there is at least an implication that ral coalification path for vitrinite pal precursors for alginite. There is, some of the aliphatic entities are and the artificial path for hydro- as yet, no evidence for the formaconverted to aromatics during coal- thermal carbonification of cellulose. tion of kerogens from diatoms. ification. A further implication is Heating cellulose with clay at 150 The present studies on the mechathat the loss of methylene carbons °C yields products in which the nisms of coalification at Argonne sometimes observed may typically celluloselike structures still pre- are still in the early stages, but the occur either by fragmentation reac- dominate. Winans notes that it is early evidence suggests that major tions or by conversion to aromatics. generally accepted that cellulose is progenitors such as lignin or lipids The increase in aromaticity of artifi- easily removed in the diagenetic could survive the diagenetic stages cial products is believed to be simi- stage of coalification, leaving lig- of coalification. They could then be lar to that observed in artificial coals nin to be preferentially concentrat- transformed directly to highly aroof higher rank. Reduction of the ed with the phenol derivatives and matic (vitrinite) and highly aliphataliphatic character in the artificial lipids. There is also independent ic (alginate) macromolecules by therproducts with greater reaction times evidence that the cellulose is prefer- mal catalysis. further reinforces this belief. As entially lost while the lignin conThe current research into direct coalification proceeds, the data sug- centrates during coal formation. At coal formation implies, among othgest that structures in the artificial present the artificial coalification of er things, that the fundamental orproducts become more and more cellulose does not produce solid ma- ganic structures in coal derived dicrosslinked through the aromatic terials chemically similar to vitrinite. rectly from lignin should be much groups. This is in agreement with However, the possibility of a minor less diverse than those from ran13 C NMR data acquired. contribution from cellulose and/or domly altered materials. In addition, Clay minerals are important to its derivatives in coalification can- the artificial coalifications provide excellent models for the complex this artificial coalification process. not be excluded totally. Acid treatment of the clays accelerOne of the more elusive mecha- macromolecular structure of coal and ates the reactions a bit but even the nisms is probably that for the for- yet are less chemically complex beuntreated clays are "convincingly mation of aliphatic macromolecules cause of the pure source materials. catalytic," according to Winans. in oil shale kerogens or coal al- The next step in the research is to Transformation of lignin certainly ginates. Such materials have been make use of isotopic labels to furdoes not occur in the absence of the synthesized from algal fatty acids. ther probe structural transformations clays. The clays of choice are mont- These acids are important lipid con- during coalification. Ultimately, the morillonite varieties, but kaolinite stituents of algae and are very object is to define coal structures and illite clays are also effective, if abundant. Nonmarine algae gener- and how they were formed. to a lesser degree. Combinations of ally are considered to be the princiJoseph Haggin, Chicago the various clays don't seem to have an effect different from that of the individual kinds. The presence of AlBr3 also appears to catalyze the artificial coal- A new gas-treating agent developed ture adjacent to the nitrogen atom ification process. However, it is not by Exxon Research & Engineering to form a hindered amine. Control certain that the structures of prod- Co., Florham Park, N.J., selectively of the amine molecular structure ucts obtained with AlBr 3 are similar removes h y d r o g e n sulfide from makes it possible to tailor the agents to those of the corresponding coal gases. The company says it can in- for specific treating functions. vitrinites. crease s c r u b b i n g capacity more The company has completed labHigh-temperature pyrolysis of lig- than 40%, compared to other gas- oratory, pilot plant, engineering, nin from 350 to 400 °C does not treating agents and processes. and commercial application studies effect the transformation into coalSelective removal of hydrogen on the new agent. The studies, it like materials c o r r e s p o n d i n g to sulfide is economically preferred in says, show that the agent is an atvitrinite and/or lignite. Even in the refinery and production applica- tractive replacement for other selecpresence of clay, such high-temper- tions, including Claus sulfur plant tive hydrogen sulfide removal proature reactions did not produce tail gas cleanup, when there are no cesses now in commercial use, inproducts consistent with the natu- process needs to remove other gases. cluding both methyldiethanol amine ral evolutionary path to vitrinite. The new agent, called Flexsorb SE, and direct conversion processes. Loss of catalytic effects by the clays has been designed specifically to Exxon R&E expects formally to was observed when the reactions react preferentially with hydrogen offer Flexsorb SE for licensing soon. were carried out in the absence of sulfide rather than carbon dioxide. It says it also plans to offer hindered air. It is apparent that the lignin The agent is one of a family of amine technology that can make imfunctional groups, which are suscep- gas-treating agents being developed provements in removal of both cartible to oxidation, are very easily by Exxon R&E based on a new amine bon dioxide and hydrogen sulfide oxidized. chemistry. Company researchers using amines in an organic solvent, Another matter that has piqued have found that the effectiveness and in removal of carbon dioxide the interest of the Argonne group of treating agents can be improved with an amine-promoted hot potasis the similarity between the natu- by placing a bulky molecular struc- sium carbonate solution. D
Exxon agent selectively removes H2S from gases
November 21,1983 C&EN
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