Organic Chemistry of Coal - American Chemical Society

15 Hydrotreatment of Coal with AlCl /HCl and Other 3

Downloaded by NORTH CAROLINA STATE UNIV on October 19, 2012 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0071.ch015

Strong Acid Media J. Y. LOW

and D. S. ROSS

SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025

Most current processes for upgrading coal to cleaner fuels require stringent reaction conditions of high temperatures and pressure. Less severe reaction conditions are needed to make coal upgrading economically feasible. The objective of this work was to investigate catalyst systems for upgrading coal to clean fuels under moderated conditions. In this work, homogeneous acid catalysts are of particular interest because they allow intimate contact with the coal and are not liable to coal ash founding. The most common homogeneous catalysts studied i n coal upgrading belong to the general class of molten salt catalyst (1-5) and include halide salts of antimony, bismuth, aluminum, and many of the transition metals. Most often, these molten salts have been studied at high temperature and i n massive excess (1-5). We have performed a systematic study of the use of some of these molten salts as homogeneous acid catalysts for upgrading of coal at relatively low temperatures and i n moderate quantities. In our i n i t i a l work to establish relatively mild reaction conditions that would still give relatively good conversions, we conducted a series of experiments to determine the role of HCl, A1C1 , and H i n coal hydrocracking. We examined the effects of temperature and residence time, studied catalyst/coal weight ratios of 1/1 to 3/1, then chose the standard reaction conditions for the screening of several acid catalysts. The effectiveness of the catalysts was judged by the solubility of the treated coal in THF and pyridine or both, and by the gas yields. In some cases where gasification was significant, gas yields were the only c r i t e r i a used. 3

2

Experimental Studies We used I l l i n o i s No. 6 coal pulverized by b a l l milling under nitrogen to -60 mesh and then usually dried i n a vacuum oven at 115°C overnight. Pennsylvania State University supplied beneficiated coal samples (PSOC-26) as well as an unbeneficiated sample (PSOC-25) for use i n some experiments. The beneficiated 0-8412-0427-6/78/47-071-204$05.00/0 © 1978 American Chemical Society In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


15.

LOW AND ROSS

Hydrotreatment

of

205

Coal

c o a l has the f o l l o w i n g elemental a n a l y s e s : C, 77,2%; H, 5.05% N, 1.69%; S, 2.08%; ash, 2.0%. The experiments were c a r r i e d out i n e i t h e r a r o c k i n g 500-ml autoclave f u l l y l i n e d w i t h T e f l o n or i n a 300 m l - H a s t e l l o y C MagneDrive s t i r r e d autoclave from Autoclave Engineers. In general, the r e a c t o r was charged with c o a l and c a t a l y s t , evacuated, then f i l l e d with 0.7 mole of HC1 ^~ 500 p s i ) and 800 p s i of hydrogen. The r e a c t i o n mixture was heated to and kept a t the r e a c t i o n temperature f o r a given p e r i o d . A f t e r the r e a c t i o n , the r e a c t o r was cooled slowly to room temperature. The gases were analyzed by gas chromatography to determine hydrogen, methane, ethane, and propane contents. The r e a c t o r was then depressurized and the r e a c t i o n mixture washed w i t h water u n t i l the washings were neutral. The f i l t e r e d c o a l products were then allowed to dry i n a vacuum oven at 115°C overnight. The t r e a t e d product c o a l was u s u a l l y c h a r a c t e r i z e d by elemental analyses (C, Η, Ν ) , by molecular weight determinations, and by s o l u b i l i t i e s i n THF and p y r i d i n e . THF and p y r i d i n e s o l u b i l i t i e s were determined by s t i r r i n g a 0.50 g sample of the product c o a l i n 50 ml THF or p y r i d i n e at room temperature f o r 1 hr, f i l t e r i n g the mixture i n a medium p o r o s i t y s i n t e r e d g l a s s f i l t e r , and then washing the r e s i d u e with f r e s h solvent (~ 50 ml) u n t i l the washings were c l e a r . Results and D i s c u s s i o n AlCl /HCl. In a s e r i e s of runs i n a r o c k i n g T e f l o n - l i n e d autoclave, we f i r s t studied the r o l e of HC1, A1C1 , and H i n c o a l hydrocracking using 5 g each of A1C1 and c o a l , at 190°C ( j u s t above the melting point of A1C1 ), f o r 15 hr. As shown i n Figure 1, one or more of the three components were absent i n Runs 1 to 6 and i n Run 9, and i n each case, no i n c r e a s e i n THF and p y r i d i n e s o l u b i l i t i e s was observed. In Run 10, where a l l three components were present, s o l u b i l i t i e s increased s u b s t a n t i a l l y , suggesting that the A1C1 /HC1 system was a c t i v e . The purpose of Runs 7 and 10 was to assess the importance of HC1 i n the system under these c o n d i t i o n s ; however, the r e s u l t s are not unequivocal. Here, the presence i n the c o a l of proton sources, such as phenolic groups and traces of water, undoubtedly hydrolyzes some of the A1C1 , producing HC1. These runs i n d i c a t e that no added HC1 i s r e q u i r e d f o r c o a l hydrocracking at these lower temperatures At higher r e a c t i o n temperatures (210°C) and shorter r e a c t i o n time (5 h r ) , the added HC1 c l e a r l y i n c r e a s e s the conversion (Runs 21 and 25), suggesting that the e f f e c t i v e c a t a l y s t i n the system must c o n t a i n the elements of HCl and A1C1 . We a l s o studied the e f f e c t of p o t e n t i a l Η-donor hydrocarbons and temperature. We based our work on the r e s u l t s of S i s k i n (6), who found that saturated, t e r t i a r y hydrocarbons serve as e f f e c t i v e hydride donors i n the strong acid-promoted hydrogenolysis of benzene. In our system, they proved i n e f f e c t i v e (Runs 17, 22, 24, a

3

2

3

3

3

3

3

In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

In Organic Chemistry of Coal; Larsen, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1978. IS

THF Solubility

50 60

RUN NO.

2

3

2

a) DMB = 2,3-Dimethylbutane b) MCP = Methylcyclopentane

AICI3/H2

AICI /H /HCI

H

Figure 1.

a

a

2

3

2

AICI /H /HCI/MCP

AICI3/H2

3

b

a

210°C, 5 hr

X

30

40

S O L U B I L I T Y (%) 20

1 9 5 C , 15 hr

10

Acid-catalyzed hydrocracking of beneficiated Illinois No. 9 coal

Pyridine Solubility

2

AICI /N /HCI/DMB

3

AICI /N /DMB

Coal Heated Alone In Evacuated Bulb

2

AICI /H /HCI 3

2

2

2

AICI3

AICI3/HCI

3

AICI /HCI/N

3

3

3

AICI /H /HCI

AICI /H /HCI (5 hr)

190 C, 15 hr

40

HCI/H

2

30

SOLUBILITY (%) 20

AICI /H /HCI/DMB

2

10

HCI

Untreated Coal

RUN| NO.


50

60


15.

LOW AND ROSS

Hydrotreatment

of

Coal

207

and 26, Figure 1). Higher temperatures allowed s h o r t e r r e a c t i o n times. The r e s u l t s f o r Run 17 (only 5 hr at 195°C) are comparable to those f o r Runs 7 and 10 (15 hr, 190°C). Runs at 195°C f o r 15 hr were f a r more e f f e c t i v e , and the conversion f o r Run 15 at 210°C f o r 5 hr i s about the same as that f o r Run 16 at 195°C f o r 15 hr. Next, we s t u d i e d the e f f e c t s of the c a t a l y s t / c o a l weight r a t i o on product character and c o a l product y i e l d s i n both the T e f l o n - l i n e d and the H a s t e l l o y C a u t o c l a v e s . At a weight r a t i o of 1.0, the two systems y i e l d e d products w i t h s t r i k i n g l y d i f f e r e n t pyridine s o l u b i l i t i e s : about 13% and 60% with the metal and Tefl o n equipment, r e s p e c t i v e l y (Figure 2). Increasing the c a t a l y s t / c o a l r a t i o to 2.0 increased s o l u b i l i t i e s to above 90% f o r both systems, but a f u r t h e r r a t i o increase a c t u a l l y caused s o l u b i l i t i e s to decrease s l i g h t l y . The s o l i d product recovery a l s o decreased with i n c r e a s i n g c a t a l y s t / c o a l r a t i o . As shown i n Figure 2, at a 2.0 r a t i o only about h a l f the c o a l was recovered as a s o l i d product. The other h a l f was converted to a mixture of methane and ethane. The s o f t e n i n g p o i n t f o r the THF-soluble fraction was about 150°C; however, the p y r i d i n e - s o l u b l e f r a c t i o n d i d not melt even a t temperatures up to 280°C. Figure 3 presents data on the H/C r a t i o s f o r products from both systems. The c o a l products from the T e f l o n - l i n e d r e a c t o r have c o n s i s t e n t l y higher H/C r a t i o than those from the H a s t e l l o y C reactor. R e s u l t s i n the H a s t e l l o y C autoclave were unchanged when a l o o s e l y f i t t i n g T e f l o n l i n e r was used. We have no d e t a i l e d explanation f o r the e f f e c t of autoclave s u r f a c e on the r e s u l t s , but p a s s i v a t i o n of the metal s u r f a c e by some minimum q u a n t i t y of c a t a l y s t i s part of the answer. Whatever the mechanism, the Teflon surface i s h e l p f u l . The c a t a l y s t system g a s i f i e s some of the c o a l d i r e c t l y to methane and ethane. This r e s u l t and the e f f e c t s of temperature on c o a l conversion are shown i n Table I. The t a b l e shows data from runs at 210°C f o r r e a c t i o n times from 45 min to 5 hr, and at 300°C f o r a 90 min r e a c t i o n time. The 210°C data are from an e a r l i e r phase of our work, where the g a s i f i c a t i o n was not q u a n t i f i e d , and the g a s i f i c a t i o n was determined by d i f f e r e n c e . For the 300°C work, the q u a n t i t i e s of gases and r e s i d u e were determined independently, and thus, the mass balances f o r these runs are not e x a c t l y 100%. The 300°C runs are a l l f o r 90 min, and Runs 83 and 85 show s t r i k i n g degrees of g a s i f i c a t i o n . More than 90% of the carbon i n the c o a l was converted to a 50/50 mixture of methane and ethane i n these experiments. In the next three runs, no HC1 was present, and we observe a cumulative e f f e c t of i t s absence. The degrees of g a s i f i c a t i o n d e c l i n e s e v e r e l y , and a l l the s o l i d c o a l products recovered have d e c l i n i n g p y r i d i n e s o l u b i l i t i e s and H/C r a t i o s . Kawa et a l . (2) observed a s i m i l a r e f f e c t f o r HC1.



208

ORGANIC CHEMISTRY OF COAL

CATALYST/COAL

Figure 2.

(wt/wt)

Effect of autoclave surface and catalyst I coal ratio on coal conversion.

The AlClj/HCl system was used with reaction temperature of 210°C, for 5 hr in a stirring Hastelloy C autoclave or rocking Teflon-lined autoclave.



LOW AND ROSS

Hydrotreatment

of

Coal

2 CATALYST/COAL

3 (wt/wt)

Figure 3. Comparison of H/C atomic ratio of treated product coal vs. effects by different reactors and catalyst/coal ratios. For runs at 210°Cand5hr.



210

Table I THE EFFECT OF RESIDENCE TIMES ON COAL GASIFICATION (4 g I l l i n o i s No. 6 c o a l , 8 g A1C1 , 500 p s i HC1, 800 p s i H , i n 2 300 ml s t i r r e d H a s t e l l o y C autoclave) 3


2

Run

Residence Time

67

5 hr

Coal Residue %Recovered %Pyridine Solubility a

% H/C

Coal , Gasified

0.83

61

b

210°C

46

C

39

97

5 hr

48

87

0.82

52

b

41

4 hr

49

91

0.84

51

b

66

90 min

47

96

0.85

53

b

45 min

72

93

0.82

28

b

71

45 min

66

97

0.82

34

b

83

90 min

18

78

0.72

96

d

85

90 min

18

83

0.74

90

d

69

C

300°C

86

e

90 min

30

60

0.75

72

d

87

e

90 min

49

31

0.68

56

d

88

e

90 min

68

28

0.64

36

d

°Based on 4 g of c o a l . ^Based on unaccounted f o r s o l i d product. Run with 3 g c o a l and 6 g A1C1 . 3

^Determined independently. CHz,/C H - 1/1. Traces of propane were seen i n Runs 86, 87, and 88. 2

e

6

Run without HC1


15.

LOW AND ROSS

Hydrotreatment

of

211

Coal

These data can be explained by the f o l l o w i n g scheme: 1 Coal H/C = 0.79

2 Coal product

Ha/catalyst

•

Ci + C

2

H /catalyst 2

Char

3 ' H/C

H /no c a t a l y s t 2


k . Thus, the hydrogenr i c h , p y r i d i n e - s o l u b l e c o a l product accumulates and can be i s o l a t e d . At higher temperatures, the r e l a t i v e r a t e s of steps 1 and 2 are reversed, k > k i , and g a s i f i c a t i o n i s the major e f f e c t . C l e a r l y , both A1C1 and HC1 are necessary f o r e f f e c t i v e catalysis. When HC1 i s e l i m i n a t e d , c a t a l y s t e f f e c t i v e n e s s i s reduced, steps 1 and 2 are suppressed, and step 3 becomes dominant. With the l e s s e n i n g degrees of g a s i f i c a t i o n , the c o a l r e s i d u e appear to be i n c r e a s i n g l y c r o s s - l i n k e d and depleted i n hydrogen, p o s s i b l y a r e s u l t of chemistry at the autoclave s u r f a c e . HC1 alone (Figure 1) not only i s i n e f f e c t i v e , but a l s o promoted char formation. 2

2

3

Other Lewis/Bronsted Combinations. Several a c i d c a t a l y s t s were screened i n two s e r i e s of t e s t s at two c a t a l y s t concentrat i o n l e v e l s , 210°C, 5 hr, 800 p s i H ( c o l d ) , and 0.7 mole HX (X = Br, CI, or F ) . We found c a t a l y s t a c t i v i t y to vary c o n s i d e r ably from one s e r i e s to the next (Figure 2). C a t a l y s t / c o a l weight r a t i o f o r the f i r s t s e r i e s was 1/1. A l l catalysts studied at t h i s r a t i o , except A l B r and A1C1 , were i n e f f e c t i v e , reducing THF and p y r i d i n e s o l u b i l i t i e s s i g n i f i c a n t l y , perhaps because of i n t e r n a l condensation i n the s t a r t i n g c o a l . The c o a l products i n these runs are probably h i g h l y c r o s s - l i n k e d . A1C1 was c o n s i d e r ably more e f f e c t i v e than A l B r , and HBr alone (Run 30) was, not surprisingly, ineffective. These r e s u l t s i n d i c a t e a c a t a l y s t e f f e c t i v e n e s s of A1C1 > A l B r » S b C l = SbF * Z n C l - T a F - N i S 0 - C 0 S O 4 - HBr. In the second s e r i e s , a constant molar q u a n t i t y of c a t a l y s t was used: 0.045 moles c a t a l y s t /4 g c o a l , equivalent to 6 g A l C l / 4 g c o a l . The o r d e r i n g here i s SbBr - S b C l > A l B r > A1C1 > N i ( A A ) > T a F » SbF - M0CI5 - WC1 (AA = a c e t y l a c e t o n a t e ) . Thus T a F , which S i s k i n (6) found e f f e c t i v e l y hydrocracked benzene to mixed hexanes, i s not at a l l e f f e c t i v e under our c o n d i tions. S i m i l a r l y , Z n C l , the w e l l known c o a l conversion c a t a l y s t , 2

3

3

3

3

3

3

3

3

2

2

5

5

4

3

3

3

3

3

6

5

2


5

212

ORGANIC CHEMISTRY OF

COAL

i s not e f f e c t i v e under these c o n d i t i o n s , perhaps because under our r e l a t i v e l y mild c o n d i t i o n s , Z n C l i s not molten (mp 283°C). F i n a l l y , the favorable antimony bromide and c h l o r i d e r e s u l t s are s i m i l a r to those reported by S h e l l (1). In Run 35 (Table I I ) , with A1C1 /HC1, we used unbeneficiated c o a l . Here, the THF s o l u b i l i t y of the product c o a l increased by almost a f a c t o r of 2, to 40%. The p y r i d i n e s o l u b i l i t y increased s l i g h t l y , to 66%. Since p y r i d i n e i s g e n e r a l l y a b e t t e r solvent f o r c o a l l i q u i d s than i s THF, the considerable increase i n THF s o l u b i l i t y suggests that more lower molecular weight products are obtained when u n b e n e f i c i a t e d c o a l i s used. A l s o , the mineral matter present i n the unbeneficiated c o a l c l e a r l y aids the hydro cracking process, suggesting that the mineral matter i n the c o a l i s an e f f e c t i v e c a t a l y s t under a c i d c o n d i t i o n s . 2


3

Summary In s t u d i e s with mixtures of Lewis and Bronsted (proton) a c i d s as c a t a l y s t s , we have found that with hydrogen some mixtures con v e r t I l l i n o i s No. 6 c o a l to f u l l y p y r i d i n e - s o l u b l e products and 50/50 mixtures of methane and ethane. The A1C1 /HC1 system was studied most e x t e n s i v e l y , and i t was found that at 210°C (410°F) and 45 min residence time, about 70% of the c o a l was converted to a hydrogen-enriched, f u l l y p y r i d i n e - s o l u b l e product and the remainder, to methane and ethane. A 90 min or longer residence time y i e l d e d 50% gases. At 300°C (572°F), more than 90% of the carbon i n the s t a r t i n g c o a l was converted to methane and ethane. Neither HC1 nor A1C1 alone was e f f e c t i v e ; when used along, e i t h e r system y i e l d e d a s o l i d product r e l a t i v e l y low i n p y r i d i n e s o l u b i l i t y and depleted i n hydrogen r e l a t i v e to the s t a r t i n g c o a l . Reaction runs i n an autoclave f u l l y l i n e d with T e f l o n gave f a r b e t t e r r e s u l t s than those i n a H a s t e l l o y C autoclave. A screening study of s e v e r a l acids showed that at a 1/1 c a t a l y s t / c o a l weight r a t i o , the order of e f f e c t i v e n e s s i s A1C1 > AlBr » SbCl - SbF κ Z n C l - T a F - NiSO^ - CoS0 . With a constant r a t i o of a given molar quantity of c a t a l y s t to mass of c o a l , the order i s SbBr * S b C l > A l B r > A1C1 > N i ( A A ) > TaF » SbF « MoCl - WC1 . (AA = acetonylacetonate.) 3

3

3

3

3

2

3

5

3

3

3

4

3

2

5

s

5

6

Acknowledgment

No.

The f i n a n c i a l support f o r t h i s work from DOE EF-76-C-01-2202 i s g r a t e f u l l y acknowledged.

under

Contract


15.

LOW AND ROSS

Hydrotreatment

213

of Coal

Table I I TREATMENT OF ILLINOIS NO. 6 COAL WITH H /STRONG ACID SYSTEMS 2

Run No.

Catalyst

Pressurel ( p s i ) HX H

System

2

(a) Constant Weight


28

AICI3/HCI/H2

a

800

500

23

58

800

500

40

66

35

A1C1 /HC1/H

29

AlBr /HB /H

27

AlBr /HBr/H

30

HBr/H

31

SbCl /HCl/H

32

TaF /HF/H

2

1100

33

SbF /HF/H

2

1100

44

ZnCl /HCl/H

56

CoS0 /H S0*/H

2

1300

57

NiS0 /H S0z,/H

2

1300

3

3

2

C 2

2

3

2

980

33g

9

27

820

50g

11

32

1000

2

3

5

3

2

4

800

2

2

A

800

2

2

S o l u b i l i t i e s (%)b THF Pyridine

2

6

-

1

22g

-

13

16g

< 1

4

-

9

68. 6g

< 1

< 1

68.6g

< 1

< 1

25

47

30

59

-

95

31g 500

500

(b) Constant Molar Quantity* 1

45

A1C1 /HC1/H

48

AlBr /HBr/H

2

1100

49

SbCl /HCl/H

2

800

50

3

3

3

800

2

500 70g 500

TaF /HF/H

2

900

14g

11

20

52

SbF /HF/H

2

1150

14g

< 1

< 1

54

MoCl /H

1300

-

8

16

55

WC1 /H

1300

-

6

12

61

SbBr /HBr

43

95

62

Ni(AA) /HCl/H

70

MoCl /HCl/H

5

5

5

6

2

2

850

3

2

5

2

2

59g

800

500

ND

800

500

< 1

e

+

+

38 4

In t h i s s e r i e s of experiments, 5 g of c o a l was t r e a t e d a t 210°C f o r 5 hr i n a rocking T e f l o n - l i n e d autoclave. > c Moisture-ash-free b a s i s . Unbeneficiated c o a l was used. Srhese experiments used 0.045 moles of c a t a l y s t per 4 g c o a l . A s t i r r e d H a s t e l l o y C autoclave was used. ND = Not determined.




214

Literature Cited 1. Wald, Μ., U.S. Patent 3,543,665 (November 24, 1970). 2. Kawa, W., S. Freidman, L. V. Frank, and R. W. Hiteshue, Amer. Chem. Soc., Div. Fuel Chem. (1968), Preprint 12 (3), 43-7. 3. Qader, S., R. Haddadin, L. Anderson, and G. Hill, Hydrocarbon Process (1969), 48 (9), 147. 4. Kiovsky, Τ. Ε., U.S. Patent 3,764,515 (October 9, 1973). 5. Zielke, C. W., R. T. Struck, J. M. Evans, C. P. Costanza, and E. Gorin, I & Ε C Process Design and Development (1969), 5, (2), 151, and references therein. 6. Siskin, M., J. Amer. Chem. Soc. (1974), 95, 3641. RECEIVED

February 10,

1978


Organic Chemistry of Coal - American Chemical Society

Recommend Documents