Energy & Fuels 1992,6,49&502
498
Methylation of Naphthalene by Methane over Substituted Aluminophosphate Molecular Sieves Simon J. X. He and Mervyn A. Long* School of Chemistry, University of New South Wales, Kensington, NSW 2033, Australia
Moetaz I. Attalla and Michael A. Wilson* CSIRO Division of Coal and Energy Technology, PO Box 136, North Ryde, NSW 2113, Australia
Received February 20, 1992. Revised Manuscript Received May 5, 1992
The catalytic activity of substituted aluminophosphate molecular sieves, ElAPO-5 (El = Pb, Cu, Ni, and Si), in the activation of methane for direct methylation of naphthalene has been investigated at 400 O C under elevated pressures of methane in an autoclave. In the presence of the as-synthesized catalysts, methylation of naphthalene was observed by gas chromatography and 'H Nh4R spectroscopy. The major identifed products in the methylation experiments were the two monomethylnaphthalenes together with small amounts of ethyl and dimethylated products and dinaphthalene. CuAPO-5, PbAPO-5, and SAPO-5 gave conversions of 15-16% in 1h, whereas "0-5 showed lower activity. Based on the naphthalene remaining, up to 21% naphthalene conversion was obtained when a catalyst incorporating both Cu and Si was used. Introduction The majority of work involving catalytic decomposition of methane has revolved around alkaline earth and rare earth metal oxide catalysts.' It is believed that methane activation is promoted by oxide ions which are instrumental in the formation of methyl or methylene radicals as a first step in the overall process.2 This catalytic activation of methane does not operate at the typical low temperatures (400 "C) which might be employed for selective thermal decomposition of organic compounds and their reaction with methane. However, recently we have been able to demonstrate that microporous aluminophoephate catalysts3can activate elemental hydrogen at relatively low temperature^.^ Moreover, the catalytic activity was enhanced by the incorporation of common metals such as lead and bismuth, and we were able to show that these catalysts can methylate toluene with methanol and convert methanol to dimethyl ethere6 Since the mechanism by which these catalysts react with methane is different from that of the rare earth oxides we have explored the possibility of using these catalysts for low-temperature activation of methane. The results shown below for the reaction of methane with naphthalene clearly demonstrate activation and methylation and show that microporous aluminophosphates have potential for a range of new uses of methane derived from natural gas or other sources. Experimental Section Preparation of Catalysts. Microporoue aluminophosphate catalysts are desginated AlP04-5 or SAPO-5,etc., depending on their molecular crystalline network! Three types were used here (1) Hutchings, G.L.; Scurrel, M. S.; Woodhouse, J. R. Chem. SOC.Reu. 1989, 18, 251. ( 2 ) Hutchings, G.L.; Woodhouse, J. R.; Scurrel, M. S. J. Chem. SOC., Faraday Tram. 1 1989, 2507. (3) Wileon, S. T.; Lok,B. M.; Meseina, C. A,; Cannan, T. R.; Flanigen, E. M. J. Am. Chem. SOC.1982, 104, 1146. (4)Garnett, J. L.; Kennedy, E. M.; Long, M. A.; Watson, A. J. Chem. Commun. 1988, 763. (5) Garnett, J. L.; Kennedy, E. M.; Long, M. A.; Than,C.; Watson, A. J. Stud. Surf. Sci. Catal. 1988, 36, 389.
Table I. Catalysts Structural Information % of surface catalyst A1p0,-5 molar compositiond no. type phas2 MeOz SiOz AIOz PO2 m2/g 1 AlP0,-5 2 Pb/Ab043 4 5
5' PbAPO-5' NiAPO-5 NiAPO-5-
>99
0
0
0.5
0.5
PbO: 40.0 wt %' >95.5 >98%
0.06
0
0.48 0.46
NiO: 1.16 wt %'
395.4 44.1 310.1 349 386
red
SAPO-5
6 7 8
CUSAPO-5' Cu/SAPO-
9
CuAPO-5
>95% >98% >98%
0 0.06
0.08 0.49 0.43 0.05 0.46 0.44
442.9 311.7
>99%
0.05
0
290.5
5' 0.48 0.46
Determined by X-ray diffraction. Measured by BET method. 'These pairs of catalysts are distinguished by the way the metal was introduced into the catalysts as described in the Experimental Section. dThe molar compositions were determined by ICPAES. 'The percentage of Me0 is expressed on an added weight basis. with various metal loadings. These catalysts used are listed in Table I and details of the methods by which they were prepared are outlined below. Catalyst I: AlFQp5 Aluminophosphate Molecular Sieve. In a typical preparation, phoephoric acid (26.45 g, Analytical Reagent grade (AR), 85%) was diluted with distilled water (69.94 g) in a glass vessel suitable for autoclave experiments and then pseudoboehmite (15.70 g, 74.2% A1203 balanced with water) was gradually added under strong agitation until the reactants were well mixed. Tetraethylammonium hydroxide (TEAOH) (42.13 g, AR, 20% solution in water) was then added to the reaction mixture while stirring, to produce a white gel. The mixture within the glass vessel was sealed in a stainless stael reactor (autoclave) and placed in an oven a t 150-200 OC for 24 h for hydrothermal crystallization. After cooling of the reactor to room temperature in ambient air,solids were recovered by filtration. The solids were washed with hot water to a pH of 6-7 and dried at 100 "C overnight. The catalyst was then calcined by the following procedure. Under a stream of air, the sample was heated to 100 OC at 35 OC/h (6) Flanigen, E. M.; Patton, R. L.; Wilson, S. T. Stud. Surf. Sci. Catal. 1988,37,13-27. Wilson, S . T.and Flanigen, E. M. ACS Symp. Ser. 1989, 398, 329-345.
0887-0624/92/25oS-0~98$03.00/0 0 1992 American Chemical Society
Methylation of Naphthalene by Methane
expt no. 1 2
3 4
5 6 7 8 9 10
Energy & Fuels, Vol. 6, No. 4,1992 499
Table 11. Conversion of Naphthalene and Selectivity of Products at 6.9 MPa (Cold Pressure) for 1 h catalyst total naph distribution of products, % ratio naph wt, conversions, % 2-Me 1-Me ethyl di-Me" di-naphb S-Me/l-Me no. wt, I tsve g 6.2 49.14 40.23 0.00 0.00 10.63 1.22 2.70 6.6 51.62 42.31 0.00 0.00 1 0.30 AlPO4-5 6.07 1.22 2.70 1.16 2 0.30 11.8 55.64 38.49 1.64 3.07 PbfAlP04-5 2.70 1.45 14.7 0.99 3 0.30 PbAPO-5 47.99 40.03 2.32 8.66 1.20 2.70 NiAPO-5 11.8 55.33 26.91 1.42 1.98 4 0.30 14.36 2.06 2.70 12.4 54.67 32.05 0.50 2.70 NiAPO-5-red 10.08 1.71 5 0.30 2.70 0.71 6.82 SAPO-5 16.2 49.87 41.45 6 0.20 1.16 1.20 1-80 21.0 0.75 CUSAPO-5 47.39 41.63 9.25 0.97 7 0.30 1.14 2.70 21.1 46.42 40.58 0.90 9.68 2.42 1.14 8 0.31 Cu/SAPO-5 2.73 0.80 CuAPO-5 9 0.30 14.8 48.75 41.33 0.00 9.12 1.18 2.70
"Five dimethylnaphthalene isomers were identified. The sum of areas representing all these compounds was used in the calculation. *Three isomers of dinaphthalene, lJ-, 1,2-, and 2,2 were clearly separated by GC. The sum of areas representing all these compounds waa used in the calculation. then kept at 100 OC for 0.5 h followed by a second temperature programmed step of 35 OC/h until 750 OC was reached. Subsequently the sample was kept at 750 OC for 1h, before cooling to room temperature. Catalysts 2 and 3 A1P04-5with Lead Incorporation. Lead was introduced into molecular sieves by two conventional methods, namely the wet and hydrothermalcrystallization (HTC) methods. Catalysts prepared by these two methods are designated Pb/ m o 4 - 5 and PbAPO-5, respectively, in accord with the nomenclature adopted e1sewhere.B~~ was first synthesized as above. Lead nitrate Catalyst 2, (2.69 g, AR) was dissolved in distilled water and the solution was heated to 30 OC. Ap04-5 catalyst (3.00 g) was slurried into the solution to form a suspension. The suspension was then stirred at 30 OC for 3 h and dried on a rotary evaporator to yield a fine powder. The dried powder was calcined under a stream of air except that the upper in a similar manner to that used for temperature was limited to 500 OC and the sample was held at 500 OC for 6 h. The catalyst prepared by this method contains lead oxide carried on the surface of the microporous AlP04-5 (catalyst 1). Catalyst 3, phosphoric acid (8.09 g, 85%), was diluted with distilled water (6.05 g) in a glass vessel similar to that above. A mixture of lead nitrate (1.09 g) and pseudoboehmite (4.60 g) was then gradually added to the diluted phosphoric acid solution under strong agitation until the reactants were well mixed. TEAOH (25.70 g 20% solution in water) was then added to the stirred reaction mixture. The mixture was then sealed within the glass vessel in a stainless steel reactor and allowed to stand at room temperature for 30 min before being placed in an oven at 150-200 OC for 24 h for HTC.After HTC, the reaction was cooled rapidly and the solid product was recovered by fitration. After washing with hot water to a pH of 6-7 and drying at 100 OC overnight, the sample was calcined in a stream of air using a temperature program as for catalyst 1,except that the sample was held at the upper limit of 750 OC for only 5 min. Catalyst 4: A1P04-5Catalysts with Nickel Incorporation. Nickel sulfate hexahydrate (1.74 g) was diesolved in distilled water (22.00 g) to which phosphoric acid (39.3 g, 85%) was added. Pseudoboehmite (21.6 g) and TEAOH (115 g, 20% solution water) were added as described above. However, in this synthesis the mixture waa placed in an autoclave with a Teflon liner at 150-200 OC for 24 h. After cooling, washing with hot water to pH of 6 7 , and drying overnight at 100 "C, the sample was calcined as for catalyst 1,except in this case the upper temperature limit was 700 OC. Catalyst 5: Reduced Form of NiAPO,-S. A reduced form of NiAPO-6 catalyst was obtained by passing a H2 stream through the catalyst at 400 OC for 6 h at about 5 mL/min. Catalyst 6 Silicon-Substituted AlPO with A1PO4-5Phase. Phosphoric acid (5.27 g, 85%) was diluted with distilled water. Pseudoboehmite(3.74 g) was then gradually added to the diluted H3P04solution under strong agitation until the reactants were well mixed. TEAOH (16.83 g, 20% solution in water) was added
to the reaction mixture with stirring. Si(OCzH6)4(0.52 g) was finally added to the mixture which was subsequently stirred for about 10 min and sealed into a stainless steel reactor with glass liner. The mixture was allowed to stand at room temperature for 30 min before being placed in an oven at 150-200 OC for 24 h for hydrothermal crystallization (HTC). After cooling, the product was recovered as described above and dried overnight at 100 OC. Calcination was carried out under a stream of air using the same temperature program as that for catalyst 3. Catalyst 7: Copper- and Silicon-Cosubstituted AlPO with APO& P h e . This was synthesized as for catalyst 6 but copper nitrate ( C U ( N O ~ ) ~ - ~ . ~ was H~O added ( ~ ) }to the dilute phosphoric acid. The amount of the components in the sample were adjusted so the molar relationship (Si + P) = (Cu + Al) was maintained. The recovered catalyst was light green in color and is designated CUSAPO-5. Catalyst 8 Copper-Exchanged SAF'O-5 with AlPO& P h e . The preparation involved two steps. SAPO-5 (catalyst 6) was first synthesized and copper was then exchanged onto the SAPO-5 rather than incorporated into the thermal synthesis. A copper nitrate solution in water (30 mL, 3 M)was warmed to 55 OC. SAPO-5 (1.5 g) was then added with stirring. The suspension was further stirred at 55 OC for 3 h and then filtered. The recovered solids were washed thoroughly with distilled water and dried in air. The above exchange and recovery procedures were repeated a further two times. The fial product was then dried in an oven at 100 "C overnight to yield a fine blue solid, designated Cu/SAPO-5. Catalyst 9: A m & Catalysts with Copper Incorporation. The procedure for the preparation of this catalyst was the same as that described above for catalyst 7 except [Si(OC2H6),]was not added. The catalyst was green in color. Catalyst Characterization. The catalysts were characterized by powder X-ray diffraction (XRD), nuclear magnetic resonance spectroscopy,and surface area measurements as described elsewhere! Table I gives a brief summary of the structure of the various catalysts as deduced on the basis of these measurements. In all cases when the metal was introduced during the synthesis (catalysts 3, 4, 5, 7, and 9), the micropores were not seriously occluded by the introduced metal. XRD patterns for all metal me's were similar to those for pure mo4-5.It is eeeumed that only in the case of catalysts 2 and 5 was the metal present as the oxide carried on the surface. Methylation Procedures. Naphthalene (AR grade for GC standard) was used without further purification. GC analysis confirmed the absence of detectable quantities of methylnaphthalenes or other impurities. Details of the proportions of catalyst and naphthalene used in the experimenta are listed in Table II. The naphthalene and catalyst accurately weighed into a glass liner were placed into a 1-L Parr rocking autoclave which was charged to a pressure of 6.8-6.9 MPa with methane. The veasel was then heated to 400 OC at a rate of 4 OC/min and kept at 400 OC for 1h. The temperature was measured by means of a thermocouple inserted in a well inside the autoclave. The
(7) Cabello, J. A.; Campelo, J. M.; Garcia, A.; Luna,D.; Marinas, J. M. J . Catal. 1985, 94,1-9.
(8) He, S. J. X. Ph.D. Thesis, University of New South Wales, Amtralia, 1992.
He et al.
500 Energy & Fuels, Vol. 6, No. 4,1992
products and unreacted naphthalenewere recovered by dissolution in chloroform and the catalyst was then separated by filtration. The chloroform solution was concentrated on a rotary evaporator and analyzed by a variety of techniques as outlined below. Product Analysis Procedures. A Hewlett Packard (HP5890A) gas chromatograph was used to measure the proportions of various compounds formed. Detection was by flame ionization and separation was brought about by a methyl silicone coated capillary column (30 m X 0.35 mm OV-1 column or 25 m X 3 pm BP-1 column from SGE). A nitrogen flow rate of 4-5 mL/min was used with temperature programming from 40 to 250
After use in the methylation r u n
OC.
Conversion of naphthalene (%) was calculated from the s u m of the areas of all products in the GC trace with weightings for the oligomers, divided by the sum of the areas of all products, with weightings for the oligomers, and unreacted naphthalene. Likewise selectivity was calculated as area of compound sel (%) = x 100 sum of all product areas Reproducibility was found to be within 10%. Gas chromatography mass spectrometry (GC/MS) was carried out on a Hewlett Packard 5890 gas chromatograph and chemical data system. Chromatography was carried out on a 50-m Hewlett Packard ultra No. 2 capillary column. The capillary column was kept at 30 OC for 2 min after injection, after which the temperature was raised by 4 OC/min to 280 O C . Products were identified on the basis of retention time, library matching, and known ionization ~atterns.~ Solution NMR spectroscopy was performed on a Bruker AMX5OO instrument operating at 125 MHz for carbon. 13Cspectra were obtained with inverse gated decoupling and a recycle time of 10 a. lH spectra were obtained using a recycle time of 2 8. NMR data were consistent with the GC/MS results outlined above.
Results and Discussion Before discussing the results in detail, it should be pointed out that the thermodynamics of the reaction
lie far to the left. However, the methane concentration is >lo2 times that of naphthalene and hydrogen is consumed by reduction of metal oxide present. Thus the amount of methylnaphthalene formed is not negligible. From standard free enthalpies and entropies and a knowledge of the concentration of gases, we predict the reaction to produce about 18% methylnaphthalene in agreement with our best results discussed below. Blank runs in which methane was replaced by nitrogen were also carried out with naphthalene and several of the catalysta,and no producta of decomposition were observed. The extents of conversion of naphthalene to other products over the various catalysts, in the presence of methane, as measured by the amount of naphthalene remaining, are shown in Table 11. Substantial conversions were observed with all catalysts at the end of the 1 hour reaction period, and to our surprise, some conversion of naphthalene was also achieved in the absence of added catalyst (experiment 1,Table 11). This latter result suggests that some catalysis can occur on the walls of the autoclave, or per se,methane is far more reactive under these reaction conditions than previously supposed. The results obtained for methane-naphthalene reactions with catalyst (Table 11) gave (within experiment error) conversions similar to the blank run with no catalyst. However, a marked catalytic effect was observed with the (9) Davies, I. L.; Bartle, K. D.; Williams, P. T.; Andrews, G. E. Anal. Chem. 1988,60, 204.
Before use i n the methylation run
c
Figure 1. Typical XRD spectra before and after a methylation run. The XRD spectra are recorded from 28 = 40' to 2 O .
other modified aluminophosphates. APo4-5 incorporated with lead and copper, which were previously found to activate methane a t 1 atm pressure and elevated temperatures,8 showed again relatively high activity for methylation of naphthalene (experiments 4 and 10, Table 11) compared with plain A1P04-5. The highest conversions were achieved with the catalysts incorporating both copper and silicon. The crystal structure (A1PO4-5phase) of the catalysts after methylation was shown by X-ray diffraction to be unchanged. The patterns of the XRD spectra were essentially the same before and after methylation experiments, except that the relative intensities of the lower degree peaks ( 7 . 5 O and 13') decreased (Figure 1). This phenomenon was expected because organic material absorbed by the sample might enhance the X-ray shielding. A similar observation on hydration of zeolites was reportad by Break.lo Moreover, samples containing nonframework metal were not as stable as those with incorporated metals. A lead mirror (black, experiment 3) and a copper mirror (red, experiment 9) were observed on the glass liner of the reaction autoclave on completion of these experiments, although the XRD patterns in both cases did not change after the methylation runs. The selectivity of the products from the methylation of naphthalene is shown in Table 11. The major products were l-methyl- and 2-methylnaphthalene with 2-methylnaphthalene being dominant. This isomer is more stable than the l-methyl isomer." Over aluminosilicates at 450 "C, l-methylnaphthalene is transformed to 2-methylnaphthalene and small amounts of dimethylnaphthalenes and naphthalene." Moreover, the ease of demethylation (10) Break, D. W.; Eversole, W. G.; Milton, R. M.; Reed, T. B.; Thomas, T.L. J . Am. Chem. SOC.1956, 78, 5963. (11) Cullinane, N. M.; Chard, S. J. Nature 1948, 161, 690.
Methylation of Naphthalene by Methane
Energy & Fuels, Vol. 6, No. 4, 1992 501
Table 111. Thermal Stability of Methylnaphthalene under Nitrogen at 6.9 MPa (Cold Pressure) for 1 ha selectivity of individual product, % naph (CllHlO) (ClIHlZ) dinaphthalene (C&i14) expt no. total convn, % (C1&a) 2-Me l-Me ethyl di-Me 1,l' 1,2' 2,2' 11 29.34 59.90 30.67 0.00 3.69 2.80 1.20 1.74 0.00 5.13 19.33 4.81 2.83 3.61 12 26.66 64.29 a Note experiment 11 was carried out with l-methylnaphthalene as starting material. Experiment 12 was carried out with 2-methylnaphthalene as starting material.
160 4.
Naphthalene 2-Me naphthalene I -Mr naphthalene elhulnaDhthalene
I20
8U
40
II
JI
B 2100
200
2880
3120
0 480
960
1600
2240
2880
Figure 2. Typical gas chromatogram of products from treatment of naphthalene with catalyst and methane (experiment 9).
of the methylnaphthalenes is l-methyl > 2-methy1.12J3 Thermodynamic data are available on alkyhaphthalene~'~ which also show the greater stability of the 2-isomer over the l-isomer. A typical gas chromatogram is shown in Figure 2. The other products from the reaction are l-methyl, ethyl (probably 2-ethyl), dimethyl, and dinaphthyl products. The formation of dinaphthyl materials without methylation suggests that naphthalene radicals are formed either by abstraction by methyl radicals, probably on surfaces, or by direct hydrogen abstraction. The presence of ethylnaphthalene is evidence for the recombination and hydrogen abstraction from ethane, or more likely, hydrogen abstraction from methylnaphthalene (probably 2-methyl). Fairly high percentages of dimethylnaphthalene were formed in the cases of the more active catalysts (experiments 8 and 9, Table 11). The formation of dimethylnaphthalene could be the result of attack of methyl radicals on methylnaphthalene product and/or demethylation of 2-methylnaphthalene (experiment 12, Table 111). Table I1 also shows the ratio of 2-methyl- to 1methylnaphthalene formed. The values differ from each other for various catalytic experiments, which suggests that the ratios of these two products are not that of thermal equilibrium under these reaction conditions. Two major possible processes in the reaction system might follow the catalytic formation of l-methyl- and 2methylnaphthalene. These are first, thermal isomerization of l-methyl- to 2-methylnaphthalene and, second, demethylation of 2-methylnaphthalene, both being reactions shown independently to occur at these temperatures (see below). Catalysts with incorporated lead and copper/ silicon were more active for promoting methane, presumably to form methyl radicals; therefore, although random formation of l-methyl- and 2-methylnaphthalene may have been possible, the lower 2-Me to l-Me ratios observed may (12) Graber, W. D.; Huttinger, K. J. Fuel 1982, 61, 505. (13) Nelson, P. F.; Huttinger, K. J. Fuel 1986, 66,354. (14) Milligan, F. E.; Becker, E. D.; Pitzer, K. 5.J. Am. Chem. SOC. 1956, 78, 2707.
have been the result of the subsequent processes of isomerization and demethylation. In contrast, NiAPO-5 was not as active for methane activation, and activation of naphthalene with expected shape selectivity on the surface of the nickel based catalysts could be more dominant, leading to the more space-favored product, 2-methylnaphthalene, rather than l-methylnaphthalene. Therefore, the ratio of 2-methylnaphthaleneto l-methylnaphthalene was higher for NWO-5. A similar explanation may apply to the blank and plain A1P04-5 experiments. In principle, the actual selectivity of the catalyst alone could be calculated by subtracting the yields of products produced in the noncatalyzed experiments; however, the errors are probably too large to make such a quantitative comparison. It is clear that the ratios differed widely for different catalytic experiments and that the selectivity for 2-methylnaphthalene would be even greater if the uncatalyzed yields were subtracted for these experiments. In a separate set of experiments, 1- and 2-methylnaphthalenes were heated in the same autoclave under the same conditions but in the absence of methane. The results of these experiments are shown in Table 111. The principal product formed in each case was naphthalene, but, in addition, substantial isomerization to the other methyl isomer was observed for l-methylnaphthalene but not for 2 -methylnaphthalene. The two isomers were not formed in thermal equilibrium. It is thus possible in the methylation reactions of naphthalene that some of the l-methylnaphthalene formed as a primary product of reaction may have undergone partial isomerization to 2methylnaphthalene on the catalyst or the steel reactor walls. An interesting observation from Table I11 is the formation of ethyl and dimethylnaphthalene when the substrate was 2-methylnaphthalene, but not when the substrate was the l-methylnaphthalene. In conclusion, it is clear that some of the microporous substituted aluminophosphates included in this study efficiently activate methane at 400 O C under elevated pressures. It is highly likely that methyl radicals are formed, as is observed with alkaline earth oxide catalysts at much higher temperatures (750-800 O C ) , 1 6 and these radicals are available to methylate appropriate organic species. Some modified forms of Alp0 catalysts have been shown to have activity for the oxidative coupling of methane16 and for promoting hydrogen isotope exchange in hydrocarbon^.^ Thus hydrocarbon radical formation appears to be a feature of modified APO, and in some instance pure Alp04catalyts. In the case of pure Alpo4-5 catalysts reactivity has been ascribed to defect sites in the lattice."
The full role of the metal and of the microporous nature of the catalyst is not revealed by this preliminary study of naphthalene methylation, but it is likely that these (15) Lin, L. H.; Wang, J. X.; Lunsford, J. H. J. Catal. 1988,111,302. (16) Iton, L. E.; Choi, I.; Desjardins, J. A.; Naroni, V. A. Zeolites 1989, 9(6), 535. (17) Endoh, A.; Mizoe, K.; Tautaumi, K.; Takaiehi, T. J . Chem. SOC., Faraday Tram. 1989,85,1327.
502
Energy & Fuels 1992,6, 502-511
catalysts could have significant application when methylation is required on a large commercial scale. These reactions might also be promoted by basic oxide catalysts at the much-higher temperatures (700-900 "C) at which they exhibit methane coupling reactivity. Acknowledgment. We thank Mr. R. Quezada for
GC/MS analysis. The Australian Institute of Nuclear Science ACARP and the Australian Research Grant Scheme are acknowledged for financial assistance. Registry No. CHI, 74-82-8;Pb,7439-92-1; Ni, 7440-02-0; Si, 7440-21-3;Cu, 7440-50-8;naphthalene, 91-20-3;l-methylnaphthalene, 90-12-0; 2-methylnaphthalene, 91-57-6.
Basic Hydrodynamic Characteristics of a Fluidized-Bed Incinerator S. C. Saxena,* V. N. Tanjore, and N. S. Rao Department of Chemical Engineering, The University of Illinois at Chicago, P.O.Box 4348, Chicago, Illinois 60680 Received September 30,1991. Revised Manuscript Received March 30, 1992
A pilot plant fluidized-bed incinerator facility is described, which consists of an air supply system, a fluidized-bed incinerator, a gas analysis unit, and an off-gas cleanup system. For preheating the combustion air a propane burner system was developed and successfully tested. The fluidization quality of the bed is investigated by computing and analyzing the pressure fluctuation history data of an inert dolomite bed over a period of 92 s using statistical functions such as standard deviation, probability density function, skewness, kurtosis, autocorrelation, and power spectral density function. Measurements are taken over a wide temperature range from ambient (298K)to 1287 K. Two different cofiiing fuels, propane gas and coal, used for the combustion of low calorific fuels are examined. Coal combustion and carbon utilization efficiencies are determined as a function of temperature and gas fluidization velocity. Conditions leading to the lowest carbon monoxide emission levels in the flue gas have been identified. All these data have revealed the optimum operating conditions for the efficient thermal destruction of waste materials in a fluidized-bed incinerator in relation to a specific inert bed and based on considerations of carbon monoxide emission.
Introduction Destruction and disposal of waste materials by incineration is a commonly adopted technology from the dawn of civilization. Numerous publications on the subject and considerable industrial manufacturing experience and design guides are availab1e.l4 Fluidized-bed incineration has been used with considerable success for a variety of wastes.613 These and other studies have indicated that fluidized-bed incineration can successfully handle, within stringent environmental pollution emission limits,a variety of specialized wastes which cannot be thermally disposed of by other thermal techniques. This has become possible because of the well-known properties of fluidized beds. Of special relevance are the good gas-solids contacting, efficient solids mixing, high particle concentration, and uniform temperature distribution. Such systems can be operated even at higher temperatures, if necessary, particularly for hazardous and toxic wastes easily and this has encouraged the application of this technology to such materials which can be chemically decomposed to simple inert components only at high temperatures. Further, the successful removal of toxic pollutants by in situ absorption in the appropriate inert bed material has added another dimension in popularizing this technology. This work has explored some of these features in a specially designed pilot-plant facility and these results are reported here. *Towhom all correspondence should be addressed. 0887-0624/92/2506-0502$03.00/0
In particular, a dolomite bed was used, and its different hydrodynamic properties were investigated to establish those optimum conditions for incineration. In order to suitably combust to low calorific value wastes, it is essential to cofire the waste with an appropriate auxiliary fuel. (1) Corey, R. C., Ed. Principles and Practices of Incineration; John Wiley and Sons: New York, 1969. (2) Niessen, W. R. Combustion and Incineration Processes; Marcel1 Dekker Inc.: New York, 1984. (3) Brunner, C. R. Incineration Systems-Selection and Design; Van Nostrand Reinhold Co.: New York, 1984. (4) Martin, E. J.; Johnson, J. H. Hazardous Waste Management Engineering; Van Nostrand Reinhold Co.: New York, 1987. (5) Bartok. W.: Lvon. R. K.: McIntvre. A. D.: Ruth. L. A.: Sommerlund; R. E. Comb&tdrs: 'Appli&tiom &d bign'Considerations. Chem. Eng. Prog. 1988,84, 54. (6) Kotani, T.; Mikawa, K. Combustible Materials Recovery and MSW Fluidized-Bed Incineration in Japan. AIChE Symp. Ser. 1988,84, 44. (7) Furlong, D. A.; Wade, G. L. Combustion of Municipal Solid Waste in a Fluidized-Bed. AIChE Symp. Ser. 1972,68, 152. (8)Makanski, J. Agri-Waste-Fired Plants Settle on Bubbling Beds. Power 1989, 133,93. (9) Bulewicz, E. M.; Kandefer, S.; Jurys, C. Fluid Bed Combustion of Waste Materials and Difficult Fuels. R o c . Tenth Int. Conf. Fluidized Bed Combust., San Francisco, CA, 1989,1, 85. (10) Copeland, G. G. Industrial Waste Disposal by Fluidized Bed Oxidation. AIChE Symp. Ser. 1972, 68, 63. (11) Hickman, H. L.; Turner, W. D.; Hopper, R.; Hasselries, F.; Kuester, J. L.; Treznk, G. J. Therm1 Conuersion Systems for Municipal Solid Waste; Noyes Publication: Park Ridge, NJ, 1984. (12)McFee. J. N.: Rasmussen. G.P.: Yound. C. M. The Design and Demonstration of a 'Fluidized-Bed Incinerator' for the Destruciion of Hazardous Organic Materials in Soh.J. Hazardous Mater. 1986,12,1!29. (13) Dry, R. J.; LaNauze, R. D. Combustion in Fluidized Beds. Chem. Eng. Prog. 1990, 84, 31.
0 1992 American Chemical Society
