mm diameter) and placed in the oven overnight at 60 ◦ C to allow polymerisation to occur After the polymerisation of HIPE, solid PolyHIPE Polymer (PHP) cylinders were removed from the tubes and sliced into mm thick discs The void volume in PHP was 90% The polymerisation-crosslinking reactions and chemical structure of PHP are shown in Figure Figure Polymerisation-crosslinking reactions between styrene and divinyl benzene and the chemical structure of PolyHIPE Polymer (PHP) 2.7.3 Sulphonation of PolyHIPE Polymer To increase the absorptive capacity of PHP, discs were soaked in concentrated H2 SO4 (97%) for 2.5 h During this time the containers were agitated periodically to ensure that both surfaces of the discs remained in contact with the acid After soaking, the discs were removed from the acid, placed on the microwave turntable and microwaved at 850 W, 180 ◦ C for 5×30 s periods with four alternating cooling periods They were inverted after the third heating interval so as to reduce the occurrence of uneven heating On cooling, the discs were washed in deionised water for 10 min, rinsed and the process repeated once more They were then left to dry in a fume cupboard, once dried the discs were then ready to be used in gas cleaning The sulphonation reaction of PolyHIPE Polymer with sulphuric acid and the chemical structure of sulphonated PolyHIPE Polymer (s-PHP) are shown in Figure Figure Sulphonation reaction of PolyHIPE Polymer with concentrated sulphuric acid and production of sulphonated PolyHIPE Polymer (s-PHP) Journal of Energy Chemistry Vol 22 No 2013 2.8 Tar analysis The sample extracts collected were analysed for tars by gas chromatography/mass spectroscopy (GC/MS) using an HP 5971A GC/MS The column used was an HP 5MS 30 m×0.25 mm i.d, 0.25 μm film thickness The carrier gas was high purity helium (99.999%) at a flow rate of 1.0 mL·min−1 The temperature programme was: initial 50 ◦ C where it was held for min, then to 325 ◦ C at a rate of ◦ C·min−1 , where it was held for another The injector temperature was set at 250 ◦ C and μL of each sample was injected in the split mode with a split ratio of 50 : MS was operated in the electron ionization (EI) mode at the electron energy of 70 eV The transfer line and ion source temperatures were 280 ◦ C and 160 ◦ C, respectively Identification of the tars was done using the NIST spectral library and the MassBank high resolution mass spectral database; quantitative analysis was carried out in full scan mode in the range of 50–500 u using internal and external standards 2.9 Scanning electron microscopy-energy dispersive X-ray (SEM-EDX) analysis Investigation of the microstructure of sulphonated PHP was carried out using Environmental Scanning Electron Microscopy (ESEM) Identification of the substances deposited on the fractured surfaces of PHP was done using SEM-EDX 2.10 Tar dew point calculation The tar dew point of each mixture of tars produced was calculated using the tar dew point model developed by the Energy Research Centre of the Netherlands (ECN) [38] This model has an accuracy of ±3 ◦ C in the temperature range of 20–170 ◦ C and is the sum of all the dew point values of each tar species present It is based on the behaviour of ideal gases and Raoult’s law and Antoine equation are applied for calculation of the dew point of a mixture of hydrocarbons, using the vapour pressure data of individual compounds Only tars with molecular weights between toluene and coronene are consid- 431 ered, the heavier Class1 tars are not included in the calculation Since Class tars have high tar dew points at low concentration, this means that the actual tar dew point for syngas containing these tars is higher than the calculated value Results and discussion 3.1 Tar scavenging from syngas using sulphonated PolyHIPE Polymer (s-PHP) The performance of s-PHP in scavenging tar from syngas was investigated using a flow-through system in which syngas from the gasifier flowed through a packed bed of s-PHP particles ( = 25 mm, thickness = mm) The s-PHP particles were loaded into the filter box (Figure 1) and retained by a stainless steel mesh to ensure that carryover of PHP from the filter box to the induced draft fan did not occur The sPHP was exposed over a period of h to 150 m3 of syngas containing tar Simultaneous tar collection was carried out at sampling Points S2 and S3 immediately before and after the s-PHP packed bed (Figure 1) GCMS chromatograms of the tars in syngas collected before and after passing through the s-PHP bed are shown in Figure and Figure 5, respectively The identification of various peaks together with massto-charge ratio (m/z) is shown in Table It can be seen from Figures and that a large number of components have been reduced except for m-xylene/p-xylene and ace napthylene As discussed below, this may be due to tar reaction with s-PHP Nevertheless, there is substantial reduction in the overall tar content in syngas following extraction with s-PHP Quantitative analysis of tar removal was also carried out in order to determine the tar extraction capacity of s-PHP The tar removed by the s-PHP was extracted by supercritical fluid extraction using liquid CO2 as described in Section 2.6 Quantitative analysis of the tar extracted from the s-PHP was conducted and it was found that s-PHP captured 0.11 g total tar/g s-PHP used The compounds found in the extracted tar are categorised into their respective tar class in Table which also shows the calculated dew point of the tar decreased from 90 ◦ C to 73 ◦ C Figure GCMS chromatogram of tar in syngas before tar extraction (sampling location S2 before the filter box shown in Figure 1) Full scale of the abundance is 65000 units 432 Galip Akay et al./ Journal of Energy Chemistry Vol 22 No 2013 Figure GCMS chromatogram of tar in syngas after tar extraction with s-PHP (sampling location S3 after the filter box in Figure 1) Note that the full scale of abundance is 25000 units Table Identification of tar components from the tar collected from syngas Peaks 10 11 12 13 14 15 16 m/z 94 106 106 152 NA 166 168 178 178 192 246 204 NA 202 202 Compounds phenol m-xylene, p-xylene o-xylene acenaphthylene unknown fluorene dibenzofuran phenanthrene anthracene methylphenanthrene hexadecanoic acid 9,10-bis(chloromethyl) anthracene unknown fluoranthene unknown pyrene Table Tar compounds extracted by supercritical CO2 from sulphonated PolyHIPE Polymer which was exposed to tar laden syngas Tar class Tar dew point Tar dew point before extraction Compounds unknown 3-phenoxy-1,2-propanediol 2,4-dibenzyl-3,4-dimethylpyridine 3-phenylpropanal 2-pyridinecarbonitrile 4-nitrobenzaldehyde 3-formyl-2-methyl indole 3-hydroxy-4-methoxybenzaldehyde acenapthylene fluorene benzophenone oxime benz[anthracene] phenanthrene anthracene 4,5-methylene phenanthrene 9,10-bis(chloromethyl) anthracene fluoranthene H-dibenzo[b,d] pyran pyrene 73 ◦ C 90±6 ◦ C Several of the tar compounds extracted from the PHP were not present in the syngas sampled before the PHP bed This suggests the possibility of tar conversion promoted by active –SO3 H sites on PHP This view is further strengthened by the fact that the –SO3 H sites have been used for the selective removal of surface active species in the demulsification of crude oil-water emulsions [14,15] and it was also used as a solid-state acid for ammonia removal from the reaction mixture following ammonia synthesis Therefore, PHP does not only simply act as a filter adsorbing the tars but also interacts with these compounds The tar compounds contained in the syngas after flow through the s-PHP are listed in Table It is evident that many of the Classes and compounds were removed by the s-PHP and no longer present in the syngas However, the appearance of some previously undetected compounds such as styrene in syngas may be due to leaching of the unreacted styrene dissolved in PHP On the other hand, other previously undetected compounds, 1,2-benzenediol and 3-phenoxy-1,2propanediol are likely to be due to tar reaction in the s-PHP Figure shows the changes in concentration and composition of the tar classes after syngas flow through the s-PHP Table Tar compounds in syngas after flow through sulphonated PolyHIPE Polymer Tar class Compounds unknown phenol 1,2-benzenediol 3-phenoxy-1,2-propanediol styrene dibenzofuran acenaphthylene phenanthrene fluoranthene pyrene It can be seen from Table that use of the sulphonated PHP decreased the tar dew point to 72.6 ◦ C, however since Class tars are also present, this value is not the true tar dew point Use of this material as the sole syngas clean up system would require the true tar dew point be determined experimentally so as to prevent the deposition of tar on equipment downstream of the gas clean up system Overall, s-PHP was 83% efficient in the removal of tar from the syngas With respect to the individual tar classes the efficiency of s-PHP for removal of Classes 1, 2, 3, and tars was 95%, 81%, 83%, 80% and 85% respectively, as shown in Figure The high removal efficiency of Classes and tars exhibited by PHP provides strong evidence for the potential use of a combination of primary tar removal within the gasifier, which is followed by use of a secondary treatment system consisting of a packed bed of s-PHP as means of syngas polishing Syngas tar analysis before and after s-PHP extraction as well as analysis of tars extracted from PHP indicate that both polar tars (Class 2) and non-polar tars (Classes 1,3,4,5) have been absorbed by s-PHP Journal of Energy Chemistry Vol 22 No 2013 433 Figure Concentration of tars in each class before and after PHP 3.2 Interactions between tars and sulphonated PolyHIPE Polymer The interactions between tar and sulphonated PHP were investigated by examining s-PHPs used in tar extraction Figure 7(a) shows the presence of tar deposits within the pores of s-PHP after exposure to tar loaden syngas Through use of SEM-EDX in Figures 7(b), 7(c) and 7(d), droplets of tar associated with fragments of char embedded in the microporous network were identified, providing clear evidence that tar scavenging is not limited to adsorption on the external surfaces of the polymer but that it also occurs across the interconnected pore network Although tars consist primarily of C, H and O, during gasification of FCB ash forming elements and elemental sulphur released to the syngas will also adsorb onto droplets of tar [28] The SEM-EDX spectra produced of Points 0, and in Figure 7(a) are shown in Figures 7(b), 7(c) and 7(d) Both Figures 7(b) and 7(c) show the presence of C, H, O and S (which comes from the PHP itself) as well as the main ash forming elements in FCB In Figure 7(d) the SEM-EDX of sulphonated PHP alone is shown It was noted during the collection of PHP after removal of the tar species from the syngas, that the PHP species no longer had a spongy texture but had become extremely brittle and readily broke into small pieces when compressed Although mechanical characteristics of s-PHP changed upon reaction with tars, we have not determined their tar absorption capacity as a function of time on-stream Our on going studies indicate that once s-PHPs become saturated, it is possible to treat them chemically with acid to reverse the elasticity of s-PHPs and to oxidise the tar compounds Investigation of the sulphonated PHP morphology after exposure to the syngas using ESEM showed that: (i) adsorption of tar by sulphonated PHP occurred not only on the surface of the particles but also inside the PHP particles as well; (ii) associations of tar droplets and char particles ranging from 20−80 μm were captured in the microporous network as the syngas flowed through the PHP monoliths Figure ESEM and EDX examinations of PolyHIPE Polymers after tar deposition (a) ESEM image of tar droplets and char captured in sulphonated PHP (fractured surface) after h exposure to syngas (×1000) Points 0, and indicate the location at which EDX spectra shown below were taken (b, c, d) EDX spectra of Points 0, and from Figure 7(a) The EDX spectra of Point shows the spectrum of PHP only Note the difference in elemental composition as compared with the spectra of the char and tar at Points and 3.3 Mechanism of tar removal The mechanism of tar removal from syngas can be explained by the confinement phenomenon [1,39] which has 434 Galip Akay et al./ Journal of Energy Chemistry Vol 22 No 2013 been utilised in process intensification including bioprocess intensification [13], tissue engineering [12], separation processes [14,15], agro-process intensification [6,7] and more recently in chemical catalysis [39] In general terms, according to the confinement phenomenon, the behaviour of matter (including cells/bacteria and reactive chemical species) is dictated by the size and biochemical/chemical structure of the confinement media in which the matter is present Clearly, the size of the confinement media must be comparable with the size of the matter that is confined Although the size of the individual molecules are small compared with that of the pores of PHP, nevertheless, surface active or polar molecules can grow as clusters through aggregation within the PolyHIPE Polymers as shown previously [40,41] These structures are highly stable (low entropy) especially in the presence of confinement media and hence, there is a driving force for such molecules to diffuse from the bulk fluid (liquid or gas) into the confinement media where they are stabilised In liquid systems, this phenomenon was successfully applied to oil-water demulsification [14,15], chemical catalysis [39] and surfactant separations [40,41] In the case of tar removal from syngas, there is an additional driving force for tar diffusion into s-PHP from syngas due to the chemical reactivity of tars As shown before (Section 3.1) tars appeared to undergo chemical changes upon adsorption by s-PHP, therefore tar diffusion enhancement based on chemical potential can be expected It is clear that there is a chemical potential driven diffusion of tar molecules from the bulk of the syngas Once within the pores, some of these molecules undergo chemical reaction which are stabilised It may be possible to use such tar loaden s-PHPs from gasification of biomass as slow release natural herbicides so that when herbicidal effectiveness disappear, these s-PHPs can then act as soil additives in agro-process intensification [6,7] Although such applications require further research, the current method of tar removal illustrates the potential of s-PHP in an integrated holistic biorefinery technology Tar removal can be further intensified by process intensification fields such as electric and plasma fields with or without PolyHIPE Polymer We have recently shown that tar removal efficiency can be increased over 98% [5] using such hybrid methods which also crack tars, thus increasing its calorific value while enabling syngas for catalytic conversion to fuels and chemicals such as ammonia This tar removal method was also applied to syngas cleaning in a MWe capacity gasifier (scaled up version of the current gasifier) and produced clean gas as indeed observed by the change in the flared syngas as shown in Figure Figure 8(a) shows the orange colour of the flared syngas before tar extraction with s-PHP while Figure 8(b) illustrates the colour of the flared syngas after tar extraction The description of this MWe gasifier was disclosed previously [42,43] Figure Visual demonstration of the tar cleaning effectiveness by the method carried out with MWe scaled-up gasifier Colour of the flare (a) before syngas cleaning, (b) after syngas cleaning Conclusions We have shown that tar extraction from syngas using sulphonated PolyHIPE Polymers can result in 83% tar removal and substantial depression of tar dew point from ca 90 ◦ C to 73 ◦ C with un-optimised tar removal capacity ca 0.1 g tar/g s-PHP This method is especially useful as a Journal of Energy Chemistry Vol 22 No 2013 secondary measure of tar removal The reactivity of the tars after captured by s-PHP has been demonstrated The sustainability of the technique can be further enhanced by sPHP as a chemical intermediate (high temperature solid acid) in the reactive removal of ammonia from product stream in ammonia synthesis as described recently [3] followed by tar/hydrocarbon removal from gasification process water remediation [42] This ammonia containing s-PHP can then be used as soil additive for the multiple roles of [6,7] (a) slow release fertiliser, (b) natural herbicide, (c) water and nutrient in the soil, (d) synthetic rhizosphere (SRS) [6,7] in order to enhance water and nutrient uptake through the plant root system, and (e) support for nitrogen fixing bacteria as part of the SRS function Our estimates indicate that, these functions can be carried out sustainably at a production cost of ca 10 £/kg s-PHP Acknowledgements This work was supported by the EU FP7 Integrated Project (COPIRIDE) Andrea Jordan was supported for her PhD studies by a National Development Scholarship from the Government of Barbados and a research grant from the Barbados Light and Power Company Limited which also supplied fuel cane bagasse for the experiments Abdulaziz Mohamed was supported for his PhD studies by the Libyan Ministry of Higher Education and Scientific Research We are grateful for all the support received References [1] Akay G In: Lee S ed Encyclopaedia of Chemical Processing New York: Marcel Dekker, 2006 183 [2] Akay G The Chemical Engineer, 2006, 784: 27 [3] Akay G International Patent Publication PCT WO/2012/025767 2012 [4] Akay G, Dogru M, Calkan O F, Calkan B In: Lens P, Westermann P, Haberbauer M, Moreno A ed Biomass for Fuel Cells— Renewable Energy from Biomass Fermentation London: IWA Publishing, 2005 51 [5] Akay G, Al-Harrasi W S S, El-Nagger A A, Chiremba E, Mohamed A H, Zhang K World Patent Application, PCT/GB2013/050125 2013 [6] Akay G, Burke D R Am J Agric Biol Sci, 2012, 7: 150 [7] Akay G, Fleming S Green Process Synth, 2012, 1: 427 [8] Akay G, Bokhari A M, Byron V J, Dogru M In: Galan M A, Del Valle E M ed Chemical Engineering: Trends and Developments London: Wiley, 2005 171 [9] Akay G, Noor Z Z, Calkan O F, Ndlovu T M, Burke D R US Patent, 07820729 2010 [10] Akay G, Calkan B, Hasan H, Mohamed R European Patent Application, EP 09749167.4 2010 [11] Burke D R, Akay G, Bilsborrow P E J Appl Polym Sci, 2010, 118: 3292 435 [12] Akay G, Birch M A, Bokhari M A Biomater, 2004, 25: 3991 [13] Akay G, Erhan E, Keskinler B Biotechnol Bioeng, 2005, 90: 180 [14] Akay G, Vickers J US Patent 8177985 2012; European Patent, 1307402 2012 [15] Akay G, Pekdemir T, Shakorfow A M, Vickers J Green Process Synth 2012, 1: 109 [16] Henner P, Schiavon M, Druelle V, Lichtfouse E Org Geochem, 1999, 30: 963 [17] Smith M J, Flowers T H, Duncan H J, Alder J Environm Pollut, 2006, 141: 519 [18] Hagner M, Pasanen T, Lindqvist B, Lindqvist I, Tiilikkala K, Penttinen O P, Setala H Agr Food Sci, 2010, 19: 13 [19] Akay G, Jordan C A Energy Fuels, 2011, 25: 2274 [20] Kirkels A F, Verbong G P J Renew Sust Energ Rev, 2011, 15: 471 [21] Saidur R, Boroumandjazi G, Mekhilef S, Mohammed H A Renew Sust Energ Rev, 2012, 16: 1217 [22] Dincer I, Cengel Y A Entropy, 2001, 3: 116 [23] Dincer I, Rosen M A Exergy: Energy, Environment and Sustainable Development New York: Elsevier, 2007 [24] Li C S, Suzuki K Renew Sust Energ Rev, 2009, 13: 594 [25] Rabou L P L M, Zwart R W R, Vreugdenhil B J, Bos L Energy Fuels, 2009, 23: 6189 [26] Rapagna S, Gallucci K, Di Marcello M, Matt M, Nacken M, Heidenreich S, Foscolo P U Bioresour Technol, 2010, 101: 7123 [27] Huang J, Schmidt K G, Bian Z Energies, 2011, 4: 1163 [28] Jordan C A, Akay G Biomass Bioenerg, 2012, 42: 51 [29] Rapagna S, Gallucci K, Di Marcello M, Matt M, Foscolo P U Chem Eng Trans, 2010, 21: 415 [30] Jordan C A, Akay G Fuel Process Technol, 2013, 106: 654 [31] Jordan C A, Akay G Fuel, 2012, 91: 253 [32] van Paasen S V B, Kiel J H A Tar Formation in a Fluidised-bed Gasifier—Impact of Fuel Properties and Operating Conditions (ECN-C–04-013) 2004 [33] Torres W, Pansare S S, Goodwin J G Catal Rev-Sci Eng, 2007, 49: 407 [34] Wu C F, Wang L Z, Williams P T, Shi J, Huang J Appl Catal B, 2011, 108: [35] Blanco P H, Wu C F, Onwudili J A, Williams P T Energy Fuels, 2012, 26: 2107 [36] Wang L, Weller C L, Jones D D, Hanna M A Biomass Bioenerg, 2008, 32: 573 [37] CEN/TS 15439: 2006 Biomass Gasification—Tar and Particles in Product Gases—Sampling and Analysis, (2006) [38] ECN-Biomass: Energy Research Centre of The Netherlands., 2009 Thersites the ECN Tar Dew Point Site Available from http://www.thersites.nl/completemodel.aspx [39] Akay G World Patent Application, PCT/GB2013/050122, 2013 [40] Akay G, Wakeman R J J Membr Sci, 1994, 88: 177 [41] Akay G, Wakeman R J Chem Eng Sci, 1994, 49: 271 [42] Akay G, Dogru M, Calkan O F The Chemical Engineer, 2006, 786: 55 [43] Dogru M, Akay G Japanese Patent, 2006-53894 2011