Ajoy Raje

Fischer-Tropsch synthesis over iron-based catalysts in a slurry reactor. Reaction rates, selectivities and implications for improving hydrocarbon productivity

Abstract A promoted iron Fischer-Tropsch synthesis catalyst is used in a slurry reactor to evaluate and compare the selectivity and yields of total hydrocarbons, light alkenes (C2-C3) and intermediate range (C6-C16) linear-α-alkenes for syngas derived from natural gas and coal. The catalyst has a high hydrocarbon yield of 0.6 g (of hydrocarbon)/h-g Fe at high CO conversions (>85%). The syngas derived from coal produces a slightly higher total hydrocarbon yield than natural gas-derived syngas, due to a lower reactor partial pressure of water which inhibits the Fischer-Tropsch reaction rate. The natural gas-derived syngas produces a lighter and more paraffinic hydrocarbon product than coal-derived syngas. The selectivity and yields of light alkenes as well as the intermediate range linear-α-alkenes decrease considerably with reaction time and CO conversion for syngas derived from both sources. The yields of these valuable products can be considerably improved by a lower single-pass reactor CO conversion with recycle of unconverted syngas or by using reactors in series. The syngas derived from coal produces a slightly lower ethylene and propylene yield, but a higher intermediate-range linear-a-alkene yield than that of natural gas-derived syngas.

Second row transition metal sulfides for the hydrotreatment of coal-derived naphtha I. Catalyst preparation, characterization and comparison of rate of simultaneous removal of total sulfur, nitrogen and oxygen

Abstract Naphtha derived from an Illinois No. 6 coal contains appreciable quantities of sulfur-, nitrogen- and oxygen-containing compounds. The hydrotreatment of this naphtha has been evaluated over unsupported transition metal sulfide catalysts of the second row in the Periodic Table. The catalysts were prepared by a room temperature precipitation reaction. Surface areas, crystalline phase and particle size distributions were determined by Brunauer-Emmet-Teller (BET), X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. A comparison of average particle sizes calculated from these three techniques has enabled the understanding of the morphology of the transition metal sulfides. The catalysts exhibit a so-called volcano plot for the HDS of dibenzothiophene. Similar so-called volcano plots are also exhibited for the simultaneous hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and the hydrodeoxygenation (HDO) of the coal-derived naphtha containing a mixture of heteroatoms. The order of reactivity of the transition metal catalysts is the same for all three of the processes. Ruthenium sulfide (RuS 2 ) is the most active catalyst for HDS, HDN and HDO of the coal-derived naphtha.

Fischer-Tropsch synthesis: Process considerations based on performance of iron-based catalysts

Alternative reactor configurations and the utilization of a low-alpha versus high-alpha iron-based catalyst are compared for the Fischer-Tropsch synthesis based on actual catalyst performance. The use of coal-derived synthesis gas with a low H2/CO ratio requires a judicious balance between the rates of the Fischer-Tropsch and water-gas shift reactions. The hydrocarbon space-time yield is considerably increased by using either a reactor with recycle or a series of reactors with low syngas conversion per pass instead of a single-pass reactor with high syngas conversion. The production of gasoline and diesel-range hydrocarbons by downstream processing of the Fischer-Tropsch reaction products involves both hydrocracking and oligomerization. The difference between processing the products from a low-alpha and a high-alpha iron-based catalyst lies merely in the relative sizes of the hydrocracking and oligomerization reactors required. In addition, it is advantageous to use a low-alpha catalyst from the viewpoint of Fischer-Tropsch slurry reactor operation.

Second row transition metal sulfides for the hydrotreatment of coal-derived naphtha II. Removal of individual sulfur compounds

Abstract The disappearance of individual sulfur compounds has been investigated during the hydrotreatment (simultaneous removal of sulfur, nitrogen and oxygen) of coal-derived naphtha over each of the bulk second row transition metal sulfides. The sulfur compounds in the naphtha mainly consist of thiols/sulfides, thiophene and substituted thiophenes. Thiols/sulfides are, in general, more easily converted than thiophenic compounds are. Lighter thiols/sulfides are intermediates in the conversion of higher boiling thiols/sulfides or thiophenes. Side chain alkyl CC bond breaking is predominant during the disappearance of thiophenes over the Zr and Nb catalysts while CS bond breaking is predominant over the other catalysts. Thiophenic compounds are hydrogenated prior to desulfurization over the Mo, Ru, Rh and Pd sulfides. Highly substituted thiophenes are the compounds most difficult to convert over the Mo, Ru, Rh and Pd sulfides. The substituted thiophenes exhibit different reactivity trends over molybdenum sulfide, on one hand, and the Group VIII sulfides, on the other, indicating different adsorption modes and surface mechanisms for their conversion over these catalysts. Individual sulfur compounds do not follow first order kinetics and the disappearance rate is limited by product inhibition. The overall removal of sulfur does not follow simple first or second order kinetics since the individual compounds do not react in parallel, independent or first order reactions.

Catalytic hydrotreatment of Illinois No. 6 Coalderived naphtha: Comparison of molybdenum nitride and molybdenum sulfide for heteroatom removal

Abstract The hydrotreatment of naphtha derived from Illinois No.6 coal was investigated using molybdenum sulfide and nitride catalysts. The two catalysts are compared on the basis of total catalyst weight. Molybdenum sulfide is more active than molybdenum nitride for hydrodesulfurization (HDS) of a coal-derived naphtha. The rates of hydrodeoxygenation (HDO) of the naphtha over both catalysts are comparable. For hydrodenitrogenation (HDN), the sulfide is more active than the nitride only at higher temperatures (>325°C). Based upon conversion data, the naphtha can be lumped into a reactive and a less reactive fraction with each following first-order kinetics for heteroatom removal. The HDS and HDN rates and activation energies of the less reactive lump are smaller for the nitride than for the sulfide catalyst.

Hydrotreatment of coal-derived naphtha. Properties of zeolite-supported Ru sulfide catalysts

Abstract A Ru (0.77 wt.%)/zeolite catalyst was prepared and tested for the hydrotreatment of Illinois No. 6 coal-derived naphtha. It was found that this catalyst exhibited significant hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) activities. Furthermore, the nitrogen compounds convert as easily as sulfur compounds, in contrast to most of the hydrotreatment catalysts where the HDS reaction is much more rapid than HDN. A comparison on the basis of nitrogen converted per gram of active metal or on the cost of the catalyst indicates that for HDN, the Ru(0.77)/zeolite is superior to a Ru(0.77)/alumina, a commercial CoMo/alumina or a NiMo/alumina catalyst.

Catalytic hydrotreatment of Illinois No. 6 Coal-derived naphtha: The removal of individual nitrogen and sulfur compounds over MoS2 and Mo2N

Abstract The conversion of individual nitrogen and sulfur compounds present in Illinois No. 6 coal-derived naphtha was determined as a function of reactor residence time. The major nitrogen compounds in the naphtha are anilines, quinolines and pyridines. The major sulfur compounds are thiols, sulfides and thiophenes. The conversion of the heteroatom (nitrogen and sulfur) compounds are different and depend on the heteroatom compound class. Substituted anilines are the most difficult to convert amongst the nitrogen compounds while substituted thiophenes and benzothiophenes are the most difficult to convert for the sulfur compounds; this applies for both MoS 2 and Mo 2 N catalysts. Mo 2 N is more active than MoS 2 for the conversion of pyridine and quinoline compound classes. However, MoS 2 is more active for the conversion of the aniline compound class. Hydrogenation, at least partly, precedes C S bond breaking for the hydrodesulfurization of thiophene over both MoS 2 and Mo 2 N. The effect of additional methyl groups in decreasing the conversion of thiophenes is large for MoS 2 but relatively small for Mo 2 N. Deviations from first-order kinetics are seen for the conversion of thiophenes, probably due to product inhibition of the reaction rate.

Deactivation of iron-based catalysts for slurry phase Fischer-Tropsch synthesis

Deactivation rates and aged catalyst properties have been investigated as a function of time on stream for iron-based Fischer-Tropsch catalysts in the presence/absence of potassium, and/or silicon. There is a synergism in activity maintenance with the addition of both potassium and silicon to an iron catalyst. The addition of silicon appears to stabilize the surface area of the catalyst. Catalysts containing only iron or added silicon with or without potassium consist mainly of iron oxide at the end of the run. However, iron carbides are the dominant phase of the iron catalyst with added potassium alone. Catalyst surface areas increase slightly during synthesis. The bulk phase of the catalyst does not correlate to the catalyst activity. The partial pressure of water in the reactor is lower for potassium-containing catalysts and is not a reliable predictor of catalyst deactivation rate.

A comparison of reactors in coal liquefaction

Abstract The data presented in this study illustrate the similarities and differences in the yield and selectivities obtained from different types of coal liquefaction reactors. The results suggest that the comparison of data in the literature obtained from different reactors should be done with careful consideration. The differences and similarities in the yields obtained depend not only on the reactor type but also on the feedstock employed and the residence time in the reactors. Data generated using microreactors are adequate for the selection of operating conditions for conversion in larger scale reactors.