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Ind. Eng. Chem. Res. 1989,28, 1596-1600
Bhasin, M. M.; Ellgen, P. C.; Hendrix, C. D. Catalyst Composition and Process for Oxidation of Ethylene to Ethylene Oxide. United Kingdom Patent GB 2,043,481 (to Union Carbide Corp.), 1980. Carberry, J. J. Chemical and Catalytic Reaction Engineering; McGraw-Hill: New York, 1976. Carra, S.; Forni, L. Aspetti Cinetici della Teoria del Reatore-Chimico. Tamburirni, Milan, 1974. Froment, G. F.; Bischoff, K. B. In Chemical Reactor Analysis and Design; John Wiley and Sons: New York, 1979. Gilles, E. D.; Hofmann, H. Bemerkung zu der Arbeit: An Analysis of Chemical Reactor Stability and Control. Chem. Eng. Sci. 1961, 5, 328. Nielsen, R. P.; La Rochelle, J. H. (to Shell Oil Co.) Catalyst for Production of Ethylene Oxide. U.S. Patent 3,962,136, 1976.
Pan, D.-F.; Schnitzlein, K.; Hofmann, H. Design of the Control Scheme of a Concentration-Controlled Recycle Reactor. Ind. Eng. Chem. Res. 1988,27,86-93. Perlmutter, D. D. Stability of Chemical Reactors; Prentice-Hall: New York, 1972. Silva, J. M. Cascade Temperature Control System for the Berty Reactor. Ind. Eng. Chem. Res. 1987,26, 179-180. Van Heerden, C. The Character of the Stationary State of Exothermic Processes. Proc. of the 1st European Symposium on Chemical Reaction Engineering; Pergamon Press: Amsterdam, 1958; p 133.
Receiued for reuiew November 18, 1988 Accepted June 7, 1989
Naphtha Reforming Capacity of Catalysts with Different Metallic Functions Javier M. Grau and Jose M. Parera* Instituto de Inuestigaciones en Catdlisis y Petroqulmica, INCAPE, Santiago del Estero 2654, 3000 Santa Fe, Argentina
The aromatizing capacity and the deactivation produced by coke and sulfur of metals supported on A120,-C1 catalysts were studied for the reforming of n-paraffins (C7-Cl0) and naphtha cuts (light and heavy) under commercial conditions. The metallic components of the catalysts were Pt(0.3%), Pt(1.14%), and Pt(0.30% )-Re(0.30%)-S(0.04% ) for balanced metal and Pt(0.22 % )-Re(0.44 % )-S(0.064%) for skewed metal. Both Pt(0.3%) and Pt-Re balanced-metal catalysts are more selective toward aromatics with n-C7 and n-C8, while Pt(1.14%) and Pt-Re skewed-metal catalysts are better with n-C9 and n-Clo. Regarding the naphtha cuts, the balanced-metal catalyst produces a higher increase in octane number for the light cut than the skewed-metal catalyst, while the skewed is better for the heavy cut. T h e skewed catalyst produces more gas with both cuts. This catalyst is more stable and has a greater activity recovery after being deactivated by coke deposition. The thiophene deactivation is similar in both catalysts. Naphtha reforming is a catalytic process that increases the gasoline octane number mainly by an increment in the aromatic hydrocarbons concentration. A new catalyst composed of platinum supported on an acidic oxide was introduced after World War 11. The first catalyst of this generation was patented by Haensel (1949). When the processes is operated at high pressures (30-35 kg cm-2), these catalysts have a good selectivity toward aromatics and an acceptable stability with operation cycles of about 10 months. Nearly 20 years later, bimetallic catalysts appeared. Kluksdahl (1968) patented the addition of rhenium as a second metal to platinum. The most common concentrations of Pt and Re used in the process are of similar values (generally 0.3%), and the process (Rheniforming E) allows us to reduce the working pressure to 8-15 kg cm-2,with greater activity, selectivity, and stability than the monometallic catalyst (Gates et al., 1978). This equal-metal or balanced-metal catalyst was rapidly adopted in most of the reforming plants, and since it is more sensitive to poisoning by sulfur (Menon and Prasad, 1976),a more severe feed hydrodesulfuration is necessary. About 7 years ago, the same company, Chevron (US.), introduced a new catalyst with more Re than Pt (Rheniforming F), which is called a “skewed-metal” or skewed catalyst. According to Larsen (1986),this high Re catalyst presents greater activity and stability than the normal balanced-metal catalyst. These properties could allow for operation at a lower pressure and a lower hydrogen to hydrocarbon ratio, conditions that favor aromatization. Because of its high stability, Moorehead (1986) recom-
mends using the skewed catalyst in the last reactor. Knowing the behavior of catalysts with different compositions of the metallic component, mono- as well as bimetallic catalysts, for the reforming of different feeds could be useful in the selection of the catalyst as a function of the reformer charge. Changes in the selectivity as a function of feed composition using catalysts with the same metallic components (0.3% Pt, 0.3% Re) but different acid functions (alumina with different chlorine concentrations) were studied in a previous paper (Grau et al., 1988). In this paper, the activity, selectivity, and stability of four catalysts with the same acid function but different metallic functions are studied with n-paraffins of C7-Clo. The catalysts used are two monometallic catalysts with different Pt charges and two commercial bimetallic catalysts, Pt-Re, one with the same concentration of Re and Pt and the other with skewed concentrations, twice as much Re as Pt. Two hydrodesulfurized naphtha cuts doped with n-paraffins are also tested with the bimetallic catalysts.
Experimental Section Materials. 1. Catalysts. The monometallic catalysts were prepared by impregnation of r-Alz03 CK 300 supplied by Ketjen Cyanamid (Amsterdam) with an aqueous solution of HzPtC&-HCl,according to the technique of Castro et al. (1981). The bimetallic catalysts were of a commercial origin. The chlorine content of the catalyst samples was adjusted by passing a gaseous stream of air-HC1-water through the sample, following the method of Castro et al. (1983). To avoid the initial hyperactivity, the bimetallic
0888-588518912628-1596$01.50/0 0 1989 American Chemical Society
Ind. Eng. Chem. Res., Vol. 28, No. 11, 1989 1597 Table I. Catalyst Characteristics wt%
catalyst Pt/A1,0, Pt/A1203 balanced Pt-Re/A1203 skewed Pt-Re/A1203
Sg,d C1" Sb m2 g-' 0.80 196 0.82 190 0.76 0.040 178 0.75 0.064 186
wt% wt% w t %
Pt Re 0.30 1.14 0.30 0.30 0.22 0.44
a Measured by the modified Volhard-Charpenter method. Measured chemically (HI reduction and titration with SnC1,). BET specific surface area, measured with a Micromeritics Accusorb 2100.
Table 11. Properties of the Naphtha Cuts navhtha cut property light heavy 0.715 0.735 density, g cm-3 71.0 RON 66.5 95 112 mean molec wt mean bp, OC 100 134 124-154 bp range, "C 85-128 OAPI 66.4 61.0 Table 111. Composition of the Naphtha Cuts and Paraffin-Doped NaDhtha Cuts (Weight Percent)" naphtha cut light doped light heavy doped heavy 4.4 7.8 13.0 7.4 37.8 39.3 13.4 15.9 18.4 12.2 18.8 32.0 2.7 19.0 3.8 22.5 6.4 0.0 4.2 0.0 61.6 73.8 64.6 79.0 12.7 8.7 8.3 4.9 10.1 11.3 16.6 6.0 1.7 1.2 6.7 4.0 25.1 21.2 14.9 31.0 2.1 1.3 3.1 2.3 4.3 2.9 2.4 1.4 2.9 1.8 0.0 0.0 2.7 0.0 0.0 1.6 7.4 5.0 10.3 6.1 "Ci = paraffins of i carbon atoms; NCi = naphthenes of i carbon atoms; ACi = aromatics of i carbon atoms; Ptotal = total paraffins; Ntotal = total naphthenes; Atotal = total aromatics. All the cuts had vestiges of Cb paraffins not included in the table.
catalysts were sulfurized before their use according to the method of Apesteguia et al. (1978). The main catalyst characteristics are shown in Table I. 2. Feeds. Pure n-paraffms (C,-C,,, Carlo Erba RP) and two naphtha cuts with different boiling point ranges were
used as the liquid feed. The cuts were the effluents of a hydrodesulfuration unit, with a sulfur concentration of 0.8 ppm for the light cut and 1.8 ppm for the heavy cut. The cuts were doped with n-paraffins to increase the boiling point difference. Before use, the feed was dried by passing it through a bed of 4A molecular sieves. The main properties of the naphtha cuts are shown in Table 11, and their compositions as well as the compositions after doping with paraffins are shown in Table 111. 3. Gases. Hydrogen, deoxygenated and dried by passing it through a copper bed at 500 "C and a 4A molecular sieves bed, respectively, was provided by AGA. Catalytic Tests. Two types of tests were performed. (a) To study the activity and selectivity of the four catalysts, pure n-paraffins were fed during 5 h, at a pressure of 15 kg cm-2, 500 "C, WHSV = 4 h-l, and molar ratio Hz/n-paraffins = 6. (b) To study the selectivity of the two bimetallic catalysts as a function of feed and analyze their resistance to coking and poisoning by sulfur, long runs were performed with the doped naphtha cuts. This five-period test lasted 24 h. In periods 1 ( 4 h), I11 (6 h), and V (7 h), the operational conditions were the same that in test a. In period I1 (4 h), the pressure was reduced to 3.5 kg cm-z and the H,/HC molar ratio reduced to 2 in order to increase the coke deposition, keeping the temperature and WHSV at the values of period I. During period IV (3 h), the conditions were the same as those in period 111, but the feed was doped with thiophene (150 ppm S) in order to have poisoning by sulfur. All tests were performed in a stainless steel fixed bed tubular reactor (20-mm i.d.) similar to the one described by Sad et al. (1980). The charge of the catalyst was 1.5 g of 35-80-mesh particles. The products were analyzed by gas chromatography with a 100-m capillary squalane coated column and a FID. From the product distributions in the effluent, the research octane number (RON) of liquid reformate and other parameters were calculated with correlations developed by Figoli et al. (1980).
Results Reforming of II -Paraffins. Table IV shows parameters representative of the activity, selectivity, and stability of catalysts obtained at 5-h time on stream, when the catalyst is almost stabilized. The research octane number, the aromatic concentration in the liquid reformate (Atli, = mass of total aromatics X 100/mass of the liquid effluent), and the production of gases (gas = mass of light paraffins (C,-C,) in the effluent X 100/mass of the charge) depend on the n-paraffin fed and the catalyst metallic
Table IV. Total Conversion, Research Octane Number, Concentration of Products or Group of Products in the Effluentnvb Concentration of Aromatics in the Liquid Effluent," Percentage of Selectivities to Hydrocracking, Isomerization, and Aromatization.' and Carbon Percentage on the Catalyst"(Values at the End of the Catalytic Test) Pt(0.22)-Re(0.44)-Sd Pt(0.30)d Pt(l.14)d Pt(0.30)-Re(0.30)-Sd feed n-C7 n-C8 n-C9 n-Clo n-C7 n-Cs n-Cg n-Clo n-C7 n-C8 n-Cg n-Clo n-C7 n-C8 n-Ce n-C,o conv 97.4 98.2 97.4 97.3 98.1 98.8 99.7 99.0 93.5 98.2 98.8 98.3 96.0 99.2 99.5 98.9 93.1 97.5 95.0 86.6 92.6 97.0 98.0 98.0 85.1 89.1 86.1 83.2 81.2 89.1 93.1 94.1 RON 5.9 4.2 3.7 1.7 1.8 1.5 5.2 3.0 2.5 2.5 1.2 1.2 1.7 1.4 3.5 2.5 PCl 27.0 28.0 30.0 29.0 39.0 31.0 28.0 28.0 33.0 37.0 42.0 46.0 52.0 47.0 41.0 37.0 gas 25.3 20.0 26.2 34.0 23.8 19.2 16.2 15.6 38.1 30.6 29.4 29.5 21.2 21.3 21.2 22.5 PCb-PClo 2.8 2.5 1.8 1.4 AC* 7.4 4.4 1.2 0.6 2.8 1.2 1.2 1.3 0.7 0.8 4.8 3.3 23.8 12.0 6.5 5.8 32.1 11.3 6.8 5.7 27.8 4.2 3.9 3.5 39.4 7.1 3.0 1.3 AC7 16.9 9.3 8.6 27.1 6.6 5.4 0.2 0.3 35.2 11.5 9.8 0.4 0.9 40.5 9.7 4.9 AC8 0.3 20.2 24.7 34.7 39.7 0.3 16.9 14.3 29.9 30.2 Ace+ Atti, 65.3 72.2 62.6 52.1 61.0 72.2 77.5 78.3 43.1 51.4 49.3 45.4 55.8 59.8 64.1 64.3 33 37 42 46 52 47 41 37 39 31 28 28 SH 27 28 30 29 20 21 21 22 36 30 29 29 SI 24 19 25 33 15 23 19 16 38 41 31 33 29 25 28 32 38 50 56 57 SA 49 53 45 38 carbon 0.70 0.74 0.88 1.31 0.80 0.82 1.36 1.42 0.02 0.02 0.08 0.10 0.16 0.18 0.40 0.42
" In weight percent. Same symbols as in Table 111. Gas: PC1-PCI. function.
Hydrocracking, SH; isomerization, SI; aromatization, SA. dMetallic
1598 Ind. Eng. Chem. Res., Vol. 28, No. 11, 1989 Table V. Concentration of the Aromatic in the Effluent,O'bRON Recovery: RON Drop: and Carbon Percentage on the Catal~st"*~ (Values at the End of Each Period of the Catalytic Test) doped light naphtha cut doped heavy naphtha cut Pt(0.30)-Re(0.30)-Sf Pt(0.22)-Re(0.44)-Sf Pt(0.30)-Re(0.30)-Sf Pt(0.22)-Re(0.44)-Sf prod period PV PI11 pv PI PI11 PV PI PI PI11 pv PI PIIr 10.1 8.8 3.0 9.2 8.9 1.8 2.3 2.4 2.5 12.9 10.1 3.0 AC6 19.8 18.2 5.9 26.1 19.6 21.7 18.1 3.3 3.5 5.9 4.4 4.9 AC7 2.1 2.9 2.1 3.8 3.4 2.9 4.6 3.2 0-xyl 3.7 2.2 3.0 4.5 7.6 4.7 4.0 8.8 7.4 3.9 6.9 7.0 4.1 8.0 5.2 4.0 m-xyl 1.8 1.5 2.6 2.2 3.1 3.0 3.0 1.4 1.5 3.0 1.9 1.4 P-XYl 3.2 3.1 2.7 3.5 3.2 1.0 1.4 1.o 1.0 3.5 1.4 1.5 EtBz 12.6 14.3 9.6 9.7 18.7 0.8 18.1 0.4 AC,+ 36.2 39.3 37.4 46.0 47.6 38.3 30.2 29.5 42.2 36.8 Atotal 51.2 38.8 23.5 87.5 52.9 88.8 64.0 90.8 88.8 33.3 % rec RON 13.0 1.0 8.0 1.0 4.5 1.5 1.0 7.0 ARON 2.14 2.84 0.55 0.75 %C Same symbols as in T & J e111. % rec RC-. = IRON at the enL 3f the normal perioi after deactivation ( P ~orI Pv) -,.I weight percent. - RON atthLbeginning of the same periodl/lRON at the end of the normal period before deactivation (PI or Pm) - RON at the beginning of the normal period after deactivation (Pin or Pv)J. dARON = IRON at the end of the normal period before deactivation (PIor Pm)l- IRON at the end of the normal period after deactivation (PI,, or Pv)l. e % C = carbon percentage on the catalyst. /Metallic function.
components. In the mono- and bimetallic catalysts with the smaller metallic charge, the values of RON and aromatic concentration increase from n-C7to n-C&decreasing then with an increase in the n-paraffin length. Meanwhile, in catalysts with a greater metallic charge, both parameters always increase when the n-paraffin length increases from n-C7to n-Clo. The activity (RON) in both catalysts increases when the metal concentration increases (except for n-C7).Regarding the gas production, in catalysts with the greater metallic concentration, mono- or bimetallic, the production decreases with an increase in the n-paraffin length, being just the opposite in the case of catalysts with lower metal concentrations. It is clear that catalysts with a larger metallic content are more convenient for n-C9and n-Clo, catalysts with a smaller amount of metal being the most convenient for n-C7. For n-C&the results are influenced little by the metallic concentrations. The selectivities to isomerization (SI = conversion to isoparaffins X 100/total conversion), aromatization (SA = conversion to aromatics X 100/total conversion), and hydrocracking (SH = conversion to n-paraffins of lower carbon atom number than that fed X 100/total Conversion) are shown in Table IV. It can be seen that, under the operational conditions of the test, monometallic catalysts are more selective to aromatics than the bimetallics, and regarding hydrocracking, the situation is just the opposite. For both catalysts, when n-C7and 8" are fed, the aromatization is greater and the hydrocracking is smaller for the catalysts with the lower metal concentration, whereas when n-C9and n-Cloare fed, the differences in selectivities are just the opposite. These results show that, regarding selectivity for n-C, and n-cs,the best catalysts are the ones with the lower metal concentrations and that, for n-Cgand n-CIo,the best catalysts are those with the higher metal concentrations. Table IV also shows that, under the operational conditions used, the conversion is high for the four catalysts and that, for each kind of catalyst, it is higher for the catalyst with the higher metal charge. For each kind of catalyst, coke formation is higher on the catalysts more concentrated on the metals, and the monometallics produce more coke than the bimetallics. The increase in the concentration of the metallic component increases the hydrogenation-dehydrogenation capacity of the catalysts, thus producing an increase in methane, nonsaturated hydrocarbons, and coke, as shown by Beltramini et al. (1985) for Pt/A1,0, in the reforming of a heavy naphtha. The results on dehydrocyclization of n-Cg and n-CIoon balanced-metal Pt-Re/Al,O, are similar to the ones of Szebenyi
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Figure 1. Octane number and gas formation as a function of time for the doped commercial light naphtha cut with balanced-metal and skewed-metal Pt-Re catalysts. Pt(0.30)-Re(0.30)/A1203-CI: RON (0);% gases (A).Pt(0.22)-Re(0.44)-S/A1203-Ck RON (0);% gases (A). PI+: periods I-V of the catalyst test.
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Figure 2. Octane number and gas formation as a function of time for the doped commercial heavy naphtha cut with balanced-metal and skewed-metal Pt-Re catalysts. Same symbols as in Figure 1.
and Szechy (1978), who used a commercial catalyst under similar operational conditions. Reforming of Doped Naphtha Cuts. The runs were performed with doped naphtha cuts to check the selectivities observed with pure feeds and to analyze the PtRe/A1,03 catalyst resistance to coking and sulfur poisoning. Figures 1and 2 and Table V show the catalyst behavior with the two doped cuts. The RON can be taken as indicative of the catalyst activity (activity for dehydrocyclization and isomerization)and gas formation as indicative of cracking activity, which decreases the liquid yield. For the light cut, the balanced-metal catalyst always produces a higher RON value and a lower gas formation than the skewed-metal catalyst. The higher RON value is due to the higher aromatic concentration, as shown in Table V.
Ind. Eng. Chem. Res., Vol. 28, No. 11, 1989 1599 For the heavy cut, the balanced-metal catalyst produces a lower RON and lower gas formation than the skewedmetal one. These results with naphtha cuts confirm the results obtained with n-paraffins in the sense that the skewed-metal catalyst is better for heavy feeds. Table V also shows parameters representative of the catalyst stability: the percentage recovery of reformate RON when the coked or sulfur-deactivated catalyst is operated for a period under normal conditions (% rec RON); the decrease in RON by irreversible deactivation by coke or sulfur (ARON); and the carbon deposited on the catalyst at the end of the test (% C). It can be seen that the skewed-metal catalyst shows the greatest recovery of activity and that the difference of recovery is larger in the case of deactivation by coking. In the case of poisoning by sulfur, the recovery during a 7-h operation period under normal conditions is about 90% of the deactivation. The carbon deposition on the catalyst is greater in the case of the skewed-metal catalyst; nevertheless, the deactivation is smaller than in the balanced-metal catalyst.
Discussion According to Sachtler (1984), rhenium atoms on the bimetallic catalyst surface can be oxidized (Reo2)or completely reduced (Reo). According to Johnson and Leroy (1974) and Margitfalvi et al. (1984), Reo2 or Re is responsible for an increment in the available activated hydrogen; then, hydrogenolysis and coke precursor hydrogenation will be more important in bimetallic catalysts. Parera et al. (1986) also showed that the introduction of Re increases the hydrogenation capacity of the monometallic catalyst, increasing the hydrogenolysis and decreasing the coke deposition. Regarding the coke formation, Parera and Beltramini (1988) showed that the difference in the deactivation by coke between mono- and bimetallic catalysts is due to the different coke distributions: on Pt-Re/A1203, a smaller fraction of coke is deposited on the metallic function, which maintains a constant activity. Jossens and Petersen (1982) stated that the addition of Re to a Pt/A1203catalyst modifies only the metallic function, while alumina is not affected. If alumina were the same for our catalysts, all differences would be ascribed only to the different metallic functions. Sachtler (1984) stated that on Pt-Re/A1203 a part of the Re atom forms a surface complex with alumina and chlorine. This would produce changes in the acid function and its selectivity, affecting the main reforming reactions, which are controlled by the acid function. Nacheff et al. (1987) showed later that only 10% or even less of the total Re is Re4+. This means that a very small amount of Re4+is distributed on a very large A1203 surface so that the influence of this oxidized Re on the total A1203performance is negligible. We think that the influence of hydrogen spillover is an important point that is not taken into account sufficiently in the literature. The main reforming reactions are acidcontrolled, and the acid mechanism involves protons, hydride ions, and hydrogen, the concentration of these species being modified when activated hydrogen spillover is present on the acid surface. Traffano and Parera (1986) showed that, for 50% or more Re in the Pt-Re metallic function, the hydrogen spillover is decreased or nullified. Then, the metallic function not only produces olefins and other hydrocarbons transported to the acid function but also provides activated hydrogen influencing the controlling steps on the acid function. The hydrogenationdehydrogenation activity and the activated hydrogen formation and spillover depend on the catalyst metallic phase composition. The presence of Re increases the
hydrogenolysis and decreases the activated hydrogen spillover. A very small fraction (0.4-0.8%) of the catalyst surface is covered by the metallic component. Nevertheless, the metallic function influences the whole reacting system because there are metal-catalyzed reactions (like naphthene dehydrogenation) and bifunctional reactions (like paraffin dehydrocyclization and isomerization), the first step occurring on the metal. The metallic function also influences the steps on the acid function, regulates the kind and amount of compounds that migrate to the acid function, transforms the products received from the acid function, and provides activated hydrogen that migrates (spillover)and reacts on the acid function. Then, changes in the metallic function composition produce changes in the catalyst performance in a complicated and, up to date, practically unpredictable way. The phenomenon is very complicated, and the scientific knowledge available at present does not allow us to predict the activity, selectivity, and stability of naphtha reforming catalysts. In this case, scientific studies tend to explain the catalytic behavior of successful commercial catalysts. The catalysts were semiempirically found, applying only some general rules of catalysis and a lot of experience. For the bimetallic catalysts in their partially sulfided form, the experimental results indicate that the skewedmetal catalyst is more convenient for rather heavy naphtha cuts. For these cuts, the skewed-metal catalyst produces more aromatics but also more gases than the balancedmetal catalyst. The main advantage of the skewed-metal catalyst is its stability, producing an even larger total amount of coke. Probably, the increase in Re keeps the metallic component of the catalyst more free from coke, and the total increase in the coke is caused by an increase of coke on the support, where hydrogen spillover is decreased. One disadvantage of the skewed-metal catalyst is the high gas production, which is higher than that of the balanced-metal catalyst. The catalyst comparison was made at the same operational pressure, and since the skewed-metal is more stable, the process can be operated at lower pressure. Under this condition, an improvement in selectivity will be produced, the gas formation will be decreased, and the aromatic production will be increased. Registry No. Pt, 7440-06-4; Re, 7440-15-5; S, 7704-34-9; H3C(CH2)&H3,142-82-5; HSC(CHZ)&HS, 111-65-9; H,C(CH&CH3, 111-84-2; H3C(CHJ&H3, 124-18-5; C, 7440-44-0.
Literature Cited Apesteguia, C. R.; Petunchi, J. 0.; Garetto, T. F.; Parera, J. M. Presulfurizacidn de catalizadores de Pt/A1203para reformado de naftas. In Actas 6 O Simposio Iberoamericano de Catblisis; Nogueira, L., Schmal, M., Frety, R., Lam, Y. L., Eds.; COPPE/ UFRJ: Rio de Janeiro, Brasil, 1978; Vol. 2, pp 641-654. Beltramini, J. N.; Churin, E. J.; Traffano, E. M.; Parera, J. M. Influence of Pt Concentration on Activity and Combustion of Coke on Pt/AI2O3. Appl. Catal. 1985,19, 203-206. Castro, A. A.; Scelza, 0. A.; Benvenuto, E. R.; Baronetti, G. T.; Parera, J. M. Regulation of the Chlorine Content on Pt/Al2O9 Catalyst. J . Catal. 1981, 69, 222-226. Castro, A. A.; Scelza, 0. A.; Baronetti, G. T.; Fritzler, M. A.; Parera, J. M. Chlorine Adjustment in A1203 and Naphtha Reforming Catalysts. Appl. Catal. 1983, 6, 347-353. Figoli, N. S.; Sad, M. R.; Beltramini, J. N.; Jablonski, E. L.; Parera, J. M. Influence of the Chlorine Content on the Behavior of Catalysts for n-Heptane Reforming. Ing. Eng. Chem. Prod. Res. Dev. 1980, 19, 545-551. Gates, B. C.; Katzer, J. R.; Schuit, G. C. A. Chemistry of Catalytic Processes; McGraw-Hill: New York, 1978; p 290. Grau, J. M.; Verderone, R. J.; Pieck, C. L.; Jablonski, E. L.; Parera, J. M. Selectivity of Pt-Re-S/Al2O3-C1 Reforming Catalyst as a Function of Feed Composition. Ind. Eng. Chem. Res. 1988,27, 1751-1754.
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Ind. Eng. Chem. Res. 1989,28, 1600-1607
Haensel, V. Alumina-platinum-halogen Catalyst. U.S. Patent 2,479,109, Aug 16, 1949; Reforming a Gasoline. US. Patent 2,479,110, Aug 16, 1949. Johnson, M. F. L.; Le Roy, V. M. The State of Rhenium in PtRe/A1203Catalysts. J. Catal. 1974, 35, 434-440. Jossens, L. W.; Petersen, E. E. Fouling of a Platinum-Rhenium Reforming Catalyst using Model Reforming Reactions. J. Catal. 1982, 76, 265-273. Kluksdahl, H. E. Reforming a Sulfur-free Naphtha with a Platinum-Rhenium Catalyst. U S . Patent 3,415,737, Dec 10, 1968. Larsen, P. A. In Question and Answer Session-Hydroprocessing; Ketjen Catalysts Symposium; Rijnten, H. Th., Lovink, H. J., Eds.; AKSO Chemie Ketjen Catalysts: The Netherlands, 1986; p 75. Margitfalvi, J.; Gobo16s, S.; Kwaysser, E.; Hegedus, M.; Nagy, F.; Koltai, L. Role of Rhenium in Bimetallic Reforming Catalysts. React. Kinet. Catal. Lett. 1984,24, 315-321. Menon, P. G.; Prasad, J. The Role of Sulfur in Reforming Reactions on Pt-A1,03 and Pt-Re-A1,03 Catalysts. Proceedings of the 6th International Congress on Catalysis; Bond, G. C., Wells, P. B., Tompkins, F. C., Eds.; The Chemical Society: London, 1976; Vol. 2, pp 1061-1070. Moorehead, E. L. In Question and Answer Session-Hydroprocessing; Ketjen Catalysts Symposium;Rijnten, H. Th., Lovink, H. J., Eds.; AKSO Chemie Ketjen Catalysts: The Netherlands, 1986; p 76.
Nacheff, M. S.; Kraus, L. S.; Ichikawa, M.; Hoffman, B. M.; Butt, J. B.; Sachtler, W. M. H. Characterization and Catalytic Function of Reo and Re4+in Re/A1,03 and Pt-Re/Al,03 Catalysts. J. Catal. 1987, 106, 263-272. Parera, J. M.; Beltramini, J. N.; Querini, C. A.; Figoli, N. S. Comparison of the Hydrogenating Capacities of Pt, Re and Pt-Re/ A120, in n-Hexane Reforming. Prepr. Pap.-Am. Chem. Soc., Diu. Pet. Chem. 1986,31, 744-750. Parera, J. M.; Beltramini, J. N. Stability of Bimetallic Reforming Catalysts. J. Catal. 1988,112, 357-365. Sachtler, W. M. H. Selectivity and Rate of Activity Decline of Bimetallic Catalysts. J. Mol. Catal. 1984,25, 1-12. Sad, M. R.; Figoli, N. S.; Beltramini, J. N.; Jablonski, E. L.; Lazzaroni, R. A.; Parera, J. M. Evaluation of Activity, Selectivity and Stability of Catalysts for Naphtha Reforming. J.Chem. Technol. Biotechnol. 1980, 30, 374-383. Szebenyi, I.; Szechy, G. Aromatization of n-Nonane and n-Decane over a Platinum-Rhenium Catalyst. Acta Chim. Acad. Sci. Hung. 1978, 98(1),115-132. Traffano, E. M.; Parera, J. M. Re Influence on Hydrogen Spillover on Pt-Re/A1203. Appl. Catal. 1986,28, 193-198. Received for review October 11, 1988 Accepted June 7, 1989
Advanced Two-Stage Gasification System. 1. Experimental Results Rajendra S. Albal,* Anthony F. Litka, Koon G. Neoh,?Leonard F. Westra, J. A. Woodroffe, David B. Stickler, and Richard E. Gannon Avco Research Laboratory, Inc., 2385 Revere Beach Parkway, Everett, Massachusetts 02149
This paper, which describes an advanced two-stage gasification system, consists of two parts: part 1describes the experimental results, and part 2 describes the process evaluation. In part 1,Avco’s concept of two-stage coal gasification that utilizes very rapid coal pyrolysis is reviewed. Its potential technical and economic advantages are also reviewed. A moderately large-scale (1ton of coal/h) entrained flow reactor facility was designed, constructed, and operated to obtain critical rapid pyrolysis kinetic data at conditions approaching those applicable for commercial reactors. Major factors that limit the product gas yield were identified and were optimized to the extent possible so as to maximize the coal carbon conversion to synthesis gas. Extensive intrusive diagnostics were used to study the effects of coal rank, coal carbon loading, and pyrolyzer inlet gas temperature on coal carbon conversion, exit gas temperature, and exit gas composition. The experiments were conducted under well-defined heating rate and mixing conditions in the pyrolyzer; hence, the data are not device specific and should have a general application. The system design studies (part 2) show that, when the experimental data on the rapid pyrolysis operation are incorporated into a two-stage gasification process design, distinct economic advantages over available single-stage processes can be projected. The results show that Avco’s two-stage process has about a 6% advantage for coal conversion to methanol over currently available major gasification processes as well as a 10-15% reduction in the oxygen consumption for a near-term process design. For an advanced system, the reduction in oxygen consumption is projected to be 20-25%.
Introduction and Background Rapid Pyrolysis. In the design of a gasification process, the knowledge of the mass of volatiles released is important because it dictates the amount of carbon available in the gas phase for homogeneous reactions as well as the amount of carbon in the residual char that must be consumed by heterogeneous reactions. As the time when the major uses of coal involved processes in which the coal was burned or carbonized as relatively large lumps, heating rates were limited to less than 100 K/min. Under these conditions, decomposition extended for periods of several minutes and t Current
address: University of Singapore, Singapore. address: ARC0 Chemical Company, Newtown Square, P A 19073.
* Current
the volatile content of coal, as indicated by the ASTM proximate analysis, was appropriate. The interest in burning pulverized coal, in which the heating rates were much greater than 100 K/min, led to results that showed that the standard proximate analysis was not relevant in the high-heating rate, high-temperature processes because volatile yields, appreciably higher than those predicted by proximate analysis, could be obtained. A multitude of papers (Anthony et al., 1975; ASTM, 1975; Badzioch and Hawksley, 1970; Coates et al., 1974; Eddinger et al., 1966; Fitzgerald and van Krevelen, 1959; Gannon and Krukonic, 1972; Gibson and Gregory, 1971; Gray et al., 1974; Howard and Essenhigh, 1967; Johnson, 1976; Jones et al., 1964; Juntgen and van Heek, 1968; Kimber and Gray, 1967; Kobayashi, 1976; Kobayashi, et al., 1976; Loison and Chauvin, 1964; Lowenstein and von Rosenberg, 1977;
0888-5885/89/2628-1600$01.50/0 0 1989 American Chemical Society
