- Email: [email protected]
Evaluation of the hydroliquefaction potential of Chinese coals: Three case studies
Fuel Processing Technology, 22 (1989) 161-174
161
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
E v a l u a t i o n of the H y d r o l i q u e f a c t i o n P o t e n t i a l of Chinese Coals: T h r e e Case Studies JINSHENG GAO
East China University of Chem. Technology, 130 Meilong Road, 20037 Shanghai (P.R. China) PEIFANG ZHANG* and HANS HENNING OELERT
TU Clausthal, Erzstr. 18, D-3392 Clausthal-Zellerfield (F.R.G.) (Received October 10th, 1988; accepted December 8th, 1988)
ABSTRACT In bench-scale autoclaves the hydroliquefaction cross-checking tests of three typical Chinese low rank coals were performed under different conditions. The methods of coal evaluation for hydrogenation reactivity are discussed, focused upon the influence of important parameters - temperature, pressure, residence time, solvent and catalyst. The experimental results indicate that with fewer than 20 cross-checking tests by appropriate parameter variations the hydroliquefaction behaviour of the coals used could be evaluated rather satisfactorily. Shengli lignite and Yanzhou HV-bituminous coal have a high reactivity for liquefaction processing. With coal-derived slurry oil under not too severe conditions a coal conversion of ca. 80% and an oil yield of more than 50% were obtained. Xianfeng lignite is younger and therefore more sensitive than Shengli lignite. By optimizing the process parameters, an oil yield of more than 50% could possibly be attained. This paper should provide information of interest for a perspective on coal liquefaction in China.
INTRODUCTION
For hydroliquefaction the reactivity of coals can be empirically, but scarcely rationally estimated, e.g. for hard coals by the relationship between coal conversion and reflectance [1] and for lignites by precalculation of conversion from analytical data [2]. But each coal must be tested individually and step by step, at first by laboratory screening, then by technical tests. The important parameters to be examined are as follows [3]: (1) temperature, because coal hydrogenation is directly related to thermal fragmentation and recombination, (2) pressure, related to H-availability, (3) residence time, because of kinetics of parallel and consecutive reactions, Present address: Dow Stade GmbH, Btitzflethersand, Postfach 1120, D-2160 Stade (F.R.G.).
0378-3820/89/$03.50
© 1989 Elsevier Science Publishers B.V.
162
(4) solvent or slurry oil, related to coal solubility, thermal destruction of solvent and H-transfer potential from solvent. (5) catalyst, because of H-transfer potential and in situ upgrading of primary products. Points (1)-(3) are major physical parameters, (4) and (5) are equally important, but are more chemically oriented. If all 5 parameters are to be investigated by complete cross-checking, there will be a minimum of 32 tests necessary with one catalyst and 360 tests for full scale testing. This would be almost impossible to implement, and very expensive. Therefore, only a limited amount of testing based on experience for each coal was undertaken. As a case study this paper will discuss hydroliquefaction evaluation for three Chinese typical low-rank coals, obtained from important mines in the provinces of Yunnan, Inner Mongolia and Shandong. It should provide interesting information for a perspective on coal hydroliquefaction in China. EXPERIMENTAL
Feedstocks
Three coal samples were received from mines, but not necessarily representative for a whole mining area. Basic analytical data are compiled in Table 1. The slurry oils used were a recycle oil (RO) from a pilot plant, anthracene TABLE1 Analytical data of coal samples Coal
Origin
Water (wt.%)
Ash (w.f.) (wt.%)
Volatile (d.m.f.) matter (wt.%)
1. Xian-Feng 2. Shengli 3. Yanzhou
Yunnan Inner Mongolia Shandong
20.0 7.61" 1.90
3.23 18.72 8.40
48.44 45.39 44.74
Coal
1. Xiang-Feng 2. Shengli 3. Yanzhou *Predried.
Elemental analysis (d.m.f., wt.% ) C
H
N
S
S (total)
O (diff. )
H/C
69.63 71.05 79.90
4.94 4.91 5.40
2.14 0.78 1.22
0.43 0.68 2.14
0.63 1.08 4.14
22.86 22.58 11.34
0.85 0.83 0.81
163 TABLE 2 Analytical data of slurry oils Slurry oil
l~I (g/mol)
1. RO 2. AO 3. VRW
244 175 1410
Slurry oil
Asphaltene (wt.%)
1. RO
2. AO 3. VRW
Elemental analysis (d.m.f., wt.% ) C
H
N
S
H/C
88.40 91.77 86.52
10.40 6.24 11.44
0.32 0.44 0.59
0.78 0.56 1.45
1.40 0.81 1.58
Viscosity/(mm2/s)
Conradson test (wt.%)
4.0 3.5 2.1
0.3 2.6 21.7
50°C
100 °C
14.5 7.0 4300*
3.4 5.0 700
*Kinematic viscosity measured at 70 °C. TABLE 3 Composition of catalysts (wt.%) Catalyst*
Fe203
Si02
T i O 2 A1203 CaO
1. BRM 2. SRM 3. HI
33.96 7.15 71.06
12.80 8 . 6 8 20.28 2.45 2 2 . 6 0 0.53
4. CMN
Co 1.6-2.3, Mo 10-14, Ni 5-6.5, A120377-84
32.23 20.40 2.83
MgO
3.22 0.40 4 4 . 0 7 1.33 0.70 0.55
Na20
K20
CuO
NiO
7.26 1.71 0.03
0.08 0.36 0.64
0.39 -0.39
0.98 0.33 0.64
*BRM {Bayer red mud), SRM (Shandong red mud), HI (Hainan iron ore), CMN (Co/Mo/Ni/ A1203-catalyst). oil (AO) a n d a v a c u u m residue ( V R W ) . T h e i r a n a l y t i c a l d a t a are c o m p i l e d in T a b l e 2. F u r t h e r e x p e r i m e n t s were m a d e w i t h tetralin. T h e applied c a t a l y s t s a n d t h e i r c o m p o s i t i o n are s h o w n in T a b l e 3.
Autoclave T h e e x p e r i m e n t s were p e r f o r m e d in two t y p e s of autoclaves: (A) a rockingtype f r o m A m i n c o Corp., U S A , u s i n g a s h a k e f r e q u e n c y o f 1 H z a n d fast h e a t i n g a n d cooling at a rate of 15 K / m i n . (B) a stirred t y p e f r o m H a a g e G m b H , F R G , u s i n g a stirring speed of 500 r p m a n d h e a t i n g or cooling at a rate of 10 K / m i n .
164
During the experiments the temperature was varied, and the pressure was recorded. At reaction condition temperature deviation was less t h a n _+2 K.
Experimental procedures All experiments were made with coal (d.m.f.) : slurry oil ratio of 1 : 1.6 in autoclave A and 1 : 3.3 in autoclave B, prepressurised with H2 to the given initial pressure. After cooling, the product gases (G) were released into a plastic bag and analyzed by GC. The non-gaseous products were separated into residue (R, benzene insoluble), asphaltenes (A, benzene soluble but cyclohexane insoluble), product oil and slurry oil (O) remained together, containing more or less reaction water. The total mass balance for each experiment was checked; those with a mass balance >/97% were considered as valid. Calculation methods for H2-consumption; coal conversion and product distribution (G, R, A and O) are given in detail elsewhere [2,4 ]. All data mentioned above were related to coal (d.m.f.), for coprocessing in VRW the data were in addition related to total feed. For these tests a portion of non-gaseous products was taken directly from the autoclave into the distillation flask and weighed, then water and naphtha (light oil, b.p. 200 °C) were vacuum distilled off at 95°C and 40 mbar. Control experiments, using slurry oil only, were also performed. From experience relative m a x i m u m errors for different products portions are about + 2% for coal conversion; + 1% for R; + 1% for A; __2% for O and N; and _+0.2% for H2-consumption (2). RESULTS AND DISCUSSION
Case one: hydroliquefaction of Shengli lignite Shengli lignite is characterized by a moderate a m o u n t of volatile matter and a rather low H/C-ratio of 0.83, but rich in ash. Its oxygen content is in a normal range. From experience it is expected that this lignite will be sensitive to temperature and will be at risk at high temperatures; it will also be sensitive to residence time and require standard catalyst and H-transfer potential. Therefore, the following parameter variations were selected for screening: Standard catalyst in standard recycle oil; Full range of temperatures from 380 to 460 ° C; Normal variation of residence time from 0 to 60 min and three types of solvents, from recycle oil through petroleum vacuum residue to tetralin under sufficient initial hydrogen pressures.
165
The experimental results are compiled in Table 4. From experiments 4-1 to 4-4 with a variation from 380 to 460°C, the sensitivity for this type of lignite is observed. The first increase from 380 to 410 ° C increased conversion by 14% and oil yield by 8%, reducing residue by 14%. At the low temperature of 380°C the conversion achieved was not high, but a rather satisfactory oil yield of 38% with an O/A-ratio of 3.13 and an O/coal conversion-ratio of 0.67 was already obtained. This indicates that the average activation energy of the reactions involved in the formation of extractable liquids is lower for low rank coals t h a n that for moderate and high rank coals, which is also consistent with the general and long-accepted understanding of the structural character of low rank coals, which comprise more low molecular weight substances and few condensed structure units in the crosslinked macromolecular network [5]. Between 410 and 435 °C there is a level maximum range of ca. 74% conversion with an oil yield of 48% and a constant asphaltene yield of 15%. From 435°C to 460°C the conversion and also the oil yield reduced drastically by 24%, residue increased correspondingly by 25% and gas production rose apparently from 12.8% up to 16.8%. It may be recognized that this reaction system at a high temperature of 460 ° C can no longer inhibit the regressive reactions, leading to more residue and gases. The experiments 4-6 to 4-8 were performed under the following conditions: 435 ° C, initial H2-pressure 11 MPa, standard slurry oil and catalyst. T h e y show that a short residence time up to 30 min has a high impact on coal dissolution and liquefaction, reducing residue by 15% and asphaltenes by 4% and thus increasing oil yield by 18% to 47.5%. For a longer residence time from 30 to 45 min only a moderate influence was observed, decreasing residue by a further 5% and also increasing oil yield by 5% but with no impact on asphaltenes, which remain constant at about 10%. In comparison to recycle oil, tetralin, a standard H-donor solvent, favoured the hydroliquefaction for this lignite. Though no catalyst was added, at a nominal reaction time of 0 min a rather high conversion of 77% with an oil yield of 47% was already obtained, which corresponds to the results from experiment 4-2 with RO at 60 min. Prolonging the residence time up to 30 min reduces the residue by 9% with an increase of oil yield by 10%. Between 30 and 60 min the influence on coal conversion became negligible, because at 30 min 86% conversion was already reached, but asphaltenes were further hydrocracked, converting into oil and gas. These results indicate that the residence time has a general influence on coal conversion, H2-consumption and particularly the product distribution. The experiments 4-12 and 4-13 come under the heading of coprocessing. U n d e r the conditions applied a rather satisfactory coal conversion of ca. 67% with relatively high n a p h t h a yields of 23% to 31% (on coal) or 22% to 25% (on total feed) were obtained, exceeding those from Rhein brown coal under the same conditions (experiment 4-14 and the literature [6] ). Comparing the
166 TABLE 4 Experimental results of Shengli lignite (based on coal d.m.f. ) (a) No.
Reaction condition Solvent
Catalyst
PH2 (MPa)
4-1 4-2 4-3 4-4 4-5
RO RO RO RO RO
3.6%BRM + 0.6%Na2S 3.6%BRM+0.6%Na2S 3.6%BRM+0.6%Na2S 3 . 6 % B R M + 0.6%Na2S
4-6 4-7 4-8
RO RO RO
3.6%BRM÷0.6%Na2S 3.6%BRM+0.6%Na2S 3.6%BRM+0.6%Na2S
4-9" 4-10" 4-11"
tetralin tetralin tetralin
----
4-12 4-13 4-14"*
VRW VRW VRW
3.6%BRM +0.6%Na2S 3.6%CMN÷0.6%S
H2-uptake (%)
Conversion (%)
T (°C)
t (min)
9 9 9 9 9
380 410 435 460 435
60 60 60 60 60
1.30 1.80 2.14 1.96 2.20
57.5 71.8 74.2 49.7 57.9
11 11 11
435 435 435
0 30 45
0.84 1.80 1.90
51.6 66.9 71.6
9 9 9
410 410 410
0 30 60
0.54 1.20 1.54
77.1 86.2 86.7
12 12 12
440 440 440
30 30 30
2.04 2.52 0.74
66.3 68.5 50.4
Based on total feed 4-12 4-13 4-14"*
1.04 1.21 0.59
(b) No.
Product distribution (wt.%) R
G
N+O
A
O/A
4-1 4-2 4-3 4-4 4-5
42.5 28.2 25.8 50.3 42.1
8.4 11.7 12.8 16.8 13.7
38.2 46.3 48.6 24.2 30.1
12.2 15.6 14.9 10.7 16.3
3.13 2.97 3.92 2.26 1.85
4-6 4-7 4-8
48.4 33.1 28.4
9.5 11.0 12.1
28.9 47.5 52.1
14.0 10.2 9.3
2.06 4.66 5.60
4-9* 4-10" 4-11"
22.9 13.8 13.3
10.1 11.0 13.6
46.9 57.0 60.8
20.6 19.4 13.8
2.27 2.89 4.41
R
G
N
O+A
33.7 31.5 49.6
10.7 9.1 9.2
23.2 31.4 14.7
34.4 30.5 27.2
----
22.4 25.3 19.2
58.9 57.6 54.8
----
4-12 4-13 4-14"*
Based on total feed 4-12 4-13 4-14"*
15.2 14.4 22.3
4.5 3.9 4.3
*In autoclave B, otherwise in autoclave A. **With Rhenish brown coal.
167
coprocessing tests with run 4-7, applying recycle oil under almost identical conditions, similar results were observed, indicating that here the influence of solvent might be negligible. But with run 4-10, applying tetralin, a higher conversion of 20% and an increased oil yield of 10% were achieved over the previous tests. Runs 4-3 and 4-5 show that a once-through catalyst (Bayer red mud) is favourable in the liquefaction process for this lignite, reducing residue by 16% and increasing conversion by 16% and oil yield by 18%. In comparison with red mud a Mo/Ni-catalyst for coprocessing was very beneficial for the formation of naphtha, but increased the conversion by only 2%. The cross-checking experiments performed are successful for evaluating the hydroliquefaction potential of Shengli lignite and show that this lignite has a very high reactivity. Under normal conditions the optimum temperatures are at 420-440 ° C, for which a residence time of 30-60 min is appropriate. Bayer red mud is effective and also economical. This lignite may be chosen for further coprocessing testing.
Case two: Hydroliquefaction of Xian-Feng lignite Xian-Feng lignite is low in ash, average in volatiles, also low in sulfur and about normal in oxygen content. With an H/C-ratio of 0.85 it might be an acceptable liquefaction feedstock. From experience a regular sensitivity to temperature along with the demand for a catalyst can be expected, but the question whether the hydroliquefaction process depends strictly on H-transfer potential of solvents is yet open. Therefore, the following conditions were chosen for screening: standard catalyst, moderate temperature range from 380 to 440 ° C, residence time range from 15 to 60 min and sufficient pressure, but with variation in two coal-derived and one petroleum-derived solvent and also tetralin. The experimental results are compiled in Table 5. With normal slurry oils this lignite showed a striking tendency to the formation of char already at a moderate temperature of 410 ° C. Under the conditions applied the conversions obtained ranged from 50 to 65%, being 10-15% lower than those with Shengli lignite. In spite of increasing the initial H2 pressure from 9 MPa up to 12 MPa, the recombination reactions remained the main obstacle for converting the coal into liquid, because the conversion was not substantially enhanced and char in lump form was observed, but this should not lead to the conclusion that this lignite is less reactive. Run 5-1 at a low temperature of 380 ° C showed already a rather high n a p h t h a yield of ca. 20% with a total liquid yield of 45%, and a temperature increase of 30 K up to 410 ° C reduced residue only by 7%, but an increased naphtha yield of 13%. This observation is consistent with the results of supercritical extraction with toluene under 20 MPa pressure at 410 ° C, where an oil yield of 36% was obtained [7]. It might be recognized that a combination of thermal dissolution and destruc-
168 TABLE 5 Experimental results of Xian-Feng lignite No.
Reaction condition
H2-uptake (%)
Conversion (%)
Solvent
Catalyst
PH~ (MPa)
T (°C)
t (min)
5-1 5-2 5-3 5-4
RO RO RO RO
3 . 6 % B R M +0.6%Na2S 3 . 6 % B R M + 0.6%Na2S 3 . 6 % B R M + 0.6%Na2S 3.6%BRM+0.6%Na2S
9 9 12 12
380 410 435 435
60 60 15 60
0.93 1.41 1.35 1.81
50.6 57.4 54.2 65.1
5-5 5-6
AO A0
3.6%BRM +0.6%Na2S 3.6%BRM + 0.6%Na2S
9 9
410 435
60 15
1.49 1.49
50.7 46.4
5-7*
Tetralin
-
9
435
60
1.20
85.3
5-8 5-9
VRW VRW
3.6%BRM +0.6%Na2S 3.6%CMN÷0.6%S
12 12
440 440
30 30
1.81 2.52
57.4 54.9
Based on total feed 5-8 5-9 No.
1.0 1.27
---
Product distribution R %
G %
N %
O+A %
5-1 5-2 5-3 5-4
49.4 42.6 45.8 34.9
6.8 10.1 9.4 9.1
19.3 32.8 19.8 27.3
25.4 15.9 26.4 30.5
5-5 5-6
49.3 53.6
8.6 8.3
21.8 23.2
21.8 16.4
5-7
14.7
12.1
58.6(N+O)
15.8(A)
5-8 5-9
42.6 45.1
10.0 10.1
21.8 15.5
27.4 31.8
4.5 4.6
22.0 19.5
55.0 56.8
Based on total feed 5-8 5-9 *In autoclave B.
19.5 20.4
169
tion happens at ca. 400 ° C for this lignite and it needs rather more transferable hydrogen to stabilize radical fragments, even at moderate temperatures. This is demonstrated by run 5-7. Using tetralin under the conditions of 435 ° C, 9 MPa, 60 min and no catalyst addition, a high degree of conversion of 85% with a total oil yield of ca. 60% was obtained. Due to the shortage of transferable hydrogen the results of tests using anthracene oil were worse than those with recycle oil. In comparison with Shengli lignite in coprocessing runs, the conversion data of this lignite were lower by 10%, but higher by 5% than those from Rhenish brown coal in run 4-14. This study has shown that under conditions which promote hydrogenation reactions and suppress recombination reactions this lignite can be readily converted into liquids. A more detailed investigation is necessary to optimize this process for this lignite. At a higher hydrogen pressure and with a high active catalyst providing sulfur the oil yield might well exceed 50% at temperatures above 430 ° C. This must be examined further.
Case three: Hydroliquefaction of Yanzhou coal Yanzhou coal has an acceptable ash content, it is high in volatiles and very high in sulfur but has a rather low H/C-ratio of 0.81. From experience it is expected that the hydroliquefaction process of this coal will be sensitive to temperature but operable at moderate temperatures, will require average residence times, and will be normally dependent on a good coalderived solvent. Whether it is also sensitive to catalysts and whether low grade solvents are acceptable, these questions are still open. Therefore, the following conditions were chosen for screening: Temperature range 390-475°C, but standard residence time 30-60 min, moderate and higher initial H2 pressures 9 MPa and 11-12 MPa, wide variation of catalysts in anthracene oil for comparison but cross-checking against a petroleum VR. The experimental data are summarized in Table 6. To study the influence of the temperature two sets of experiments under equivalent conditions with RO and AO were performed. With RO, at a rather mild temperature of 410 °C for hydroliquefaction of bituminous coals, the conversion approached already 80% along with an oil yield of 36% but also a rather high asphaltene yield of 43%. An increase of 25 K up to 435°C reduced the residue by only 4% but substantially increased the oil yield by 12%. Because of the moderate initial hydrogen pressure applied and the rather small gas volume of ca. 65 ml in the autoclave the residue increased considerably with further temperature increase at 475 °C up to 55%, the asphaltene fraction in disproportionation reactions converted mostly into residue and gas. This indicates that at higher temperatures the hydrogenation reactions can no longer compete with regressive or recombination reactions.
170 TABLE 6 Experimental results of Yanzhou coal (a) No.
Reaction condition Solvent Catalyst
Pm (MPa)
H2-uptake
Conversion
(%)
(%)
T (°C)
t (rain)
9 9 9 9
410 435 430 475
60 60 60 60
1.76 2.36 2.11 1.84
79.5 83.7 68.0 44.7
6-1 6-2 6-3 6-4
RO RO RO RO
3.6%BRM + 0.6%Na2S 3.6%BRM + 0.6%Na2S 3.6%BRM + 0.6%Na~S 3.6%BRM+0.6%Na2S
6-5 ' 6-6 6-7 6-8 6-9
AO AO AO AO AO
2 %H1 .+ 1.2%FeSO4 + 0.6%Na2S 2%H1+ 1.2%FESO4 + 0.6%Na2S 2%H1 + 1.2%FESO4 + 0.6%Na2S 2%H1+ 1.2%FeSO4 + 0.6%Na2S 2%BRM + 1.2%FeSO4 + 0.6%Na2S
11 11 11 11 11
390 420 450 475 475
60 60 60 60 60
2.07 2.19 2.92 3.14 3.11
59.5 61.0 81.2 85.7 88.1
6-10 6-11 6-12 6-13
AO AO AO AO
2%BRM+l.2%FeSO4+0.6%Na2S 2%SRM+l.2%FeSO4+0.6%Na2S 2%CMN+0.6%S --
11 11 11 11
450 450 450 450
60 60 60 60
2.91 2.85 3.71 2.72
84.2 78.6 91.4 70.6
6-142 6-15 6-16 6-17 6-18 6-193
VRW VRW VRW VRW VRW VRW
3.6%BRM +0.6%Na2S 3.6%BM+0.6%Na~S 3.6%Mo/Ni+0.6%S 3.6%CMN +0.6%S ---
12 12 12 12 12 12
440 460 440 460 440 440
30 30 30 30 30 30
2.00 2.25 2.16 2.38 1.75 1.90
67.5 68.4 66.1 66.8 57.8 43.6
Based on total feed 6-14 6-15 6-16 6-17 6-18 6-19
1.12 1.44 1.19 1.49 1.02 1.10
m
m
B
~6-5 ~ 6-13 in autoclave B,otherwise in autoclave A. 26-14~6-19 all data on coal (d.m.f.) based are related to blank experiments only with VRW and by 440°C or 460°C. 36-19 Illinois No. 6 coal.
171 TABLE 6 (continued)
(b) No.
Product distribution (wt.%) R
G
N+O
A
O/A
6-1 6-2 6-3 6-4
20.5 16.3 32.0 55.3
2.4 5.1 8.7 13.4
36.2 48.4 49.6 31.6
42.7 32.6 11.8 1.5
0.85 1.48 4.20 21.10
6-5 6-6 6-7 6-8 6-9
40.5 39.0 18.8 14.3 11.9
8.3 8.7 8.4 13.1 11.7
11.2 15.4 29.7 10.0 47.4
42.1 39.1 46.0 65.7 32.1
0.27 0.39 0.65 0.15 1.48
6-10 6-11 6-12 6-13
15.8 21.4 8.6 29.4
9.4 10.0 5.7 9.1
45.0 16.7 57.9 24.1
32.7 54.8 31.5 40.1
1.38 0.30 1.84 0.60
R
G
N
O+A
2.6 6.7 4.3 5.1 4.0 2.2
20.4 9.5 14.5 25.3 0 7.5
46.5 54.5 49.5 38.8 55.6 35.8
1.7 3.9 2.5 3.2 2.3 4.9
21.3 24.3 18.9 30.9 12.5 22.7
61.6 55.4 62.7 48.9 65.6 58.0
6-14 6-15 6-16 6-17 6-18 6-19
32.5 31.6 33.9 33.2 42.2 56.4
On total feed 6-14 6-15 6-16 6-17 6-18 6-19
16.5 17.8 17.1 18.5 20.6 15.5
With a low grade solvent AO the coal conversion and gas yield increased with increasing temperature in the range between 390 and 475 ° C. From 420 to 450°C a m a x i m u m increase in conversion by 20% was observed. Further increase of the temperature up to 475 °C reduced still the residue by 4.5 % but led to an enhanced gas production of 4.7%. Although this solvent has a good potential for dissolving the coal and its products, in this reaction system there is a shortage of transferable hydrogen for the conversion of asphaltenes into oils.
172
Therefore, the asphaltene fraction always represented the greatest portion of converted coal. From the results mentioned, a regular sensitivity of this coal to temperatures was revealed. Under moderate severity rather high conversions in excess of 80% with ca. 50% oil yield were obtained. Extensive research has been performed in the area of coal liquefaction catalysts [8]. The question of interest is whether once through catalysts are active for this sulfur-rich coal. The runs 6-7 to 6-13, aiming at examination of the relative activity of iron-containing materials for hydroliquefaction were carried out under constant conditions using AO as solvent. Considering the high sulfur content (Stota14.14%, Spyr. 1.73% ) and no catalyst addition, a tolerable conversion of 70% was achieved, but with a low O/A-ratio of 0.6 only. The relative activity with regard to conversion and particularly to formation of oils is Co/Mo/Ni/Al203 > Bayer red mud > Hainan iron ore > Shandong red mud > no catalyst addition. Relying on the double functions of CMN and intrinsic pyrite, run 6-12 gave a m a x i m u m conversion of 91% with 57% oil yield. Bayer red mud showed a satisfactory activity, in comparison with Hainan ore (run 6-7) the conversion increased by 3% and still greater oil yield enhancing by 15% was obtained. With Shandong red mud the conversion obtained of 79% is not low. But the asphaltene portion is too high. Comparing run 6-8 using Hainan ore with run 6-9 applying BRM, a substantial difference in O/A-ratio was also observed. It is demonstrated that the conversion of asphaltenes into oils requires rather active catalysts to force hydrogen transfer and to stabilize ruptured fragments and prevent their recombination. The rather high activity of BRM might be referred to the rational combination of effective components, e.g. Fe203, TiO2, A1203 etc. Hainan iron ore has only Fe203 as its most important component. Shandong red mud contains only 7% Fe203 and too high a CaO content of 44% which is normally considered an inhibitor for hydrogenation. Cross-checking tests for coprocessing of Yanzhou coal with a petroleum vacuum residue were also performed focusing on the reactivity of this coal under the conditions applied. Changes in temperature and use of catalysts were examined to determine whether high coal conversion and a desirable range of products could be achieved, yielding informative data for process application. The runs 6-14 to 6-17 show that the coal conversion stayed almost constant at ca. 67% in spite of temperature or catalyst changes, but striking differences in naphtha yields were observed varying between 18.9 and 30.9% based on total feed and between 9.5% and 25.3% based on coal (d.m.f.). In comparison to operation without catalyst, BRM increased coal conversion by 10% and naphtha yield by 9% based on total feed or 20% related to coal. In the case with CMN catalyst operation an increase of 9% for conversion and 6% or 14.5% for naphtha yields were obtained. The influence of catalysts on naphtha yields were different with a different temperature. This should be further investi-
173 gated. Comparing run 6-18 with 6-19 using Illinois coal a striking increase of 14% in conversion was observed, which is consistent with current literature [9,101. From the results quoted above the hydrogenation reactivity of Yanzhou coal could be generally evaluated. As expected, this coal reveals rather satisfactory liquefaction behaviour not only in coal derived slurry oils, but also in petroleum vacuum residue. Bayer red mud as a catalyst is appropriate. SUMMARY ( 1 ) With a total of fewer than 20 cross-checking tests with appropriate variation in temperature, hydrogen pressure, residence time, solvents and catalysts the hydroliquefaction potential of three typical Chinese coals could be evaluated satisfactorily. (2) Shengli lignite has a rather high reactivity in hydroliquefaction and also in coprocessing. Its sensitivity to temperature and residence time is normal. Bayer red mud is an effective catalyst for this lignite. (3) Xian-Feng lignite is more sensitive than Shengli lignite to temperature and H-transfer potential. A more detailed investigation is necessary to optimize its conversion process. It could possibly be taken as feedstock for hydroliquefaction, particularly for coprocessing. (4) Yanzhou coal is very rich in sulfur and has a high reactivity for converting into liquids. In the normal range of temperature, time and H-transfer potential it is not very sensitive. Bayer red mud catalyst shows a rather high activity for this coal. ACKNOWLEDGEMENTS This work has been supported from cooperative research grant 1/60 122 by Stiftung Volskwagenwerk, Hannover and by Chinese Nature Science Fund. The authors are grateful to both of them.
REFERENCES 1 Strobel, B., Friedrich, F., KSlling, G., 1982. Das Verhalten verschiedener Kohlen bei der Hydrierung. VortragsverSffentlichungen. Haus der Technik, Essen, 453: 47. 2 Oelert,H.H., Dlugosch-Meyn,S., Morys-Kolm, M., 1985. Evaluation of the liquefaction potential of lignites. ISBN 3-9800765-6-3, TU Clausthal, Vol. 3. 3 Romey,I., Paul, P.F.M. and Imarisio, G., 1987. Synthetic Fuels from Coal. Graham & Trotman (published for the Commission of the European Communities), London, p. 259. 4 Schmidt, H., 1986. LSsungsmitteleinfluss auf die Steinkohlenhydrierung. Dissertation, TU Clausthal, p. 22. 5 Derbyshire,F.J., Davis, A. and Lin, R., 1986. Coal liquefaction by Molybdenum catalysed hydrogenation in the absence of solvent, Fuel Processing Technol., 12: 127.
174 6
Gao, J.S., Zhang, P.F. and Oelert, H.H., 1989. Examination of the hydroliquefaction behaviours of Chinese lignites. Fuel Sci. Technol. Int., 7 (3): 293. 7 Institute of Coal Chemistry, Yunnan, 1986. Report of Research projects (unpublished), Investigation on the supercritical extraction of Yunnan lignites (Chinese), Vol. 20. 8 Charcosset, H., Bacaud, R. and Besson, M., 1986. On the chemical effects on catalysts in the direct liquefaction of coal. Fuel Processing Technol., 12: 189. 9 Curtis, L.W., Guin, J.A., Pass, M.C., 1987. Coprocessing of coal with heavy petroleum crudes and residuea. Fuel Sci. Technol. Int., 5: 245. 10 Zhang, P.F., Gao, J.S. and Oelert, H.H., 1988. Untersuchungen zum hydrierenden Verfltissigung der chinesischen Kohlen. Erdiil, Erdgas & Kohle, 11: 470.
161
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
E v a l u a t i o n of the H y d r o l i q u e f a c t i o n P o t e n t i a l of Chinese Coals: T h r e e Case Studies JINSHENG GAO
East China University of Chem. Technology, 130 Meilong Road, 20037 Shanghai (P.R. China) PEIFANG ZHANG* and HANS HENNING OELERT
TU Clausthal, Erzstr. 18, D-3392 Clausthal-Zellerfield (F.R.G.) (Received October 10th, 1988; accepted December 8th, 1988)
ABSTRACT In bench-scale autoclaves the hydroliquefaction cross-checking tests of three typical Chinese low rank coals were performed under different conditions. The methods of coal evaluation for hydrogenation reactivity are discussed, focused upon the influence of important parameters - temperature, pressure, residence time, solvent and catalyst. The experimental results indicate that with fewer than 20 cross-checking tests by appropriate parameter variations the hydroliquefaction behaviour of the coals used could be evaluated rather satisfactorily. Shengli lignite and Yanzhou HV-bituminous coal have a high reactivity for liquefaction processing. With coal-derived slurry oil under not too severe conditions a coal conversion of ca. 80% and an oil yield of more than 50% were obtained. Xianfeng lignite is younger and therefore more sensitive than Shengli lignite. By optimizing the process parameters, an oil yield of more than 50% could possibly be attained. This paper should provide information of interest for a perspective on coal liquefaction in China.
INTRODUCTION
For hydroliquefaction the reactivity of coals can be empirically, but scarcely rationally estimated, e.g. for hard coals by the relationship between coal conversion and reflectance [1] and for lignites by precalculation of conversion from analytical data [2]. But each coal must be tested individually and step by step, at first by laboratory screening, then by technical tests. The important parameters to be examined are as follows [3]: (1) temperature, because coal hydrogenation is directly related to thermal fragmentation and recombination, (2) pressure, related to H-availability, (3) residence time, because of kinetics of parallel and consecutive reactions, Present address: Dow Stade GmbH, Btitzflethersand, Postfach 1120, D-2160 Stade (F.R.G.).
0378-3820/89/$03.50
© 1989 Elsevier Science Publishers B.V.
162
(4) solvent or slurry oil, related to coal solubility, thermal destruction of solvent and H-transfer potential from solvent. (5) catalyst, because of H-transfer potential and in situ upgrading of primary products. Points (1)-(3) are major physical parameters, (4) and (5) are equally important, but are more chemically oriented. If all 5 parameters are to be investigated by complete cross-checking, there will be a minimum of 32 tests necessary with one catalyst and 360 tests for full scale testing. This would be almost impossible to implement, and very expensive. Therefore, only a limited amount of testing based on experience for each coal was undertaken. As a case study this paper will discuss hydroliquefaction evaluation for three Chinese typical low-rank coals, obtained from important mines in the provinces of Yunnan, Inner Mongolia and Shandong. It should provide interesting information for a perspective on coal hydroliquefaction in China. EXPERIMENTAL
Feedstocks
Three coal samples were received from mines, but not necessarily representative for a whole mining area. Basic analytical data are compiled in Table 1. The slurry oils used were a recycle oil (RO) from a pilot plant, anthracene TABLE1 Analytical data of coal samples Coal
Origin
Water (wt.%)
Ash (w.f.) (wt.%)
Volatile (d.m.f.) matter (wt.%)
1. Xian-Feng 2. Shengli 3. Yanzhou
Yunnan Inner Mongolia Shandong
20.0 7.61" 1.90
3.23 18.72 8.40
48.44 45.39 44.74
Coal
1. Xiang-Feng 2. Shengli 3. Yanzhou *Predried.
Elemental analysis (d.m.f., wt.% ) C
H
N
S
S (total)
O (diff. )
H/C
69.63 71.05 79.90
4.94 4.91 5.40
2.14 0.78 1.22
0.43 0.68 2.14
0.63 1.08 4.14
22.86 22.58 11.34
0.85 0.83 0.81
163 TABLE 2 Analytical data of slurry oils Slurry oil
l~I (g/mol)
1. RO 2. AO 3. VRW
244 175 1410
Slurry oil
Asphaltene (wt.%)
1. RO
2. AO 3. VRW
Elemental analysis (d.m.f., wt.% ) C
H
N
S
H/C
88.40 91.77 86.52
10.40 6.24 11.44
0.32 0.44 0.59
0.78 0.56 1.45
1.40 0.81 1.58
Viscosity/(mm2/s)
Conradson test (wt.%)
4.0 3.5 2.1
0.3 2.6 21.7
50°C
100 °C
14.5 7.0 4300*
3.4 5.0 700
*Kinematic viscosity measured at 70 °C. TABLE 3 Composition of catalysts (wt.%) Catalyst*
Fe203
Si02
T i O 2 A1203 CaO
1. BRM 2. SRM 3. HI
33.96 7.15 71.06
12.80 8 . 6 8 20.28 2.45 2 2 . 6 0 0.53
4. CMN
Co 1.6-2.3, Mo 10-14, Ni 5-6.5, A120377-84
32.23 20.40 2.83
MgO
3.22 0.40 4 4 . 0 7 1.33 0.70 0.55
Na20
K20
CuO
NiO
7.26 1.71 0.03
0.08 0.36 0.64
0.39 -0.39
0.98 0.33 0.64
*BRM {Bayer red mud), SRM (Shandong red mud), HI (Hainan iron ore), CMN (Co/Mo/Ni/ A1203-catalyst). oil (AO) a n d a v a c u u m residue ( V R W ) . T h e i r a n a l y t i c a l d a t a are c o m p i l e d in T a b l e 2. F u r t h e r e x p e r i m e n t s were m a d e w i t h tetralin. T h e applied c a t a l y s t s a n d t h e i r c o m p o s i t i o n are s h o w n in T a b l e 3.
Autoclave T h e e x p e r i m e n t s were p e r f o r m e d in two t y p e s of autoclaves: (A) a rockingtype f r o m A m i n c o Corp., U S A , u s i n g a s h a k e f r e q u e n c y o f 1 H z a n d fast h e a t i n g a n d cooling at a rate of 15 K / m i n . (B) a stirred t y p e f r o m H a a g e G m b H , F R G , u s i n g a stirring speed of 500 r p m a n d h e a t i n g or cooling at a rate of 10 K / m i n .
164
During the experiments the temperature was varied, and the pressure was recorded. At reaction condition temperature deviation was less t h a n _+2 K.
Experimental procedures All experiments were made with coal (d.m.f.) : slurry oil ratio of 1 : 1.6 in autoclave A and 1 : 3.3 in autoclave B, prepressurised with H2 to the given initial pressure. After cooling, the product gases (G) were released into a plastic bag and analyzed by GC. The non-gaseous products were separated into residue (R, benzene insoluble), asphaltenes (A, benzene soluble but cyclohexane insoluble), product oil and slurry oil (O) remained together, containing more or less reaction water. The total mass balance for each experiment was checked; those with a mass balance >/97% were considered as valid. Calculation methods for H2-consumption; coal conversion and product distribution (G, R, A and O) are given in detail elsewhere [2,4 ]. All data mentioned above were related to coal (d.m.f.), for coprocessing in VRW the data were in addition related to total feed. For these tests a portion of non-gaseous products was taken directly from the autoclave into the distillation flask and weighed, then water and naphtha (light oil, b.p. 200 °C) were vacuum distilled off at 95°C and 40 mbar. Control experiments, using slurry oil only, were also performed. From experience relative m a x i m u m errors for different products portions are about + 2% for coal conversion; + 1% for R; + 1% for A; __2% for O and N; and _+0.2% for H2-consumption (2). RESULTS AND DISCUSSION
Case one: hydroliquefaction of Shengli lignite Shengli lignite is characterized by a moderate a m o u n t of volatile matter and a rather low H/C-ratio of 0.83, but rich in ash. Its oxygen content is in a normal range. From experience it is expected that this lignite will be sensitive to temperature and will be at risk at high temperatures; it will also be sensitive to residence time and require standard catalyst and H-transfer potential. Therefore, the following parameter variations were selected for screening: Standard catalyst in standard recycle oil; Full range of temperatures from 380 to 460 ° C; Normal variation of residence time from 0 to 60 min and three types of solvents, from recycle oil through petroleum vacuum residue to tetralin under sufficient initial hydrogen pressures.
165
The experimental results are compiled in Table 4. From experiments 4-1 to 4-4 with a variation from 380 to 460°C, the sensitivity for this type of lignite is observed. The first increase from 380 to 410 ° C increased conversion by 14% and oil yield by 8%, reducing residue by 14%. At the low temperature of 380°C the conversion achieved was not high, but a rather satisfactory oil yield of 38% with an O/A-ratio of 3.13 and an O/coal conversion-ratio of 0.67 was already obtained. This indicates that the average activation energy of the reactions involved in the formation of extractable liquids is lower for low rank coals t h a n that for moderate and high rank coals, which is also consistent with the general and long-accepted understanding of the structural character of low rank coals, which comprise more low molecular weight substances and few condensed structure units in the crosslinked macromolecular network [5]. Between 410 and 435 °C there is a level maximum range of ca. 74% conversion with an oil yield of 48% and a constant asphaltene yield of 15%. From 435°C to 460°C the conversion and also the oil yield reduced drastically by 24%, residue increased correspondingly by 25% and gas production rose apparently from 12.8% up to 16.8%. It may be recognized that this reaction system at a high temperature of 460 ° C can no longer inhibit the regressive reactions, leading to more residue and gases. The experiments 4-6 to 4-8 were performed under the following conditions: 435 ° C, initial H2-pressure 11 MPa, standard slurry oil and catalyst. T h e y show that a short residence time up to 30 min has a high impact on coal dissolution and liquefaction, reducing residue by 15% and asphaltenes by 4% and thus increasing oil yield by 18% to 47.5%. For a longer residence time from 30 to 45 min only a moderate influence was observed, decreasing residue by a further 5% and also increasing oil yield by 5% but with no impact on asphaltenes, which remain constant at about 10%. In comparison to recycle oil, tetralin, a standard H-donor solvent, favoured the hydroliquefaction for this lignite. Though no catalyst was added, at a nominal reaction time of 0 min a rather high conversion of 77% with an oil yield of 47% was already obtained, which corresponds to the results from experiment 4-2 with RO at 60 min. Prolonging the residence time up to 30 min reduces the residue by 9% with an increase of oil yield by 10%. Between 30 and 60 min the influence on coal conversion became negligible, because at 30 min 86% conversion was already reached, but asphaltenes were further hydrocracked, converting into oil and gas. These results indicate that the residence time has a general influence on coal conversion, H2-consumption and particularly the product distribution. The experiments 4-12 and 4-13 come under the heading of coprocessing. U n d e r the conditions applied a rather satisfactory coal conversion of ca. 67% with relatively high n a p h t h a yields of 23% to 31% (on coal) or 22% to 25% (on total feed) were obtained, exceeding those from Rhein brown coal under the same conditions (experiment 4-14 and the literature [6] ). Comparing the
166 TABLE 4 Experimental results of Shengli lignite (based on coal d.m.f. ) (a) No.
Reaction condition Solvent
Catalyst
PH2 (MPa)
4-1 4-2 4-3 4-4 4-5
RO RO RO RO RO
3.6%BRM + 0.6%Na2S 3.6%BRM+0.6%Na2S 3.6%BRM+0.6%Na2S 3 . 6 % B R M + 0.6%Na2S
4-6 4-7 4-8
RO RO RO
3.6%BRM÷0.6%Na2S 3.6%BRM+0.6%Na2S 3.6%BRM+0.6%Na2S
4-9" 4-10" 4-11"
tetralin tetralin tetralin
----
4-12 4-13 4-14"*
VRW VRW VRW
3.6%BRM +0.6%Na2S 3.6%CMN÷0.6%S
H2-uptake (%)
Conversion (%)
T (°C)
t (min)
9 9 9 9 9
380 410 435 460 435
60 60 60 60 60
1.30 1.80 2.14 1.96 2.20
57.5 71.8 74.2 49.7 57.9
11 11 11
435 435 435
0 30 45
0.84 1.80 1.90
51.6 66.9 71.6
9 9 9
410 410 410
0 30 60
0.54 1.20 1.54
77.1 86.2 86.7
12 12 12
440 440 440
30 30 30
2.04 2.52 0.74
66.3 68.5 50.4
Based on total feed 4-12 4-13 4-14"*
1.04 1.21 0.59
(b) No.
Product distribution (wt.%) R
G
N+O
A
O/A
4-1 4-2 4-3 4-4 4-5
42.5 28.2 25.8 50.3 42.1
8.4 11.7 12.8 16.8 13.7
38.2 46.3 48.6 24.2 30.1
12.2 15.6 14.9 10.7 16.3
3.13 2.97 3.92 2.26 1.85
4-6 4-7 4-8
48.4 33.1 28.4
9.5 11.0 12.1
28.9 47.5 52.1
14.0 10.2 9.3
2.06 4.66 5.60
4-9* 4-10" 4-11"
22.9 13.8 13.3
10.1 11.0 13.6
46.9 57.0 60.8
20.6 19.4 13.8
2.27 2.89 4.41
R
G
N
O+A
33.7 31.5 49.6
10.7 9.1 9.2
23.2 31.4 14.7
34.4 30.5 27.2
----
22.4 25.3 19.2
58.9 57.6 54.8
----
4-12 4-13 4-14"*
Based on total feed 4-12 4-13 4-14"*
15.2 14.4 22.3
4.5 3.9 4.3
*In autoclave B, otherwise in autoclave A. **With Rhenish brown coal.
167
coprocessing tests with run 4-7, applying recycle oil under almost identical conditions, similar results were observed, indicating that here the influence of solvent might be negligible. But with run 4-10, applying tetralin, a higher conversion of 20% and an increased oil yield of 10% were achieved over the previous tests. Runs 4-3 and 4-5 show that a once-through catalyst (Bayer red mud) is favourable in the liquefaction process for this lignite, reducing residue by 16% and increasing conversion by 16% and oil yield by 18%. In comparison with red mud a Mo/Ni-catalyst for coprocessing was very beneficial for the formation of naphtha, but increased the conversion by only 2%. The cross-checking experiments performed are successful for evaluating the hydroliquefaction potential of Shengli lignite and show that this lignite has a very high reactivity. Under normal conditions the optimum temperatures are at 420-440 ° C, for which a residence time of 30-60 min is appropriate. Bayer red mud is effective and also economical. This lignite may be chosen for further coprocessing testing.
Case two: Hydroliquefaction of Xian-Feng lignite Xian-Feng lignite is low in ash, average in volatiles, also low in sulfur and about normal in oxygen content. With an H/C-ratio of 0.85 it might be an acceptable liquefaction feedstock. From experience a regular sensitivity to temperature along with the demand for a catalyst can be expected, but the question whether the hydroliquefaction process depends strictly on H-transfer potential of solvents is yet open. Therefore, the following conditions were chosen for screening: standard catalyst, moderate temperature range from 380 to 440 ° C, residence time range from 15 to 60 min and sufficient pressure, but with variation in two coal-derived and one petroleum-derived solvent and also tetralin. The experimental results are compiled in Table 5. With normal slurry oils this lignite showed a striking tendency to the formation of char already at a moderate temperature of 410 ° C. Under the conditions applied the conversions obtained ranged from 50 to 65%, being 10-15% lower than those with Shengli lignite. In spite of increasing the initial H2 pressure from 9 MPa up to 12 MPa, the recombination reactions remained the main obstacle for converting the coal into liquid, because the conversion was not substantially enhanced and char in lump form was observed, but this should not lead to the conclusion that this lignite is less reactive. Run 5-1 at a low temperature of 380 ° C showed already a rather high n a p h t h a yield of ca. 20% with a total liquid yield of 45%, and a temperature increase of 30 K up to 410 ° C reduced residue only by 7%, but an increased naphtha yield of 13%. This observation is consistent with the results of supercritical extraction with toluene under 20 MPa pressure at 410 ° C, where an oil yield of 36% was obtained [7]. It might be recognized that a combination of thermal dissolution and destruc-
168 TABLE 5 Experimental results of Xian-Feng lignite No.
Reaction condition
H2-uptake (%)
Conversion (%)
Solvent
Catalyst
PH~ (MPa)
T (°C)
t (min)
5-1 5-2 5-3 5-4
RO RO RO RO
3 . 6 % B R M +0.6%Na2S 3 . 6 % B R M + 0.6%Na2S 3 . 6 % B R M + 0.6%Na2S 3.6%BRM+0.6%Na2S
9 9 12 12
380 410 435 435
60 60 15 60
0.93 1.41 1.35 1.81
50.6 57.4 54.2 65.1
5-5 5-6
AO A0
3.6%BRM +0.6%Na2S 3.6%BRM + 0.6%Na2S
9 9
410 435
60 15
1.49 1.49
50.7 46.4
5-7*
Tetralin
-
9
435
60
1.20
85.3
5-8 5-9
VRW VRW
3.6%BRM +0.6%Na2S 3.6%CMN÷0.6%S
12 12
440 440
30 30
1.81 2.52
57.4 54.9
Based on total feed 5-8 5-9 No.
1.0 1.27
---
Product distribution R %
G %
N %
O+A %
5-1 5-2 5-3 5-4
49.4 42.6 45.8 34.9
6.8 10.1 9.4 9.1
19.3 32.8 19.8 27.3
25.4 15.9 26.4 30.5
5-5 5-6
49.3 53.6
8.6 8.3
21.8 23.2
21.8 16.4
5-7
14.7
12.1
58.6(N+O)
15.8(A)
5-8 5-9
42.6 45.1
10.0 10.1
21.8 15.5
27.4 31.8
4.5 4.6
22.0 19.5
55.0 56.8
Based on total feed 5-8 5-9 *In autoclave B.
19.5 20.4
169
tion happens at ca. 400 ° C for this lignite and it needs rather more transferable hydrogen to stabilize radical fragments, even at moderate temperatures. This is demonstrated by run 5-7. Using tetralin under the conditions of 435 ° C, 9 MPa, 60 min and no catalyst addition, a high degree of conversion of 85% with a total oil yield of ca. 60% was obtained. Due to the shortage of transferable hydrogen the results of tests using anthracene oil were worse than those with recycle oil. In comparison with Shengli lignite in coprocessing runs, the conversion data of this lignite were lower by 10%, but higher by 5% than those from Rhenish brown coal in run 4-14. This study has shown that under conditions which promote hydrogenation reactions and suppress recombination reactions this lignite can be readily converted into liquids. A more detailed investigation is necessary to optimize this process for this lignite. At a higher hydrogen pressure and with a high active catalyst providing sulfur the oil yield might well exceed 50% at temperatures above 430 ° C. This must be examined further.
Case three: Hydroliquefaction of Yanzhou coal Yanzhou coal has an acceptable ash content, it is high in volatiles and very high in sulfur but has a rather low H/C-ratio of 0.81. From experience it is expected that the hydroliquefaction process of this coal will be sensitive to temperature but operable at moderate temperatures, will require average residence times, and will be normally dependent on a good coalderived solvent. Whether it is also sensitive to catalysts and whether low grade solvents are acceptable, these questions are still open. Therefore, the following conditions were chosen for screening: Temperature range 390-475°C, but standard residence time 30-60 min, moderate and higher initial H2 pressures 9 MPa and 11-12 MPa, wide variation of catalysts in anthracene oil for comparison but cross-checking against a petroleum VR. The experimental data are summarized in Table 6. To study the influence of the temperature two sets of experiments under equivalent conditions with RO and AO were performed. With RO, at a rather mild temperature of 410 °C for hydroliquefaction of bituminous coals, the conversion approached already 80% along with an oil yield of 36% but also a rather high asphaltene yield of 43%. An increase of 25 K up to 435°C reduced the residue by only 4% but substantially increased the oil yield by 12%. Because of the moderate initial hydrogen pressure applied and the rather small gas volume of ca. 65 ml in the autoclave the residue increased considerably with further temperature increase at 475 °C up to 55%, the asphaltene fraction in disproportionation reactions converted mostly into residue and gas. This indicates that at higher temperatures the hydrogenation reactions can no longer compete with regressive or recombination reactions.
170 TABLE 6 Experimental results of Yanzhou coal (a) No.
Reaction condition Solvent Catalyst
Pm (MPa)
H2-uptake
Conversion
(%)
(%)
T (°C)
t (rain)
9 9 9 9
410 435 430 475
60 60 60 60
1.76 2.36 2.11 1.84
79.5 83.7 68.0 44.7
6-1 6-2 6-3 6-4
RO RO RO RO
3.6%BRM + 0.6%Na2S 3.6%BRM + 0.6%Na2S 3.6%BRM + 0.6%Na~S 3.6%BRM+0.6%Na2S
6-5 ' 6-6 6-7 6-8 6-9
AO AO AO AO AO
2 %H1 .+ 1.2%FeSO4 + 0.6%Na2S 2%H1+ 1.2%FESO4 + 0.6%Na2S 2%H1 + 1.2%FESO4 + 0.6%Na2S 2%H1+ 1.2%FeSO4 + 0.6%Na2S 2%BRM + 1.2%FeSO4 + 0.6%Na2S
11 11 11 11 11
390 420 450 475 475
60 60 60 60 60
2.07 2.19 2.92 3.14 3.11
59.5 61.0 81.2 85.7 88.1
6-10 6-11 6-12 6-13
AO AO AO AO
2%BRM+l.2%FeSO4+0.6%Na2S 2%SRM+l.2%FeSO4+0.6%Na2S 2%CMN+0.6%S --
11 11 11 11
450 450 450 450
60 60 60 60
2.91 2.85 3.71 2.72
84.2 78.6 91.4 70.6
6-142 6-15 6-16 6-17 6-18 6-193
VRW VRW VRW VRW VRW VRW
3.6%BRM +0.6%Na2S 3.6%BM+0.6%Na~S 3.6%Mo/Ni+0.6%S 3.6%CMN +0.6%S ---
12 12 12 12 12 12
440 460 440 460 440 440
30 30 30 30 30 30
2.00 2.25 2.16 2.38 1.75 1.90
67.5 68.4 66.1 66.8 57.8 43.6
Based on total feed 6-14 6-15 6-16 6-17 6-18 6-19
1.12 1.44 1.19 1.49 1.02 1.10
m
m
B
~6-5 ~ 6-13 in autoclave B,otherwise in autoclave A. 26-14~6-19 all data on coal (d.m.f.) based are related to blank experiments only with VRW and by 440°C or 460°C. 36-19 Illinois No. 6 coal.
171 TABLE 6 (continued)
(b) No.
Product distribution (wt.%) R
G
N+O
A
O/A
6-1 6-2 6-3 6-4
20.5 16.3 32.0 55.3
2.4 5.1 8.7 13.4
36.2 48.4 49.6 31.6
42.7 32.6 11.8 1.5
0.85 1.48 4.20 21.10
6-5 6-6 6-7 6-8 6-9
40.5 39.0 18.8 14.3 11.9
8.3 8.7 8.4 13.1 11.7
11.2 15.4 29.7 10.0 47.4
42.1 39.1 46.0 65.7 32.1
0.27 0.39 0.65 0.15 1.48
6-10 6-11 6-12 6-13
15.8 21.4 8.6 29.4
9.4 10.0 5.7 9.1
45.0 16.7 57.9 24.1
32.7 54.8 31.5 40.1
1.38 0.30 1.84 0.60
R
G
N
O+A
2.6 6.7 4.3 5.1 4.0 2.2
20.4 9.5 14.5 25.3 0 7.5
46.5 54.5 49.5 38.8 55.6 35.8
1.7 3.9 2.5 3.2 2.3 4.9
21.3 24.3 18.9 30.9 12.5 22.7
61.6 55.4 62.7 48.9 65.6 58.0
6-14 6-15 6-16 6-17 6-18 6-19
32.5 31.6 33.9 33.2 42.2 56.4
On total feed 6-14 6-15 6-16 6-17 6-18 6-19
16.5 17.8 17.1 18.5 20.6 15.5
With a low grade solvent AO the coal conversion and gas yield increased with increasing temperature in the range between 390 and 475 ° C. From 420 to 450°C a m a x i m u m increase in conversion by 20% was observed. Further increase of the temperature up to 475 °C reduced still the residue by 4.5 % but led to an enhanced gas production of 4.7%. Although this solvent has a good potential for dissolving the coal and its products, in this reaction system there is a shortage of transferable hydrogen for the conversion of asphaltenes into oils.
172
Therefore, the asphaltene fraction always represented the greatest portion of converted coal. From the results mentioned, a regular sensitivity of this coal to temperatures was revealed. Under moderate severity rather high conversions in excess of 80% with ca. 50% oil yield were obtained. Extensive research has been performed in the area of coal liquefaction catalysts [8]. The question of interest is whether once through catalysts are active for this sulfur-rich coal. The runs 6-7 to 6-13, aiming at examination of the relative activity of iron-containing materials for hydroliquefaction were carried out under constant conditions using AO as solvent. Considering the high sulfur content (Stota14.14%, Spyr. 1.73% ) and no catalyst addition, a tolerable conversion of 70% was achieved, but with a low O/A-ratio of 0.6 only. The relative activity with regard to conversion and particularly to formation of oils is Co/Mo/Ni/Al203 > Bayer red mud > Hainan iron ore > Shandong red mud > no catalyst addition. Relying on the double functions of CMN and intrinsic pyrite, run 6-12 gave a m a x i m u m conversion of 91% with 57% oil yield. Bayer red mud showed a satisfactory activity, in comparison with Hainan ore (run 6-7) the conversion increased by 3% and still greater oil yield enhancing by 15% was obtained. With Shandong red mud the conversion obtained of 79% is not low. But the asphaltene portion is too high. Comparing run 6-8 using Hainan ore with run 6-9 applying BRM, a substantial difference in O/A-ratio was also observed. It is demonstrated that the conversion of asphaltenes into oils requires rather active catalysts to force hydrogen transfer and to stabilize ruptured fragments and prevent their recombination. The rather high activity of BRM might be referred to the rational combination of effective components, e.g. Fe203, TiO2, A1203 etc. Hainan iron ore has only Fe203 as its most important component. Shandong red mud contains only 7% Fe203 and too high a CaO content of 44% which is normally considered an inhibitor for hydrogenation. Cross-checking tests for coprocessing of Yanzhou coal with a petroleum vacuum residue were also performed focusing on the reactivity of this coal under the conditions applied. Changes in temperature and use of catalysts were examined to determine whether high coal conversion and a desirable range of products could be achieved, yielding informative data for process application. The runs 6-14 to 6-17 show that the coal conversion stayed almost constant at ca. 67% in spite of temperature or catalyst changes, but striking differences in naphtha yields were observed varying between 18.9 and 30.9% based on total feed and between 9.5% and 25.3% based on coal (d.m.f.). In comparison to operation without catalyst, BRM increased coal conversion by 10% and naphtha yield by 9% based on total feed or 20% related to coal. In the case with CMN catalyst operation an increase of 9% for conversion and 6% or 14.5% for naphtha yields were obtained. The influence of catalysts on naphtha yields were different with a different temperature. This should be further investi-
173 gated. Comparing run 6-18 with 6-19 using Illinois coal a striking increase of 14% in conversion was observed, which is consistent with current literature [9,101. From the results quoted above the hydrogenation reactivity of Yanzhou coal could be generally evaluated. As expected, this coal reveals rather satisfactory liquefaction behaviour not only in coal derived slurry oils, but also in petroleum vacuum residue. Bayer red mud as a catalyst is appropriate. SUMMARY ( 1 ) With a total of fewer than 20 cross-checking tests with appropriate variation in temperature, hydrogen pressure, residence time, solvents and catalysts the hydroliquefaction potential of three typical Chinese coals could be evaluated satisfactorily. (2) Shengli lignite has a rather high reactivity in hydroliquefaction and also in coprocessing. Its sensitivity to temperature and residence time is normal. Bayer red mud is an effective catalyst for this lignite. (3) Xian-Feng lignite is more sensitive than Shengli lignite to temperature and H-transfer potential. A more detailed investigation is necessary to optimize its conversion process. It could possibly be taken as feedstock for hydroliquefaction, particularly for coprocessing. (4) Yanzhou coal is very rich in sulfur and has a high reactivity for converting into liquids. In the normal range of temperature, time and H-transfer potential it is not very sensitive. Bayer red mud catalyst shows a rather high activity for this coal. ACKNOWLEDGEMENTS This work has been supported from cooperative research grant 1/60 122 by Stiftung Volskwagenwerk, Hannover and by Chinese Nature Science Fund. The authors are grateful to both of them.
REFERENCES 1 Strobel, B., Friedrich, F., KSlling, G., 1982. Das Verhalten verschiedener Kohlen bei der Hydrierung. VortragsverSffentlichungen. Haus der Technik, Essen, 453: 47. 2 Oelert,H.H., Dlugosch-Meyn,S., Morys-Kolm, M., 1985. Evaluation of the liquefaction potential of lignites. ISBN 3-9800765-6-3, TU Clausthal, Vol. 3. 3 Romey,I., Paul, P.F.M. and Imarisio, G., 1987. Synthetic Fuels from Coal. Graham & Trotman (published for the Commission of the European Communities), London, p. 259. 4 Schmidt, H., 1986. LSsungsmitteleinfluss auf die Steinkohlenhydrierung. Dissertation, TU Clausthal, p. 22. 5 Derbyshire,F.J., Davis, A. and Lin, R., 1986. Coal liquefaction by Molybdenum catalysed hydrogenation in the absence of solvent, Fuel Processing Technol., 12: 127.
174 6
Gao, J.S., Zhang, P.F. and Oelert, H.H., 1989. Examination of the hydroliquefaction behaviours of Chinese lignites. Fuel Sci. Technol. Int., 7 (3): 293. 7 Institute of Coal Chemistry, Yunnan, 1986. Report of Research projects (unpublished), Investigation on the supercritical extraction of Yunnan lignites (Chinese), Vol. 20. 8 Charcosset, H., Bacaud, R. and Besson, M., 1986. On the chemical effects on catalysts in the direct liquefaction of coal. Fuel Processing Technol., 12: 189. 9 Curtis, L.W., Guin, J.A., Pass, M.C., 1987. Coprocessing of coal with heavy petroleum crudes and residuea. Fuel Sci. Technol. Int., 5: 245. 10 Zhang, P.F., Gao, J.S. and Oelert, H.H., 1988. Untersuchungen zum hydrierenden Verfltissigung der chinesischen Kohlen. Erdiil, Erdgas & Kohle, 11: 470.