Prospect and current status of recycling waste plastics and technology for converting them into oil in China

Prospect and current status of recycling waste plastics and technology for converting them into oil in China Guang-Hua Zhang a,∗ , Jun-Feng Zhu a , A Okuwaki b a College of Chemistry and Chemical Engineering, Shaanxi University of Science & Technology, Xianyang 712081, China b College of Environmental Studies, Tohoku University, Sendai 980-8579, Japan Received 13 June 2006; received in revised form 13 November 2006; accepted 15 November 2006 Available online 13 December 2006 Abstract In the paper, the authors present the current situation of recycling waste plastics and technology of converting waste plastics into oil in China The process of pyrolysis and pyrolysis-catalytic upgrade method has been evaluated in terms of technology and economics The conditions of a plant, that is to be constructed for converting waste plastics to oil, such as collecting system, transportation distance of waste plastics, sorting method and controlling over secondary pollution, are investigated In addition, the commercialization and area of research on this technology in China are proposed © 2006 Elsevier B.V All rights reserved Keywords: Waste plastics; Consumption of plastics; Converting plastic wastes into oil; Pyrolysis reactor; Catalytic pyrolysis Contents ∗ Introduction Current status of recycling waste plastics Corresponding author Tel.: +86 29 33579787; fax: +86 29 33579787 E-mail address: zhanggh@sust.edu.cn (G.-H Zhang) 0921-3449/$ – see front matter © 2006 Elsevier B.V All rights reserved doi:10.1016/j.resconrec.2006.11.007 232 232 Present technology and industrialization for converting plastic wastes to fuel oils 3.1 Pyrolysis 3.2 Pyrolysis-catalytic upgrade The representative pyrolysis equipment for waste plastics in China The development of technology and industry for converting waste plastics to oil Acknowledgements References 234 235 236 237 237 238 238 Introduction With a view to the environmental protection and reduction of non-regeneration resource, recycling technology for converting to oil from plastic wastes has drawn much attention in China Some universities and institutes have developed the basis theories and the technology for industrialization of plastic liquefaction (Huang et al., 2002; X.-X Li et al., 2002) Many patents on the converting technology have been adopted Many pilot plants have been built up near Beijing, Nanjing, Xi’an, etc But, some problems have appeared accordingly Firstly, there being no effective collecting system and transportation and sorting the collected waste plastics simply by manual, as a result, the collected plastic wastes cannot satisfy the continuous production on a large scale Secondly, the secondary pollution has not been seriously considered in the process of waste plastics The environmental considerations deals with heat energy waste exhaust gas emission, water and dust waste, and the like Thirdly, there is no technological standard for the recycling of plastic wastes in China The article expatiates upon the current situation of plastic wastes and their recycling technology for recovering to oil in China Current status of recycling waste plastics As one of the most fast developing industries in China, the plastic industry maintains a growth rate of more than 10% per year The output of plastics in China reached 26.8 Mt in 2003 (Liao, 2004) Fig shows the consumption of plastics In comparison with developed countries in terms of average consumption, it can be seen that the quantity is less in China The average consumption was about 17.5 kg in 2000 (Yang, 2001) Fig indicates the usage proportion of plastics in the different fields in 2000 while Fig 3, the proportion in sorting the waste plastics (Liao, 2004) Fig shows the output of recycling plastic wastes in China (Liao and Liu, 2000) The reusing plastic wastes have been dramatically increasing from 1996 to 2005 There are many collection points being distributed in the cities and countries According to the survey of the Committee of Economy and Trade of China, the recycling output of the plastic wastes in China was up to Mt in 2005 (Tan, 2006) Comparing Fig with Fig 4, it can be found that the quantity of plastic wastes in China is still less than that of plastic consumption, and the proportion of recycling plastic wastes merely reaches one-fifth of the consumption (Ji et al., 2000) The post consumer recycled polyvinyl chloride (PVC) is less than other category of plastic wastes in China Comparing Fig with Fig 5, shows that it is necessary to investigate how to recover PVC wastes Fig Consumption of plastics in China Fig Usage proportion of plastics by different fields The statistic evidence indicates that the recycled plastic wastes account for 0.4–1.5% of Municipal Solid Waste in China (only 0.14 Mt per year at Beijing) Another source of plastic wastes is the collected farm films For instance, the amount of farm film wastes approximately was 150–225 kg/104 m2 in 2004 at Shaanxi, Heilongjiang, Jilin and Liaoning provinces of China (Yang, 2001) Fig Sorting proportion of plastics in 2003 Fig Output of recycled plastic wastes in China Present technology and industrialization for converting plastic wastes to fuel oils The pyrolysis is a principal way to convert plastic wastes to fuel oil The yield of fuel oils is under 55% with this method For this reason, the pyrolysis-catalytic upgrade method has been employed recently (Liao and Liu, 2000) The production of fuel oils based upon these methods can reach 55–75%, depending on the composition of plastic wastes All the plastic wastes collected are present together in China Sorting the mixed waste plastics by Fig Proportion and sorts of recycling plastic waste in China manual is inefficient Only mixed plastic wastes for being converted to oil can be accepted in China 3.1 Pyrolysis The pyrolysis by direct heating (Fig 6) was adopted to produce the paraffin and crude oil from the plastic wastes in the 1990s in China The small-scaled process is featured by facilitation, convenience and low equipment investment The system consists of feed-supply, pyrolysis reactor, fractionating tower, heating and temperature controller and device for filling the plastics into the pyrolysis reactor The capacity of this pilot plant is 1000 tonnes/annum However, the temperature caused by pyrolysis is higher and all the Fig Pyrolysis process of generating fuel oil from the waste plastics reactive time is longer than the other methods else The octane number of gasoline gained is relatively low and the pour point of diesel oil is high More paraffin is produced in the process of pyrolysis Although this process is simple and convenient, the converting rate and yield is still lower The pyrolysis rate and yield should be promoted by a catalyst, like silica–alumina catalyst or diatomite, etc (Liu and Chen, 2001) Before the catalyst and plastic waste is mixed within the pyrolysis reactor, the plastic waste must be cleaned The total yield of fuel oil is 50–65%, relying on the composition of plastic waste during pyrolysis But, one problem is how to recycle the catalyst, carbon and other residua after pyrolysis This process is also called the catalytic pyrolysis The other problem for this process is the pyrolysis equipment’s corrosion incurred by PVC in mixed plastic wastes Therefore, it is strongly recommended to establish a reasonable sorting system and apply a efficient technique to eliminate hydrochloric acid 3.2 Pyrolysis-catalytic upgrade Since the total yield of fuel oil with pyrolysis is still lower and the quality of oil is not satisfied as gasoline and diesel oil, the upgrade by catalyst for the crude products gained with pyrolysis can be used Having improved the quality of finished oil, this process has been widely used in many factories (X.-X Li et al., 2002) Fig shows the flowchart of pyrolysis-catalytic upgrade, which has been adopted in factories to treat the mixed plastic wastes The system consists of the knapper, extrusion machine, pyrolysis reactor, catalytic upgrade reactor, fractionating tower, heating and temperature controller, separator of oil and water, and oilcan The factory nearby Beijing used it to produce the fuel oil The finished oil consists of gasoline (60%) and diesel oil (40%) The total yield reaches as high as 72.5% (Wang et al., 2003) Fig Pyrolysis-catalytic upgrades technique of plastic wastes in China Fig Pyrolysis equipment for mixture of plastic waste (1) Pyrolysis reactor; (2) stirrer; (3) motor; (4) pipe; (5) heavy oil separator; (6) oil tank According to the yield of converting waste plastics to oil in China, the plastic wastes weighing 1.92 tonnes can produce tonne of fuel oil A plant with a capacity of tonnes/day will need 1728 tonnes of plastic wastes annually Supposing the average content of plastic wastes is that the Municipal Solid Wastes account for about 0.5% for cities and 0.3% for countryside (Ji et al., 2000), the economic transportation distance will be within 200 km or so As the economic support from local government is short, and the whole process from collecting, transporting, sorting to converting must be in accordance with marketing rule, the plant has to face towards a big risk in converting plastic wastes to fuel oil The representative pyrolysis equipment for waste plastics in China Comparing the fixed bed catalytic reactor with fluidized bed reactor (Kiran et al., 2000; Bruce et al., 1999; W.-H Li et al., 2002), it can be seen that the structure of pyrolysis reactor is very simple Fig presents the representative pyrolysis device for waste plastics, reported by a Chinese patent (Qian, 2002) The device is made of the carbon steel or stainless steel As a contemporary reactor, it is impossible to be developed into any larger scale equipment to rationalize the operations, inclusive of automatic control and more same reactor units The development of technology and industry for converting waste plastics to oil The law and regulation for recycling plastic waste has been enacted and the efficient collecting system has formed with the economic development of China There are many parks and residential areas in China placing collection points for waste plastics The recycling of plastic wastes is becoming a new attractive field in that it can save resource and protect the environment The National Committee of Recycling and Utilization of Plastic Wastes was founded as early as 1992 in China Its duty is to guide the recycling and utilization of waste plastics The current status of technology for converting plastic wastes to oil can adapt itself to the actuality of China The plants with a capacity of 1000 tonnes/annum have been running nearby many cities in China (Tan, 2006), but, there are many subsequent problems to be solved in the near future In China, the further tasks are to constitute the standards for process and products of post-consumer recycled plastics and to adopt the more advanced pyrolysis technologies for waste plastics, such as fixed bed catalytic reactor or fluidized bed reactor, referring to the experiences of developed countries, like Germany and Japan, especially (Kiran et al., 2000; Miller et al., 2005; Scott et al., 1999; Chen, 2005; Shi and Chuai, 2006) In addition, the type of pyrolysis reactor must be designed to suit the mixed waste plastics and small-scaled and middle-scaled production The scientist should pay more attention to exploring the recycling and pyrolysis of waste PVC and the optimization of operational conditions of pyrolysis for waste plastics (Shah et al., 1999; Tan, 2006; Ali and Siddiqui, 2005; Jale et al., 2001; Miranda et al., 2001) A novel and more efficient catalyst ought to be studied for the process of pyrolysis and pyrolysis-catalytic upgrade technique, and the mechanism of pyrolysis should also be explored (Park et al., 1999) From the view of environmental protection as well as the economics, a novel and reasonable technology is needed This is the responsibility of the governments and the producers The reuse of waste plastics, one of the avenues to tackle the resource shortness, will be able to play a vital role in the near future in China Acknowledgements The project is sponsored by Institute of Environmental Protection and Economy on Energy, Xianyang, China We are also very grateful to professors Ma Hong-rui and Liu Bao-jian of Shaanxi University of Science & Technology for their dedications References Ali MF, Siddiqui MN Thermal and catalytic decomposition behavior of PVC mixed plastic waste with petroleum residue J Anal Appl Pyrolysis 2005;74(1–2):282–9 Bruce JM, Leo AB, Franco B J Anal Appl Pyrol 1999;51:157–66 Chen F-Z Reclaiming technology of Japanese used plastics World Plastic 2005;23(3):50–62 Huang Y, Yan H-X, Zhang Q-Y Liquid fuel manufactured from waste plastics cracking Plastics 2002;31(4):36–40 (in Chinese) Jale Y, Azhar U ddin M, Kazuo I, et al Polym Degrad Stab 2001;73:335–46 Ji X, Qian J-L, Wang J-Q, et al Prospect and current situation of technologies for converting plastic waste to oil in China Environ Protect Chem Ind 2000;20(6):18–22 (in Chinese) Kiran N, Ekinci E, Snape CE Recycling of plastic wastes via pyrolysis Resour Conserv Recycl 2000;29(4):273–83 Li W-H, Li Y-H, Qin Q, et al Study on industrial apparatus to produce gasoline and diesel by catalytic cracking for waste plastics Appl Chem Ind 2002;1(31):44–6 (in Chinese) Li X-X, Shi Y-F, Yu H-R Preparation of fuel oil from plastic waste by catalytic cracking Environ Protect Chem Ind 2002;22(2):90–4 (in Chinese) Liao Z-P, Liu Y-J Status of plastics processing industry and suggestions on its development Modern Chem Ind 2000;20(7):5–8 (in Chinese) Liao Z-P Situation of china plastics industry in 2003 China Plastics 2004;18(6):1–7 (in Chinese) Liu G-Z, Chen E-T Catalytic cracking of scrap plastics into gasoline and diesel oil by a pilot experiment unit Environ Sci Technol 2001;98(6):9–10 (in Chinese) Miller SJ, Shah N, Huffman GP Conversion of waste plastic to lubricating base oil Energy Fuels 2005;19(4):1580–6 Miranda R, Pakdel H, Roy C, et al Polym Degrad Stab 2001;73:47–67 Park DW, Hwang EY, Kim JR, et al Polym Degrad Stab 1999;65:193–8 Qian C-L A novel equipment of pyrolysis for converting plastic waste to oil, CN 2540412; 2002 Scott DS, Majerski P, Piskorz J, Radlein D, Barnickel M Production of liquid fuels from waste plastics Can J Chem Eng 1999;77(5):1021–7 Shah N, Rockwell J, Huffman GP Conversion of waste plastic to oil: direct liquefaction versus pyrolysis and hydro-processing Energy Fuels 1999;13(4):832–8 Shi B-Y, Chuai C-Z Research development of technology using waste plastics and cracked catalyst producing fuel oil Plastic Sci Technol 2006;34(3):61–2 (in Chinese) Yang H-D Retrospect and prospect, development situation and trend of China plastics industry China Plastics 2001;15(6):1–9 (in Chinese) Tan Y-W Current situation in the Chinese plastics recycling market Chem Fibers Int 2006;56(3):182–5 Wang L, Luo G-H, Li Q Progress of waste plastics pyrolysis Chem Ind Eng Progr 2003;22(2):130–4 (in Chinese)