Ind. Eng. Chem. Res. 1994,33,2272-2279
2272
Use of a Novel Short Contact Time Batch Reactor and Thermogravimetric Analysis To Follow the Conversion of Coal-Derived Resids during Hydroprocessing He Huang, William H. Calkins: and Michael T. Klein Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716
The conversion of two coal-derived nondistillable residua (resids) in tetralin during hydroprocessing has been examined. A novel laboratory scale batch reactor capable of operation up to 450 O C and 17 MPa (2500 psi) under well-defined contact times from a few seconds to 30 minor longer was used. Thermogravimetric analyses, augmented by gas chromatography and gas chromatography/mass spectrometry, were used to follow the course of the conversion. Two resids, one derived from Wyodak subbituminous coal and another from Pittsburgh bituminous coal, were found to differ in their reactivity toward conversion to soluble or lower boiling materials. In the absence of a catalyst, the insoluble resids became solubilized in tetralin to some degree. However, even at long reaction times and high temperatures there was no indication of a breakdown in molecular weight or molecular structure as shown by thermogravimetric analysis and laser desorption high resolution mass spectrometry. In the presence of a presulfided Ni/Mo on alumina catalyst there was a much higher degree of solubilization and a definite indication of molecular breakdown. 1. Introduction Direct coal liquefaction produces a substantial amount of high boiling, nondistillable residuum. The amount and character of this resid depends upon the coal used and the conditions and reaction times of the liquefaction process. Because of its high boiling point and potential thermal instability, this material is not suitable for processing in a conventional petroleum refinery. In a commercial liquefaction process as visualized today, therefore, this material would be recycled to the process to recover its energy value. Furthermore, this recycle oil has also been shown to actually have a beneficial effect (i.e., increased oil yield) in the liquefaction process (Whitehurst et al., 1980; Grint et al., 1994). Since these resids are complex and high boiling materials, their performance in the recycling process is not well understood or currently predictable. To this end, considerable analytical work has been accomplished for characterization purposes (Ibrahim and Seehra, 1992; Malhotra and McMillen, 1992; Solom and Pugmire, 1992; Stock and Cheng, 1992). These analyses have provided important structural information, but reactivity information during hydroprocessing is lacking. Some measure of the ability to convert these resids to lower boiling, fuelgrade products is critically needed for design and scale-up purposes. For example, it is important to know the dependence of reactivity on resid origin, preparation method, reaction conditions, and catalyst. This motivated the present study of the reactivity of coal-derived resids. A critical part of this program has been the development of a laboratory scale short contact time batch reactor (SCTBR) (Huang et al., 1993) capable of running reactions up to 450 "C and 2500 psig at welldefined reaction times from a few seconds to 30 min or longer. This reactor is simple in design and can be conveniently operated in the laboratory. Herein we report on its use to carry out hydroprocessing reactions of two resids to lower boiling, lower molecular weight material. In addition, these studies also required a rigorous means of followingthe resid conversion. For this purpose, a novel application of thermogravimetric analysis (TGA), augmented with gas chromatography and, to a lesser extent, 0888-5885/94/2633-2272$04.50/0
gas chromatography/mass spectrometry (GC/MS),served to provide a fast and convenient measure of resid conversion. Together, the novel SCTBR and TGA-centered analytical protocol allowed acquisition of important coalresid reactivity information under conditions approximating those of resid recycling during the coal liquefaction process. 2. Experimental Section 2.1. Apparatus. The design and operation of the SCTBR reactor system have been described in detail previously (Huang et al., 1993). A schematic diagram of this equipment is shown in Figure 1. The 30 cm3 reactor is capable of containing up to 17 MPa (2500 psig) at temperatures up to 550 "C. The 21 f t lengths of 316 stainless steel tubing used for the preheater and precooler are 1/4 in. 0.d. with wall thicknesses of 0.035 in. In operation, both the empty preheater and reactor are immersed in a Techne IFB-52 fluidized sand bath. They are brought up to the predetermined reaction temperature prior to the start of the reaction. High pressure hydrogen gas provided the driving force to deliver the reaction mixture under study from a small blow case into the empty reactor through the preheater tubing. Hydrogen gas was then bubbled through the reactor from the bottom to supply the hydrogen for the liquefaction reaction and to provide the agitation needed in the heterogeneous reaction system. The degree of agitation is controlled by the exit gas flow rate from the top of the reactor. A small watercooled condenser and disengaging space to prevent loss of solvent or other low boiling materials are located above the reactor and before the let-down valve. The temperature of the reactant mixture (ca. 30 g) approaches the desired reaction temperature to within 5-8 "C during the transport process (approximately 0.3 s) and quickly recovers to the desired reaction temperature within 30 s. This temperature is maintained within f l "C during the experiment. At a preselected reaction time, high pressure hydrogen gas is again used to drive the reactor contents from the reactor into a cold receiver through the precooler. Both receiver and precooler are immersed in a water bath. 0 1994 American Chemical Society
Ind. Eng. Chem. Res., Vol. 33, No. 10, 1994 2273
Cha&r Cooling Water
I
7-
Thermocouple
I-
1 Coding Rercrvoir
I
L
L
U
U
I
------S a n
d 4 4
L- - - - _ - -
I
Water B
d
Figure 1. SCTBR reactor apparatus for the conversion of coal-derived resid. Table 1. Ultimate Analyses of the Two Coal-Derived Resids from Wilsonville Pilot Plant Runs 259 and 260 ultimate anal., wt % MAF
sample resid 1 plant: Wilsonville run number: 259 sample designator: V1067 sampling point: 2nd stage product feed coal: Pittsburgh Seam, Ireland Mine resid 2 plant: Wilsonville runnumber: 260 sample designator: V1067 sampling point: 2nd stage product feed coal: Wyodak & Anderson Seam, Black Thunder Mine
Cooling of the product mixture to about 25 "C is achieved within 0.3 s. The thermogravimetric analyzer (TGA) was a Model 51 TGA (TA Instruments, New Castle, DE). Gas chromatography was performed on a Hewlett-Packard H P 5970 series I1 GC equipped with a flame ionization detector. The gas chromatography/mass spectrometry also used a Hewlett-Packard HP5970 series I1 GC equipped with a H P Series mass selective detector. Laser desorption high resolution mass spectrometry (HRMS) was accomplished for fourselected samplesusing a FT2000, Extrel (Madison, WI) instrument with a COZlaser and stainless steel sample disks. 2.2. Materials Studied. The two 850 O F distillation resids, one derived from Pittsburgh bituminous coal (denoted as resid 1)and another from Wyodak subbituminous coal (resid 2), were obtained from the Wilsonville Pilot Plant Runs 259 and 260, and prepared and composited by CONSOL Research. These solids were ground by CONSOL to about 14 mesh. Ultimate analyses for these two resids are shown in Table 1. The catalyst was a presulfided Ni/Mo on alumina (Shell 324) (10.5 wt % Mo and 2.08 w t 5% Ni). The presulfiding was accomplished in a distillate oil a t the Wilsonville Plant. The oil was removed and the catalyst dried and ground under nitrogen by CONSOL.
C H
N
S 0 (din ash, wt % as detd C H
N S 0 (dif) ash, wt % as detd
90.24 6.39 1.05 1.49 0.83 10.21 91.03 6.56 1.15 0.09 1.17 18.30
Table 2. Overview of Experimental Program. variahles
contact time, min temperature, "C Hz pressure, psig reside solvent ratio catalyst
5,10) 20) 30 412,435 1500 reaid 1 and resid 2 2:l) 31,51b(tetralin:resid) none, Criterion (Shell) 324 catalyatc Arranging experiments by combination of the reaction conditions given in this table. Running a few experiments at selected conditions. Samples provided by CONSOL.
*
2.3. Resid Conversion Reactions. All reactions were run as mixtures of tetralin (T,the donor solvent) and resid (R) over a range of T/R, temperature, and catalyst. For each reactor run 5-10 g of resid was used together with added tetralin to make up the desired T/R ratio. The program for reactor runs are summarized in Table 2. Holdup of material on the surfaces of the reactor, preheater, and precooler prevented complete recovery of the reaction products. Recoveries varied from about 6590 wt % depending upon the amount of tetralin used. The measure of conversion and subsequent analytical results were therefore based on representative aliquots. That this method of sampling was representative of the reactor content was demonstrated by running TGA on two tetralin-
2274 Ind. Eng. Chem. Res., Vol. 33, No. 10, 1994 Table 3. TG Analyses on Two Tetralin-Treated Resid Control Samples TGA results, %
sample T/R time,min T,OC VM FC ash 25 23.9 53.9 22.2 WR103" 3 25 23.8 54.2 22.0 WR103RSb 3 N/A 30 25 19.2 49.5 31.3 3 NIA WR203' 3 30 25 19.2 49.3 31.5 WR203RSb a The solid filter cakes treated with tetralin at room temperature without going through the reactor. b The solid filter cakes treated with tetralin at room temperature processing through the reactor. 0
resid t tetralin mixture with/without catalyst
IW
1W
300
4CQ
500
6QO
700
Time (mi")
Figure 3. TG scan on a liquid filtrate of catalyzed conversion.
[t (min) and T ("C))
Q products stream
L J. J. filtration
I
liquid
I
I
solid
I
GC, GC/MS, and slow ramp TGA
u Figure 2. Scheme of the reaction product workup procedure.
treated resid control samples: one was analyzed directly, and the other was put through the reactor at room temperature. The TGA parameters (see section 2.5) of these unreacted resid control samples are shown in Table 3. The impressive match shows the aliquot to be an excellent representation of the entire sample. The reactor system is cleaned in place by a series of tetralin washes. The wash effectiveness is monitored by analysis of the wash streams. Five 30 cm3 washes are required to obtain about 99% sample recovery. 2.4. Reaction Product Workup Procedure. The reaction products were analyzed according to the scheme of Figure 2. This resulted in the production of a liquid filtrate, which consisted mainly of tetralin and dissolved resid, and a solid filter cake, which consisted of unconverted or partially converted solid resid. These two fractions were analyzed separately. The TGA of the liquid filtrate shown in Figure 3 demonstrates that no mineral matter is contained in the liquid sample. This is critical, as the conversion measurements are based on the relative ash contents of the converted product and the original unreacted solid resid. Figure 3 illustrates that both the tetralin content (including
those materials boiling close to tetralin) and the amount of higher boiling materials in the liquid filtrate could be determined by TGA in nitrogen. GC and GC/MS provided an indication of the number of the compounds boiling in the range of tetralin in the liquid filtrate, although much of the dissolved product was still too low in volatility to be detected. In summary, the liquid filtrate consisted of low boiling products of tetralin conversion, a tetralinsoluble portion of the original resid, and material formed by breakdown of the resid into tetralin soluble substances. Figure 3 also shows the differential weight loss curve, Le., DTG (differential thermogravimetric curve) or evolution pattern. Two distinct peaks are evident, one representing the evolution of tetralin and some other low boiling materials, and the second broader peak indicating evolution of other materials in the range of 300-400 "C due to either volatilization or pyrolysis. These DTG curves thus help identify the various weight loss processes occurring during the TGA. Sharp peaks are indicative of evolution of a single material, or several substances boiling very close to each other. A broad peak is indicative of many processes occurring over a broad temperature range either by volatilization or by pyrolysis. DTG can be used to distinguish between simple volatilization and pyrolysis when run at both atmospheric pressure and under vacuum (Schwartz et al., 1987). A peak occurring at relatively low temperature is likely to be volatilization. High temperature peaks are probably due to pyrolysis or a combination of volatilization and pyrolysis of high boiling materials. In this study, all TG scans were run at atmospheric pressure. A change in the DTG curve or evolution pattern, particularly as replotted against temperature as in Figure 11,is an indication of a change in the materials being evolvedeither in the direction of greater volatility (probably lower molecular weight) or to more intractable higher molecular weight materials. These changes in DTG patterns can be quantitatively expressed by two characteristic variables: peak evolution temperature (Tpe&)and mean evolution temperature (Tme,). Tpe& is defined as the evolution temperature at is defined as the mean maximum evolution rate. T, evolution temperature weighted by the evolution rate. Mathematically, F(evo1ution rate)iTi Tmean
--
(1)
C(evo1ution rateli 1
Two sets of reacted and unreacted liquid filtrate samples were prepared for laser desorption high resolution mass
6.186 % "VM '
90
- 1000
k-
I
-
70
/' /
SI 0
63.11% I.
// Reddue: 40.03 %Ash 1 a0
'
1
Nl
'
1 00
'
1
m
0
' 100
60
I
0
1 50
spectrometry by placing the samples on small stainless steel disks and then drying to remove most of the tetralin for laser desorption. The amounts of the tetralin soluble resid plus that converted in the hydroprocess were estimated by quantitative comparison of the ash fraction of the solid filter cake with that of the unreacted resid. This measured the total disappearance of the resid from the solid sample. To this end, the solid filter cake was dried in a vacuum oven at 100 "C for 48 h, and then ground in a mortar and pestle and dried again to remove any residual tetralin. 2.5. Determination of Resid Conversion. A representative TG scan on the solid filter cake resulting from reaction without any catalyst is shown in Figure 4. The weight loss resulting from heating in nitrogen at a ramp of 10 "C/min to 600 "C defines the amount of volatile matter (VM). For this illustrative sample VM was 13.6 wt 5%. Further weight loss occurred at 600 "C after the introduction of oxygen. This was due to the oxidation of the remaining combustible material, the so-called "fixed carbon (FC)", in the cake, which amounted to 46.3 wt 5% for the illustrative sample of Figure 4. The lack of further weight loss at 600 "C and during a ramp of 100 "C/min to 900 "C in oxygen defined the balance as the ash residue (40.0 wt 5%). Thus the three phases, Le., (1)the ramp to 600 "C in nitrogen; (2) the oxidation at 600 "C; and (3) the ramp to 900 "C in oxygen, provided measures of VM, FC, and ash, respectively, for uncatalyzed samples. The experimental error for determination of the TGA characteristic variables (VM, FC, and ash) is less than &0.5% of the measured values. Significant proportions of the resids are soluble in tetralin at room temperature (48-55 wt 5% for resid 1and 37-42 wt % for resid 2, depending on the tetralin to resid ratio). During hydroprocessing,some of the insoluble resid is converted to tetralin soluble material. The total extent of the solubilization ( D ) can be estimated by comparing the weight fraction of ash present in the reacted resid with that of the original coal-derived resid. Since the ash is not consumed during the liquefaction and remains in the solid, D can be derived based on an ash balance:
where W,, represents the weight of resid, W , the weight of the reacted sample, A, the weight fraction of ash in the original resid, and A, the weight fraction of ash in the reacted sample.
1
'
150
1
'
7.00
1
I o 150
Time (mi")
Time (Inin)
Figure 4. Representative TG scan on a solid filter cake of an uncatalyzed run.
'
100
Figure 5. Representative TG scan on a solid filter cake of acatalyzed run.
The degree of solubilization D is given by:
rearranging and substituting eq 2 into eq 3 provides
(
D = 1-
1)
X
100
(4)
a working expression for the determination of solubilization. D is the sum of the room temperature soluble resid and the resid which has become solubilized in the or solubilization hydroprocessing. Actual conversion (XD) of the tetralin-insoluble resid during the liquefaction process can be estimated by subtracting the soluble portion of the resid at time zero (DtP0)from that a t time t (Dt), i.e.,
XD= D, - D,=,
(5)
2.6. Determination of CatalyzedResidConversion. For a catalyzed sample, the 600 "C-oxidized residue includes the ash from the resid and partially oxidized catalyst. Since' the mineral matter (ash) from the resid was used as a reference for determination of conversion, the total amount of the ash determined by TGA from a catalyzed sample must be decomposed into the contributions from the resid ash and catalyst ash in order to calculate conversion using eqs 4 and 5. A representative TG scan on the solid sample produced from a catalyzed resid is shown in Figure 5. Three distinct stages are apparent. In the first,"VM" consists of VM from resid and some weight loss of the catalyst; the second represents "FC" from the resid and weight loss due to the first stage of catalyst oxidation; and the third stage, which includes the temperature ramped at 100 to 1000 "C and holding a t 1000 "C for 120 min in oxygen, completes the oxidation of the catalyst, leaving an ash which consists of ash from the resid plus ash from the final stage of catalyst oxidation. The basis for the deconvolution of the catalyst ash and resid ash is thus the comparison of TG scans for catalyzed resid samples with a TG scan on the sulfided catalyst only, such as that shown in Figure 6. Running the catalyst only at 10 "C/min to 600 "C, the first drop in weight is detected. As oxygen is added at 600 "C, the second drop in weight is obtained, designated as the first stage of catalyst oxidation. Finally, running in oxygen from 600 "C at 100 "C/min to 1000 "C and holding at 1000 "C for 120 min to a constant weight, a third drop in weight was observed. This loss in weight was due presumably to the complete
2276 Ind. Eng. Chem. Res., Vol. 33, No. 10,1994 100
7
1000
f
I
I
I
I
I
I
Resid derived from Pittsburgh bituminous coal
600
F 400
-
804
/ 7 0 , 0
, 0
k
,
,
I/
s
71.23%
,
1
1W
1
150
1
'
1w
250
412°C 412°C
0 Time
(minj
Figure 6. TG scan on the presulfided catalyst of Mo-Ni on alumina.
oxidation of the catalyst, leaving the residue as the ash from the catalyst (i.e., metal oxides). This third drop in weight is caused solely by the second stage of catalyst oxidation, because there is no such drop for the uncatalyzed resid sample alone (see Figure 4). Therefore, the amount of the catalyst in the catalyzed resid sample is proportional to the third drop obtained by TG scan, i.e.,
Resid derived from Wyodak-Anderson subbituminous coal
(7)
For these catalyst-resid mixtures, the measured 1000 "C ash residue (At) is the sum of the resid ash and the catalyst ash, Le., A,
+ A, = A,
(8)
Solving A , from eqs 7 and 8 gives At A, = -
l+k
In order to use eq 4 to calculate D, the ash content of resid in the catalyzed resid sample must be calculated on a catalyst-free basis, i.e.,
Substituting eqs 6 and 9 into eq 10 provides A, =
At 1- CY(A,WOC- A t ) ( l + k)
(11)
a working formula for the catalyzed resid conversion using eqs 4 and 5.
0
-
12
-
10
-
-
8 -
-
6 -
-
4 -
*
where Ccat.is the concentration (wt % ) of the catalyst in the catalyzed resid sample, A m o c the weight fraction of a 600"C residue, At the weight fraction of a 1000"C residue which is the total amount of catalyst ash and resid ash, and a a scale constant which can be determined by the TG scans of catalyst alone. a was also determined using a calibration sample consisting of a mixture of the catalyst and resid treated by tetralin at room temperature and the comparable values were obtained. A constant weight ratio of catalyst to resid (i.e., R C = 1:l)was used throughout the reactor runs. Therefore, the ratio of the ash from the catalyst (A,) to the ash from the resid (A,) in the catalyzed sample will be a constant from run to run, i.e.,
433T 433oc
4 -
5
0
10
20
15
25
410'C
30
35
Time, min
Figure 7. Conversion kinetics for uncatalyzed resids conversion at T/R= 3.0. Table 4. Numerical Values of Coefficients a and k
coefficient resid 1 resid 2
cy
k
7.55 10.35
5.87 3.79
Calibration experiments using the catalyst in a reference sample of T:RC (tetra1in:resid:catalyst)= 3:l:lprovided the numerical values of Coefficientsa and k. The resulting coefficients are given in Table 4. 3. Results and Discussion 3.1. Conversion of Resid to Tetralin-Soluble Materials. Reaction time dependence of conversion XDfor uncatalyzed conversion of resids 1 and 2 are shown in Figure 7 for T = 412 and 435 "C at T/R = 3. For uncatalyzed 30 rnin reactor runs of resid 1, X D was only about 1 wt 5% at 412 "C and 6 wt % at 435 "C. For uncatalyzed 30 rnin reactor runs of resid 2, XDwas about 2 wt % at 410 "C and about 13 wt % at 434 "C. By this measure, resid 2 was about twice as reactive as resid 1. Conversion (XD) versus reaction time for catalyzed resids 1 and 2 at T:R:C = 3:l:lis shown in Figure 8. For reaction of resid 1 at 415 "C, XDincreased with reaction time about 10 wt % after 30 min. This is 10 times higher than the increase observed for the uncatalyzed run. For reaction of resid 1 at 434 "C,XD increased with time about 17% at 20 min. Then it levels off. This is about 4 times higher than observed in uncatalyzed runs. Reaction of resid 2 at T:R:C = 3:l:lwas more facile than for resid 1. At 415 OC, X D increased with time about 31.6% for 30 min. This is 15 times higher than observed for uncatalyzed runs. At 440 "C, XD increased about 33% after 10 min. Then it levels off. This is approximately 8 times higher than observed for uncatalyzed runs. It is interesting to note that the asymptotic value Of XDin Figure 8 is independent
Ind. Eng. Chem. Res., Vol. 33, No. 10, 1994 2277 I
I
I
I
I
I
I
0.6 I
1
'
1
1
Resid derived from Plttsburgb bituminous c o d
5 V
30
-
subbitumiuous cod 0
I
I
I
I
I
I
I
5
10
15
20
25
30
35
0.6
0.4
03 0.2
0.1
0 25'C
somin,4 ° C
26%
somin,4U'C
E S a F C r n D
Figure 9. D,VM,, and FC, in the resids treated or reacted with tetralin under various conditions at T/R = 3.0.
normalized VM (VM,) and FC (FC,) based on original resid are plotted at various reaction conditions for resids 1 and 2 in Figure 9. The VMn was calculated by
Time, mi,
Figure 8. Conversion kinetics for catalyzed resids conversion at T R C = 3:l:l. Table 5. Effect of Tetralin to Resid (T/R) Ratio on Uncatalyzed Resid Conversion (Reaction Time: 30 min) sample resid 1 calibration of resid 1 WRlOl WR103 WR104 reactor runs of resid 1 c1002 c1m Cl008 ClOlO C1014 C1016 resid 2 calibration of resid 2 WR201 WR203 WR204 reactor runs of resid 2 C2015 C2009 C2016 C2018 C2024 C2026
T/R N/A
T,OC N/A
TGA results, % VM FC ash 54.1 35.0 10.9
5 3 2
25 25 25
22.2 23.9 29.9
53.7 53.9 49.2
24.1 22.2 20.9
54.8 50.9 47.8
5 3 2 5 3 2 N/A
413 412 412 436 435 434 N/A
17.4 23.0 27.3 9.9 20.1 20.1 44.4
59.4 54.5 49.8 64.2 54.6 53.5 37.3
24.2 22.5 22.9 25.9 25.3 26.4 18.3
55.0 51.6 52.4 57.9 56.9 58.7 N/A
5 3 2
25 25 25
15.7 19.2 22.6
52.6 49.5 48.1
31.7 31.3 29.4
42.3 41.6 37.6
5 3 2 5 3 2
413 410 412 434 434 434
15.9 20.4 18.3 15.9 13.6 19.9
51.3 47.3 48.1 46.3 46.4 42.0
32.8 32.3 33.5 37.9 40.0 38.1
44.2 43.4 45.4 51.7 54.3 52.0
Do N/A
a D: The amount of resid dissolved in the tetralin, which was calculated by eq 4.
of temperature. The catalyzed reactivity of resid 2 is higher than that of resid 1 as was observed for uncatalyzed conversions. Table 5 summarizes the effect of tetralin to resid ratio (T/R= 2-5) on XDat two temperatures. No obvious effect of dilution on the kinetics of conversion is evident. This is because of the heterogeneous nature of the solubilization process under the conditions and concentrations used. It should be noted, however, that the simultaneous homogeneous reaction in which the soluble resid material reacts with the tetralin is probably sensitive to T/R ratio. To determine the principal source of the soluble components of the resids treated with tetralin, D and
where VMQa is the value determined by a TG scan. Similarly, FC, = FC,(
1- D)
(13)
where FCQais the value determined by a TG scan. Figure 9 shows that the principal source of the dissolution portion (about 80 wt %) appears to come from the VM in the resid. 3.2. Changes in DTG with Conversion. The TGA evolution pattern provides a rough indication of the molecular weight range of the converted materials in the liquid filtrate. To this end, slow ramp TGA (1or 5 "C/ min) was run to obtain evolution rate versus temperature for the liquid filtrate from the unreacted sample (treated with tetralin a t room temperature), and resids 1 and 2 reacted without catalyst at approximately 435 "C. The DTG results summarized in Figure 10 indicate a bimodal distribution in the evolution patterns of the soluble resid portions. That is essentially independent of the thermal history of the sample, that is, no change in the evolution patterns could be detected during the uncatalyzed reactor runs except for the formation of a small amount of low boiling materials in the liquid filtrate. This is the case even though some resid has become soluble. Figure 11 summarizes the evolution rates (DTG) vs temperature for the liquid samples from the unreacted resids treated with tetralin a t room temperature and reacted for 5 min at 434 "C and 30 min at 435 "C in the presence of catalyst. Clearly the evolution patterns for liquid product from catalyzed reactions are shiftedto lower temperature than the room temperature sample. These trends are summarized as the tabulation of T w and Tmean for the room temperature and reacted samples in Table 6. For longer reaction times, Tm- and T w decreased by about 60 and 50 "C, respectively. Similar behavior was observed for the catalyzed conversion of resid 2. It is interesting to note that the higher temperature peak
2278 Ind. Eng. Chem. Res., Vol. 33, No. 10, 1994 0.02
,
I
,
,
.............. 0 ............
,
1
6
timinatff34%
30 min at 4.36%
0012
o'w 0.02
1
1
./
1
0
I
1-2
I
200
I
300
250
I
6
4w
350
450
600
Temperature, OC
Figure 10. Evolution rate versus temperature (DTG vs 2") determined by slow ramp TGA (5 "C/min) for the liquid filtrates of uncatalyzed resids conversion at T/R = 3.0. x~0-3
t
I
I
I
I
Resid 1 4
3
2
$
1
i
d o .*I { s
s
4
3 2
I
0 200
250
300
350
4w
450
500
Temperature, "C
Figure 11. Evolution rate versus temperature (DTG vs 27 determined by slow ramp TGA (1 OC/min) for the liquid filtrates of catalyzed resids conversion at T R C = 3:l:l.
disappears after catalytic reactions, but is unchanged for reactions without catalyst. The laser desorption HRMS results for four liquid filtrate samples of the two resids (unreacted and reacted with catalyst at 435 OC for 30 min) indicated molecular weight range for both resids of approximately 300-600 Daltons. Also bimodal molecular weight distributions were observed for all four samples; however, there was an
Table 6. Peak Evolution Temperatures (!I'M) and Mean Evolution Temperatures (T-) of the Liquid Filtrates from the Catalyzed Resid Conversion
resid 1+ catalyst 0 min 5 min at 434 OC 30 rnin at 435 OC resid 2 + catalyst 0 min 30 rnin at 442 "C
320 318 273
349 322 291
307 214
321 282
observed shift to lower molecular weight during the reaction in the catalyzed samples. 3.3. Formation of Lower Boiling Products. Summation of GC peak areas showed that there is up to 0.5 wt '% concentration for uncatalyzed runs, and 2 wt % concentration for catalyzed runs of material boiling close to tetralin in the liquid filtrate resulting from resid conversion. This represents about 5 75 for uncatalyzed reaction and 20 % for catalyzed reaction of the resids which have been converted to low boiling material. These low boiling substances consist of more than 50 individual compounds detected by GC, each too low in concentration to be identified. The G U M S used in this work is not sensitive enough to detect these many low boiling materials in the very low concentrations involved. 4. Summary and Conclusions 1. The combination of reaction in the SCTBR (Short Contact Time Batch Reactor) with TGA of both liquid and solid products provides a direct and reproducible means of indicating the breakdown of coal-derived resids under liquefaction conditions. 2. A method has been devised for determination of the resid ash in the presence of catalyst using TGA, so that conversion of catalyzed resids can be calculated. 3. The conversion of resid to tetralin-soluble material was determined by relating the inorganic matter (ash) in the reacted resid with that of the unreacted resid. Conversion of uncatalyzed tetralin-insoluble resids to tetralin soluble products in this study was very low (< 10 wt % ) under coal liquefaction conditions; however, up to 50 wt % of the resid was tetralin soluble at room temperature. Up to 80% (ash-free basis) of the room temperature tetralin insoluble resid was solubilized in tetralin-using sulfided Ni/Mo on alumina catalyst at 434 OC for 10 min. While hydroprocessing at liquefaction conditions, and particularly in the presence of Ni/Mo on alumina catalyst, was effective for converting tetralininsoluble to tetralin-soluble material, and for reducing the average molecular weight, only a small fraction (about 20 wt %) of this material was converted to the boiling range of gasoline or diesel fuel. 4. A progressive decrease in the temperature evolution range (DTG) of the catalytically solubilized materials with reaction time was observed. Thermal experiments revealed no such change. 5. The resid derived from Wyodak subbituminous coal was somewhat more reactive than that from Pittsburgh bituminous coal. 6. The principal source of tetralin-soluble or solubilized materials comes from the volatile matter in the resids.
Acknowledgment The assistance and advice of F. P. Burke, R. A. Winschel, and S. D. Brandes of CONSOL Inc. in preparation and analysis of the resid and catalyst samples used in this
Ind. Eng. Chem. Res., Vol. 33, No. 10,1994 2279 project is gratefully acknowledged. The laser desorption high resolution mass spectrometry was done by G. R. Nicol. This work was supported by subcontract from CONSOL Inc. under U.S.DOE Contract No. DE-AC22-89PC89883.
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