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Catalyst Assessment for Upgrading Short-Contact-Time SRC to Low Sulfur Boiler Fuels S. S. SHIH, P. J. ANGEVINE, R. H. HECK, and S. SAWRUK Mobil Research and Development Corporation, Paulsboro, NJ 08066
Solvent refined coal (SRC) can be upgraded via catalytic hydroprocessing into low sulfur fuels (1,2). Reduced process cost can be affected by several factors, including the following: higher catalyst activity, improved utilization of hydrogen, and optimized SRC concentration in the feedstock. To this end, a series of commercial and proprietary catalysts was evaluated for the hydroprocessing of 50 wt % W. Kentucky short contact time SRC (SCT SRC). The commercial catalysts tested were alumina-based and were known to have good hydrotreating activity for heavy petroleum or coal-derived liquids. The rates of hydrogenation and pore size distribution will be discussed. A developmental catalyst with relatively high desulfurization and efficient hydrogen utilization was tested in a constant temperature aging run to establish process conditions needed to produce 0.4 wt % sulfur boiler fuels. Experimental The experiments were conducted in a continuous down-flow fixed bed pilot unit. The feedstock, 50 wt % W. Kentucky/SRC recycle solvent blend, was prepared in a charge reservior and transferred to a weigh cell by gravity flow. Both the charge reservior and weigh cell were kept at 350°F. After the reactor, hydrogen and light gases were separated from hydrotreated o i l through high (300°F) and low (75°F) temperature separators in series. To maintain fluidity of the high SCT SRC concentration blend, a l l lines and valves from the charge reservior to the high temperature separator were heat-traced to 340-420°F. The detailed description of the pilot unit is
0097-615 6/ 81 /015 6-0175$05.00/0 © 1981 American Chemical Society Sullivan; Upgrading Coal Liquids ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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a v a i l a b l e elsewhere (1). The s e l e c t i o n of SCT SRC as the feed was based on a recent f i n d i n g that the hydrogen u t i l i z a t i o n e f f i c i e n c y f o r production of hydrogen-rich c o a l l i q u i d s can be improved by coupling m i l d short r e s i d e n t time h y d r o l i q u e f a c t i o n (to produce SCT SRC) w i t h c a t a l y t i c hydroprocessing (3). The c a t a l y s t s were p r e s u l f i d e d w i t h a 10% H2S/H2 mixture and t e s t e d at a r e a c t o r pressure of 2000 p s i g and a hydrogen c i r c u l a t i o n of 5000 scf/B. Each c a t a l y s t was subjected to a standard sequence of temperatures and l i q u i d h o u r l y space v e l o c i t i e s , ranging from 720-800°F and 0.5-2.0 h o u r " , r e spectively 1
R e s u l t s and
Discussions
Fresh C a t a l y s t P r o p e r t i e s . Three M o b i l c a t a l y s t s were t e s t e d and have been i d e n t i f i e d as HCL-1, -2, and -3. Because of the p r o p r i e t a r y nature of these c a t a l y s t s , p r o p e r t i e s have been excluded. The major p r o p e r t i e s of the four commercial and two developmental c a t a l y s t s are shown i n Table 1. The four commercial c a t a l y s t s evaluated were NiMo/Al203: Harshaw s 618X and HT-500, and American Cyanamid s HDN-1197 and HDS1443. The NiMo c a t a l y s t s were t e s t e d i n a greater number than the C0M0 c a t a l y s t s because i t had been thought that improved hydrogénation a c t i v i t y was needed to t r e a t the h i g h l y r e f r a c t o r y SRC. A l s o , nickel-promoted hydroprocessing c a t a l y s t s form l e s s coke than cobalt-promoted c a t a l y s t s , p o s s i b l y r e s u l t i n g i n b e t t e r s t a b i l i t y . The 618X, HT-500, and HDS-1443 c a t a l y s t s a l l have s i m i l a r metals l o a d i n g ; t h e i r major d i f f e r e n c e i s found i n surface area, going from r e l a t i v e l y low to medium to h i g h , r e s p e c t i v e l y . The s h i f t i n surface area can a l s o be seen i n the d i f f e r e n t pore s i z e d i s t r i b u t i o n s . Harshaw 618X has a w e l l - d e f i n e d d i s t r i b u t i o n w i t h 77% of i t s pore volume i n the 100-200l diameter region. HT-500 has a broader d i s t r i b u t i o n and smaller median s i z e , having h a l f of i t s pore volume i n the 80-100A r e g i o n . HDS-1443 has a bimodal d i s t r i b u t i o n : i t has most of i t s pores i n 30-80Â, but i t a l s o has some 200Â+ pores. HDN-1197 has a higher metals l o a d i n g than the other NiMo c a t a l y s t s and a l s o most of i t s pores i n the 30- 80X r e g i o n . Two developmental c a t a l y s t s were evaluated i n t h i s study. These i n c l u d e Amocat 1A and IB, r e c e n t l y developed by Amoco f o r t e s t i n g i n the H - C o a l Process (4^. Both c a t a l y s t s were made of the same support and had p r i m a r i l y 100- 2 0 0 l pores w i t h some macropores (>1000Â). Amocat IB i s an unpromoted M0/AI2O3 1
1
R
w h i l e 1A
is
C0M0/AI2O3.
Fresh A c t i v i t y Comparisons. The nine c a t a l y s t s have been d i v i d e d i n t o two groups i n order to s i m p l i f y the a c t i v i t y comp a r i s o n s . Group A i s made up of the more a c t i v e d e s u l f u r i z a t i o n c a t a l y s t s and i n c l u d e s M o b i l HCL-2, M o b i l HCL-3, American Cyanamid HDS-1443, and Amocat 1A. Group Β included M o b i l HCL1, Harshaw 618X, American Cyanamid HDN-1197, and Amocat IB.
Sullivan; Upgrading Coal Liquids ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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For the a c t i v i t y comparisons, the heteroatom removals (and CCR reduction) are p l o t t e d versus r e a c t o r temperature at a l i q u i d h o u r l y space v e l o c i t y of 1.0. Consequently, c a t a l y s t a c t i v i t y can be compared on the b a s i s of temperature requirements f o r a c h i e v i n g s p e c i f i c l i q u i d product heteroatom (or CCR) contents. The comparisons of d e s u l f u r i z a t i o n a c t i v i t i e s are shown i n F i g u r e 1 and F i g u r e 2 f o r Group A and Group Β c a t a l y s t s , r e s p e c t i v e l y . A t the 80% d e s u l f u r i z a t i o n l e v e l , M o b i l HCL-2 i s 10-15°F more a c t i v e than HDS-1443, followed by HCL-3, Harshaw 618X, and Amocat 1A (Figure 1). Suface area and pore s i z e d i s t r i b u t i o n seem to be important parameters f o r the f r e s h c a t a l y s t a c t i v i t y . The r e l a t i v e l y high f r e s h a c t i v i t y of HDS-1443 may be p a r t i a l l y explained by i t s high surface area and presence of macropores (Table 1). The presence of macropores may be r e s p o n s i b l e f o r the improvement of the r e l a t i v e p o s i t i o n s of HDS-1441 and Amocat 1A at more severe c o n d i t i o n s (0.5 LHSV). The importance of pore s i z e d i s t r i b u t i o n a l s o e x p l a i n s the low a c t i v i t y of HT-500, which has 75% of i t s pore volume i n the 30-10oX r e g i o n . Cyanamid HDN-1197 seems to have a high d e s u l f u r i z a t i o n a c t i v i t y (Figure 2). However, i t y i e l d s an inhomogeneous product, probably due to i t s high hydrogénation a c t i v i t y coupled w i t h i t s s m a l l pore s i z e . Inhomogeneous products have a l s o been observed i n the upgrading of r e g u l a r SRC by small pore c a t a l y s t s (1). The SCT SRC, w i t h i t s high p o l a r asphaltenes content, i s p a r t i c u l a r l y s u s c e p t i b l e to " f r o n t end, back end" i n c o m p a t i b i l i t y . The ranking of deoxygenation a c t i v i t y was very s i m i l a r to t h a t of the d e s u l f u r i z a t i o n a c t i v i t y (Figure 3 ) . The r e s u l t s may suggest t h a t , l i k e d e s u l f u r i z a t i o n , the deoxygenation r e a c t i o n could occur without pre-hydrogenation. The comparison of d e n i t r o g e n a t i o n a c t i v i t i e s i s shown i n Figure 4. M o b i l HCL-3 was the most a c t i v e c a t a l y s t f o l l o w e d by M o b i l HCL-2 and Harshaw 618X. The CCR r e d u c t i o n a c t i v i t y f o r the nine c a t a l y s t s i s s i m i l a r l y p l o t t e d as a f u n c t i o n of temperature i n Figure 5 and F i g u r e 6. M o b i l HCL-2, HCL-3, and Amocat IB are the most a c t i v e c a t a l y s t s . G e n e r a l l y , heteroatom removal can be achieved w i t h only minor changes i n chemical s t r u c t u r e . However CCR r e d u c t i o n i n SCT SRC occurs w i t h s i g n i f i c a n t a l t e r a t i o n of GEC c l a s s e s , p r i m a r i l y toward the formation of l e s s p o l a r compounds. The c l a s s e s of W. Kentucky SCT SRC, separated by GEC (gradient e l u t i o n chromatography), are given i n Table 2 and show that 75% of the SRC i s p o l a r and noneluted p o l a r asphaltenes.
Sullivan; Upgrading Coal Liquids ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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Percent Sulfur Removal
Temperature, F 0
Figure 1. Comparison of desulfurization activities, Group A catalysts: (O) Har shaw 618X, Ο Mobil HCL-2, (A) HDS-1443, (VJ Mobil HCL-3, (o) Amocat 1A
Figure 2. Comparison of desulfurization activities, Group Β catalysts: (O) Har shaw 618X, Ο HT-500, (A) Mobil HCL-1, (V) Amocat IB, (o) HDN-1197
Sullivan; Upgrading Coal Liquids ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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Catalytic Assessment of SRC
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