Reaction coal liquefaction

These reactors contain suspended solid particles. A discontinuous gas phase is sparged into the reactor. Coal liquefaction is an example where the solid is consumed by the reaction. The three phases are hydrogen, a hydrocarbon-solvent/ product mixture, and solid coal. Microbial cells immobilized on a particulate substrate are an example of a three-phase system where the slurried phase is catalytic. The liquid phase is water that contains the organic substrate. The gas phase supplies oxygen and removes carbon dioxide. The solid phase consists of microbial cells grown on the surface of a nonconsumable solid such as activated carbon. 

A New Outlook on Coal Liquefaction Through Short-Contact-Time Thermal Reactions Factors Leading to High Reactivity... 

These observations suggest that new coal liquefaction technology may be possible based on short contact time reactions. The purpose of this and the related papers in this volume by R.H. Heck and W.C. Rovesti is to show some potential advantages for optimized or integrated short contact time liquefaction processes over conventional technology. 

In catalytic coal liquefaction processes, reaction temperatures must be high in order to insure that thermal reactions disrupt the coal structure to the point that the catalyst can act on the products. 

Other Reaction Products. In addition to SRC, gas, light oil, and a filter cake of unreacted coal and inorganic materials are produced in the first step of the short residence time coal liquefaction process. One of the objectives of short residence time coal liquefaction is to minimize the loss of hydrogen to gases and light oil. 

A question then arises as to whether the CSD recovery is being limited by the preasphaltene content produced from direct products of coal liquefaction or whether by low liquefaction severity a more thermally sensitive product is produced resulting in retrogressive reactions of liquefaction products to "post-asphaltenes." There is some indication that "virgin" preasphaltenes, primary products of coal dissolution, are more easily recovered via CSD as shown in Table VII however, "postasphaltenes" made from thermal regressive reactions are not. 

In this paper the effects of kinds of coal, pasting oil, catalyst and reaction temperature on coal liquefaction are illustrated, and a few kinetic models for catalytic liquefaction of five coals carried out in an autoclave reactor are proposed. 

Various mechanisms and kinetics of coal liquefaction have been proposed and examined by many investiga tors(l,2,4-8). As a general kinetic model of coal lique-action, scheme 1 was assumed. The reaction rate of every reaction step in the scheme assumed to be first order with respect to reacting species and dissolved hydrogen. A few typical cases of a general kinetic model and the general characteristics for their cases are illustrated on Table 3. When compared these typical figures, the curves are apparently different in shape. 

The effects of various reaction conditions on the reaction rate and the mechanism of coal liquefaction were investigated.Conclusions are summarized as follows ... 

Under the same reaction conditions, the reaction rate are depend on the mechanism of coal liquefaction and kinds coal and catalyst. The reaction rate is in the following order Morwell> Bukit... 

Effect of Reaction Conditions on Solubility. Earlier results ( ) suggested investigation of the ZnCl -methanol system as a coal-liquefaction medium based on high product solubility, low... 

Table 2 Coal liquefaction by pyrene derivatives (reaction temp.=370°C, solvent/coal=3/l)...

Figure 2. Effect of reaction temperature on coal liquefaction yield. Coal = It-mann solvent = decacyclene solvent.coal ratio = 3 1.

The important elementary reactions of coal liquefaction are the decomposition of coal structure with low bond dissociation energy, the stabilization of fragments by the solvent and the dissolution of coal units into the solution. 

While, oxygen containing structures of coal must be playing important parts in the course of coal liquefaction. It will be key points that what kinds of oxygen containing structure are decomposed and what kinds of structure are formed in the course of reaction. It has been proposed (5,6) and recently stressed (2-11) that the units of coal structure are linked by ether linkage. 

We have studied the thermal decomposition of diaryl ether in detail, since the cleavage of ether linkage must be one of the most responsible reactions for coal liquefaction among the various types of decomposition reaction and we found that the C-0 bond of polynucleus aromatic ethers is cleaved considerably at coal liquefaction temperature. 

The object of this paper is to draw attention to the possible importance of concerted molecular reactions, of the type termed pericyclic by Woodward and Hoffman (1), in the mechanism of coal liquefaction. 

The HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied MO) levels for hydrogen donors used in coal liquefaction are not yet well known, but the principles involved can be illustrated with the group transfer reaction between molecular hydrogen, a (4n+2)e donor with n=0, and naphthalene, a (4m)e acceptor with m=l ... 

Results showing the effectiveness of the A1- and A2-dialins in coal liquefaction relative to control solvents, naphthalene, Decalin, and fetralin, are presented in Tables 3.1 and 3.2. In both these tables, each row provides the conversion of the coal sample to each of hexane-, benzene-, and pyridine-solubles (plus gases) by the indicated solvent. Table 3.1 contains data derived at a temperature of 400 C and a reaction time of 0.5 hr. Among the control solvents, it can be seen that the naphthalene... 

At typical coal liquefaction conditions, namely temperatures from 300 to 400 C and reaction times on the order of 1 hr, hydrogen transfer from model CIO donors, the A1- and A2-dialins, to model C14 acceptors, anthracene and phenanthrene, occurs in the sense allowed by the Woodward-Hoffman rules for supra-supra group transfer reactions. Thus, in the conversion of the C14 substrates to their 9, 10 dihydro derivatives the dialins exhibited a striking reversal of donor activity, the A dialin causing about twice as much conversion of phenanthrene but only one-tenth as much conversion of anthracene as did A2-dialin. 

The preceding experiments offer preliminary support to our notion that pericyclic pathways might be intimately involved in the mechanism of coal liquefaction. More specifically, the results indicate that pericyclic group transfer reactions constitute a plausible pathway for the transfer of hydrogen from donor solvents to coal during liquefaction. 

Fundamental studies of coal liquefaction have shown that the structure of solvent molecules can determine the nature of liquid yields that result at any particular set of reaction conditions. One approach to understanding coal liquefaction chemistry is to use well-defined solvents or to study reactions of solvents with pure compounds which may represent bond-types that are likely present in coal [1,2]. It is postulated that one of the major routes in coal liquefaction is initiation by thermal activation to form free radicals which abstract hydrogen from any readily available source. The solvent may, therefore, function as a direct source of hydrogen (donor), indirect source of hydrogen (hydrogen-transfer agent), or may directly react with the coal (adduction). The actual role of solvent thus becomes a significant parameter. 

Emphasis in this study was placed upon two reactions carried out at 450°C with sample times between 0 and 180 min. The reference run is that of HgPh, neat, and the second run is the hydrogen-transfer reaction of HgPh withdibenzyl, in which the benzyl radical is formed at conditions typical of coal liquefaction. 

Numerous implications on the fundamental chemistry of coal liquefaction can be drawn from the observed reaction of solvent isomerization and adduction. The literature indicates that... 

Shah, Y. T., Reaction Engineering in Direct Coal Liquefaction. Addison-Weslcy publishing Company, London, 1981. 

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