Preasphaltene extraction

For the toluene extractions, the work-up procedure was as described previously (j> ). In the supercritical water experiments, most of the extract was insoluble in water, after cooling and lowering of the pressure, and precipitated out in the condenser and receiver from which it was collected by washing with acetone and then THF. The remainder of the extract was found in the aqueous suspension which was evaporated to dryness on a rotary evaporator and the residue extracted with acetone and THF. The solvents were removed under reduced pressure from the combined acetone and THF solutions to give the total extract. This was then extracted with hot toluene and the cooled solution filtered to give the preasphaltene fraction. After the toluene was removed under reduced pressure from the filtrate, the residue was re-dissolved in a small volume of toluene and a 20 fold excess of pentane added to precipitate the asphaltene which was filtered off. The pentane and toluene were then removed from the filtrate under reduced pressure to give the oil. For the NaOH extractions, the NaOH solutions were neutralised with HC1. The insoluble extract was washed with water and then extracted with THF. Removal of the THF gave the total extract. 

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. 

Extraction of Preasphaltenes into Methanolie Triton-B. A sample of preasphaltenes (42.0 g) was placed in a Soxhlet thimble and extracted with methanol for 48 h. The methanol extract was evaporated to dryness to give 4.4 g (10.6%) of methanol-soluble residue. The undissolved solids were removed from the thimble and dried in vacuo. This methanol-insoluble preasphaltene fraction was used in several subsequent experiments. 

Other acids used for precipitation of preasphaltene bases from a two-phase system are listed in Table II, together with some information about the salts obtained and the bases recovered from them. Citric and glycerophos-phoric acids were chosen for their lipophobic anions, which should ensure complete precipitation or extraction from the hydrocarbon solvents. 

The fact that part of the nonbasic fractions of the asphaltene or preasphaltene samples could be dissolved in aqueous sodium hydroxide was surprising, for when untreated samples are extracted with aqueous base, almost nothing is removed. Removal of the nitrogen bases evidently frees the acidic components for reaction with hydroxide, even though the bases are only weakly basic and should not be able to compete with hydroxide ion for the acidic components. Presumably this is a question of wetting, contact, or occlusion. 

Husack and Golumbic (4) reported the isolation of the phenolic acids from asphaltenes by extraction into Claisen alkali (KOH in water/methanol). In a somewhat similar approach, H-coal preasphaltenes were treated with several methanolic hydroxide solutions. The results, shown in Table V, show that 10%-12% of the preasphaltenes are soluble in methanol alone. Substantially more of these materials dissolve in 1.5M sodium or lithium hydroxide solutions. The greatest amounts of preasphaltenes were extracted by 1.5M solutions of quaternary ammonium hydroxide bases. Because Triton-B (ben-zyltrimethylammonium hydroxide) in methanol was capable of dissolving 65% of the preasphaltene materials, it was used in a more elaborate fractionation scheme. 

A sample of methanol-insoluble preasphaltenes (89.4% of the starting preasphaltenes) was treated with 1.5M methanolic Triton-B 49% of undissolved material remained. Extracting the filtrate with petroleum ether gave 6% of a nonpolar fraction. Water added to the methanolic phase precipitated insoluble Triton-B salts, which yielded 28% of acids upon acidification. The filtrate from these salts, largely aqueous, contained soluble Triton-B salts, from which a further 14% of acids was obtained. The material balance of the methanol-insoluble preasphaltene was thus 97%. The elemental analyses of these fractions are shown in Table VI. 

Table V. Separation of Preasphaltenes by Extraction with Basic Methanol...

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