Separation coal asphaltenes

Composition of H-Coal Asphaltenes and Preasphaltenes Acid-Base Separations and Oxidative Degradation... 

The solvent fractionation scheme for separating coal liquid products into flve fractions propane-soluble (oil) propane-insoluble and pentane-soluble (resin) pentane-insoluble and benzene-soluble (asphaltene) benzene-insoluble and carbon disulfide-soluble (carbene) and carbon disulfide-insoluble (carboid) was described previously (1,2). 

SRC, a detailed examination of the composition of these coal liquids is of fundamental importance. Numerous procedures have been published previously for investigating the composition of liquids derived from coal. In general, these procedures combine separation techniques with a variety of spectroscopic methods to provide the desired quantity of structural information. The separation techniques used include methods based on solubility fractionation (4,5), methods combining solubility fractionation and adsorption chromatography (6), and liquid chromatographic procedures for chemical fractionation (7,8). Chemical reactions also have been used to separate coal liquid asphaltenes into acidic and basic fractions (9). 

Solvent solubility has been used to separate coal tar pitch [65] into heptane solubles, heptane insolubles but toluene soluble (asphaltenes), and toluene insolubles (preasphaltenes). The same pitch was separated into acetone-soluble, pyridine-soluble, and pyridine-insoluble fractions [66]. The same pitch, a coal digest, and a low-temperature coal tar were similarly fractionated [67,68]. 

The iron sulphide in South African coals is a mixture of pyrite and marcasite (18). Although marcasite is known to transform into pyrite at elevated temperatures, separate spiking experiments were performed to see if pyrite or marcasite would show a preferential catalytic effect. The addition of pyrite and marcasite minerals (-200 mesh), to the coal showed equivalent total conversions, and yields of oil and asphaltene. 

The separation of coal liquids by gel permeation chromatography using lOOA Styragel columns and solvents such as THF and toluene has been reported elsewhere (7.8.9.13.14). Coal liquids and petroleum crude are similar in their physical appearance as well as the complexity in composition. The major difference between the two is that petroleum crude does not contain oxygenated compounds, such as alkylated phenols, in substantial quantity. In addition, the average linear molecular size of petroleum derived asphaltenes (15.16) is much larger than that of coal derived asphaltenes (. ... 

The proton nmr spectrum of fraction 2 of the S02 solubles resembles that of asphaltenes as reported by other workers (1). The elemental composition and the GPC size distribution agrees with the values published for coal derived asphaltenes (1,3). Fractions 3 and 4 of the S02-solubles were separated and identified by GC-MS (see Figures 4 and 5). These fractions contain only a small amount of alkanes. The components are listed in Tables I and II. 

A Co-Mo-AlgOs catalyst (Harshaw CoMo 0402T, 3% CoO - 15% M0O3) was used In some experiments either with or without potassium carbonate. Pyrlte Isolated from coal was also used as a catalyst with potassium carbonate In some experiments. Anthracene oil obtained from Crowley Tar Products Company was used as the start-up solvent. In the recycle runs with Sheridan Field Coal (W-74-45), 80% of the anthracene oil was gradually replaced by coal-derived oil after nine recycles. The benzene and pentane used for separation of oil, and asphaltene were Fisher solvent grade. 

In modern terms, asphaltene is conceptually defined as the n-pentane-insoluble and benzene-soluble fraction whether it is derived from coal or from petroleum. There are a number of procedures used to isolate asphaltene (2-7), all of which appear to be reproducible (8) but do not necessarily provide equivalent end-products. The similarity between coal- and petroleum-derived asphaltenes begins and ends at the definition of the separation procedure. Puzinauskas and Corbett s (9) comments on asphalt may be paraphrased and applied to asphaltene. They state that the broad solvent classification is unfortunate it leads to misconceptions that petroleum and coal materials are alike, or at least similar. However, these two classes of materials differ not only in their origin, mode of manufacture and uses, but also in their chemical composition and physical behavior. 

We believe it is important, at this time, to establish a documented historical review of asphaltenes and the separation/characterization procedures used by early petroleum and coal chemists to profile crude oils and the products of coal hydrogenation. We shall explore the most important differences between petroleum- and coal-derived asphaltenes. 

Figure 1. Solvent separation of a COED coal liquid into oils, asphaltenes, and...

Vacuum-still bottoms from the H-coal liquefaction process were separated into acid, neutral, and basic fractions by precipitation with acids or by extraction with bases. About one-third of the preasphaltene and one-sixth of the asphaltene fraction were precipitated by acids equivalent weights of the bases were in the range 1200-1800 for preasphaltenes and 600-800 for asphaltenes. The acidic components were obtained either by extraction with aqueous sodium hydroxide or by extraction with benzyltrimethylammonium hydroxide in methanol. About one-fifth of the asphaltene and one-fourth of the presasphaltene fractions were obtained as acids, and up to 10% as amphoteric substances. Nitrogen and sulfur were present in all fractions found. Deno axidation (CF3C02H, H202, H 04) gave dicarboxylic acids from malonic to adipic in addition to mono acids. 

The phosphotungstate salts cannot be used for equivalent weight determinations, for their characteristically variable composition leads to inconsistent titration results. However, treatment of the salts with aqueous sodium hydroxide led to recovery of the free bases in reproducible amounts. These results show that one-fifth of the high molecular weight asphaltenes and one-third of the preasphaltenes are precipitated as phosphotungstate salts. Considerably less of the unfractionated H-coal vacuum-still bottoms and none of the low molecular weight asphaltenes and oils and resins were separated in this manner. 

Samples of each of the coal derived materials were reacted separately in the presence of several catalysts in a 70 ml batch autoclave using a 1 1 slurry of tetralinrmaterial at 425 C with an initial hydrogen pressure of 6 MPa for 1 hour at reaction temperature. The products from these reactions were separated into oils, asphaltenes, preasphaltene and THF insolubles. 

Solvent fractions of coal liquids such as oils, resins, asphaltenes, and carboids may be separated because of their different polarity, molecular weights, and degree of aromatic character. The composition of coal liquids appears to be more closely related to the liquefaction process used rather than to the type of coal used. For example, oils and resins produced in SRC processes appear to have higher molecular weight, more aromatic average molecules than those contained in either pyrolysis or catalyzed hydrogenation coal liquids. This suggests less breakdown of coal and coal liquefaction intermediates to smaller. 

Goldberg et al. have also measured the ESR parameters of liquefaction products of a high-volatile bituminous coal separated into oils, asphaltenes, a benzene-methanol soluble (BMS) fraction and benzene-methanol insoluble (BMI) fraction. The spin concentration N decreased in the sequence BMI > BMS > asphaltene > oil, whereas the g-value decreased in the opposite sequence, a result essentially in agreement with those of... 

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