James W. Clarke

Estimation of the concentration of donatable hydrogen in a coal solvent by n.m.r.

Abstract 1 H and 13 C nuclear magnetic resonance (n.m.r.) spectroscopies have been used to study the changes in composition of a hydrogenated anthracene oil solvent that occur during extraction of a UK bituminous coal. It has been shown that the principal hydrogen donor groups in the solvent are hydroaromatic and naphthenic rings in hydroaromatic species. Good agreement was achieved between the concentration of donatable hydrogen estimated from n.m.r., and the amount of hydrogen transferred from the solvent during exhaustive extraction.

Filtration in coal liquefaction. Influence of digestion conditions in the filtration of non-hydrogenated coal digests

Abstract A series of experiments has been carried out to study the way in which preparation conditions of coal digests influence filtration rate. It was shown that a relation exists between cake resistivity and digestion temperature and time, and therefore good control over digestion conditions is important for rapid filtration. Particular attention must be paid to the design of the reactor to ensure that all the material is given the same heat-treatment. The optimum residence time occurs when repolymerization of the dissolved coal commences.

Filtration in coal liquefaction. Influence of filtration conditions in non-hydrogenated systems

Abstract A series of experiments has been carried out to study the effects of filtration conditions upon the rate of filtration of non-hydrogenated coal digests. The results show the dependence of cake resistivity on both the filtration temperature and pressure. Filter cakes were found to be compressible, resulting in smaller increases in rate with increasing pressure than with incompressible cakes. The filtration temperature determines the packing of residual solids in the cake which in turn affects the cake resistivity. An empirical relation has been derived between filtration temperature and resistivity. With increasing temperature there is an increase in filtration rate due to the reduced viscosity, but a reduction owing to a higher packing density of solids in the filter cake.

Kinetics of coke formation from coal solutions

Abstract The reaction kinetics for the formation of mesophase from coal solutions has been studied under conditions similar to those experienced in a delayed coker preheater coil, i.e. at temperatures from 475 to 525 °C approached at high heating rates. The degree of polymerization of the heat-treated materials has been assessed by their solubility in two solvents, cyclohexane and quinoline. An approximation has been made in order to make a kinetic analysis for the formation of insolubles in a non-isothermal system. It has been found that the polymerization of the dissolved coal component, as evidenced by the formation of quinoline insolubles during the heat-treatment of concentrated coal solutions, is essentially a second-order reaction with an apparent activation energy of ≈190 kJ mol−1. The formation of cyclohexane insolubles from the diluent oil is a slower reaction showing first-order kinetics.

Reactivity of cycloalkanes during the solvent extraction of coal

Abstract The reactivity of cycloalkanes, either alone or as part of a solvent mixture, during the solvent extraction of coal at 430 °C has been studied. When used with polyaromatic compounds (⩾ 3 rings) as solvents, cycloalkanes participate in hydrogen donation reactions giving rise to high extraction yields of the coal.

Filtration in coal liquefaction.: 2. Relation between digestion conditions and filtration rate

Abstract In systems for the liquefaction of coal by solvent extraction, removal of the undissolved solids from the liquefaction products is a fundemental part of the process. For separation of solids by filtration to be economically viable, it is essential to achieve high filtration rates. The influence of the extraction conditions, temperature, residence time and coal feed size, on the rate of filtration has been investigated. It has been shown that the rate of filtration is sensitive to the presence of a gel-like intermediate formed during the dissolution of the coal. The formation of this intermediate imposes limitations on the choice of digestion conditions, in particular the coal feed size. However, by inducing polymerization, the gel can be stabilized, thus allowing significantly improved filtration rates to be achieved.

Filtration in coal liquefaction: filtration of digest prepared from lignite

Abstract The filtration characteristics of digests prepared from bituminous coals and lignites are compared. In the case of bituminous coals the filtration rate is sensitive to the presence of gel-like material formed during the early stages of digestion; with lignite the formation of a gel intermediate is undetectable, and it may not form at all. The impact of this difference in dissolution mechanism upon reactor design is considered.

Filtration in coal liquefaction: 1. Influence of coal type

Abstract Commercial solvent extraction systems for coal must be able to process coals with various properties. In this study the influence of coal type upon the extraction yield of coal and the filtration of extraction products has been investigated. All the coals used gave high extraction yields in hydrogenated solvent but resultant products exhibited considerable differences in rates of filtration. This variation in filtration rates is dependent upon particle size, concentration and composition of the residual solids. No simple relation was found to relate coal type with filtration rate.

Filtration in coal liquefaction — influence of filter membrane on filtration

Abstract The influence of filter membrane upon the filtration of coal digest has been investigated. A selection of filter precoats and wire screens were assessed for suitability in coal liquefaction. It has been shown that the parameters which control the formation of filter cake are: size of aperture, solids concentration of the digest, velocity of liquid through the aperture and attitude of the filter bed.

Filtration in coal liquefaction: preparation of filter aid from filter cake

Abstract In this study the preparation of filter aid from filter cake is considered. Two methods of preparation, carbonization at 550–600 °C and combustion at 800–1000 °C, are used and the optimum conditions determined. The performance of the products is assessed as both a precoat and body feed by comparison with a commercial grade of diatomite. It is shown that efficient filter aids, with performances comparable to that of diatomite, may be produced from filter cake.