85
Ind. Eng. Chem. Process Des. Dev. 1980, 19, 85-91
Continuous Hydroliquefaction of Subbituminous Coal in Molten Zinc Chloride Clyde W. Zielke,” Edgar B. Klunder, Joseph T. Maskew, and Robert T. Struck Conoco Coal Development Company, Research Division, Library, Pennsylvania 75729
Hydrocracking coal directly in molten zinc chloride on a continuous basis was demonstrated in a small stirred unit for the first time using ZnCl,/coal ratios varying from 0.83 to 1.83. A kinetics study on hydrocracking Colstrip subbituminous coal was made using a ZnCl,/coal ratio of 1.O over the following ranges of the variables: H2 pressure, 13.89 and 20.79 MPa; temperature, 385 to 427 O C ; and residence times from 31 to 193 min. The conversion rates were correlated by a semiempirical rate model that fits the data well. Yield data correlations allow prediction of the yield distribution at a given conversion. The work demonstrated in single-pass operation yields equivalent to as high as 0.754 m3of C4 X 200 O C and 0.180 m3 of +200 O C distillate per metric ton of MAF coal. The naphtha had a research octane number of 92.3. The +200 O C distillate should make a premium fuel oil since it contained less than 0.04% nitrogen and sulfur.
Introduction The use of molten metal halides of the Lewis acid type for hydrocracking of coal and coal extract was extensively investigated by Consol Research (the predecessor of Conoco Coal Development co.) during 1964-1967 under a research contract with the U.S. Office of Coal Research. A complete description of the work is available in reports by Consolidation Coal Co. to the OCR (1968a, 1968b). Summary papers dealing with some of this work have also been presented by Zielke et al. (1966a,b, 1969) and Struck et al. (1969). Most of that work was done with zinc chloride as the catalyst using bituminous coal extract as the feed. Hydrocracking of the extract and regeneration of the spent catalyst by a fluidized combustion technique were both demonstrated in continuous bench-scale units and have been reported in the above references. On a batch scale, extensive hydrocracking work has been done using not only extract as feedstock but also coal directly as reported previously by Consolidation Coal Co. (1968a) and by Zielke et al. (1966b, 1976). Both bituminous and subbituminous coals were investigated and both were excellent feedstocks for zinc chloride hydrocracking. Furthermore, regeneration of a synthetic spent melt that simulated melt produced by direct coal hydrocracking was successfully demonstrated in the continuous bench-scale regeneration unit. Adequate coal ash rejection and excellent zinc chloride recovery were obtained. In addition to the work of Conoco Coal Development Co., other workers have been active in the field of molten metal halide catalysis, particularly Shell workers (Kiovsky, 1973; Kiovsky and Petzny, 1972a,b; Kiovsky and Wald, 1972,1975;Loth and Wald, 1974; Wald, 1970,1973,1974). A contract beginning in January 1975 was signed with the Office of Coal Research to accelerate the zinc halide process work. Conoco Coal Development Co. is the prime contractor and Shell Development is a participant and subcontractor. Prior t o this contract, direct hydrocracking of coal with molten zinc chloride catalyst had not been demonstrated in a continuous unit. The direct hydrocracking process has some potential economic advantages over a two-step process consisting of coal extraction followed by hydrocracking the SRC therefrom. Hence, an experimental program was undertaken to demonstrate direct hydrocracking of coal with molten zinc chloride catalyst in a continuous bench-scale unit. A further goal was to get 0019-7882/80/1119-0085$01.00/0
Table I. Feed Coal Analyses moisture, wt %
4.0-4.6 M F Basis
volatile matter fixed carbon FeS, other ash MAF Basis hydrogen carbon nitrogen oxygen ( b y difference) organic sulfur screen size, pm, wt % o n 297 149 74 44 -44
41.73 46.63 0.58 11.06 4.96 76.16 1.11 17.07 0.70 0.6 2.7 21.6 28.8 46.3
kinetic data to be used for design and economic studies and for interpretation of results in larger units. These objectives have been accomplished. This paper presents the results of this study and a kinetic correlation. Experimental Section Feedstock. The feedstock used for all of the work to be described was Colstrip coal which is a subbituminous coal from the Rosebud seam in southern Montana. It was dried by heating under nitrogen to 350 O F in a rotary kiln and then cooling. The dried coal was ground in a roller mill a t ambient temperature under an “inert” gas containing 4-5% oxygen. The ground coal was stored in sealed plastic bags. Analyses of the coal as used are given in Table I. Catalyst. The zinc chloride used was J. T. Baker analyzed reagent, 97 to 98% pure, dried under vacuum in the molten state in a stirred tank at 700 O F before use. After this treatment, the zinc chloride contained generally about 1.2 wt 70zinc oxide and about 1.0 wt % moisture. Coal Slurry Vehicle. The coal was fed to the hydrocracker as a slurry. A slurry consisting of 40 wt % of the Colstrip feed coal and 60% Neville Chemical Co. LX-745 solvent, a complex, heavy, aromatic petroleum-derived solvent, was used in the first few runs made in the unit. Analyses of the Neville solvent are given in Table 11. Thereafter, the slurry consisted of approximately 30 wt 70 Colstrip coal and 70% vehicle, composed of a solution of 8 wt % of polystyrene in benzene. The polystyrene was 1979 American Chemical Society
86
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 1, 1980
Table 11. Neville Solvent Analvses
TBP distillation, wt % -261 “C 261 X 278 278 X 340 340 X 350 350 X 475 +475 viscosity, Pa-s at 20 “ C ultimate analysis, wt % hydrogen carbon nitrogen oxygen sulfur
2.3 5.6 24.3 29.2 32.1 6.5 0.064
7.53 91.14 0.07 0.15 1.11
9
Tank
Figure 1. Simplified flow diagram of bench-scale (1kg/h) hydrocracker.
added to increase the viscosity of the benzene so as to make a slurry with sufficient body for reliable pumping a t the low rate required, i.e., 0.2 to 1.6 kg/h. Eight percent polystyrene gave a vehicle having a viscosity of 0.014 Pa-s a t ambient temperature. The simple, low boiling, benzene-polystyrene vehicle was used so that yields from the coal could be distinguished from those from the vehicle and collected for use in subsequent characterization and reactivity studies. This could not be done using the high-boiling, complex Neville solvent. This is possible with the benzene-polystyrene vehicle because the benzene in the vehicle is essentially inert to ZnC1, hydrocracking and the polystyrene goes largely to known low-boiling products. Equipment. A simplified flow diagram of the continuous bench-scale hydrocracker is given in Figure 1. The unit has a nominal capacity of 1 kg/h of coal. It is rated a t 29.41 MPa operating pressure at 454 “C. The feed coal is mixed with an oil vehicle and fed as a slurry to the reactor which is a stirred autoclave. The hydrogen feed joins the slurry feed stream and enters the reactor with the slurry via a dip tube that exits near the bottom of the molten, stirred pool. The pool consists mainly of zinc chloride catalyst, high-boiling carbonaceous oils, “unconverted” coal, coal ash, and materials that derive from interaction of the catalyst with the heteroatoms of the coal, Le., zinc sulfide, zinc chloride ammoniates, and zinc oxide. The zinc chloride is pumped in the molten state at about 371 “C to the reactor as a separate stream. The reactor is 76 mm in diameter by 229 mm high and generally is operated with a liquid inventory of 400 cm3 that weighs 440 to 570 g depending on conditions. The reactor pool is stirred by a 51 mm 0.d. Autoclave Engineers Dispersimax impeller having six 13 X 13 mm turbine-type blades. This type of stirrer pumps gas from the vapor space into the liquid pool via a hollow stirrer shaft. The reactor has two 8 mm wide baffles. The liquid level in the reactor is controlled by a weir through which all gaseous and liquid materials exit and pass to a melt-vapor separator. The melt-vapor separator is an empty vessel the
same size as the reactor that is held at the same temperature as the reactor. The spent melt flows by gravity from the separator to the high-pressure spent melt collection system. The gases and vapors pass overhead to the distillate collection system where the condensable products are collected. The fixed gases are then let down through a back-pressure control valve to atmospheric pressure and they then proceed to sampling and metering. Metallurgy. Zinc chloride can cause typical chloride ion stress corrosion cracking of austenitic stainless steel, especially in the presence of liquid water. Low-temperature zones such as the product condensation train should be made of metals such as Inconel 600 or Hastelloy C-276 which are not subject to cracking. Type 316 stainless steel was generally successfully used for the reactor, the meltvapor separator, the residue receivers, part of the catalyst system, and for distillate receivers. These vessels were used because they were on hand and because of the difficulty of procuring Inconel or Hastelloy in a reasonable delivery time. Less success was experienced with the 316 stainless steel fittings and valves used which failed frequently because of stress corrosion cracking. Operations and Data Workup. A line-out period of 3 h or longer was usedsufficient for at least three changes of reactor liquid inventory after reaching reasonably steady conditions before proceeding to the material balance period. The balance period generally ranged from 3 to 8 h. Workup of the products was the same as described previously (Zielke et al., 1966a). All material balance products were collected and analyzed and the results consolidated. Elemental balances were then made and the zinc balance was forced by adjusting the residue collected. This avoided errors due to possibly differing holdups in the product catalyst collection vessels a t the start and end of the balance period. The carbon balance was then forced by adjusting the distillate collected to allow for possible distillate collection errors that might occur when switching distillate receivers. The nitrogen, oxygen, and sulfur balances were forced by assuming the unaccounted for products to be NH3, HzO,and H2S,respectively, that reacted with the catalyst. Chlorine was forced by assuming that the unaccounted for chlorine was present as the double salt, ZnC12.NH4C1. The hydrogen consumption was then obtained by difference between the hydrogen in the products and that in the feedstock (exclusive of H2 gas). After forcing all elemental balances, the overall material balance also closes and product yields are obtained on this basis as percentages of the moisture- and ash-free (MAF) organic feed which includes the MAF feed coal and the coal slurry vehicle. In the case of runs made with the benzenepolystyrene coal slurry vehicle, the net yields from coal are then obtained by subtracting the yields from the vehicle only from the total yields using coal slurry. The yields from coal only are expressed as weight percent of the MAF coal. The yields from the vehicle are obtained from blank runs, at similar severity of conditions, in which the benzene-polystyrene vehicle only (no coal) was processed in the hydrocracker with ZnCl, catalyst. Since products from the vehicle are low-boiling, the higher-boiling materials in the runs feeding coal slurried with the benzene-polystyrene vehicle are largely coal-derived, uncontaminated by the vehicle. A breakdown of coal yields from runs made with Neville solvent as the vehicle is not available because blank runs were not made with this solvent. Conversion, as used here, is the conversion of extract to products boiling below 475 “C a t normal atmospheric pressure, calculated by subtracting the percentage of +475
Ind. Eng. Chem. Process Des. Dev., Vol. 19,
Table 111. Typical Yields from a R u n Feeding 92 wt % Benzene-8 wt % Polystyrene run no. conditions temperature, "C total pressure, MPa P-, MPa ZnCl,/vehicle, wt ratio residence time, min product vields. wt % of vehicle C,-C, C, x 200 "C distillate 260 x 4 7 5 "C distillate + 475 "C distillate MEK-sol. in product catalyst MEK-insol. in product catalyst analysis of C, x 200 " C distillate, wt % methylcyclopentane benzene toluene ethylbenzene isopropylbenzene other
Table IV. Effect of the Type of Coal Slurry Vehicle run no.
16D 413 24.23 18.65 1.11 59 0.16 97.31 1.88 0.09 0.07 0.02 0.43 94.31 0.48 2.86 0.23 1.69
"C residue from 10070. Because of the heat sensitivity of the materials involved, the 475 "C cut point in a distillation is defined as 240 "C in the pot, which is a simple flask, when the pressure is 1 torr. Discussion of Results The variables and the ranges or levels at which they were investigated are: vehicle type, Neville solvent, or 92% benzene-8% polystyrene; temperature, 385,399,413, and 427 "C; total pressure, 16.65 and 24.23 MPa, 2400 and 3500 13.89 and 20.79 MPa, 2000 and 3000 psig; nominal PH2, psig; residence time, 31-193 min; WHSV, 382-1490 kg of M F coal/h-m3; ZnC12/MF coal, ut ratio, 0.83-1.83; nominal H z rate, 1.87 m3/kg of MAF feed; stirring speed, 800 and 1100 rpm. Good unit operability was demonstrated over these ranges of the variables. Coal gave the same unusual response to continuous ZnClz hydrocracking as was obtained earlier with coal extract (Consolidation Coal Co., 1968a; Zielke et al., 196610). The characteristics are rapid reaction rates, a high yield of gasoline-range naphtha with a low hydrocarbon gas yield, and a high ratio of iso- to normal paraffins in the gasoline, which has a Research Octane Number of about 90 without reforming. These properties are due to the Lewis acid nature of the zinc chloride and the use of massive quantities of the catalyst (>0.8:1.0 with coal), so that nitrogen in the feedstock cannot appreciably destroy its acid character. The offgases from the unit are free of H2S and NH, since these react with ZnC12and are retained in the catalyst as ZnS and ZnC12.xNH3. The relatively low gas yield and high C4 X 200 "C gasoline yield is due to the fact that gasoline-boiling range compounds including single ring aromatic structures such as benzene are almost completely inert to further cracking by ZnC12catalyst, as was shown in previous work. Thus, the benzene vehicle was ideal to minimize contamination of the products from coal. Typcial yields from a blank run are given in Table 111. Effect of Solvent Type. Similar runs using highboiling Neville solvent (a good coal extraction solvent) and low-boiling polystyrene-thickened benzene (a very poor coal extraction solvent) gave similar results regarding operability and conversion. The conditions and conversions of the runs are given in Table IV. It further has been shown in this and other work that benzene and naphtha produced in the process are very refractory to further hydrocracking by ZnC12catalyst (Consolidation Coal Co., 1968a; Zielke et al., 1966a). The significance of these
No. 1, 1980 87
9c
45
10
conditions coal slurry vehicle type
Neville a a Solvent 70 70 wt % of vehicle in coal slurry 60 temperature, "C 413 413 413 total pressure, MPa 24.23 24.23 24.23 P%, MPa 21.13 20.03 20.37 ZnCI,/MF coal, wt ratio 1.5 1.5 1.5 stirrer speed, rpm 800 800 800 residence time, min 95 92 96 conversion t o -475 "C products, 75.3 75.7 78.0 wt % MAF coal a
9 2 wt % benzene-8 wt % polystyrenc.
Table V.
Effect of Stirring Speed run no.
conditions temperature, "C total pressure, MPa Pu.. MPa z;;%~,IMF coal, wt ratio residence time, min stirring speed, rpm stirred pool density, kg/L product yields, wt % MAF coal
c,-c, . c4
x 200 " C distillate 200 x 475 "C distillate - 4 7 5 'C distillate MEK-sol. in product catalyst MEK-insol. in product catalyst CO + CO, H,O N, 0 , S, T H t o catalyst conversion to -475 "C products, wt % H, consumed, wt % C,
a
15
C0r-2~
413 24.23 20.24 0.94 155 800 1.77
413 24.23
6.2 5.1 41.2 17.7 7.8 6.2 4.6 15.6 2.1 81.4 7.1
3.3 3.3 48.0 16.4 5.3 6.8 3.9
1.0 155 1100 1.43
84.0 7.6
Results based on correlations of data at 1100 rpm.
findings is that, processwise, naphtha can be used to supplement the heavier oil that is used as the coal slurrying vehicle, if necessary, because of an insufficient yield of the latter with little, if any, detriment to the process. Effect of Stirring Speed. The initial work was done a t a stirring speed of 800 rpm; however, the kinetics study was conducted a t a stirring speed of 1100 rpm in an effort to assure that the results would reflect chemical reaction rate control and not control by mass transfer of hydrogen from the gaseous to the liquid phase. The effect of stirring speed is shown in Table V. The data indicate a relatively small effect of stirring speed going from 800 to 1100 rpm, manifested chiefly in a lower C1-C4 gas yield and a higher C5 X 200 "C naphtha yield. Thus, it seems likely that the runs a t 1100 rpm, a t least up to 413-427 "C are under a reaction rate control regime. The relatively high activation energies for the hydrocracking reactions, shown below, which are characteristic of chemical reaction rate control, tend to confirm this. Effect of ZnCl,/Coal Ratio. Increasing the ratio of ZnC12-to-coalabove 1.0 gives a substantially higher conversion and yield of C5 X 200 "C naphtha. The effect is much larger a t mild conditions than a t more severe conditions. This is shown in Table VI, which gives run data where the ZnC12/MF coal ratio was increased from 1.0 to 1.83 a t 385 "C, 16.65 MPa total pressure, and also from 0.96 to 1.62 at 413 "C, 24.23 MPa total pressure. The higher conversion and naphtha yields are accompanied by higher gas yields a t the higher ZnClz/coal ratio.
88
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 1, 1980
Table VI.
Effect of Zinc Ch1oride:Coal Ratio run no. conditions temperature, "C total pressure, MPa pH,, MPa ZnCl,/MF coal, wt ratio residence time, min stirrer speed, r p m product yields, wt % MAF coal C1-G
24
Cor-1"
21B
32
385 16.65 13.55 1.83 41 1100
385 16.65
413 24.23 20.09 1.62 40 1000
413 24.23 19.06 0.96 35 1000
2.5 3.5 34.0 18.0 3.1 17.0 7.9 18.6 2.4 72.0 7.0
0.7 1.4 16.0 21.5 5.5 34.0 5.5
3.0 4.3 38.1 15.4 7.8 14.5 5.7 15.4 3.0 72.0 7.2
1.9 2.0 25.5 24.2 7.0 20.7 5.0 16.7 3.1 67.3 6.1
c4
C, x 200 "C distillate 200 x 475 "C distillate + 4 7 5 "C distillate MEK-sol. in product catalyst MEK-insol. in product catalyst CO + CO, + H,O N , 0, S, + H t o catalyst conversion t o -475 "C products, wt % H, consumed, wt % ''
1.0 41 1000
55.0 6.0
Results based o n correlations of data at ZnCl,/MF coal ratio of 1.0
t
0.1.
90
83 70
60
ic-0
50
M
40 60
80 100
,
IM
RESIDENCE T I M E ,
40
140 I60 I80 Mo
MINUTES
Figure 3. The +475 "C MEK-insoluble residue yield as a function of residence time.
30
IO
0:
A
20
40 60
k
Id0
120
140 I60 180
RESIClEMCE T I M E , MINUTES
hoo
'
Figure 2. Variation of conversion with residence time showing the fit of the calculated curves based on the kinetic correlation with the experimental data points.
Kinetics Data. Data were obtained in a kinetics study over the following ranges or levels of the variables: temperature, 385,399,413, and 427; total pressure, 16.65 and 24.23 MPa; nominal PH2,13.89 and 20.79 MPa; residence time, 31-193 min; stirring rate, 1100 rpm; ZnC12/MF coal, w t ratio, 1.0 f 0.1; nominal H2 feed rate, 1.87 m3/kg of MAF organic feed; coal slurry, coal, -100 mesh Colstrip, 30 wt 7'0, vehicle (92 wt % benzene-8 wt % polystyrene), 70 wt %. A stirring rate of 1100 rpm was used to ensure that the rate data would be representative of chemical reaction rate control, not mass transfer control. A ZnCl,/coal ratio of 1.0 was selected because this level likely would be preferred economically even though higher rates may be obtained a t higher ZnC12/coal ratios. Figure 2 is a plot of conversion vs. residence time that shows the experimental points and the "fit" to these points of curves calculated from the mathematical correlation based on a kinetics model. It can be seen from this figure that a conversion as high as 87% of the MAF coal was experimentally achieved and that there is a rapid initial conversion of the coal to as high as 70% in 30 min residence time, after which conversion takes place a t a much slower rate. This type of behavior was observed previously also using bituminous coal extract as the feed (Consolidation Coal Co., 1968a; Struck et al., 1969). The correlation is based on a model similar to that employed successfully in previous work with extract: the
organic coal consists of a number of species which react by first-order reaction a t differing rates (Consolidation Coal Co., 1968a; Struck et al., 1969). To simplify the mathematics, it has been assumed that only two species are present: one that reacts at a fast reaction rate and one that reacts at a slower rate. In the previous work it was assumed, as the batch data used in that work indicated, that a third species which was unconvertible was present. In this study, it has been assumed that the organic material in the coal is 100% convertible. This is based on the fact that the refractory MEK-insoluble residue is low, as low as 3% on MAF feed coal a t 188 min residence time, and appears to continue to decline with time as the leastsquares straight lines for the 16.65 and 24.23 MPa data show in Figure 3. This indicates that at least 97% or more of the coal is convertible. Hence, for correlation purposes, the assumption of 100% convertibility is reasonably valid even though there may be in reality a small refractory heel of less than 3% of the organic coal. For a series of n continuous stirred-tank reactors, having the same volume, with an irreversible first-order reaction, the fraction of unconverted material, f , is given by the following expression (MacMullin and Weber, 1935; Potter, 1965) 1 = (1
+ ks)n
This expression may be written as 1-N f = - + -N 1 + k,O 1 + k20 for a single, stirred-tank reactor in which two independent first-order reactions occur simultaneously as was assumed for the kinetics model, where f = the fraction of unconverted moisture- and ash-free (MAF) coal; N = 0.60 = the
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 1, 1980
89
Table VXX. Correlation Fit temp, "C
press., MPa
z$a
385
24.23 16.65 16.65 24.23 16.65 24.23 16.65 24.23 16.65 24.23 24.23 24.23 16.65 24.23 24.23
20.31 13.82 13.76 20.10 14.24 19.68 13.89 20.24 13.13 19.06 19.55 19.62 12.93 20.17 19.68
399
413
427
res. time, min
conversion, % MAF coal
wt
30.7 71.7 181.7 33.7 33.2 75.6 78.0 193.4 161.5 34.7 94.1 190.2 156.9 36.8 88.8
obsd
calcd
52.7 61.0 17.6 60.3 59.1 63.0 69.7 18.9 80.5 67.3 77.4 87.0 80.6 73.3 78.0
49.7 62.7 75.7 59.7 59.5 10.4 70.7 81.9 79.8 66.5 78.6 86.2 84.3 73.4 83.4
CONVERSION,
WT 7.
OF MAF COAL
Figure 5. Hydrogen consumption and yield of C,-C3 and C4 as a function of conversion.
1 Oo1i40
1427T 142
'
144
413'C
1'46
399T
148 IOOO/'K
385T 150
1
i52
Figure 4. Reaction rate constants vs. reciprocal temperature.
fraction of the organic material in the coal converted via the fast reaction; 0 = average residence time in the continuous reactor, weight of liquid phase in the reactor divided by the weight rate of liquid product per minute; liquid is "natural" liquid existing at reactor conditions, i.e., catalyst plus unvaporized oil; kl = first-order reaction rate constant for conversion of coal on an MAF basis via the fast reaction, min-'; k2 = first-order reaction rate constant for conversion of coal on an MAF basis via the slow reaction, min-'; n = number of reactors in series. In applying the equation to fit the data, a value of N was assumed first. Then k2 was evaluated first by substituting into the correlation equation conversion and time data from a long residence time run (about 180 min). In this case, the fast reaction is essentially complete so that, as a first approximation in the estimation of k2,the expression N/(1 klO) could be assigned a value of zero. A first approximation of kl was then made by substituting into the correlation equation the first estimate of k2 and time and conversion from a short residence time run (about 33 min). By an iterative procedure, the best values of kl and k2 were then obtained for the assumed value of N. It was found that the assumption that 60% of the coal is converted by the fast reaction and 40% by the slow reaction fits the data well as shown in Figure 2 and Table VII. The data of Figure 2 and Table VI1 show that there is, if any, only a minor effect of pressure on conversion which is in agreement with the previous work with extract. This indicates that there is good potential for carrying out a commercial process a t a relatively low hydrogen partial
+
I IO'
50
60
BO
70
C O N V E R S I O N , WT
X
90
103
OF MPF C O A L
Figure 6. Yields of C6 X 200 "C, C6 X 475 "C, and total C5+ distillates as functions of conversion.
pressure of about 13.89 MPa. Figure 4 shows on a semilog plot the reaction rate constants for the fast and slow reactions as a function of reciprocal temperature. The constants for the fast reaction for Colstrip coal, as obtained by this correlation, are somewhat lower than those obtained previously for Pittsburgh seam bituminous coal extract. They vary from 66% as high a t 385 O C to 90% as high at 427 OC. The kinetic constants for the slow reaction are much lower for the coal than for the extract and the activation energy is much lower. For example, the constants for the coal vary from 24% as high as those for the extract at 385 "C to only 4% as high a t 413 "C. The lower rates probably reflect differences between subbituminous coal and Pittsburgh seam bituminous coal rather than differences between coal and extract. Product Yields. The yields of the various organic products from the matrix of the kinetics hydrocracking data correlate well with conversion. This is shown in Figures 5,6, and 7. The straight lines drawn through the data points of Figures 5, 6, and 7 have been determined by least squares. Figure 5 shows that the hydrogen consumption, C4 yield, and C1-CB gas yield increase as conversion increases from 50 to 87%. Gas yields, however, are relatively low even at 87% conversion. This is typical
90
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 1, 1980
Table VIII. Analyses of Products ( w t % )
c, x
200°C distill ate
hydrogen carbon nitrogen oxygen sulfur zinc chlorine phosphorus density BRONu BMON~ DRONC PlNiA copper corrosion strip
11.51 88.23 0.00066 0.12 0.00035
0.0045
__
0.791 90.6 78.7 92.3 17.7i34.7147.6 1 B (pass)
200 x 475 " C distillate
+ 4 7 5 'C distillate
+475 " C MEKS residued
9.50 90.01 0.0040 0.47 0.0121 < 0.1 p p m 0.0033
8.12 90.24 0.015 1.52 0.04 0.01 0.02 0.01 1.095
7.65 87.50 1.28 1.07 0.05 1.1 1.3 0.03
0.95
a Blending research octane number-based o n Reid vapor pressure of 10. Blending motor octane number-based o n Reid vapor pressure of 10. Direct research octane number-Reid vapor pressure adjusted to 8.9 by addition of 10.5% n-butane. Methyl ethyl ketone soluble carbonaceous residue in the product catalyst.
1
401
v50
60
?o
CONVERSION, WT 2
2
I
O L
+ .'
60 70 80 90 CONVERSION, WT % OF MAF COAL
100
Figure 7. Yields of +475 "C MEK-soluble and MEK-insoluble carbonaceous residue in the product catalyst melt as functions of conversion.
of ZnC1, hydrocracking. The average ratio of isobutane to n-butane for all points shown on the butane yield plot of Figure 5 is 9.2. The yields of organic distillate are given as a function of conversion in Figure 6. The points for the total C5+ distillate curve have been omitted because of the close proximity of this curve to the C5 X 475 "C distillate curve. The correlation for the total C5+distillate points is about as good as that for the C5 X 475 "C distillate. The yield of +475 "C oil that appears in the vapor stream out of the reactor remains almost constant a t 5-670 as conversion increases, but the yield of C5 X 200 "C naphtha increases with increasing conversion a t the expense of the 200 x 475 "C distillate. Combining yield data for butane from Figure 5 with the distillate yield from Figure 6 shows that a yield of 76% on MAF coal of total C,+ distillate and a yield of 58% of C4 X 200 "C naphtha were obtained at the highest demonstrated conversion of 87%. Thus, in a single-pass operation without recycle of the +200 "C distillate, a yield equivalent to 0.754 m3 of C4 X 200 "C naphtha (0.77 kg/L) plus 0.180 m3 of +200 "C distillate (1.00 kg/L) per metric ton of MF coal has been demonstrated (4.30 and 1.03 bbl/short ton, respectively). Figure 7 shows how the amounts of MEK-soluble and MEK-insoluble organic residue retained in the product catalyst decrease as the coal conversion increases. The
'lo
80 90 OF M P F COAL
EO
Figure 8. Carbon content of product catalyst melt as a function of conversion.
MEK-insoluble residue appears to be substantially lower at a given conversion a t 24.23 MPa than a t 16.65 MPa as indicated by the least-squares lines based on the data a t the two pressures. While straight lines have been drawn over the range of the data up to 80% conversion, it is apparent that curvature would develop at higher conversions since at 100% conversion the yields of these products must be zero. The amount of carbon in the effluent catalyst is a function of the yield of organic MEK-solubles and -insolubles in the spent melt. It is shown as a function of conversion in Figure 8. Processwise, it is desirable to get down to about 6% carbon in the spent melt since this is roughly the amount of carbon required to furnish the heat for carrying out the catalyst regeneration adiabatically in a fluidized combustor with excess air. It is apparent from Figure 8 that the 6% carbon level was obtained in a single-stage stirred reactor. The goal would be more easily reached in multiple reactors in series. The good correlations of yield data with conversion show that a reasonably good yield structure can be predicted for a given conversion. This, combined with the kinetics correlation for predicting conversion, whether in single or multiple reactors, provides a powerful tool for optimizing the process. Product Properties. It is beyond the scope of this paper to present comprehensive data on the product properties. A few analyses of typcial distillate products are given in Table VIII, however. It is apparent that the gasoline produced is of high quality with blending Research
91
Ind. Eng. Chem. Process Des. Dev. 1980, 79,91-97
and Motor Octane Numbers of 90.6 and 78.7, respectively, and direct Research and Motor Octane Numbers of 92.3 and 81.5, respectively. These results are similar to previous results from gasoline produced by hydrocracking bituminous coal extract with ZnC1, catalyst (Consolidation Coal Co., 1968a). These results show the ZnC1, gasoline to be an acceptable blending stock and acceptable as an unblended gasoline providing the Research Octane Number is over 91. The chlorine content of the gasoline should not be deleterious, at least by current standards, since chlorine and bromine are normally added to leaded gasolines in much greater amounts to act as lead scavengers. The 200 X 475 "C middle oil and the +475 "C heavy oil would make premium fuel oils that can meet the most stringent current environmental regulations because of their extremely low nitrogen and sulfur contents (
