Coal short-time reaction products

Short-Time Reaction Products of Coal Liquefaction and Their Relevance to the Structure of Coal... 

Farcasiu, M. "Short Time Reaction Products of Coal Liquefaction and Their Relevance to the Structure of Coal." ACS Div. Fuel Chem. Preprints 24(1) (1979) 121. 

The production of such high concentrations of radicals leads to a very unstable situation and if the radicals are not stabilized via H-donation, they undergo a variety of undesired reactions such as condensation, elimination or rearrangement (7). Neavel has shown that at short times ( 5 min) a vitrinite enriched bituminous coal can be converted to 80% pyridine soluble form in even non-donor reaction solvents (naphthalene) (8). But if reaction times are extended, the soluble products revert to an insoluble form via condensation reactions. Such condensation reactions were... 

Other Reaction Products. In addition to SRC, gas, light oil, and a filter cake of unreacted coal and inorganic materials are produced in the first step of the short residence time coal liquefaction process. One of the objectives of short residence time coal liquefaction is to minimize the loss of hydrogen to gases and light oil. 

For reactor design calculations it is necessary to know the total devolatilization rate as well as the species production rates. Therefore, one needs to include in the reactor model all the reaction rates that are available for the devolatilization of the particular coal. Kayihan and Reklaitis (8) show that the kinetic data provided by Howard, et al. (5,6) can be easily incorporated in the design calculations for fluidized beds where the coal residence times are long. However, if the residence time of pulverized coal in the reactor is short as it is in entrained bed reactors, then the handling of ordinary differential equations arising from the reaction kinetics require excessive machine computation time. This is due to the stiffness of the differential equations. It is found that the model equations cannot be solved... 

The most useful data for structural characterization were obtained in the present work by the use of short-time (1-5 min) thermal treatment with an H-donor solvent under hydrogen pressure at 425 C as the method to solubilize coal (1, 2). We will discuss how the chemical structure of the products of this reaction can be used to determine characteristic elements of the structure of coals. Other and more limited information can be obtained from the study of solid coal itself and can be used to complement the data gathered with the solubilized coal. 

The obvious danger of structural studies involving coal solubilization followed by the investigation of the reaction products is the possibility of transformation of the primary products by further reaction. However, our results (1,2) indicate that at short contact times the principal reactions involve only thermal cleavage of the weaker bonds, and therefore the intrinsic elements of the coal structure are preserved without modification. 

A corollary of this statement is the following If these polyaromatic or polycyclic saturated structures are present in the carbon skeleton of coal, they should be identified in the short-contact-time liquefaction products. The possibility of some isomerization reactions in the carbon skeleton cannot be excluded totally, but the most important fact is that no dramatic aromatization of hydroaromatic rings or saturation of aromatic rings takes place under these conditions. Many of the chemical functions also are stable under these conditions, especially the O, S, and N heterocyclic aromatic structures. Water formation by phenol dehydroxylation is minimal. In coal liquefaction under our conditions, even at long reaction times (up to 90 min) in the absence of an added catalyst, the -OH bonded to a monoaromatic ring is stable. Under the same conditions, dehydroxylation of polyaromatic phenols does occur (10). 

Short-Contact-Time Coal Liquefaction Products and the Initial Structure of Coal. Our own data and those from the literature indicate that no major changes take place in the different elements of coal structure under short-contact-time reaction conditions and at relatively low temperature. It is obvious, however, that fragmentation occurs by... 

Coal Residence Time. Because the oxidation rate is fast, there is essentially no residence time required for chemical reaction. In a plug flow reactor, coal feed rate would depend only on the oxygen input rate and the unit oxygen consumption. Moreover, if gas distribution is uniform, the oxidation would be uniform. In a continuous fluidized-bed reactor, however, residence time must be long enough to minimize the effect of the short-circuiting of untreated feed into the product. The... 

In solvent refining, coal is converted to a pyridine-soluble product after very short residence time at reaction conditions. 

For the coal studied here, a bituminous Western Kentucky 9/14 coal, dissolution of the coal has been shown to occur very rapidly, requiring less than 30 minutes to liquefy most of the coal ( 90 percent). However, a relatively long reaction time (120 min.) is required to reduce its sulfur level low enough to meet even the current standards (1). A new short residence time two-stage SRC type process has been suggested by Auburn University (2 ) for solvent refining this coal. This process has been shown to have the potential of producing a low-sulfur solid SRC product that meets the proposed NSPS. It involves the dissolution of the coal... 

Product characterization from liquefaction has not been extensive. Phi 1p and Russell (95) have examined products by Py-GCMS from metal halide catalyzed hydrogenation of a vitrinite, alginite, and inertinite, each from a different source. They were able to correlate Py-GCMS results with reaction temperature. King, et al. (96) examined the short contact time liquefaction of macerals separated by DGC from a single hvB bituminous coal. They found correlations between density and reactivity and composition of the products. 

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