Coal conversion liquefaction

Figure 6. Highly schematized depiction of the orthogonal influences of coal rank and coal type on coal grade (economic value) as reflected simply by the yield of liquids in a coal conversion (liquefaction) process (( ) reactive ingredients are vitrinite and exinite in higher rank coals, vitrinite and exinite give low yields)...

This work was supported by the Department of Energy-Fossil Energy, Division of Coal Conversion-Liquefaction. Chemical and instrumental techniques used were developed with support from the Office of Basic Energy Sciences, U.S. Department of Energy. 

Imperial Chemical Industries (ICI) operated a coal hydrogenation plant at a pressure of 20 MPa (2900 psi) and a temperature of 400—500°C to produce Hquid hydrocarbon fuel from 1935 to the outbreak of World War II. As many as 12 such plants operated in Germany during World War II to make the country less dependent on petroleum from natural sources but the process was discontinued when hostihties ceased (see Coal conversion PROCESSES,liquefaction). Currentiy the Fisher-Tropsch process is being used at the Sasol plants in South Africa to convert synthesis gas into largely ahphatic hydrocarbons at 10—20 MPa and about 400°C to supply 70% of the fuel needed for transportation. 

W. R. Eppedy and J. W. Taunton, Sixth International Conference of Coal Gasification, Liquefaction, and Conversion to Electricity, Pittsburgh, Pa., 1979. 

Many studies on direct liquefaction of coal have been carried out since the 1910 s, and the effects of kinds of coal, pasting oil and catalyst, moisture, ash, temperature, hydrogen pressure, stirring and heating-up rate of paste on coal conversion, asphaltene and oil yields have been also investigated by many workers. However, few kinetic studies on their effects to reaction rate have been reported. 

Chemical Week 1980, 128, pp 25-27. Rogers and Hill, Coal Conversion Comparisons, pp 69-71 Assessment of Technology for the Liquefaction of Coal, pp 111-15 Gulf Oil Corporation Information Brochure, "Solvent Refined Coal-II Environmental Issues and Protection Measures,"... 

If the mobile phase is present in a significant concentration, as suggested by the results of solvent extraction studies (1,8), the practical meaning of the mobile phase to coal conversion processes may be profound. In coal liquefaction, two stage processes emphasizing the mobile phase and the macromolecular structure separately could well be most economical. In devolatilization kinetics, at least two sets of kinetic parameters are necessary to model the devolatilization phenomena associated with the mobile phase and the macromolecular structure respectively since the mobile phase components devolatilize at much lower temperatures than the macromolecular structure components 0. In addition, the mobile phase appears to have a significant influence on the thermoplastic properties of coal (0 and thereby on coke quality. 

Liquefaction reactivity experiments were conducted in a 20 cm- tubing bomb reactor attached to an agitator and immersed in a fluidized sandbath. Table II lists reaction conditions used in these runs. A non-hydrogen donor vehicle (1-methylnaphthalene, 1-MN) and a hydrogen donor vehicle (9,10-dihydrophenanthrene, DHP) were used as solvents (2/1 solvent/coal wt. ratio). Coal conversion was monitored using THF extraction data corrected for the intrinsic THF solubility of untreated and treated coals. 

Taken together, these data suggest that both alkylation and the presence of chlorine ions contributed to the observed liquefaction reactivity enhancement. Although the data are preliminary, we believe that iron pwite and perhaps other species in the coal mineral matter may be chlorinated to form metal chlorides such as FeCU such species are known to be active coal conversion catalysts (1112). 

Both reactions act to reduce hydrogen bonding within the coal structure which may have a direct positive impact on liquefaction reactivity. More indirectly, these reactions lower the concentration of OH species in coal-derived products and hence, reduce the extent of retrogressive condensation via ether bridge formation. Reducing production of THF-insoluble condensation products increases the net THF-soluble coal conversion observed during the liquefaction experiment. None of the spectra from coals pretreated with alkyl alcohols and HCl showed any significant evidence of alkylation at carbon sites in the coal. 

Because of the massive "unconventional" reserves of liquid hydrocarbons afforded by oil sand bitumens and heavy oils, Canadian interests in coal conversion are generally more likely to centre on gasification than on liquefaction, and to focus on long-term supply of fuel gas (which could in many cases be substituted for oil where coal can not, and thereby reduce projected oil supply shortfalls). 

This paper touches on the chemistry of coal gasification and liquefaction comments on the current status of conversion processes and the influence of coal properties on coal performance in such processes and examines the contributions which coal conversion could make towards attainment of Canadian energy self-sufficiency. Particular attention is directed to a possible role for the medium-btu gas in long-term supply of fuel gas to residential and industrial consumers to linkages between partial conversion and thermal generation of electric energy and to coproduction of certain petrochemicals, fuel gas and liquid hydrocarbons by carbon monoxide hydrogenation. 

Hydrogen sulfide is a by-product of many industrial operations, eg, coking and the hydrodesulfurization of crude oil and of coal. Hydrodesulfurization is increasing in importance as the use of high sulfur crude oil becomes increasingly necessary (see Petroleum, refinery processes). A large future source of hydrogen sulfide may result if coal liquefaction attains commercial importance (see Coal CONVERSION processes). 

The plant processes 26,840 TPSD of low sulfur North Dakota lignite. The sulfur is 1.3 wt%/DAF coal. The coal analysis is shown in Table II. Output from the plant is 268,700 MM Btu/day of SNG, equivalent to 45,000 BOE/day. Total production of by-product elemental sulfur is 161 tons/day. This represents 78 wt% of total sulfur input from the coal feedstock. Since goal gasification and indirect liquefaction facilities are most likely to use Western low sulfur lignite or subbituminous coals, this represents the low sulfur case for coal conversion. 

The difficult task of examining the role of catalysis in coal liquefaction has been taken on by Mochida and Sakanishi. They show the catalytic requirements in various stages of coal conversion and the many complex interactions of the catalyst with coal constituents. They also point out directions for future catalysis research needed for more economical coal liquefaction, a commendable feature for processes requiring a long lead time. 

Many processes have been developed for the removal of hydrogen sulfide from gas streams. They can be classified as liquid absorption, liquid oxidation, dry oxidation, and adsorption. One of these processes is usually included in a coal gasification or liquefaction flowsheet since the coal sulfur is converted to H2S and finally elemental sulfur. The Stretford and Townsend direct HpS to S processes and the Recti sol process followed by a Claus plant are frequently included on coal conversion flowsheets (1 ). Kohl and Riesenfeld (2) present pertinent details for many commercial processes. 

---