Coal solvent composition

EFFECT OF SOLVENT COMPOSITION OF CONVERSION OF ILLINOIS 6 (BURNING STAR) COAL AT SHORT TIME (2-3 minutes, 425°C)... 

For a given coal a certain portion can be converted to soluble form very easily and is independent of solvent composition. 

Whitehurst, D.D., "Relationships Between Recycle Solvent Composition and Coal Liquefaction Behavior", Proceedings of the EPRI Coal Liquefaction Contractors Meeting, Palo Alto, Calif., May 1978. 

Solvent Composition and Recovery. The solvent was defined as the product fraction which is soluble in the hot filtrate and the THF extraction of the filter cake and which boiled between 232 C and 482 C at atmospheric pressure. One of the requirements of a commercial coal liquefaction process is that a least as much solvent be created as is used in the process. In addition, the composition of the solvent must be kept constant if it is to be... 

The microautoclave solvent activity tests measure coal conversion in a small batch reactor under carefully controlled conditions. The tests are described as Kinetic, Equilibrium and SRT. The Kinetic and Equilibrium Tests measure coal conversion to tetrahydrofuran solubles at conditions where conversion should be monotonically related to hydrogen transfer. The Kinetic Test is performed at 399°C for 10 minutes at an 8 to 1 solvent to coal ratio. The combination of high solvent ratio and low time provide a measure of performance at essentially constant solvent composition. The measured conversion is thus related to the rate of hydrogen donation from solvent of roughly a single composition. In contrast, the Equilibrium Test is performed at 399°C for 30 minutes at a 2 to 1 solvent to coal ratio. At these conditions, hydrogen donors can be substantially depleted. Thus performance is related to hydrogen donor... 

The present authors identified an optimal mixture of solvents for catalytic liquefaction in presence of pyrite. Figure 10 shows the influences of solvent composition (4HF1/Py) on the liquefaction of Morwell coal in an autoclave... 

The Effect of Solvent Compositions on the Liquefaction Behavior of Western Subbituminous Coal... 

For Belle Ayr coal, conversion up to 55% is independent of solvent composition. Beyond this point, conversion is responsive... 

Table 5 shows the composition of the solvents subjected to preheat, the solvent composition based on the percentage of preheated solvent in the total reaction solvent and the composition of the heptane solubles isolated from each reaction. The data shows that the preheated solvents are reduced in percent hydrogen and hydrogen to carbon ratio with increasing severity of preheat. The hydrogen to carbon ratio of the heptane solubles after reaction with coal is essentially the same as that of the solvent (92-03-035 + preheated solvent) which reacted with coal. 

In the studies carried out to date, eight fuels have been tested which include six synfuels and two petroleum derived fuels. The synfuels tested included SRC-II middle and heavy distillate fuels, a blend of these fuels, and one SRC fuel blended with the process donor solvent. Composition data for the various fuels are presented in Table I, where it can be seen that the coal derived liquids have a higher C H ratio than either the diesel or residual petroleum oils, indicative of a higher aromatic hydrocarbon content. The shale-derived DFM on the other hand is a highly processed fuel and has a C H ratio similar to the petroleum diesel oil. Complete analyses of all the actual fuels tested were unfortunately not available at the time of writing, and, where necessary, typical analyses have been taken from previous studies. 

Solvent Composition. In Table III the solubilities of Illinois No. 2 after treatment with KOH and various protic solvents are given. Note that both the glycols and ethanol gave similar yields of extraction products both methanol and water result in large amounts of insoluble products. The superiority of alcohols compared to water for reduction and solubilization of coal also has been noted in acid ZnCl2 melt reductions (15). 

Extract compositions depend on the particular coal/solvent system and on extraction conditions (Raj, 1979). For example, nonspecific solvents generally extract coal selectively and dissolve primarily waxy and resinons snbstances that, althongh derived from the original plant debris, may not be integral parts of the coal snbstance. 

Solvent extraction using nonreactive Hquids, such as C - or C -alcohols, benzene, or benzene-alcohol mixtures, yields generally 5—20% wax or bitumen (15). The yield and composition of the product are determined primarily by the petrologic character of the coal, not its degree of coalification. Montan wax is extracted from suitable coals for a variety of purposes. 

Three West Virginia coals were supplied by the West Virgmia Geological Survey (WVGS). The particular coals were chosen on the basis of rank, petrographic composition, and mineral matter content The coals were limited to the bituminous rank since these coals are the most amenable to the NMP solvent extraction process and are mdigenous to the Appalachian region. Some of the coal characteristics are listed in Table 2. 

In modern terms, asphaltene is conceptually defined as the normal-pentane-insoluble and benzene-soluble fraction whether it is derived from coal or from petroleum. The generalized concept has been extended to fractions derived from other carbonaceous sources, such as coal and oil shale (8,9). With this extension there has been much effort to define asphaltenes in terms of chemical structure and elemental analysis as well as by the carbonaceous source. It was demonstrated that the elemental compositions of asphaltene fractions precipitated by different solvents from various sources of petroleum vary considerably (see Table I). Figure 1 presents hypothetical structures for asphaltenes derived from oils produced in different regions of the world. Other investigators (10,11) based on a number of analytical methods, such as NMR, GPC, etc., have suggested the hypothetical structure shown in Figure 2. 

It is well known that coal reactivity depends on the solvent, the conditions of hydroliquefaction, and the composition of the coal. Different extracting solvent results in different conversion, but it can be considered that the different conversion shows a similar tendency to coal reactivity. Thus, it is desirable that the parameter representing coal reactivity shows essentially the same tendency, despite the conditions of hydroliquefaction. Accordingly comparison of parameters was carried out, using some previously reported results (2, 3). 

For example, Beynon and Cwm coals when digested in anthracene oil give extraction yields of 68% and 47% respectively. This variation can be explained by reference to the maceral composition of the coals. Beynon coal contains a lower concentration of inertinite than the Cwm coal (Table V). In experiments where relatively pure samples of petrographic species were digested in anthracene oil, exinite and vitrinite were shown to be highly soluble, whilst in comparison the inertinite was almost completely insoluble. Similar variations in reactivity of macerals have been reported from studies of solubility in pure organic solvents (1(3). 

The petrological composition is important when considering the solvent extraction of prime coking coals but with lower rank British coals the variations in petrology are less pronounced. A more frequent cause of variations in extraction yield with low rank coals (CRC 802 and CRC 902) results from ageing. The reactivity of a coal decreases substantially as the coal becomes oxidised by exposure to the atmosphere (Table III). 

A system of classifying coals for solvent extraction, based upon the extent of extraction when using anthracene oil and phenanthrene as solvents has been developed. The reactivity of the coals can be conveniently presented by superimposing the results on Seyler s coal chart. The effects of variations in maceral composition are also discussed. 

The significance of these calculations is that lower rank coals will require 5% lower conversion than higher rank coals for a given end product. Also, the more severe a coal is to be upgraded, the lower its conversion has to be in the initial phases of liquefaction. One very pertinent question to be addressed is whether or not coals can be converted to the levels shown in Figure 5 in a short contact time process. This paper will deal with that question as well as what compositional features of the coal and the solvent influence short contact time conversions. 

Beyond this easily converted portion of the coal even at short times, the composition of the solvent is important - high concentrations of H-donors and polyaromatics are beneficial. Over hydrogenation is detrimental. 

The nmr analyses of the bottoms products given in Table IV show the material to have a large aliphatic content. The aromatic/aliphatic ratios of the fractions are higher than for the whole coal because of the presence of combined phenol reaction with Tetralin reduces these ratios considerably, presumably by transfer of much of this material to the solvent-range product, but some of it must remain in the bottoms as the aromatic/aliphatic ratio of the composite bottoms product from the fractions is higher than that from the whole coal. It was not possible to calculate the contribution that the diluents, excess solvent and combined phenol, made to the aromatic H, but the large monoaromatic content of the bottoms product must be due, in part, to these. 

The amounts of exchange and addition were calculated from a hydrogen isotope mass balance of the coal products, donor solvent and gas phase hydrogen. The starting and product weights of the coal and hydrogen compositions of the coal and coal products are shown in Table IV. From the values in Table IV, the net amount of hydrogen added to the coal, H, is... 

In the spent solvents from E10, Table II, naphthalene and tet-ralin were the major products, and the four others were minor products which totaled 8 mole %. In El9, Table III shows that 20 mole % of the four minor products were formed, indicating that an appreciable fraction of tetralin was converted to species less effective in the donor process. Protium from the coal, deuterium from the gas phase or deuterium from the Tetralin is needed to form these products. An examination of the isotopic composition of each of the four products as shown in the bottom halves of Tables II and III allows observations to be made about their formation. 

An investigation of the isotopic composition of the Decal ins, which were formed as minor products in the donor solvent experiments, showed that cis-Decalin was formed preferentially. Its formation and its increased protiurn incorporation may have resulted from increased contact with the coal surface. Trans-Decal in contained less protiurn than the Tetralin, which suggests that most of the trans-Decalin was formed with deuterium from the Tetralin-di2 and deuterium gas. 

Montan wax is obtained by solvent extraction of certain types of lignite or brown coal. It has a dark colour when not treated, but it is lighter when refined. Its chemical composition includes esters of C22 C32 acids (53%), free acids (17%), free alcohols (1 2%), ketones (3 6%) and terpenoids (20 23%) [85]. 

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