Coal liquefaction stages

Catalytic hydrogenation of phenanthrene to the octahydro-stage produces both sym- and asym-isomers, although the former predominate Additionally, interconversion of the two forms tends to occur at coal liquefaction conditions. Since the... 

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. 

Derbyshire, FJ., Catalytic Coal Liquefaction by Temperature-Staged Reaction, presented at Direct Liquefaction Contractor s Review Meeting, Pittsburgh, PA (Oct. 20-22, 1986). 

Multistage coal liquefaction has been proposed to consist of the following stages, as shown in Fig. 1 [this scheme is the basis for promising processes... 

Hence, the catalysts and catalyses of coal liquefaction are reviewed with reference to the above stages. 

Solid/liquid separation is usually required at the interface of the primary and secondary stages to allow optional upgrading of the crude coal liquids of the primary liquefaction stage, by removing mineral matter, unreacted coal, heavy products, and catalysts (111, 112). Distillation, anti-solvent extraction, and centrifugation have been conventionally employed in liquefaction processes (113, 114). 

Catalysts for coal liquefaction require specific properties. Catalysts of higher hydrogenation activity, supported on nonpolar supports, such as tita-nia, carbon, and Ca-modified alumina, are reasonable for the second stage of upgrading, because crude coal liquids contain heavy polar and/or basic polyaromatics, which tend to adsorb strongly on the catalyst surface, leading to coke formation and catalyst deactivation. High dispersion of the catalytic species on the support is very essential in this instance. The catalyst/support interactions need to be better understood. It has been reported that such interactions lead to chemical activation of the substrate 127). This is discussed in more detail in Section XIII. 

The difficulty in the recovery of catalysts from unreacted coal and minerals and the poor regenerability of used catalysts forces one to use disposable catalysts, especially in the primary stage. This increases the cost of coal liquefaction considerably. This section reviews the mechanism of catalyst deactivation, design of recoverable catalysts in the primary stage, and catalyst deactivation in the secondary stage. 

All of these problems are related to the performances of the catalysts used in coal liquefaction. Very active, durable, recoverable, and regenerable catalysts are most wanted in the primary liquefaction stage, where catalyst poisons from asphaltenes and minerals are most severe. Multifunctional catalysts should be designed by selecting supports with specific functions, such as strong but favorable interactions with catalytic species, resistance to poisons, and improved properties to allow easy recovery, while maintaining high activity. 

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. 

In an effort to obtain higher value products from SRC processes, a hydrocracking step was added to convert resid to distillate liquids. The addition of a hydrocracker to the SRC-I process was called nonintegrated two-stage liquefaction (NTSL). The NTSL process was essentially two separate processes in series coal liquefaction and resid upgrading. NTSL processes were inefficient owing to the inherent limitations of the SRC-I process and the high hydrocracker severities required. 

The SRC-II process is one of several coal liquefaction processes currently under development in programs funded by the Department of Energy (DOE). Product from this process is a distillate that is relatively attractive as a feed for conversion to transportation fuels. Essentially all of the nitrogen, sulfur, and oxygen can be removed in a single catalytic hydro-treating stage to yield a naphtha that is an excellent feed for a catalytic reformer and a middle distillate fraction that is a... 

The software system, to meet the needs of the 1980 s, has wide flexibility and capabilities. For processes such as coal gasification or coal liquefaction, it can be used to perform steady state material and energy balances, calculate sizes of equipment, and carry out economic evaluations. Its flexibility can allow for the handling of coal or other solids in streams and equipment, and its capabilities allow for the simulation of many different types of process equipment and the calculations of physical properties under widely different conditions. Included in this is the ability to analyze conventional chemical and petroleum processes. Another valuable feature 1s a good preliminary cost estimation capability that permits the comparison of alternative processes on an economically consistent basis at an early stage of development. 

Cugini, A, Krastman, D. Lett, R. Balsone, G. Development of a Dispersed Iron catalysis for First Stage Coal Liquefaction Catalysis Today 19 (1994) 395-408. 

EPRI, Two-Stage Coal Liquefaction Integrated Configurations The Advanced Coal Liquefaction R D Facility, Wilsonville, Alabama, EPRI GS-7293 (May 1991). 

Nalitham, R. V., Lee, J. M., Lamb, C. W., and Johnson, T. W., Two-Stage Coal Liquefaction Process Performance with Close-Coupled Reactors, Fuel Proc. Technol., 17, 13-27 (1987). 

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