Ind. Eng. Chem. Res. 2001, 40, 1119-1124
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Assessment of Schemes for the Processing of Organic Residues from the Interior Car Decoration Industry A. M. Mastral,* R. Murillo, M. V. Navarro, M. S. Callen, and T. Garcı´a Instituto de Carboquı´mica, CSIC, Marı´a de Luna 12, 50015 Zaragoza, Spain
The industry involved in the interior decoration of cars generates different cutting organic materials as residues. Because of the present and future regulations on residue generation, this industry must look toward recycling of the corresponding cuttings. The main aim of this paper is to search for a proper and, if possible, unique process to recycle the different organic materials generated by the car internal decoration industry when the needed pieces are cut from the large original plates. That process generates huge amounts of different cutting material, which can reach several tons of each material per day. A single process would simplify the experimental installation and, in addition, would reduce costs and staff without great disturbances in the everyday work of the involved industry. The seven samples studied in this work had different compositions, ranging from natural to synthetic fibers and from pile cloth for carpeting to polyurethane (PU) and wood, depending on their specific decorative role. Therefore, different processes over a wide variable interval have been performed, with a focus on their utilization at the same installation and, if possible, their joined coprocessing. The thermal decomposition of the samples in different atmospheres, namely, inert, oxidizing, and hydrogenating atmospheres, has been carried out in different reactors including fixed-, shacked-, and fluidized-bed reactors. Advantages and disadvantages of the behavior of these samples in their recycling processes, from the point of view of emission and remaining residue generation, are noted and discussed. 1. Introduction Transport causes a huge environmental impact. Cars not only cause pollution, noise, and harmful atmospheric emissions when they are running, but also generate waste through the high amount of organic and inorganic residues generated both when the car is manufactured and when it is discarded. Obsolete vehicles become an environmental problem, as they consist of several elements that should be treated in different ways. Currently, discarded cars must be decontaminated1 from liquid elements such as chlorofluorocarbons (CFCs), oils, and fuels; dismantled into glass, plastic, and textile and foam elements; and fragmented into ferric and nonferric elements. Recycling of some of these elements, such as ferric elements, has been well-established since the 1950s, as is also the case for tires, of which 16% are being retread at the moment, with the other fractions being used in the cement industry and in combustion to generate energy.2 However, there are still elements from a car, such as plastics, textiles, and foams, for which defined final uses have not yet been found. At present, a great public refusal to build new landfills areas exists. There are proposals1 to find ways of recycling, reusing, or valorizing these elements as long as landfills are overflowing and/or rejecting these materials. In the very near future, 95% (by weight) of the vehicle should be reused or improved, allowing just 5% to be left as residue. Different governments and administrations1 are promoting suggestions on some activities in order to recycle and maintain cars and their components. These activities aim to improve * Author to whom correspondence should be addressed. Phone: 34 976 73 39 77. Fax: 34 976 73 33 18. E-mail:
[email protected].
the conception and design of recyclable components and systems, to reuse components (tires, glass, plastics, etc.), to optimize the recycling systems, or to eliminate these residues by environmentally friendly processes. Moreover, residues from cars affect not only obsolete cars but also the new car industry. In the process of new car manufacture, the residues of the same nature are generated. For instance, when pieces of plastic, wood, textiles, etc., are cut from the corresponding continuous sheet of material, some cuttings are always discarded. These cuttings can compose tons of residues from each original material per day, which must be recycled according to future regulations. The discarded materials studied in this work are a problem because, despite the fact that their weight amounts to only a few tons per day, they represent a huge volume of residues because of their low density. These cutting materials could be both an important source of energy by incineration/ combustion, although the atmospheric environmental impacts must still be assessed, and/or a source of chemicals, taking advantage of their chemical potential. As discarded tires are generated throughout the car life, they are a mainly organic residue from cars, and they have been more thoroughly processed with the intention of achieving their exploitation using coal technology;3,4 tires have been also included in this study for comparison of results. Up to now, the reuse of polymeric wastes is of very limited potential because of the problems they entail. Currently, on average, only 7% are recycled to produce low-grade plastic.5 Plastic processing has already been individually studied, as has that of some simple mixtures, in order to recover their chemical potential. Some studies show that not all plastics have the same optimum reaction conditions.6 It has been reported that four different polymers
10.1021/ie000198w CCC: $20.00 © 2001 American Chemical Society Published on Web 01/20/2001
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Table 1. Type, Description, and Composition of Major Components of the Processed Samples sample
type
description
composition
1 2 3 4 5 6 7
wood wood A23 S5 X65 PU tire
isowood lignot Glausec + NTLR + film + Bicom Glausec + NTLR + NT80 + Bicom Glausec + paper + TNT 180 PU block rubber
wood + cotton wood + glass fiber foam + glass fiber + carpet + cardboard cloth foam + glass fiber + nylon + carpet foam + carpet + glass fiber + paper polyurethane natural and synthetic elastomers
Table 2. Elemental Analysis and Ash Content of the Processed Samplesa sample
%C
%H
%N
%S
% ashes
1 2 3 4 5 6 7
50.0 51.5 53.8 46.3 53.4 65.6 88.6
5.9 6.2 6.4 5.2 6.0 6.4 8.3
0.3 0.2 4.3 3.6 4.1 7.3 0.4
0.0 0.0 0.0 0.0 0.0 0.0 1.4
0.2 0.4 18.6 14.8 14.5 0.9 3.0
a
As received.
(HDPE, LDPE, polystyrene, and polyisoprene) demonstrate a variety of behaviors when reacted individually under equivalent thermal and catalytic conditions.7 Moreover, plastic residues usually consist of mixtures of a wide variety of polymers and other materials, which are in some grade contaminated by their use. The interaction between these substances produces different results, such as reduction of their average life cycle with respect to what would be predicted from the reaction of a single plastic.5-13 For wood, gasification14-16 shows some advantages over combustion such as higher burning efficiencies, easier control, adjustable energy output, simpler reactor, and less air pollution. Commercial applications of coal and wood co-gasification in fixed-bed reactors date back to the first years of the 1800s. Currently, there are a lot of technical variations in waste wood recycling,14 but a proper use for the corresponding conversion products has not yet been found. In this work, six of the major organic samples from the residues generated daily in the cutting process of the interior decoration of automobiles have been processed in inert, oxidizing, and hydrogenating atmospheres. In addition, rubber from tires has been included in order to compare results. Samples were burned, hydrogenated, and pyrolyzed in inert and oxidizing atmospheres in an attempt to recover their chemical potential and, at the same time, reach the EU goal1 for the recycling of difficult disposal wastes. The recycling possibilities are assessed in this work. 2. Experimental Section 2.1. Samples. A total of seven different samples (see Table 1) from the car industry have been processed. The seven studied samples were characterized by elemental analysis (see Table 2). Six samples from six different cutting organic materials involved in interior decoration during car manufacturing were reduced to a particle size of 5-10 mm. Sample 7 was granulated and sifted to a particle size of 0.9 mm from rubber from a nonspecific blend of discarded tires 2.2. Processes. The seven studied samples were processed in inert, oxygen and hydrogenating atmospheres at increasing temperatures. Their behavior as a function of the process temperature was analyzed for each process.
2.2.1. Thermolysis in Inert Atmosphere. The sample devolatilization study was performed in a TGDTA92 instrument, Setaran, in inert atmosphere (N2). The program selected, after some previous tests, for the thermal gravimetric analysis, was as follows: Initial temperature ) room temperature Heating rate 1 ) 25 °C/min up to 200 °C, with this temperature maintained for 10 min Heating rate 2 ) 10 °C/min up to 500 °C, with this temperature maintained for 5 min Heating rate 3 ) 25 °C/min up to 750 °C As glass fiber was one of the components of samples 3-5, the temperature was kept lower than 750 °C to avoid melting problems. The devolatilization and remaining residue percentages, for components that are not volatile at 750 °C, are compiled in Table 3. The process was repeated four times, and the standard deviation was (2.3%. 2.2.2. Thermolysis in Oxygen Atmosphere. In the same TGDTA92 apparatus, the sample behavior in an oxygen atmosphere was studied for the following temperature program: Initial temperature ) room temperature Heating rate ) 20 °C/min up to 750 °C Final temperature ) 750 °C to constant weight loss Residues were measured by direct weight. The results obtained for devolatilization percentages and nonvolatile residues are shown in Table 4. The process was repeated four times, and the standard deviation was (2.7% 2.2.3. Combustion in a FBR. Because of the low density of some samples and because the feed into the fluidized-bed reactor at the laboratory plant was performed by gravity, it was necessary to compress the samples. In compression, only pressure was used to obtain 7 × 10-mm-sized cylindrical briquettes. Combustion was carried out in a fluidized-bed reactor (76 cm height, 7 cm i.d.) continuously fed at 725 °C with 5% excess oxygen. For emissions sampling, a cyclone to collect entrained solid products, a cooling soil to condense water, a Teflon filter of 0.5-µm mesh, and a XAD-2 resin-like adsorbent to retain emitted organic compounds were placed in succession at the reactor exit. At the end of the sampling system, a sample bag was used to collect gases for gas chromatography (GC) analysis. The particulate matter collected in the traps was extracted, and toxic emissions were analyzed by fluorescence spectroscopy in the synchronous mode (FS), according to previously published work.6 NO emissions were quantified in a gas analyzer (Fisher-Rosemount). Data obtained on particulate matter (PM), polyaromatic hydrocarbons (PAHs), COx (CO + CO2), C1-C4, and NO emissions as well as percentages of unburned remaining residues can been seen in Table 5. 2.2.4. Hydroconversion Process. The hydrogenation experiments were performed using tubing bomb4 reactors of 60 cm3 volume. Reactors were loaded with weights of sample ranging from 0.6 to 5.5 g, because of their different densities, in order to keep the full scale
Ind. Eng. Chem. Res., Vol. 40, No. 4, 2001 1121 Table 3. Sample Volatilization (%) as a Function of Thermolysis Temperature in Inert Atmosphere sample
up to 130 °C
up to 195 °C
230-300 °C
300-400 °C
400-500 °C
500-600 °C
600-700 °C
% residue at 750 °C
1 2 3 4 5 6 7
2.6 2.4 0.2 0.2 0.5 0.1 0
3.8 3.7 0.3 0.5 0.6 0.3 0
13 25 10 13 11 25 0
72 64 36 39 35 61 64
80 75 57 70 71 77 64
81 77 58 71 75 82 64
82 79 59 72 76 83 64
11 19 39 27 22 14 35
Table 4. Sample Volatilization (%) as a Function of Thermolysis Temperature in Oxygen Atmosphere sample
up to 130 °C
up to 195 °C
230-300 °C
300-400 °C
400-500 °C
500-600 °C
600-700 °C
% residue at 750 °C
1 2 3 4 5 6 7
5.2 3.6 0.2 0.4 0.5 0 0
7.1 5.3 0.5 0.6 1.0 0 0
26 40 20 18 9 15 5
77 76 63 47 31 42 65
99 97 61 64 60 64 77
99 97 78 83 80 88 78
99 98 81 84 83 98 57
0.5 1.5 19 14.9 16.5 1.4 38
Table 5. Analysis of the PAHs, COx, C1-C4, and NO Emitted in the Gas Phase, of the Particulate Matter Emission, and of the Remaining Residue from Fluidized-Bed Combustiona
sample
PAHs emitted
CO (%)
1 2 3 4 5 6 7
fluorene, anthracene fluorene, anthracene fluorene, anthracene fluorene, anthracene, pyrene fluorene, anthracene fluorene, anthracene fluorene, acenaphthene
0.2 1.1 1.2 0.9 0.7 1.1 -
a
CO2 (%)
NO (ppm)
C1-C4 (%)
solid emission (% feed)
residue (%)
10.8 9.8 6.9 8.9 11.1 9.3 -
0 0 380 170 350 390 -
0 0.2 0.6 0.3 0.2 0.4 -
0.4 0.4 0.7 0.4 0.6 0.3 5.2
0.2 0.2 29.2 25.8 17.2 0.1 35.6
725 °C, 5% excess oxygen.
of the reactor. Reactors were purged with H2 gas and charged to a final cold pressure of 1.5MPa. Two reactors placed in a holder were immersed in a fluidized sand bath preheated at 410 °C and provided with a shaking and stroking system. After 30 min of reaction, the reactors were quenched in water. Gases were collected in gas sample bags at room temperature and analyzed by GC. The solid products were removed from the reactor with dichloromethane (DCM) and extracted by Soxhlet for 24 h. The solvent was removed by rotary evaporation, and the solid residue was dried in a vacuum oven. The oil percentages were calculated by direct weight, and their functional hydrocarbon groups were analyzed by thin-layer chromatography coupled to flame ionization detection (TLCFID). Gas formation was calculated by difference. The standard deviations were (1.5% for conversion and (2% for oils. 2.3. Product Analysis. The COx and C1-C4 hydrocarbons were analyzed in a Hewlett-Packard 5890 gas chromatograph. Polyaromatic hydrocarbons were analyzed by fluorescence spectroscopy in a Perkin-Elmer LS50B luminescence spectrometer.6 NO emissions were directly analyzed in a Fisher-Rosemount BINOS 1000 gas analyzer. Samples and oils were characterized by ultimate analysis in a Carlo Erba CHNS-O EA1108 elemental analyzer. Oil compositions were analyzed by their hydrocarbon types in an Iatroscan new MK-5 instrument by TLC-FID. 3. Results and Discussion The high nitrogen and silica contents of some of the studied samples limit the variables of the recycling
process in order to meet the current legislation on NOx emissions and to avoid melting problems of the glass fiber. In the case of inorganic components, for samples 3-5, the percentage of residual material at the end of the reutilization processes is high. To reach the 95% sample elimination, an alternative use for the remaining residues should be considered. 3.1. Thermolysis in Inert Atmosphere. The sample devolatilizations (see Table 3) by thermolysis in inert (N2) atmosphere show that, in general, 750 °C is quite a low temperature. The thermolysis was not carried out at temperatures higher than 750 °C to avoid melting troubles because of the glass fiber, a component of samples 3-5. The thermal decomposition of these samples generates solids ranging from 11 to 39% (wt/ wt) of the original materials. All of the samples show a gradual decomposition, with a stage of only decomposition. Samples 1, 2, and 6, of very simple composition, show the maximum weight loss at 400 °C. The other samples, a complex blend of several materials, show it at 500 °C. Sample 1 volatilizes in a more prominent way than the other samples. The low volatility of sample 3 is remarkable because of its high glass fiber content. The obtained results show that, by inert thermolysis, the weights of the original samples would be reduced by from 89 to 61%, depending on their specific composition. In the case of samples 3-5, glass fiber is the major component of the residues, and for sample 7, the remaining residue is carbon black. It is worth pointing out that glass fiber and carbon black can be reused again. SiO2 can easily be reused7 from the remaining residues from samples 3-5, and carbon black could also
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Figure 1. Weight loss with temperature increase ratio vs temperature curve.
be reutilized as reinforcing material for low-value rubber goods. 3.2. Thermolysis in Oxygen Atmosphere. When an oxidizing atmosphere replaces the inert atmosphere, the radicals emitted in the devolatilization step will react with oxygen and will be converted into COx, NOx, SOx, and H2O. Simultaneously, the remaining solid will undergo a gas-solid reaction,8 which is to say, a complementary oxidation process with additional production of CO2 and H2O. As can be seen in Figure 1, the samples show different behaviors with increasing temperatures in the oxidizing atmosphere. On one hand, whereas samples 1, 2, and 3 show a faster weight loss, samples 4, 5, and 6 show less prominent peaks because weight loss occurs in all temperatures ranges with similar trends. On the other hand, there is also a difference in the number of peaks that can be observed during sample volatilization. A plot of weight loss with increasing temperature ratio vs temperature shows that the reaction takes place in one stage for samples 1, 2, and 5 and in two stages for samples 3, 4, and 6. The percentage of unburned material for samples 3-5 ranges from 15 to 19% of their original weights, higher than those for the other samples, as shown in Table 4. To confirm the high amount of residue obtained at microscale, samples 3-5 were treated in a muffle furnace where 5 g of each sample were burned until a constant weight was attained (850 °C for 2 h). In this way, their elevated content of remaining residue, which proved to be melted silica, was corroborated. Carbon black from sample 7 proves to be a quite inert organic material, and more appropriate variables would be needed to eliminate it by combustion. By comparing results obtained from volatilization in inert and oxidizing atmosphere, Tables 3 and 4, a reduction in residue percentages is observed in the thermolysis carried out in oxygen atmosphere, showing that the organic components are not totally transformed by inert thermolysis. This could be due to the fact that, whereas in inert atmosphere, only devolatilization of organic matter takes place, in oxidizing atmosphere, a solid-gas oxidation reaction occurs simultaneously.8 Both oxidation reactions, volatile organic matter and nonvolatile organic matter, improve the conversion of organic matter into CO2 and H2O, and so, a smaller amount of remaining residues is generated. 3.3. Fluidized-Bed Combustion (FBC). Combustion in a fluidized-bed reactor (FBR) is a process
currently used in energy generation, mainly because of the versatility of the process. Heterogeneous feeds, flexibility to modify the feed flow, easy control because of the behavior of solid particles (similar to fluids), elevated heat transfer coefficients, low excess air needs, high energy efficiency, and inorganic emissions control are its main advantages. Thus, despite the fact that FBC is a more complex technology, the studied samples were burned in a FBR. The distribution of solid and gas products obtained is shown in Table 5. It can be observed that from samples 3, 5, and 6, important NO emissions are detected, suggesting that careful combustion to meet current legislation should be performed. Actually, the trend to decrease the temperature of combustion (850 °C) to decrease thermal NOx formation and emissions was already taken into account, as the combustion was carried out at 725 °C. In addition, there is one more reason to work at 725 °C, which is to prevent silica-melting problems. Because of the huge nitrogen content of some these samples, and despite the available technology for NOx reduction, combustion does not seem to be the proper process for the recycling of these samples. Even at 725 °C, the emisions of NO alone are very close to the legislated limit for all NOx emissions. The usual combustion temperature for FBC (850 °C) would produce nitrogen oxides from the combustion process and nitrogen oxides as a consequence of their own material combustion, increasing the total NOx emissions. The most volatile organic emissions generated during the combustion process were trapped on XAD-2 resin. The analysis of the different samples by fluorescence spectroscopy18 (a more specific analytical tool for PAHs than mass spectroscopy) gave as a result very complicated fluorescent spectra. Nevertheless, the major emitted compounds were anthracene and fluorene.19 It is worth pointing out the high amount of particulate matter (PM) emitted20 with sample 7. Anthracene and fluorene do not interfere with other emitted compounds, and according to the USEPA priority pollutants list,21 their carcinogenic level is low in comparison to that of pyrene. From the fixed-bed and fluidized-bed combustion results, it could be deduced that the difficulty of the oxidation reaction in a fixed bed is reflected in the remaining residue percentages. In a fixed bed, the chemical reaction takes place only on the upper surface in a slow way, because, as the reaction takes place, the reactant’s path through the products is more difficult. In FBC, the chemical reaction takes place all around the surface, so that it is faster and easier, and so, the remaining residues show generally smaller percentages. According to the above results, it can be observed that some samples improved combustion in the FBR, such as samples 1, 2, and 6. Others samples had similar behavior, such as samples 5 and 7, and finally, opposite to what was expected, samples 3 and 4 generated higher ash percentages. The reason for this fact could be the special texture of samples 3 and 4. However, compacted by pressure, their nature is based on thin threads of very low density, which remain as unburned material. The highest residue is generated by the tire sample. This is probably because of one of its components, carbon black, which has a very stable molecule showing a very low density because of its high surface/weight ratio, as is seen with samples 3 and 4. This quality makes them very easily entrained22 from the reactor by
Ind. Eng. Chem. Res., Vol. 40, No. 4, 2001 1123 Table 6. Yields Obtained in Sample Hydroprocessinga sample
% conversion (daf)b
% oils (daf)b
% gas (daf)b
% residuec
1 2 3 4 5 6 7
74.0 68.1 83.0 90.6 95.8 99.2 71.1
7.4 9.6 29.7 36.0 15.2 31.8 59.2
66.6 58.5 53.2 54.6 80.5 67.3 11.9
25.4 31.3 41.2 32.7 20.7 0.9 31.3
a
400 °C, 1.5 MPa H2, 30 min. b daf ) dry ash free. c By weight.
Table 7. Chromatographic Analysis (TLC-FID) of the Oils Obtained from Sample Hydroprocessing in Tubing Bomb Reactorsa hydrocarbon type (%) sample
saturated
aromatic
polar
noneluted
1 2 3 4 5 6 7
15.1 1.8 0.9 0.3 1 1.5 19.2
0.1 4.4 0.1 0.2 0.6 1.8 36.5
57.3 72.4 69.9 92.2 75.9 70.8 40.4
27.5 21.4 29.2 7.4 20 26 4
a
400 °C, 1.5 MPa H2, 30 min.
the air flow. Whereas sample 7 would not generate inorganic emissions (no N and very low S content), it would create difficulties with particulate matter emissions. 3.4. Hydroconversion Process. Whereas the former studied processes are directed toward energy recovery, the hydroconversion process is focused on oil recovery. Table 6 shows different behaviors in the sample hydroconversion process. Conversions of tire and samples 1 and 2 range from 68 to 74%, whereas the rest of the samples have around a 90% conversion. The 99% conversion of sample 6 is remarkable. The conversion product distribution between oils and gas is different depending on the sample nature. Huge percentages of gas formation are observed for samples 1, 2, and 5, with oil/gas ratios lower than 0.2. For samples 3, 4, and 6, the oil/gas ratio is around 0.5. Only for sample 7 are oils the major conversion products. The possible explanation for this high gas/oil ratio is that the oils were swept from the reactor with DCM. The vacuum procedure used for solvent removal could be contributing to the apparent high gas percentage, because the most volatile oils could be lost as gases during the solvent-removal step. Gases are calculated by the difference between the conversion and oil weights, so the more volatile oils lost during solvent removal are included in the gas formation. Concerning the percentage of residues generated by the hydroconversion process, for wood samples 1 and 2, these percentages are much higher than those reached in combustion or thermolysis. For samples of mixed materials, the variations are not significant, and finally, for samples 6 and 7, the generation of solid residues by the hydroconversion process is minor. As oils are the most valuable conversion products, the oil nature has been analyzed by TLC-FID, a very common and useful analytical tool in the petrochemical industry, for their hydrocarbon group content (Table 7). The large percentage of polar products of oils from samples 1 and 2 can be explained by the polar nature of the wood, used in splash guard of quality cars.
Table 8. Ultimate Analysis of Liquid Product from Sample Hydroconversiona sample
%C
%H
%N
%S
% difference
C/H
1 2 3 4 5 6 7
70.1 72.6 77.2 76.8 71.1 75.6 85.9
8.8 7.5 8.0 8.0 7.6 8.4 10.6
1.6 1.6 6.8 7.6 4.7 8.6 1.4
0 0 0 0 0 0 0.9
19.5 18.3 8.0 7.5 16.5 7.4 2.0
8.0 9.7 9.6 9.6 9.4 9.0 8.1
a
400 °C, 1.5 MPa H2, 30 min.
Table 9. Gas Formation (%), Gas Composition,a and Gas Heating Value from Sample Hydroconversion at 400 °C, 1.5 MPa H2, and 30 min sample
% gas formation
1 2 3 4 5 6 7
49.3 39.8 44.2 49.5 77.1 66.8 8.5
a
gas composition %CO %CO2 %C1-C4 11.5 17.1 2.1 2.2 1.5 0.6 1.9
38.4 36.8 36.0 35.3 19.0 29.1 44.2
9.3 8.3 12.6 11.3 7.8 6.3 13.4
gas heating value (MJ/m3) 6.0 6.7 9.6 8.6 6.3 5.3 7.9
By gas chromatography.
The results obtained in previous studies of plastic thermal degradation,17 where the oils maintained the initial nature of the polymer monomer,11 suggest that the mainly polar nature of the oils analyzed is caused by the heteroatom content of the processed cutting materials. Oils from tires do not have the same distribution of hydrocarbons group as the other samples, showing an increase in saturated and aromatic groups. Styrene and polybutadiene, the main components of the used rubber, have aromatic and saturated hydrocarbons in their structure. In addition, during pyrolysis, their long aliphatic chains undergo cyclation reactions, which are the cause of their corresponding high oil aromaticity. The hydroconversion process of the samples supposes an increase in the carbon, hydrogen, and nitrogen percentages in the oils generated (Table 8) compared to the elemental analysis of the original samples (Table 2). These increases agree with the high percentage of CO2 emitted and the inorganic components in the remaining residues. High percentages of nitrogen present in the oils could be reduced by the addition of an appropriate catalyst in the recycling process. If this problem is solved, these oils can be considered useful because of the absence of sulfur-containing compounds and their high hydrogen content. These oils could be used in clean energy generation, such as alternative transport fuels, or to obtain hydrogen, one of the most promising future energy sources. The other conversion products, the gases, have been analyzed, and their composition is compiled in Table 9. Their contents in light hydrocarbons make them a possible source of energy. The gas heating value calculated with CO and gas hydrocarbon content ranges from 5 to 9.5 MJ/m3, which is low compared to the heating value of natural gas,12 which ranges from 37 to 41 MJ/ m3. However, it is between water gas heating value (10.5 and 12.5 MJ/m3) and the producer gas heating value (4.4 and 5.3 MJ/m3). It is worth pointing out that gases from samples 1-6 do not contain hydrogen sulfide. 4. Conclusions After assessing the data obtained, it could be concluded that the studied sample reutilization involved
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enormous difficulties and that the automobile organic residues should be recycled separately, sometimes by the same process but with different variables and sometimes by different processes. However, their recycling would not only be compulsory to follow the law but would also be helpful by providing energy to the industry involved, direct energy either by combustion or through the recovered gases and oils. The proper process for samples 1 and 2 seems to be combustion. Neither remaining residues nor harmful emissions would be generated. For the five remaining samples, thermal conversion would facilitate the control of toxic emissions. The recycling of samples 3-5 by combustion would generate bulky amounts of residues, ranging between 25 and 20% of the original sample, along with NO and pyrene emissions. The significant amounts of particulate matter emitted would also produce a negative environmental impact. For these samples, inert pyrolysis seems to be more adequate followed by later elimination of the N heteroatom from the recovered oils. It is easier to remove nitrogen components in oils than to abate emissions from hot gas. The same inert pyrolysis process seems to be proper for sample 7 because it would allow recovery of quite good-quality oils. Glass fiber and carbon black remaining as residues from these samples could be reused with already available technology. Sample 6 is totally converted into oils by hydroconversion. The polarity of the corresponding oils should be reduced in a second catalytic stage. Nomenclature CFCs ) chlorofluorocarbons FBR ) fluidized-bed reactor FBC ) fluidized-bed combustion GC ) gas chromatography FS ) fluorescence spectroscopy DCM ) dichloromethane TLC-FID ) thin-layer chromatography coupled to flame ionization detection PU ) polyurethane daf ) dry ash free
Acknowledgment The authors thank PIANFEI-SOLANO S.A. Enterprise for the financial support of this work. Literature Cited (1) European Union Goal: Spanish National Residues Plan 2000-2003. Volumen II. (2) Mastral, A. M.; Calle´n, M. S.; Murillo, R.; Garcı´a, T. Combustion of High Calorific Value Waste Material: Organic Atmospheric Pollution. Environ. Sci. Technol. 1999, 33, 41554158. (3) Mastral, A. M.; Murillo, R.; Calle´n, M. S.; Garcı´a, T. Application of coal conversion technology to tire processing. Fuel Process. Technol. 1999, 60, 231-242.
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Received for review February 4, 2000 Revised manuscript received September 25, 2000 Accepted November 14, 2000 IE000198W
