Green Engineering through feedstock recycling of

Green Engineering through feedstock recycling of waste Rubber and discarded Tyre’s VOLUME: LXVI. NO – 04, APRIL 2014

Rane Ajay Vasudev, Abitha V K Abstract Green Chemistry and Green Engineering are two scientific philosophies that strive to promote sustainable development through science and technology and achieve the goals of environmental protection, health and safety of workers and consumers and less toxic products, Green Chemistry and Green Engineering provide twelve principles as a framework for scientist and engineer‟s to promote the designing of new processes and materials, new energy sources, alternative methodologies and renewable sources for the research laboratories and manufacturing industries, Green Chemistry as a scientific movement for better design and innovations in the chemical and allied industries was extended to Green Engineering which covers technological applications, engineering processes and product. When viewed at the principles of green engineering you will find at Principle no 6, the design choices for recycling various materials must be viewed as an investment; discarded tires represent a significant component of the recycling challenge. They are easily segregated, large volume part of the waste stream and present their own, somewhat unique waste utilization problems. The major problem lies in finding approaches that are both economically and environmentally sound. Some of the methods of utilizing scrap tires that have been investigated are: burning, pyrolysis, use in cleaning up oil spills, road surfaces, roofing materials, and playground surfaces, While some of these approaches have been put into practice, the scrap tire disposal problem is still clearly a case where supply far outstrips available uses, and new methods of utilization (or technological advances to extend existing ones) are clearly needed. The whole issue is complicated by many alternative proposals, varying government legislation and preferences, incomplete technical information, and economic uncertainties. In the following article various methods like gasification and partial oxidation, thermal process, catalytic cracking and reforming, hydrogenation have been described which are used to recycle waste rubbers and discarded tyre‟s which led to the formation of secondary products of slightly lower value than the virgin but may be used to manufacture middle value products, Introduction Green Engineering focuses on how to achieve sustainability through science and technology. As in case of Green Chemistry, Green Engineering are covered by 12 Principles. The 12 Principles of Green Engineering provide a framework for scientist and engineer‟s to engage in when designing new materials, products, processes and systems that are benign to human health and the environment. The breadth of the principles applicability is important, the green engineering principles must be applicable, effective and appropriate otherwise these would not be principles but simply a list of useful techniques. It is also useful to view the 12 principles as

parameters in a complex and integrated system, just as every parameter in a system cannot be optimized at any one time, especially when they are interdependent, the same is true for these 12 principles. There are examples in where successful application of one principle advances one or more of the others. In some examples a balancing of principles will be required to optimize the overall system solution. The twelve principles of Green Engineering have been implemented by the scientist of American Chemical Society and are as follows: Principle

1 2 3

4

5

6

7 8 9 10 11 12

Explanation Materials and Energy must be inherently non hazardous, rather than circumstantial, (designers need to strive to ensure that all materials and energy inputs and outputs are as inherently non hazardous as possible). Prevention of waste instead of treatment, (it is better to prevent waste than to treat or clean up waste after it is formed) Design for separation and purification process, (separation and purification operations should be designed to minimize energy consumption and material use) Maximize efficiency in products and processes, (products, processes and systems should be designed to maximize mass, energy, space and time efficiency) Output – pulled versus Input – pushed, (products, processes and systems should be “out pulled rather than “input pushed through the use of energy and materials) Conserve Complexity,(embedded entropy and complexity must be viewed as an investment, when making design choices on recycle, reuse or beneficial disposition) Durability rather than Immortality, (targeted durability, not immortality should be design goal for products, after useful use of a product to disintegrate under natural conditions) Meet need, Minimize excess,(design for unnecessary capacity or capability {example- one size fits all} solutions should be considered as a design flaw) Minimize material diversity,(material diversity in multicomponent products should be minimized to promote disassembly and value retention) Integrate material and energy flow,(design of products, processes and systems must include integration and interconnectivity with available energy and market flow) Design for commercial “After life” , (products, processes and systems should be designed for performance in a commercial “after life”) Renewable rather than depleting,(material and energy inputs should be renewable rather than depleting)

All the principles mentioned are in some or the other way related to the recycling technology, but principle 6 and principle 3 are closely related to the recycling as considering the economic part, which has an important role to play while we think of recycling, feedstock recycling is limited by the process economy rather than by technical reasons. Three main factors determine the

profitability of these alternatives: the degree of separation required in the raw wastes, the value of the products obtained and the capital. According to the separation steps required, the different methods of feedstock recycling can be ordered as follows: gasification < thermal treatments < hydrogenation < catalytic cracking < chemical depolymerization. Many of the projects on recycling of waste rubber have failed in the past due to the relatively low price of the derived products which is in inverse ratio with the capital invested to setup a plant for recycling , but currently this problem is prevail over. We will now describe the individual method for feedstock recycling of waste rubber and discarded tyre‟s waste in the following paragraphs – Gasification Gasification can be considered to be a partial oxidation process of carbonaceous materials (like waste rubber and discarded tyre‟s) leading predominantly to a mixture of carbon monoxide and hydrogen, known as „synthesis gas‟ or „syngas‟ due to its application in a variety of chemical syntheses. Gasification was initially developed for coal conversion, but it has been further applied to the processing of heavy petroleum fractions and natural gas. In the last two decades, gasification has also been investigated as a method of obtaining valuable chemicals from both biomass-derived products and organic solid residues. Currently, gasification can be considered an efficient treatment for the degradation and conversion of polymeric wastes. One of its major advantages lies in the fact that it is not necessary to separate the different polymers present in the rubber wastes. Moreover, in many cases rubber wastes are gasified while mixed with other components of the solid waste stream. However, the economics of a gasification process largely depend on the value and possible applications of the synthesis gas, either as an energy source by combustion or for the synthesis of various chemicals (methanol, ammonia, hydrocarbons, acetic acid, etc.). Energy recovery via gasification of rubber waste and discarded tyre‟s is an emerging conversion technology drawing increasing interest for its potential benefits of energy recovery, landfill diversion and avoid road side area consumption.

Figure no 1: Gasification process for rubber waste and discarded tyres

Partial and controlled oxidation of rubber is used to promote rubber crosslinking in order to enhance their physical properties and improve their processability. Thus the treatment of rubbers with different peroxides, which usually results in an increase in the rubber melting temperature and a narrowing of the molecular weight distribution. On the other hand, in the thermal degradation of rubbers, it is well known that the presence of low amounts of oxygen accelerates rubber degradation, whereas at higher oxygen concentrations complete oxidation into carbon dioxide and water is predominant.

Figure no 2: Partial oxidation of rubber waste and discarded tyres A process for the oxidative decomposition of vulcanized rubber by treatment with an organic hydroperoxide under mild reaction conditions, can be applied to both natural and synthetic rubbers, and a wide range of organic peroxides can be used (tert-butylhydroperoxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, etc.). The hydroperoxide is contacted with the vulcanized rubber in a proportion of between 1 and 5 wt% in the presence of halogenated hydrocarbons as solvents and Cu or Co salts as oxidation catalysts. The reaction proceeds at temperatures around 40ᵒC and is accelerated by a supply of air or oxygen. Under these conditions, total decomposition of the rubber can be achieved after several hours of reaction, resultant product after several hours of reaction can be used as process oil, softener, compounding ingredient for rubber, modifier for asphalt, etc, Another process wherein oxidative decoupling of scrap rubber under water supercritical conditions is carried out for natural and synthetic, vulcanized and non-vulcanized, rubbers have been processed to yield a mixture of lower alkanes, alkenes, dienes, aromatics, alcohols, carboxylic acids, aldehydes and ketones, small quantities of rubber fragments, carbon dioxide, water, sulfur and nitrous oxides, and halide acids can also be formed, depending on the raw rubber. The reaction takes place above the critical water temperature and pressure in the presence

of oxygen. Under these conditions, the (rubber) polymers are very rapidly broken down through chain scission (breakage of carbon-carbon bonds), and devulcanization when starting from a vulcanized rubber (breakage of sulfur-sulfur and carbon-sulfur bonds), as well as total oxidation into carbon dioxide and water, the resulting products can be used as a fuel, with or without subsequent upgrading to obtain a fuel of higher quality, or to produce various chemicals by separation of its components. Thermal Process Thermal Process describes the methods and processes developed for breaking down polymeric materials simply by treatment at high temperature in an inert atmosphere. The type and distribution of products derived from the thermal degradation of each polymer (rubber) depends on a number of factors: the polymer (rubber) itself, the reaction conditions, the type and operation mode of the reactor, etc. Of the reaction variables, it is obvious that temperature is the most significant, because it influences both the polymer conversion and the product distribution. Stirred tanks, rotary kilns, fixed beds, fluidized beds and tray systems are examples of reactor types used for the thermal degradation of tyres. Several of these processes are now being used on a pilot plant and industrial scale. Basically, three fractions are derived from the thermal decomposition of tyres: gases, liquid oils and solid residues (10-30% gases, 38-55% oils and 3338% char at 500ᵒC – 900ᵒC) Pyrolysis of used tyres in the temperature range of 300ᵒC – 600ᵒC, in a fixed bed reactor with a nitrogen atmosphere was carried out and an increase in temperature up to 600°C caused a decrease in the yield of char, whereas it favours the production of gases and oil. Above 600ᵒC, only slight changes were observed in the product distribution. The gases were composed mainly of hydrogen, carbon dioxide, carbon monoxide, methane, ethane and butadiene, the oil fraction has an apparent molecular mass of up to 1660. A wide variety of compounds were identified in the oil with a high proportion of aromatic hydrocarbons, including polyaromatic species. FTIR analysis showed the presence of oxygenated species such as aldehydes, ketones and carboxylic acids, an increase in the char surface area with both temperature and heating rate, values up to 60 m2/g being obtained, these surface areas are large compared with those of the raw carbon blacks used in tyre manufacture, however the pyrolysis char contains a higher proportion of ash and has a larger particle size, which makes this product an alternative to carbon black only in undemanding applications. Chars from tyre pyrolysis contain about 15 wt% of minerals, mainly zinc oxide. The oils are characterized by a high chemical complexity and calorific values in the range 35-40 MJ kg-1, hence in many cases the major application proposed is their combustion to produce energy. However, the relatively low sulfur content of the oils (usually 1-2 wt %) and the presence of valuable chemicals make it feasible to process and upgrade the oils for use as a refinery feedstock. In this way, the major changes that most refineries are currently undergoing in order to increase their capacity for the processing of petroleum with increasing sulfur content

is a factor that may also favour the further refinery upgrading of the oils derived from the thermal degradation of tyres.

Figure no 3: Thermal Decomposition of discarded tyres Thermal decomposition (figure 3) is also carried under vacuum at 500ᵒC, where 54 wt% of oil, 26 wt% of carbon black, 11 wt% of gases `and 9 wt% of steel are typically produced. Vacuum tyre pyrolysis (thermal decomposition) allows the yield of the oil fraction to be increased with less production of gases and char compared with other tyre thermal decomposition methods. The oil produced was fractionated by distillation into three cuts: a naphtha fraction (bp < 204ᵒC, 27 wt %), a light oil fraction (bp = 204-305ᵒC, 17 wt %) and a heavy oil fraction (bp > 350°C, 56 wt %). The gases formed are mainly methane and ethane, with low olefin content, and can be used as a fuel with high heating value. Various alternatives have been proposed for the valorization of the solid carbon residue of tyre pyrolysis and comparison of the properties of the char with those of coal have been carried out and it is found that, the calorific value of the char is slightly higher than that of coal due to the lower ash content of the former, while both materials have sulfur contents of about 1 wt%. The feasibility of using the char generated by tyre pyrolysis as a precursor in the manufacture of activated carbon has been studied, carbons with surface areas above 500 m2 g-1 from tyre pyrolysis in batch reactors and subsequent activation of the chars by treatment with superheated

steam at temperatures in the range 800-900ᵒC, some have also obtained activated carbons with surface areas above 800 m2 g-1 by pyrolysis of tyres up to 900ᵒC, followed by activation of the resulting chars in C02 at the same temperature and these surface areas are comparable with those of commercial activated carbons. Methods for the low temperature thermal decomposition of rubber wastes, mainly in the presence of solvent or water, where a degradation of vulcanized rubber is carried at 300°C with an asphalt, after 1 h of reaction the tyre was completely degraded whereas the resulting products remained dissolved in the asphalt, similarly the treatment of butyl rubber pieces with water in a closed vessel at temperatures of about 350°C caused the depolymerization of the raw material in 1 h. When starting from halobutyl rubbers, this process leads to a partial dehalogenation of the organic products. Likewise the decomposition of rubber with supercritical water has been studied wherein treatment of rubber with water at temperatures of about 380°C led to a conversion of 43- 48% of the raw tyre into oil. Elementary analysis showed that about half of the sulfur contained in the original sample is extracted into the oil, whereas the other half remains in the solid residue. Thermal conversion of rubber wastes, mainly used and discarded tyres, has also been widely investigated and have focused on producing fractions of higher value with applications other than simply as low quality fuels. Typically, the thermal decomposition of used tyres leads to the formation of gases, oils and a solid residue or char. The gases formed are mainly H2, CO, C02, CH4 and C2H6, hence they can be used as a fuel gas. The oils are rich in aromatic hydrocarbons and have lower sulfur content than the starting tyre. In most cases it is suggested that these oils are upgraded in refineries, although they may also be a source of chemicals. Finally, the chars produced, typically with yields of over 30 wt%, have a high calorific value but also relatively high sulfur content. Different activation treatments have been described to increase the surface area of the chars in order to explore their possible use as activated carbons. There is some confusion found over the terms used to describe the thermal treatment of polymers: depolymerization, cracking, thermolysis, pyrolysis, etc. but we shall use the term pyrolysis to refer the thermal decomposition of polymeric materials at high temperatures (above 600 ºC) whereas, when the degradation takes place at lower temperatures, we shall refer to it mainly as thermal cracking, Catalytic Cracking and Reforming Catalytic cracking and reforming are based on contact of the polymer with a catalyst which promotes its cleavage. Rubber degradation proceeds in most cases by a combination of catalytic and thermal effects which cannot be isolated. The use of catalysts is also usual in chemolysis processes of plastic (polycondensed) depolymerization. However, there are two main differences between catalytic cracking and chemolysis: there is no chemical agent incorporated to react directly with the polymer in catalytic cracking methods, and the products derived from the polymer decomposition are not usually the starting monomers. Compared to the simple cleavage of the polymer by thermal effects, catalytic cracking has a number of advantages:

The polymer molecules start to break down in the presence of catalysts at considerably lower temperatures than in thermal decomposition. A significant catalytic conversion of polymer (rubber) into volatile products has been detected at temperatures as low as 200°C, compared with the value of 400ᵒC which is necessary in the thermal degradation of polymer (rubber) to observe the formation of the first gases. As a consequence, catalytic treatments of rubber materials are usually carried out at low temperatures, in contrast with the range of 500ᵒC -800°C, typical for thermal cracking and pyrolysis. When compared at the same temperature, catalytic cracking of polymers proceeds faster than thermal degradation, i.e. with lower activation energy.

Figure no 4: Catalytic Cracking of waste Rubber The products derived from the catalytic cracking of waste rubber are of higher quality than those obtained by thermal decomposition. Thus, the presence of a high proportion of branched, cyclic and aromatic structures in the oils produced lead to properties very similar to those of commercial gasolines. Moreover, the product distribution can be varied and controlled by the selection of a suitable catalyst and modification of its properties There are different processes that have been patented for the catalytic conversion of rubber/rubber and plastics mixtures without any previous thermal treatment. Waste rubber, such as used tyres, can be degraded in the presence of molten salt catalysts with properties as Lewis acids, such as zinc chloride, tin chloride and antimony iodide. The decomposition proceeds at temperatures between 380ᵒC and 500ᵒC to yield gases, oil and a residue, in proportions similar to

those obtained by simple thermal decomposition. A process for the catalytic treatment of rubber waste by reaction in the presence of Zn and Cu salts (chlorides or carbonates), at 550°C to produce char and oil fractions, the latter containing about 0.5 wt% of S and N, yet rubber wastes can also be degraded in the presence of basic salt catalysts, such as sodium carbonate, catalytic conversion of rubber by contact with a molten MgCl2/AlCl3 catalyst, whereas the degradation of polymeric materials over molten mixtures of a basic salt (NaOH or KOH) and a Cu source, mainly metallic Cu and CuO, Processes involving the use of solid acid catalysts have also been developed.

Figure no 5: Combined Catalytic and Thermal Cracking of waste Rubber Rubber wastes are first subjected to a size reduction step, followed by separation of any metals present and washing to remove any non-plastic material such as paper, labels, etc. Subsequently, the polymer wastes are dissolved or dispersed in petroleum oil, with a high content of polycyclic aromatic compounds at 300ᵒC, and catalytically transformed in an FCC reactor at temperatures of about 500°C to yield desired products (gases, oils and a residue).

Hydrogenation Hydrogenation of rubber wastes is a potentially interesting alternative for breaking down the polymer chains. Compared to treatments in the absence of hydrogen, hydrogenation leads to the

formation of highly saturated products, avoiding the presence of olefins in the liquid fractions, which favours their use as fuels without further treatment. Moreover, hydrogen promotes the removal of heteroatoms (Cl, N and S) that may be present in the polymeric wastes. However, hydrogenation suffers from several drawbacks, mainly the cost of hydrogen and the need to operate under high pressures. Although some non-catalytic hydrogenation processes have been reported, most of them require the presence of a catalyst to promote hydrogen addition reactions. Bifunctional catalysts are preferred, incorporating both cracking and hydrogenation/dehydrogenation activities. A typical catalyst includes transition metals (Pt, Ni, Mo, Fe, etc.) supported on acid solids, such as alumina, amorphous silica-alumina, zeolites, sulfated zirconia etc, although in this case the incorporation of metals, metal oxides or metal sulfides provides them with hydrogenation/dehydrogenation activity. In recent years, a lot of research effort has been focused on the co processing of coal and rubber wastes under hydrogen atmospheres, based on the possible role of the polymers as hydrogen donor for coal.

Figure no 6: Styrene Butadiene Rubber degradation pathways

The most commonly used rubber in tyre manufacture is styrene-butadiene copolymer containing about 25 wt% of styrene. The presence of a high concentration of double bonds in the rubber backbone makes the alternative of degrading rubber wastes by treatment in hydrogen atmospheres very attractive (figure 6). Moreover, because used tyres contain significant amounts of sulfur, hydrogenation also favours the removal of this undesired element as H 2S, which allows oils to be produced with lower S content than those derived from tyre pyrolysis. The catalytic hydrocracking of nonvulcanized rubber (SBR, styrene-butadiene copolymers) over superacid solids, consisting of sulfated Zr and Fe oxides, the liquids produced at 400°C over sulfated Fe203, three types of product are observed: C5-C9 paraffin‟s produced from the butadiene blocks of the polymer, alkyl benzenes derived from the styrene units, and bicyclic compounds, probably formed by catalytic side-chain cyclization reactions of alkyl benzenes. Increasing the temperature to 375- 450°C with initial hydrogen pressure of 102 atm leads to improvements in both conversion and gas yield, although the production of liquids remains with selectivities higher than 85%. Using sulfated zirconia, the product distribution changes, with a higher yield of ethylbenzene being obtained, which are related to the stronger acidity of the zirconia catalyst, the hydrocracking of SBR (figure 6), and the double bonds in the butadiene blocks may undergo partial hydrogenation and double bond migrations. β-Cleavage reactions of benzylic carbonium ions generate Cl-C3 alkyl benzenes and also longer alkyl and alkenylbenzenes with alkyl groups up to C4-Cl2. The latter can undergo intramolecular cyclization reactions to form cycloalkylbenzenes, indanes and tetrahydronaphthalenes. Likewise, β-cleavage at both ends of the butadiene units may produce C5-Cl2 paraffin‟s and olefins, as well as cycloparaffins by secondary cyclization. Finally, cycloparaffins can also be formed by dealkylation of cycloalkylbenzenes.

Figure no 7: Product distribution obtained in hydrogenation of discarded tyres

The degradation usually proceeds in the presence of catalysts: CoNi/Al203, FeMo/Cr203, Mo acetates, Cp2ZrC12, etc. In some cases, a certain positive effect has been derived from the presence of sulfur compounds, which may either be the sulfur contained in the used tyre or H2S added to the reaction mixture, the non-catalytic hydrogenation of tyres in the temperature range 350-400 ᵒC. The conversion was dependent on the temperature and was improved by the addition of tetralin as solvent when working below 400°C. However, at 400°C the presence of tetralin or hydrogen has no effect on the conversion of the tyre. These results suggest that tyre liquefaction may follow a thermal cracking or a hydrogenation mechanism, depending upon the reaction temperature. At temperatures of about 350ᵒC, hydrogenation is a necessary step before bond cleavage whereas at 400ᵒC, thermal cracking becomes predominant. The maximum conversion obtained is about 66%, which is approximately the content of volatile matter in the raw tyre, suggesting that the carbon black in the tyre does not really react under these conditions. The total gas yield obtained at 400°C was 6.2%, consisting basically of CO,CO2 and Cl-C5 hydrocarbons, the hydrocracking of scrap automotive tyres after removal of the steel wires and the textile netting present in the starting material, the results obtained in non-catalysed experiments carried out at 400ᵒC at different cold-hydrogen pressures. A maximum conversion into gas and oils of about 70% was obtained, confirming that the carbon black, which accounts for 31% of the tyre, is not reactive under these conditions. The oil/gas ratio was dependent on the hydrogen pressure; the higher the pressure the lower the gas yield (figure 7), thus, only small amounts of gases were produced at cold-hydrogen pressures above 49 atm. The oil formed had constituents like alkyl benzenes, alkylnaphthalenes and long-chain hydrocarbons in the range C8-C20. When the degradation was carried out in the presence of a Fe catalyst (red mud), the production of gases was minimized at all the pressures. The composition of the liquids was very similar to the noncatalysed reactions liquid products. The major difference was the presence of large amounts of 1 -methyl-4-isopropylcyclohexane, which indicates that a greater extent of hydrogenation occurs in the catalysed tyre degradation. Co processing of coal with rubber wastes has the same potential advantages as for coal and plastic mixtures, removal of these wastes by conversion into fuels and reduction in the amount of hydrogen consumed in the coal conversion. Co liquefaction of coal and used tyres was studied before the conversion of coal-plastic mixtures, also leading to better results regarding the presence of synergistic effects during the co processing of these two materials. In addition to the role of rubber as a hydrogen donor, the carbon black present in the used tyre has been found to have a positive catalytic effect on the conversion of coal. Conclusion Recycling is one strategy for end-of-life waste management of rubber wastes and discarded tyres, recycling increases human sense economically as well as environmentally, this leads to recent trends by a substantial increase in the rate of recovery and recycling of rubber wastes. These trends are likely to continue, but some significant challenges still exist from both technological factors and from economic or social behaviour issues relating to the collection of recyclable

wastes, and substitution for virgin material. Feedstock recycling of waste rubber and discarded tyres seems to be more attractive in comparison with mechanical recycling to face the waste rubber problems, because of its minor environmental impact and the recovery of solid, liquid and gaseous material, which are used in various chemical syntheses. Increasing the value of the products derived from feedstock recycling of polymeric wastes will also help the process economy, but degradation of rubber wastes has led to complex mixtures of hydrocarbons, suggested for use as fuels, in many cases of low quality, however little effort has been focused on using the products resulting from polymer degradation in chemical synthesis, with the exception of the various chemolysis methods which lead to the starting monomers. In recent years, the production of higher added value chemicals: gaseous olefins by high temperature pyrolysis or through catalytic treatments, waxes and a-olefins by thermal degradation of polyolefins, activated carbons from the chars obtained in used tyre decomposition, indane compounds from tyre pyrolysis oils have made feed stock recycling a sustainable process aiming towards the clean technology by Green Engineering, References 1. Green Chemistry and Green Engineering – Athanasios Valavanidis and Thomas Vlac, 2012 2. RSC Clean Technology Monographs, 1999 3. U. Hofmann and M. Gebauer, Kunststofe Germun Plrst., 1993 4. H. Bockhorn, M. Burckschat, and H. Deusser, J. Anal. Appl. Pyrol., 1985 5. S. Ogasawara, M. Kuroda, and N. Wakao, Ind. Eng. Chem. Res., 1987 6. Y. Watabe, H. Takeichi, and K. Irako, US Patent 4426459, 1984 7. S. Lee, F.O. Azzam, and B.S. Kocher, US Patent 5516952, 1996 8. H. Teng, M.A. Serio, M.A. Wbjtowicz, R. Bassilakis, and P.R. Solomon, Ind. Eng Chem. Res., 1995 9. P.T. Williams, S. Besler, and D.T. Taylor, Fuel, 1990 10. A. Napoli, Y. Soudais, D. Lecomte, and S. Castillo, J. Anal. Appl. Pyrol., 1997 11. C. Roy, US Patent 4 740 270, 1988 12. A. Chaala and C. Roy, Fuel Processing Technology., 1996 13. J.A. Conesa, R. Font, and A. Marcilla, Energy Fuels, 1996 14. A.A. Merchant and M.A. Petrich, AICHE J., 1993 15. T.J. Ulick and W.E. Carner, US Patent 5070 109, 1991 16. R.Y. Saleh, M. Siskin, and G. Knudsen, US Patent 5 283 318, 1994 17. T. Funazukuri, T. Takanashi, and N. Wakao, J. Chem. Eng. Jpn.,1987 18. R.C. Wingfield, Jr., J. Braslaw, and R.L. Gealer, US Patent 4 458 095, 1984. 19. R.C. Wingfield, Jr., J. Braslaw, and R.L. Gealer, US Patent 4 515 659, 1985 20. G.M. Platz, US Patent 5 504 267, 1996 21. J.A. Butcher, Jr., US Patent 5 315 055, 1994 22. N.Y. Chen and T.-Y. Yan, US Patent 4 108 730, 1978 23. K. Saito and M. Nanba, US Patent 4 584 421, 1986 24. T. Hirota and F.N. Fagan, Makromol. Chem., Macromol. Symp., 1992 25. W. Zmierczak, X. Xiao, and J. Shabtai, Fuel Process. Technol., 1996 26. J. Alpert, US Patent 3 704 108, 1972 27. M. Morita and T. Takamatsu, US Patent 4251 500,1981 28. P.R. Stapp, US Patent 5 158 983, 1992 29. C.J. Gibler, L.R. Chamberlain, R.A. Kemp, and S.E. Wilson, US Patent 5 162446,1992 30. Z. Liu, J.W. Zondlo, and D.B. Dadyburjor. Energy Fuels, 1994 31. L.L. Anderson, M. Callh, W. Ding, J. Liang, A.M. Mastral, M.C. Mayoral, and R. Murillo, Ind. Eng. Chem Res., 1997 32. M. Farcasiu, C.M. Smith, E.P. Ladner, and A.P. Sylvester, Fuel Chem. Preprints, Am. Chem. Soc., 1991 33. M. Farcasiu and C.M. Smith, US Patent 5061 363, 1991 34. M. Farcasiu, Chemtech, 1993

Student’s Details:

Rane Ajay Vasudev, [email protected] Institute of Chemical Technology - Matunga, Mumbai (Formerly known as UDCT Mumbai)

Abitha V K Department of Polymer Science and Rubber Technology, Cochin University of Science and Technology, Kerala [email protected]