Isomerization and Adduction of Hydrogen Donor Solvents under Conditions of Coal Liquefaction

Abstract

Hydroaromatic structures are recognized as "ideal" for liquefying coal due to their ability to readily transfer hydrogen to free radical acceptors. While hydroaromatic hydrogens are preferred, substituted aromatic solvents can compete although the latter are more likely to polymerize or adduct with the acceptors. Hydroaromatic structures rearrange to isomeric forms of enhanced stability which are less likely to transfer hydrogen. Six-membered hydroaromatics such as tetralins and octahydrophenanthrenes contract to fivemembered rings (methylindans, etc.). This isomerization is dependent upon temperature, reactor residence time, and, in particular, the level of acceptor radicals. At relatively low temperatures (300-425 OC), the isomerization process is preceded by the adduction of the original hydroaromatic donor with very stable acceptor molecules. This adduction appears to increase with high organic oxygen and sulfur structures. While rearrangements of the above type have been qualitatively known for several years, the present study has attempted to delineate both the kinetic and structural aspects involved.Periodic or semibatch operation of a continuous stirred reactor produces levels of mixing on the macroscale which are intermediate to the limits of plug flow and stirred tank operation and which can be selected and controlled to any desired level. Such a scheme is an operational alternative to the tanks-in-series or plug flow with recycle system, and provides a means of experimentally producing a desired mixing level or of increasing the yield of desired intermediates in complex reaction schemes. In this work criteria for obtaining desired mixing levels are presented, the resulting degree of segregation, J, is derived, and the influence of segregation or conversion for a second-order reaction is presented. Comparisons to the more familiar tanks-in-series and recycle-plug-flow models are included.

Kinetics of short contact time coal liquefaction. Part I: Effect of operating variables

“…Examination of the effect of temperature on the concentration of adducts (measured as depletion of oil) indicates that at least a part of the adduction is by chemical reaction, with the adduct perhaps serving as an intermediate species. Cronauer et al (1979) from their study with model compounds report that ad- duction of some species is enhanced at low temperatures. However, their experiments were not conducted at short contact times, the shortest time being 30 min.…”

Asphaltenes: Definition, Properties, and Reactions of Model Compounds

“…This is a well-documented phenomenon in tetralin, where the major formed product, methylindane, has suffered ring-contraction . Partially hydrogenated polycyclic aromatics, such as 1,2,3,4,5,6,7,8-octahydroanthracene and -octahydrophenanthrene, and 1,2,3,4,5,6,7,8,9,10,11,12-dodecahydrotriphenylene, were also observed to undergo significant ring contraction at temperatures that are much lower than in tetralin reactions. , Hence, fusing a cholestane moiety with an aromatic group, similar to the identified hopanoids by Oldenburg et al, may undergo similar reactions and activate the whole molecule to undergo further decomposition. For example, fusing an aromatic with cholestane, will make the A-ring in cholestane more susceptible to dehydrogenation during thermal cracking because the protons at C1 and C4 will become benzylic protons.…”

Kinetics of dialin thermolysis

“…Reaction (4): This reaction can be considered as equivalent to an abstraction of alpha hydrogen. Gavalas [17] lists log A = 10 and E = 2.3 kcal/mol for alpha abstraction from toluene.…”

“…Even though the 1,4-dialin isomer has a higher heat of formation than the 1,2-isomer, the net reaction is so highly exothermic, and the transition states should be sufficiently similar that the rate parameters should be identical to those of reaction (4).…”