Coal liquefaction process, data

An enormous amount of work both at bench scale and at pilot plant scale have been conducted to study the production of liquid and gaseous hydrocarbons from coal. Since most of the analytical methods are either very time consuming or very specialized, almost all the data available on the coal liquefaction process are based on distillation data or on the assumption that all products which are not insoluble solids are converted. It is known that products of liquefaction vary based on coal, reaction conditions, and media of reaction hence, conversion and yield may be based on very different products. 

The type of quantitative analytical data which are needed for modelling and kinetic studies on coal liquefaction process could not be obtained by using general analytical techniques. We have developed a new analytical approach for obtaining qualitative information as well as quantitative data on coal liquid species. Coal liquefaction produces smaller molecules from coal which is composed of larger molecular species or a matrix of larger molecular species in which smaller species are entrapped. 

The structural information obtained will be illustrated with data on asphaltenes from a Clearfield, Pennsylvania coal extract, asphaltenes from the Synthoil coal liquefaction process of the Department of Energy, and a lighter distillate asphaltene from the Exxon Donor Liquefaction Process (EDS). No attempt is made to correlate composition with sample origin or treatment as the samples derive from different coals and were obtained at different conditions. 

Nowacki, P. 1979. Coal Liquefaction Processes. Noyes Data Corporation, Park Ridge, NJ. 

Data for the kinetics of coal liquefaction have been published in the literature (1-11). A review of the reported studies has recently been given by Oblad (12). The reported data were mostly obtained in bench-scale reactors. Guin et al. (7) studied the mechanism of coal particle dissolution, whereas Neavel (7), Kang et al. (8), and Gleim (10) examined the role of solvent on coal liquefaction. Tarrer et al. (9) examined the effects of coal minerals on reaction rates during coal liquefaction, whereas Whitehurst and Mitchell (11) studied the short contact time coal liquefaction process. It is believed that hydrogen donor solvent plays an important role in the coal liquefaction process. The reaction paths in a donor solvent coal liquefaction process have been reviewed by Squires (6). The reported studies examined both thermal and catalytic liquefaction processes. So far, however, very little effort has been made to present a detailed kinetic model for the intrinsic kinetics of coal liquefaction. 

Direct-Liquefaction Kinetics All direct-liquefaction processes consist of three basic steps (1) coal slurrying in a vehicle solvent, (2) coal dissolution under high pressure and temperature, and (3) transfer of hydrogen to the dissolved coal. However, the specific reaction pathways and associated kinetics are not known in detail. Overall reaction schemes and semiempirical relationships have been generated by the individual process developers, but applications are process specific and limited to the range of the specific data bases. More extensive research into liquefaction kinetics has been conducted on the laboratory scale, and these results are discussed below. 

Coal ash is not always a deleterious material for a process. In coal liquefaction, it has been observed that the rate is increased in the presence of pyrite. In gasification, the rate is increased in the presence of alkalies. There is limited data available on the effects of materials on combustion. Although interest in synthetic fuels from coal is quite limited at present, there is an interest in developing the technical capability to permit the production of more premium fuel types from less desirable ones. The conversion of solid coal to liquid fuels has been a very demanding process in terms of the pressures and, to some extent, the temperatures that have been used. Catalysts have been required in all cases. The catalysts have been poisoned by the sulfur and other species in the mineral matter. As a result, catalyst costs and replacement rates can be quite high. A cheap, naturally occurring catalyst that came with the coal would be of significant interest. Pyrite seems to be such a material. 

The Exxon donor solvent, direct liquefaction process also used hot oil drying. In this process, LRC is dried by a high-pressure hydrogenation reactor contact with hot recycle hydrogen donor solvent prior to entering. Unfortunately, no data were developed for solvent recovery after drying becanse the dried coal and vehicle solvent were reacted immediately with hydrogen in the Uqnefaction reactor. 

Publications on successful application of realistic design models to commercial scale slurry processes are relatively scarce. Nevertheless, progress has been made, particularly in modelling slurry reactors for coal liquefaction, Fisher-Tropsch synthesis, methanol synthesis, oxydesulfurization of coal and selective hydrogenation where intermediates are the desired product. The result is encouraging, taking the lack of reliable mass transfer data at actual reactor conditions into account. 

The primary purpose of this paper is to describe the kinetics of coal liquefaction derived from a pilot-scale unit. The specific coal studied was Big Horn subbituminous coal. The experimental data were obtained in a pilot-scale Gulf patented (13) reactor. The data illustrate the effects of reactor space time and temperature on the product distribution. Since the reactor behaves as a bubble column, the intrinsic kinetics of the liquefaction process can be extracted by means of a kinematic model of the reactor. The experimental data were found to be... 

The plant will process 27,836 TPSD of Illinois No. 6 high sulfur bituminous coal containing 4.45 wt% sulfur on an as recieved basis. The output of fuel products form the plant is 15,531 BPSD of naphtha and 51,325 BPSD of syncrude. 1,178 tons per day of elemental sulfur is produced. This represents 95 wt% of the total input sulfur in the feedstock coal. Most of the remaining sulfur is still present in the liquid synthetic crude oil. From the available data for this proposed plant, the output of elemental sulfur is calculated to be 0.0176 tons per product barrel. Since a high sulfur coal was used this represents a high sulfur production case as it is likely that direct liquefaction facilities will use high sulfur Eastern bituminous coals as feedstock. 

T he ash content and trace element distribution in oils produced from coal are of concern for two different reasons—they bear on possible environmental hazards from the use of the oil and they determine the suitability of the oil for firing in gas turbines. Some trace element analyses of oils produced by the catalytic liquefaction of three coals are reported, together with analyses of the solid residues from the process. The data are neither comprehensive nor particularly accurate and are offered at this time because, in the absence of better information from other laboratories, they seem to be of some interest. 

Properties. Pilot-unit data indicate the EDS process may accommodate a wide variety of coal types. Overall process yields from bituminous, subbituminous, and lignite coals, which include liquids from both liquefaction and Flexicoking, are shown in Figure 14. The liquids produced have higher nitrogen contents than are found in similar petroleum fractions. Sulfur contents reflect the sulfur levels of the starting coals ca 4.0 wt % sulfur in the dry bituminous coal 0.5 wt % in the subbituminous and 1.2 wt % sulfur in the dry lignite. 

The methods used at BERC to characterize petroleum and coal liquids provide a means for systematic study of various alternate or synthetic crude oils. The compositional data so produced are useful for producers or refiners of such materials and give them a base for clearer comparison of all liquids produced. Data from the batch preparation of liquids and the subsequent characterization of these liquids will provide a clearer understanding of the effect of coal source on the hydrocarbon composition of the potential liquefaction products. Such information will be necessary for the proper upgrading of coals and coal liquids and will contribute to more efficient processing and end-use of these materials. 

Pyrolysis results are very important for coal characterization, as all conversion processes of coal such as combustion, liquefaction, and gasification start with a pyrolytic step. For this reason, pyrolysis was frequently used for the analysis of coals [17,18). Pyrolysis data were correlated with coal composition, coal characterization and ranking [18a], prediction of coal reactivity as well as of other properties related to coal utilization. Techniques such as Py-MS, Py-GC/MS with different ionization modes, Py-FTIR, or evolved gas analysis (EGA) [19] were described for coal analysis. Programmed temperature pyrolysis is another technique that has been proposed [17] for a complete evaluation of the two types of molecules present in coal. 

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