Energy & Fuels 1989, 3, 168-174
168
HHA HX HYC HYD HYG IND IOM Li2S MAF MCMS MN Mo Mol A1203
MoC14 MONaph NAPH NDRV
hexahydroanthracene hexadecane hydrocracking hydrogenation hydrogenolysis indole insoluble organic matter lithium sulfide moisture and ash free methylene chloride/methanol solubles 1-methylnaphthalene molybdenum molybdenum on y-alumina molybdenum chloride molybdenum naphthenate naphthalene naphthalene derivatives
NH NH3 NiMo/
nitrogen heterocycles ammonia nickel and molybdenum on ?-alumina
~ 1 ~ 0 3
NPOH OHA P-MoS2 PC TlMN TSMN TET THFS THN TOL TTON
1-naphthol octahydroanthracene precipitated molybdenum sulfide Dolvfunctional comDounds i,2,>,4-tetrahydro-f-methylnaphthalene 1,2,3,4-tetrahydro-Bmethylnaphthalene tetralin tetrahydrofuran solubles tetrahydronaphthol toluene tetralone
Registry No. Mo, 7439-98-7; MoS2, 1317-33-5; l-methylnaphthalene, 90-12-0; 1-naphthol, 90-15-3; benzothiophene, 11095-43-5;indole, 120-72-9; bibenzyl, 103-29-7.
Hydrodenitrogenation of Quinoline and Coal Using Precipitated Transition-Metal Sulfides Christine W. Curtis* and Donald R. Cahela Chemical Engineering Department, Auburn University, Auburn, Alabama 36849 Received January 25, 1988. Revised Manuscript Received December 15, 1988
The hydrodenitrogenation (HDN) of quinoline was investigated by using precipitated transitionmetal sulfides from group VIB and VI11 metals. The precipitated transition-metal sulfides have a disordered rag structure and a higher surface area than their commercial mineralogical analogues. The selectivity for quinoline HDN of the precipitated and commercial WS2, Cr2S3,and FeS, was very similar; however, the higher surface area precipitated MoS, showed a higher HDN than did its commercial analogue. Precipitated MoS2 and RuSz were comparable to CoMo/Alz03and NiMo/A1203, respectively, in their hydrogenation activity for quinoline. Pt/Si02 showed higher hydrogenation activity a t lower temperatures than the transition-metal sulfide or the commercial hydrotreating catalysts but was not as effective for HDN. The activity and selectivity of MoS2, RuS2, and NiMo/Alz03 for producing hydrocarbons and nitrogen removal in coal liquefaction reactions were also examined. Both MoS, and RuS2 produced more hydrocarbons than the thermal reaction, with RuS, being the more active of the two; however, neither was as effective as NiMo/Alz03 for hydrocarbon production and HDN of coal liquefaction products.
Introduction The effectiveness of unsupported, precipitated transition-metal sulfides as hydrogenation and hydrodenitrogenation catalysts for quinoline and coal under liquefaction conditions is investigated. Precipitated transition-metal sulfides of moderate surface areas were produced by a method developed by Chianelli and Dines' in the late 1970s. The unique physical properties of the precipitated transition-metal sulfides due to their disordered structure have been e ~ a m i n e d . ~These , ~ materials crystallize in weakly interacting layers that allow for ready intercalation of appropriate species. The precipitated transition-metal sulfides have varying surface areas dependent on the dimensions of the stacked layers and, hence, on the details of the preparation method. Although these precipitated metal sulfides are poorly crystalline, *Author to whom correspondence should be addressed.
0887-0624/89/2503-0168$01.50/0
they exhibit X-ray diffraction pattens similar to those of their commercially available crystalline metal sulfide counterparts. A number of different precipitated transition-metal sulfides have been tested for hydrodesulfurization activity by using diben~othiophene~ and are good candidates for hydrodenitrogenation studies. Development of catalysts for nitrogen removal from coal is needed since liquids derived from coal have naturally high nitrogen contents due to the nitrogen present in the feedstock. These nitrogen-containing compounds are detrimental because of their poisoning and deactivating effect on catalysts used in further refining,5 their forming NO, upon combustion, (1) Chianelli, R. R.; Dines, M. B. Inorg. Chem. 1978, 17, 2758. (2) Chianelli, R. R. Catal. Rev.-Sci. Eng. 1986,26, 361. (3) Chianelli, R. R. J. Cryst. Growth 1976, 34, 239. (4) Pecoraro, T. A.; Chianelli, R. R. J Catal. 1981, 67, 430-445. (5) Stohl, F. V.; Stephens, H. P. P r e p . Pap-Am. Chem. SOC.,Diu. Fuel Chem. 1986, 31(4), 251.
0 1989 American Chemical Society
Hydrodenitrogenation of Quinoline and Coal
and their being unstable in the product fuel, causing discoloration6 and other detrimental reactions.' As heavier feedstocks containing substantial amounts of nitrogen-containing compounds are brought into use, improved catalysts are needed to produce clean fuels. T o address these needs, new catalysts with improved hydrodenitrogenation selectivity that can withstand and maintain activity in the coal liquefaction environment must be developed. T h e objective of this study is t o determine if precipitated transition-metal sulfides can serve as effective catalysts for hydrodenitrogenation of coal and to evaluate how they compare with those catalysts already used for liquefaction. In this study, the hydrogenation activity and the denitrogenation selectivity of precipitated transitionmetal sulfides were first determined in a model quinoline system and compared t o commerical hydrotreating catalysts like CoMo/Al,O, and NiMo/A1203, which are commonly used in coal liquefaction.8 In addition, a Pt/Si02 catalyst was prepared and its activity and selectivity for hydrogenation and denitrogenation were compared to those of the precipitated transition-metal sulfides and the commerical hydrotreating catalysts. T h e precipitated transition-metal sulfides and hydrotreating catalysts most active in quinoline hydrogenation and denitrogenation were selected for evaluating their hydrodenitrogenation selectivity in coal liquefaction. Experimental Section Preparation of Catalysts. Each precipitated transition-metal
sulfide was prepared by dissolving the transition-metal chloride in ethyl acetate, with the resulting solution then added to an ethyl acetate slurry of lithium sulfide (Li2S),precipitating the transition-metal sulfide. The product was annealed with pure H2S at 400 "C, washed with 12% acetic acid, and then sulfided with 10% H2S/H2at 400 "C for 1h. The metal chlorides used were CrC13, MoCl,, WC16,FeCl,, and RuC13.3H20,producing Cr,S?, MoS2,WSz,and RuS2 All of the chemicals required for synthesis were obtained from Alfa Chemicals. A platinum on silica (Pt/SiOJ catalyst was prepared by adding 0.44 g of SiOzto 12.46 g of a 5% solution of chloroplatinic acid. Water was removed by vacuum rotary evaporation and the catalyst was dried for 16 h at 50 "C under 25 mmHg pressure. After grinding, the Pt/SiOz was reduced in a 40 mL/min Hz flow at 400 "C, producing a silvery black material. PtS, was obtained from Alfa Chemicals. The NiMo/A1203and CoMo/A1203catalysts were presulfided in a stream of 10 vol 70 HzSin H2;sulfiding was begun at 250 "C, and the temperature was raised by 50 "C every 15min until 400 "C was reached; this temperature was maintained for 1h. All supported catalysts were ground to -200 mesh before use. Quinolne Model System. Reactions were performed with the precipitated and commercial transition-metal sulfides, Pt/Si02, CoMo/A1203,and NiMo/A1203catalysts in 15cm3stainless-steel tubing bomb reactors. Five grams of a 2 wt % quinoline in hexadecane solution was used with 0.025 g of catalyst and 8.7 MPa (1250 psig) of hydrogen introduced at ambient temperature. The reactor was maintained at 380 "C for 30 min while being agitated at 850 rpm. Most of the reactions were at least duplicated. At 380 "C, about 1%of the hexadecane was hydrocracked, forming lower molecular weight cracked products that were observed in the gas chromatogram. Lower temperatures (340,320,300,250, and 200 "C) were used with the Pt/Si02 catalyst. The liquid
-
(6) Kartzmark, R.; Gilbert, J. B. Hydrocarbon Process. 1967,46(9), 143. (7)Thomson, R.B.;Chenicek, J. A.; Druge, L. W.; Symon, T. I d . Eng. Chem. 1951,43,935. (8) See, for example: Katzer, J. R.; Sivasubramanian, R. Catal. Reu.-Sci. Eng. 1979,20,155. Nalitham, R. V.;Lee, J. M.; Lamb, C. W.; Johnson, T. W. Fuel Process. Technol. 1987,17,13. Neuworth, M. B.; Moroni, E. C. Fuel Process. Technol. 1984,8,231.Stiegel, G . H.; Tischer, R. E.; Cillo, D. L.; Narain, N. K. Ind. Eng. Chem. Prod. Res. Deu. 1985, 24,206.
Energy & Fuels, Vol. 3, No. 2, 1989 169 products were analyzed by gas chromatography with a fused-silica 30-m capillary DB-5 column with a 0.2-pm f i i with FID detection and p-xylene as the internal standard. Ammonia was analyzed by using a Chromosorb 103 column and TCD detection. Coal Liquefaction Reactions. Ground Kentucky No. 11coal with a nitrogen content of 1.10% was used in the liquefaction reactions. Coal liquefactionreactions were performed with MoS2, RuS2, and NiMo/A1203as well as by a thermal method in -46 cm3stainless-steeltubing bomb reactors. The charge to the reactor was 0.5 g of coal with 0.5 g of anthracene as solvent, and, for catalytic reactions, -0.2 g catalyst/g of reactants. Reactions were performed at 425 "C for 1 h with 8.7 MPa (1250 psig) of H2 introduced at ambient temperature at an agitation rate of 850 rpm. Recovery of the product from the reactor was based upon the weights of the solid and liquid fractions. In calculating the product distributions, all losses were equally distributed among the solid and liquid fractions. The product distributions are reported on a moisture- and ash-free (maf) coal basis. Coal conversion is defined as 100% - % IOM. The liquid and solid products were separated by sequential washing with a methylene chloride-methanol (9:l v/v) solution (MCM) and tetrahydrofuran (THF). This separation produced three fractions: MCM solubles (MCMS),MCM insolubles-THF solubles (THFS),and THF insolubles. The THF insolubleswere converted to ash-free insoluble organic matter (IOM) by subtracting the mass of the coal ash and catalyst solids from the total THF insoluble mass. The MCMS fraction was further fractionated by the chromatographic method of Boduszynskilo into compound-class fractions: hydrocarbons (HC),nitrogen heterocycles (NH),hydroxyl aromatics (HA),and polyfunctional compounds (PC). Model compounds such as anthracene, acridine, carbazole, and 2-naphthol were chromatographed and verified the procedure. The hydrocarbon fraction separated from the MCMS fraction was further analyzed for anthracene hydrogenation products by using the same capillary column as for quinoline. The sample, dissolved in toluene with phenanthrene as the internal standard, was analyzed isothermally at 180 "C. Anthracene and three major hydrogenation products were observed: 9,10-dihydroanthracene (DHA), hexahydroanthracene (HHA), and 1,2,3,4,5,6,7,8-octahydroanthracene (OHA). These products were verified by comparison of their retention times with authentic compounds. However, the isomer of hexahydroanthracene formed was not determined. Some lighter hydrocracked products were also observed. In some reactions, a corrected total was calculated that provided a measure of the light cracked products produced during the reaction and observed by gas chromatography. The calculation assumed a response factor of unity and disregarded molecular weight changes. This corrected total was required to obtain reasonable recovery values due to cracking of anthracene during the reaction. The anthracene products are reported as a percentage of the anthracene charged, the sum of which represents the recovered anthracene. In addition, the chromatographic fractions of HC, NH, and HA were analyzed by Fourier transform infrared (FTIR) spectroscopy using a Nicolet Model 5SXC spectrometer with Cs12optics. The samples were prepared as thin films on KBr pellets.
Results and Discussion Quinoline Reactions. T h e activity and selectivity of precipitated transition-metal sulfides for hydrodenitrogenation of quinoline were compared to those of NiMo/A1203, CoMo/A120s, commercial transition-metal sulfides, and Pt/SiOz. The transition metals from groups VIB and VI11 chosen for this study were Cr, Mo, W, Fe, Pt, and Ru. These particular metals were chosen based upon their activity and selectivity for dibenzothiophene desulfurization displayed in the work of Chianelli and Pecoraro4 and reasonable cost. (9)Ninth Set of the X-ray Powder Data File; ASTM Technical Publication No. 48-14ASTM Philadelphia, PA,1959. (10)Boduszynski, M. M.; Hurtubise, R. J.; Silver, H. F. Anal. Chem. 1982,54,375-381.
170 Energy & Fuels, Vol. 3, No. 2, 1989 ~~
Table I. Analysis of Catalysts sulfur, wt % catalyst sample theor surface area, m2/g
Cr2S3-P4"
Cr2S3-C MoSZ-P~ MoSz-P7 MoSZ-C WS2-P2 WS2-P4
ws2-c
FeS-P2 FeS2-C RuSz-P3 RuSz-P5 NiMo/A1203 CoMo/AlzO3
44.0 49.6 37.7 41.1 25.1 24.9 39.1 57.2 30.2
48.1 48.1 40.1 40.1 40.1 25.9 25.9 25.9 36.5 53.5 38.8
19.5 12.5 30.8 24.1b 10.7 13.5 8.5 6.7 4.9 26,b 19 81.5* 174 180
The letters -P and C to the right of the sulfides represent precipitated and commercial, respectively. The numbers to the right of P indicate the batch number of the precipitated transitionmetal sulfide. * Analyses performed by Quantachrome Corp.
IPCHI ON
-
quinoline
THO - l,2,3,4 - lelrahydroquinoline CHP
-
2,3 - cyclahexenopyridlne
DHO - decohydroquinoline ( c i s and trans P A - o-propyloniline
N-PCHA-
PCHE ~ s o m e r s l PCH PB
(MPCPI
N-propylcycloherylamlne propylbenzene propylcyclohexene il,l or 1,31 propylcyclohexane
MPCP - melhylpropylcyclopenlone
PCHA- propylcyclohexylomine
Figure 1. Reaction pathway for quinoline.
analyzed and reasonable recoveries of the liquid products The composition of each precipitated transition-metal were attained. Methane (CH,) was the only hydrocarbon sulfide was confirmed by X-ray diffraction by matching gas observed. The ammonia (NH,) observed was usually the d spacings of the samples with reference patterns? The much less than it should have been based upon the denexperimental data matched the standards sufficiently to itrogenation of the liquid products. Solubility experiments confirm the identity of the metal sulfides listed above. in hexadecane showed that -70% of the ammonia was Sulfur analyses of both precipitated and commercial absorbed by the solvent, yielding inaccurate values and low transition-metal sulfides used in this study are compared recoveries. to the theoretical values in Table I. Surface area meaThe product distributions achieved from both thermal surements by dynamic BET. using N2 in He are also given and catalytic quinoline reactions are given in Table 11. in Table I. The number given on the right side of the The HYD and HDN terms given for each reaction system sulfide indicates the batch number while the letters, P and are good indicators of hydrogenation activity and deniC, represent precipitated and commercial, respectively. trogenation selectivity. Precipitated RuS2 and supported Differences in the surface areas of different batches of a NiMo/Alz03 showed the highest and nearly equivalent given transition-metal sulfide reflect the sensitivity of the HYD of -49%. Precipitated MoSz produced a HYD of surface area to preparation methods. -42% and CoMo/Alz03, -3970, while the other catalysts In the quinoline reactions, the concentration of the yielded lesser HYD amounts ranging from 25 to 31% liquid phase products is given for each compound as a mole HYD. The catalysts can be ranked according to their percentage of quinoline initially charged to the reactor and quinoline hydrogenation activity in terms of HYD: are normalized to 100%. The data are summarized in RuSz-P3 N NiMo/A1203 > MoSz-P3 N CoMo/A1203 > terms of percent of hydrogenation (HYD), percent hyWS2-P2 N Cr2S3-P4> FeS2-P2> thermal. The selectivity drodenitrogenation (HDN), and percent hydrogenolysis for hydrogdenitrogenation of quinoline was low for all of (HYG). The percent hydrogenation is the number of moles the catalysts including the commerical hydrotreating of hydrogen required to produce the observed product catalysts. Precipitated RuS2 achieved the highest HDN distribution from quinoline as a percentage of the moles of 10.8%; NiMo/A1203 and precipitated MoSz achieved of hydrogen required to produce the final end product, 8.9% and 8.0%, respectively. The primary denitrogenation propylcyclohexane ( P C H ) . T h e percent hydroproduct produced from RuS2 was propylcyclohexane denitrogenation is the summation of the mole percentages (PCH) while the denitrogenation products from NiMo/ of the components not containing nitrogen. The percent A1203,propylbenzene (PB) and PCH, was nearly equivahydrogenolysis is obtained by summing the mole perlent in amount. Precipitated MoSz produced primarily PB. centages for the compounds that have resulted from hyThus, although the amount of HDN achieved was not drogenolysis of the C-N bond. vastly different, each of these catalysts showed a different Quinoline Reaction System. The reaction pathway selectivity of the products. Likewise, RuS2-3 and (Figure 1)for quinoline under catalytic conditions has been NiMo/Alz03 were most effective for hydrogenolysis; howextensively investigated by Satterfield and c o - ~ o r k e r s . ~ ~ - l ~ever, in this case, RuSz with a HYG of 17.3% was subThe reaction pathway observed in this investigation prostantially more effective for hydrogenolysis than NiMo/ ceeded through both tetrahydroquinoline (THQ) and A1203a t 10.270,while MoS2 a t 10.3% was equivalent to 2,3-~yclohexenopyridine(CHP) to cis- and trans-decaNiMo/Alz03. The major product difference between the hydroquinoline (DHQ). The reaction pathway through two catalysts was that RuSz produced 6.5 9'0 propylaniline THQ was the primary pathway since substantial amounts (PA) while NiMo/A1203produced only 1.3%. Of the reof THQ were present compared to only small quantities maining catalysts, WS2 and CoMo/Alz03 showed a small of CHP. In the current study, the gaseous and liquid amount of hydrodenitrogenation while Cr2S3,WS2, and products from both thermal and catalytic reactions were CoMo/A1203showed some hydrogenolysis. The thermal reaction showed no denitrogenation or hydrogenolysis. As shown in Table I, commercial crystalline transition(11) Satterfield, C. N.; Modell, M.; Hites, R. A,; Declerck, C. J. I n d . metal sulfides had lower surface areas than their precipEng. Chem. Process Des. Deu. 1978, 17, 141. (12) Satterfield, C. N.; Cocchetto, J. F. I n d . Eng. Chem. Process Des. itaed analogues. The effect of the more randomly oriented Deu. 1981, 20, 53. structure of the precipitated transition-metal sulfides on (13) Satterfield, C. N.; Yang, S. H. Ind. Eng. Chem. Process Des. Deu. hydrogenation and denitrogenation of quinoline was com1984, 23, 11.
Hydrodenitrogenation of Quinoline and Coal
Energy & Fuels, Vol. 3, No. 2, 1989 171
Table 11. Product Distribution from Thermal and Catalytic Quinoline Reactions catalyst NiMo/ reaction products, mol % PCH
PB DHQt DHQc CHP PA QN
THQ HYD, % HDN, % HYG, % recovery, %
none
CroSq-P.,
MoS.,-P3
WS2-P2
FeS2-P2
0 0 0 0 0.2 f 0.3 0 82.7 f 3.3 17.1 f 3.0
0 0 0.5 f 0.5 0.3 f 0.4 1.2 f 1.1 3.1 f 0.1 2.2 f 0.3 92.7 f 1.6
1.5 f 0.2 6.4 f 0.0 19.7 f 1.1 4.6 f 0.4 2.4 f 0.7 2.4 f 0.1 1.9 f 0.6 61.1 f 0.3
0.2 f 0 0.1 f 0.1 4.8 f 0.1 1.0 f 0.1 0.5 f 0.1 0.9 f 0 1.7 f 0 90.8 f 5.6
0 0 0.5 f 0.1 0.5 f 0.1 1.4 f 0 0 15.9 f 5.6 81.7 f 5.6
7.7 f 1.0 3.0 f 0.2 26.7 f 0.4 4.7 f 1.6 1.8 f 0.2 6.5 f 0.4 1.0 f 0 48.6 f 3.0
0.5 f 0.0 1.9 f 0.1 19.8 f 0.8 4.2 f 0.1 1.2 f 0.1 1.3 f 0.2 1.6 f 0.0 69.5 f 0.9
4.0 f 0.4 4.8 f 0.2 32.0 f 2.6 7.0 i 1.0 3.3 f 0.8 1.3 f 0.1 1.2 f 0.4 46.4 f 2.6
5.0 f 0.9 0 0 90.4 f 1.6
28.8 f 0.5 0 3.1 f 0.1 83.6 f 5.7
41.7 f 1.0 7.9 f 0.2 10.3 f 0.1 75.5 f 18.9
30.9 f 0.1 0.3 f 0.1 1.2 f 0.1 88.2 f 1.6
24.5 f 1.6 0 0 86.2 f 6.8
49.1 f 10.7 f 17.2 f 89.5 f
39.0 f 0.3 2.4 f 0.1 3.7 f 0.4 89.1 f 5.1
49.5 f 1.8 8.8 f 0.1 10.1 f 0.0 79.1 f 15.3
RuSZ-P~ CoMo/AlpO:,
1.4 1.2 1.6 1.6
A1203
Table 111. Activity and Selectivity Comparison of Precipitated to Commercial Transition-Metal Sulfides
reaction products, mol % PCH
PB DHQ, DHQC
CHP
PA QN
THQ HYD, % HDN, % HYG, % recovery, %
none
Cr2S3-P4
Cr2S3-C
catalvst MoS2-P3
MoS2-C
WS2-P2
ws2-c
0 0 0 0 0.2 f 0.3 0 82.7 f 3.3 17.1 f 3.0
0 0 0.5 f 0.5 0.3 f 0.4 1.2 f 1.1 3.1 f 0.1 2.2 f 0.3 92.7 f 1.6
0 0 0 0 1.9 0 9.2 88.9
1.5 f 0.2 6.4 f 0.0 19.7 f 1.1 4.6 f 0.4 2.4 f 0.7 2.4 f 0.1 1.9 f 0.6 61.1 f 0.3
0 0 3.6 1.4 0.6 0.5 3.1 90.8
0.2 f 0.0 0.1 f 0.1 4.8 f 0.1 1.0 f 0.1 0.5 f 0.1 0.9 f 0.0 1.7 f 0.0 90.8 f 5.6
0 0 4.8 6.8 2.7 2.5 3.5 79.7
5.0 f 0.9 0 0 90.4 f 1.6
28.8 f 0.5 0 3.1 f 0.1 83.6 f 5.7
25.9 0 0 92.2
41.7 f 1.0 7.9 f 0.2 10.3 f 0.1 75.5 f 8.9
29.9 0 0.5 48.2
30.9 f 0.1 0.3 f 0.1 1.2 f 0.1 88.2 f 1.6
32.9 0 2.5 87.3
Table IV. Catalytic Activity of NiMo/A120Sand RuSain Several Reactant Systems liquid products, mol % recovery, CHP DHQ, DHQ, PB PCH HYD,% HDN.% HYG,% % THQ, as Reactant 97.7 f 3.1 0.8 f 0.7 0 0.3 f 0.6 0 1.2 f 2.1 0 0 0.4 f 0.9 0 0 90.6 f 3.4 48.7 f 5.0 1.7 i 1.2 1.1 f 0.1 2.3 f 0.3 6.8 f 0.5 32.0 f 2.6 3.9 f 0.4 3.5 f 0.7 27.8 f 2.7 7.4 f 1.1 8.5 f 1.2 91.9 f 2.3 THQ
thermal NiMo/ A1203
RuSz'
54.4
1.0
5.7
0 0
100.0f0 0 0 18.6
0
0
63.5
0
0
1.2
0
59.3
0
0.6
1.7
0
69.1
0
0.2
thermal 0 NiMo/ 0 A1203" RuS2" 0 NiMo/ A1203' RuS~" a
PA
QN
1.5
4.8
0
23.7
2.2
PA, as Reactant 0 0 0 17.2 0
8.5
PA with QN as Reactant 3.3 13.6
1.9
6.8
6.7
25.4
8.9
14.6
93.9
0
64.2
0 68.5
0 81.4
NAb NA
94.7 i 0.2 84.5
28.0
30.1
36.5
NA
94.5
22.0
27.1
35.6
NA
74.2
20.3
22.6
27.1
NA
86.8
These single reactions were verified by reactions performed 6 OC lower that showed the same trends.
pared to the effect of the crystalline or mineralogical analogues in Table 111. The transition-metal sulfides compared were Cr2S3,WS,, and MoS2; commercial RuS2 was not available. Both WS2 and Cr2S3yielded nearly the same hydrogenation activity regardless of whether they were commercial or precipitated materials. For MoS2,the precipitated metal sulfide gave higher HYD, HDN, and HYG values. The recoveries for most of the commercial and precipitated catalysts were between 75% and 90%. Only the commerical MoS2showed less recovery. The loss of quinoline may be due to loss of volatiles, to quinoline or quinoline reaction products adhering to the catalyst surface,14or to the formation high molecular products as has been observed by Stohl.Is (14) Pellegrino, J. L. Master's Thesis 1987, Auburn University. (15) Stohl, F. V. Prepr. Pap-Am. Chem. Soc., Diu.Fuel Chem. 1987, 32(3), 325.
* NA = not applicable.
Comparison of NiMo/A1203and RuSz. In the quinoline hydrogenation reaction, NiMo/A1,03 and precipitated RuS, gave comparable HYD of quinoline while RuS2 had nearly twice the HYG value of NiMo/Alz03. Further evaluation of their catalytic activity and selectivity in the quinoline system was performed to differentiate between the two catalysts. These two catalysts were tested with individual products, THQ and PA, from quinoline hydrogenation. In the THQ reaction, both catalysts achieved similar HYD (25-27%) and HDN (7.4-8.9%) of THQ, yielding trans-DHQ as the primary product as shown in Table IV. NiMo/A1203yielded more cis- and trans-DHQ than RuS,, which produced more PA and PCH. RuSz gave slightly higher HDN and achieved nearly twice as much HYG as NiMo/A1203. Reactions starting with THQ gave product distributions very similar to those using quinoline. Further experiments were required for differentiating between the catalytic activity of NiMo/A1203and RuS,;
172 Energy & Fuels, Vol. 3, No. 2, 1989
Curtis and Cahela
Table V. Effect of Temperature on Activity of Pt/SiOz for Quinoline Hydrodenitrogenation a t 200 "C at 250 "C a t 300 "C a t 320 "C a t 340 "C at 380 "C product distribn, mol % 1.8 PCH 0 0 3.4 9.7 0 0 0 0.1 0 PB DHQt DHQc
CHP PA
Q THQ HYD, % HDN, Yo HYG, '70 recovery, %
9.7 5.1 3.5 0 0.9 80.8
49.4 9.0 0.8 0 1.0 39.8
64.6 10.4 1.2 0 0 22.0
61.6 10.4 1.2 0 0 23.4
70.8 12.6 0.9 0.4 0 5.5
34.0 0 0 91.1
53.4 0 0 93.6
62.1 1.8 1.8 80.9
61.8 3.4 3.4 93.1
71.3 9.8 10.2 93.1
the next reactant used was PA, a hydrogenolysis product of QN. Substantially more hydrogenation and denitrogenation of PA was achieved with NiMo/A1,03 than with RuS2 (Table IV). The lesser ability of RuS2 to convert PA may explain the larger amount of PA observed in both the quinoline and THQ reactions with RuS2. In the PA reaction system, the NiMo/A1203 activity lay in its ability to remove the amine nitrogen and further hydrogenate the alkyl aromatic to PCH. By contrast, RuS2 was not as effective in removing the amine nitrogen and proceeding to further hydrogenation of the ring. When the amine group was removed, RuS, was nearly as effective as NiMo/A1203in saturating the aromatic ring since the ratio of PCH to P B produced from RuS, was 3.3 and that from NiMo/A1203 was 3.7. Since a substantial difference in activity and selectivity was observed between the two catalysts in the PA system but not in the THQ or QN system, the presence of quinolne or THQ may be substantially affecting catalyst activity. T o simulate the quinoline reaction system after considerable hydrogenation and hydrogenolysis, 0.2 wt 70 quinoline was added to the PA solution (2 wt % in PA). The effect of quinoline addition was a leveling of catalytic activity between the two catalysts. NiMo/A1203 was severely poisoned, resulting in substantial reductions (55-60%) in hydrogenation activity and denitrogenation selectivity while RuS, was affected to a lesser extent showing a one-fourth reduction in HYD and HDN. Thus, the presence of quinoline and THQ as well as their reaction products reduced the inherent activity of NiMo/A1203to make NiMo/Al,03 effectively equivalent to RuS2 in both activity and selectivity in the quinoline system. Similar observations have been made by Satterfield and Cocchetto,12 who performed HDN reactions with each product from quinoline hydrogenation using NiMo/A1203 in a continuous flow microreactor. Their results showed that the quinoline hydrogenation products, THQ and DHQ, adsorb more strongly on NiMo/A1203 than QN, CHP, and PA. In the catalytic reactions with both NiMo/A1203and RuS, performed in this work, quinoline was hydrogenated to THQ, DHQ, and other products. The results from Satterfield and Cocchetto12indicate that the reduction in the amount of denitrogenation of PA with quinoline addition most likely was due to the preferential adsorption of the saturated amines, THQ and DHQ, formed from the hydrogenation of quinoline. Comparison of PtS, and Pt/Si02 for HDN of QN. PtS2was obtained commercially as Chianelli and Pecoraro4 did not observe any differences between precipitated PtS2 and commercial Pts2. Recently, a catalyst containing 40% Pt has been shown to be an active hydrodenitrogenation catalyst.16 The activities and selectivities of these two Pt (16)Guttieri, M. J.; Maier, W. F. J. Org. Chem. 1984,49,2875.
75.5
catalysts in conjunction with RuS, were then compared. However, using the reaction conditions from the aforementioned precipitated transition sulfide study was not possible, since a t 380 "C, no hydrogenation products of the quinoline system were observed and many heavier products were formed. In addition, the solvent hexadecane peak was totally missing from the chromatogram. Laine et al." have studied alkyl exchange reactions between tertiary amines attempting to define hydrodenitrogenation reaction mechanisms. Occurrence of similar types of reactions with molecules such as THQ and DHQ could result in moelcules being joined together, forming heavier molecules during quinoline hydrogenation under liquefaction conditions. Other r e ~ e a r c h e r s ' ~have J ~ also observed production of higher molecular weight products from quinoline under fairly severe reaction conditions with NiMo/A1203. Therefore, to find a suitable reaction temperature for comparison, the denitrogenation selectivity of Pt/Si02 for quinoline was investigated a t temperatures ranging from 200 to 380 "C as shown in Table V. A t 200 "C, Pt/Si02 achieved slightly more hydrogenation activity than the precipitated Cr2S3and WS2 a t 380 "C, with a HYD of -34%. The activity of Pt/SiO, increased with temperature up to 340 "C, yielding -71% HYD, the highest value of HYD achieved in this study, and 9.8% HDN, giving a HDN similar to RuS, a t 380 "C. Quinoline reactions were then performed a t 200,250, and 300 "C, comparing the catalytic activity of Pt/Si02, PtS,, and RuS2 as shown in Table VI. For all temperatures, the supported P t / S i 0 2 had more hydrogenation activity than either of the sulfides. All three catalysts are compared a t 250 "C. At this temperature, Pt/Si02 was substantially more active for hydrogenation than either PtS, or RuS2, which were nearly equivalent in activity. Coal Liquefaction Reactions. The two most active precipitated transition-metal sulfides for denitrogenating quinoline, RuS, and MoS2,were chosen as the metal sulfide catalysts to be used for the coal liquefaction reactions. Of the two commercial catalysts, NiMo/A1203 showed the greater hydrogenation activity and selectivity for denitrogenation and was also chosen for the coal reactions. Thus, the efficacy of these catalysts in coal liquefaction reactions for hydrogenating and denitrogenating coal was evaluated. The Solvent Anthracene. Anthracene, chosen as the solvent for the coal liquefaction reactions, readily cracks under catalytic hydrogenation conditions.'* To test the (17)Laine, R. M.; Thomas, D. W.; Cary, L. W. J. Am. Chem. SOC. 1982,24, 1763. Laine, R.M. Catal. Reu.-Sci. Eng. 1983,25,459.Shvo, T.;Laine, R. M. J . Chem. Soc., Chem. Commun. 1980,753. (18)Weisser, 0.; Lande, S. Sulphide Catalysts, Their Properties and Applications; Pergamon Press: New York, 1973.
Hydrodenitrogenation of Quinoline and Coal
Energy & Fuels, Vol. 3, No. 2, 1989 173
Table VI. Comparison of the Activity and Selectivity of PtSI, Pt/Si02, and RuSs in the Quinoline System a t 200 OC Pt/SiOz RuSz product distribn, mol % PCH
BP DHQt DHQc CHP
PA QN THQ HYD, % HDN, % HYG, % recovery, %
0 0 9.7 5.1 3.5 0 0.9 80.8
0 0 0 0 0 0 0
34.7 0 0 91.1
PtSz 0
a t 250 "C Pt/SiOz
a t 300 OC PtSz Pt/SiOz
RuSz
100
1.6 f 0.0 0 0 0 0.5 f 0.7 97.9 f 0.6
0 0 49.4 f 5.2 9.0 f 0.4 0.8 f 1.3 0 1.0 f 1.4 39.8 f 5.3
0 0 2.5 0.4 0 0.1 0 97.0
0 0 10.0 f 1.2 1.5 f 0.1 0 0.2 f 0.3 0.5 f 0.2 87.8 f 1.8
1.8 f 1.8 0 64.6 f 10.5 10.4 f 1.4 1.2 f 1.1 0 0 22.0 f 12.6
28.6 0 0 93.2
29.1 f 0.2 0 0 87.6 f 1.9
53.4 f 2.8 0 0 93.6 f 4.5
29.8 0 0.1 92.1
33.4 f 0.5 0 0.2 f 0.3 91.8 f 3.7
62.1 f 6.4 1.8 f 1.8 1.8 f 1.8 80.9 f 3.8
0
Table VII. Product Distribution of Coal Liquefaction Reactions catalyst compound class coal product distribn, w t %
none
MoS1-5&7
18.6 f 3.8 17.0 f 3.7 14.0 f 1.4 24.4 f 3.0 9.7 f 3.9 10.8 f 1.7 5.5 f 0.7
15.1 f 1.6 34.1 2.1 19.5 f 0.1 20.1 f 2.1 3.0 f 2.7 6.0 f 5.0 2.2 f 2.1
*
15.2 f 2.7 48.8 f 2.1 18.2 f 4.5 10.3 f 2.1 0.6 f 1.1 5.8 f 3.8 1.1 f 0.5
13.8 f 4.2 58.8 f 0.3 11.0 f 0.8 6.7 f 3.7 1.8 f 0.1 4.9 f 6.8 3.0 f 6.2
recovery, % hydrogen consumptn, % coal conversn, %
95.3 f 4.0 6.2 f 0.8 94.5 f 0.7
91.8 f 3.7 8.5 f 0.8 97.8 f 2.1
92.2 f 0.2 14.2 3.6 98.9 f 0.5
*
89.3 f 2.0 15.3 f 0.6 97.0 f 6.2
anthracene product dietribn,' mol % anthracene dihydroanthracene hexahydroanthracene octahydroanthracene tot cor recovery, %
2.6 f 0.1 16.1 f 0.6 58.5 f 7.8 9.8 f 0.5 87.0 f 8.0 97.0
0.2 f 0.3 13.4 f 6.6 38.6 f 8.1 26.9 0.4 79.1 f 14.0
0 3.4 f 1.7 18.0 f 1.1 60.2 3.8 81.6 f 4.7 101.9 f 4.7
0 2.2 f 3.1 16.3 f 2.1 53.0 f 1.7 71.5 f 6.8
€35
hydrocarbons nitrogen heterocycles hydroxyl aromatics polyfunctional compounds THFS
IOM
a
*
RuSI-5
*
NiMo/Al,O,
100.6 f 3.9
Of anthracene charged.
reactivity of anthracene, four catalytic hydrogenations with NiMo/Alz03were performed. In the first reaction at 380 "C, the temperature used for quinoline hydrogenation, only 20.4% of the anthracene and its products could be recovered. Milder conditions of 350 and 300 "C resulted in higher recoveries of 51.5 and 64.9%, respectively, with the major product being OHA. Some anthracene hydrocracking was expected in the coal liquefaction system; however, the presence of nitrogen heterocycles and other agents that moderated catalyst activity sufficiently reduced the MoS2, RuS2, and NiMo/A1203 activities in the coal liquefaction reactions so that the reactions could be performed a t 425 OC with much less loss of anthracene than the reactions without coal (Table VII). The thermal reactions with coal also gave acceptable recoveries. In most of the liquefaction reactions, the total anthracene proddcts, including both hydrogenated and hydrocracked species, were measured, accounting for a 97-101 % recovery of anthracene in thermal reactions and in reactions using NiMo/A1203 and RuS,. Coal Liquefaction Reactions. Coal liquefaction reactions were then performed at 425 "C, because reactions at that temperature yielded increased amounts of THFS and decreased the amount of IOM produced compared to lower temperature reactions a t 400 OC. The product distributions obtained from thermal and catalytic liquefaction reactions are given in Table VII. The reactions performed at 425 OC yielded coal conversions ranging from 94.5% for the thermal reaction to 98.9% for the reaction with RuS?
The amount of light hydrocarbon gases produced was almost constant for all of the reactions, yielding 15% for MoSz and RuS2 and 14% for NiMo/A1203, while the thermal reaction produced nearly 19%. Thus, the amount of total liquid products produced was quite similar in all reactions, ranging from 75.9% for the thermal reaction to 83.7% for RuS2-5,thereby providing a nearly equivalent basis for directly comparing the products from different reactions. Infrared analysis of the fractions obtained from compound class separations of the MCMS fractions from the different catalytic reactions confirmed the separation. As an example, the infrared spectra of the HC, NH, and HA fractions obtained from the liquefaction reaction with NiMo/Alz03are given in Figure 2. Each spectrum was obtained as a thin film on a KBr pellet. The HC fraction shows only absorbances due to hydrocarbon stretches with no absorbances above -3100 cm-'. In contrast, both the NH and the HA fractions showed absorbances in the range 3100-3600 cm-l, indicating the presence of amine and hydroxyl groups, respectively. Comparison of the product distributions shows that the sum of the polyfunctional compound and THFS fractions decreased from 20.5% for the thermal case to 9.0% for MoS2-P5&7,6.4% for RuS2-P5,and 6.7% for NiMo/A1203. The total amount of product soluble in MCM increased by more than 10% in the catalytic reactions compared to the thermal reaction. The MCMS fractions for all catalytic reactions were similar, ranging from 76.7% for MoS2-P5&7
174 Energy & Fuels, Vol. 3, No. 2, 1989 CAlALYllC REACTION YllH
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compared to the thermal reaction, the HA fraction decreased in the presence of the catalysts with MoSz having the most and NiMo/Alz03 the least. Thus, the increased solubility of the coal-derived material in the MoSz-P5&7 and RuSz reactions compared to the thermal reaction was directly reflected in an increase in the NH and HC fractions since both the PC and HA fractions decreased. NiMo/Alz03, attaining lower NH and higher HC fractions than the transition-metal sulfides, was more effective in removing nitrogen and, thereby, performed better for denitrogenating coal than did RuSz. During liquefaction the anthracene solvent was sequentially hydrogenated from anthracene to DHA to HHA to OHA. Hydrocracking of these hydrogenated products also occurred. In the thermal reaction, 2.6% anthracene remained unconverted; this amount decreased rapidly below gas chromatographic detectability limits under catalytic conditions. DHA and HHA were a t a maximum in the thermal reaction and decreased as catalysts were used, while OHA showed a maximum with RuS2. The supported catalyst, NiMo/Alz03, yielded the most hydrocracked products. Both the OHA maximum and decrease in the sum of the anthracene hydrogenation products were due to hydrocracking of OHA. The amount of hydrocracked products is reflected in the difference between the corrected recovery and the sum of the anthracene and hydrogenated anthracene products. By analysis of the hydrocracked products as well as the hydrogenated products, all of the anthracene could be accounted for.
Summary m m 3
Figure 2. Infrared spectra of HC, NH, and HA fractions obtained
from NiMo/Alz03reactions.
to 78.3% for NiMo/A1203 Since considerably more of the heavier fractions (THFS, IOM) was upgraded in the catalytic reactions compared to the thermal reaction, a higher percentage of the total soluble products was observed in the hydrocarbon (HC) and nitrogen heterocycle (NH) fractions for precipitated MoSz and RuSz and in the HC fraction for NiMo/A1203 When the catalytic reactions are
Two precipitated transition-metal sulfides, MoSz and RuS2, possessed both hydrogenation activity and denitrogenation selectivity for quinoline under liquefaction conditions. These transition-metal sulfides rivaled the commercial hydrotreating catalysts in activity; RuS2 was comparable to NiMo/Alz03 and MoS, to CoMo/Alz03. NiMo/A1203possessed higher activity for PA hydrogenation than did RuS,; however, RuS2 was not as severely poisoned by quinoline as NiMo/Alz03. Pt/SiOz a t 340 "C was as active a catalyst for quinoline hydrogenation and denitrogenation as NiMo/AlZO3a t 380 OC. Both precipitated MoSz and RuS, achieved upgrading in coal liquefaction reactions showing higher hydrogenation activity compared to the thermal reaction; however, NiMo/A1203 showed greater hydrogenation activity and considerably more nitrogen removal.
Acknowledgment. We gratefully acknowledge the support of this work by the US.Department of Energy under Contract No. DEAC22-83PC60044. Registry No. DHA, 613-31-0; HHA, 74753-28-9; OHA, 1079-71-6; THQ, 25448-04-8; CHP, 10500-57-9; DHQ, 2051-28-7; NH,, 7664-41-7; Cr2S3, 12259-13-1; MoS2, 1317-33-5; WSz, 12138-09-9; FeSz, 12068-85-8; RuSz, 12166-20-0; Pt, 7440-06-4; Ni, 7440-02-0; Mo, 7439-98-7; Co, 7439-98-7; quinoline, 91-22-5; anthracene, 120-12-7.
