Liquefaction under atmospheric pressure

The present authors studied the solvolytic liquefaction process ( ,7) from chemical viewpoints on the solvents and the coals in previous paper ( 5). The basic idea of this process is that coals can be liquefied under atmospheric pressure when a suitable solvent of high boiling point assures the ability of coal extraction or solvolytic reactivity. The solvent may be hopefully derived from the petroleum asphaltene because of its effective utilization. Fig. 1 of a previous paper (8) may indicate an essential nature of this process. The liquefaction activity of a solvent was revealed to depend not only on its dissolving ability but also on its reactivity for the liquefying reaction according to the nature of the coal. Fusible coals were liquefied at high yield by the aid of aromatic solvents. However, coals which are non-fusible at liquefaction temperature are scarcely... 

In the present study, the liquefaction activities of pyrene, its derivatives, and decacyclene with coals of several ranks are studied to ascertain the previous ideas of liquefaction mechanism and to develop novel liquefaction process under atmospheric pressure. The coals used in the present study are non-fusible or fusible at relatively high temperature, and then gave small liquefaction yield with pyrene of a non-solvoly-tic solvent at 370°C. 

West-Kentucky, and Itmann coals of three different ranks were sufficiently liquefied with hydropyrene under atmospheric pressure at 370°C regardless of their fusibility. The analyses of hydropyrene and the coal before and after the liquefaction clearly indicate the hydrogen transfer from the solvent to the coal substance. Lower rank coals look to show rather higher reactivity in such liquefaction, probably because their constituent molecule may have smaller condensed ring. 

The liquefaction mechanism was discussed by distinguishing the fusible coal from non-fusible one. The importance of solvolytic hydrogen transfer is pointed for the liquefaction of non-fusible coal under atmospheric pressure. 

The purified water gas passes down the tube A, through coils in the vessel B, which is filled with liquid carbon monoxide boiling at atmospheric pressure [ — 190° C.). Now, since the water gas is under pressure and is passing through coils cooled to its temperature of liquefaction at atmospheric pressure, the bulk of it liquefies (theoretically more gas should be liquefied in the tubes than is evaporated outside them). 

The first process was studied by Berthelot in 1867 and was further developed in Germany by Bergius in 1910. The early Bergius process involved the reaction of H2 under atmospheric pressure with pulverized coal suspended in an oil heated to about 450°C in the presence of a catalyst such as stannous formate or Mo. The liquid oil product is separated from the solid residue and processed as ordinary crude oil. Modem developments in this coal liquefaction approach include (1) Exxon Donner Solvent (EDS) process, (2) the HRI H-Coal process, and (3) the Gulf Solvent Refined Coal SRC-II process. The major improvement of these processes over the Bergius process is in the catalyst used, allowing for milder reaction conditions. 

Full processing of chlorine gas (Fig. 6.6) takes a hot, wet vapor at approximately atmospheric pressure and converts it to a cold, dry liquid under significant positive pressure. The common processing steps therefore are cooling, drying, compression, and liquefaction. The severity of the two latter processes depends on the desired degree of recovery of chlorine as the liquid and on the composition of the gas produced in the cells. The major impurities in this gas will be ... 

The dry gas, still at approximately atmospheric pressure, can be handled safely in mild steel equipment Particularly with membrane cells, which can operate under some positive pressure, the gas, wet or dry, is suitable for some applications. In most cases, however, the next step will be compression. The pressure must be raised to a level sufficient for liquefaction at a reasonable temperature or for direct use as a gas in another process (e.g., the manufacture of ethylene dichloride). Operating conditions and the apparatus used for compression are highly variable and are the subject of Section 9.1.6. 

Most chlorine cell headers operate very close to atmospheric pressure. The accumulated pressure drop causes compressor suctions to be under vacuum, which raises the possibility of infiltration of atmospheric air. This lowers the purity of the delivered gas and makes the liquefaction process less efficient. The front end of the gas processing train therefore should be desired for low pressure drop. To this end, the drying towers... 

The liquefaction of helium by a controlled expansion process necessitates preliminary cooling because its Joule-Thomson coefficient is negative (spontaneous expansion heats the gas) down to an inversion temperature of 40 All the gases have C /C ratios very close to 5/3, the theoretical value for an ideal monatomic gas. The elements are liquid over very small temperature ranges. Plelium can be solidified only under pressure under 26 atmospheres it solidifies at 0.9 °K. 

A major source of emissions from the coal dissolution and liquefaction operation is the atmospheric vent on the slurry mix tank. The slurry mix tank is used for mixing feed coal and recycle solvent. Gases dissolved in the recycle solvent stream under pressure will flash from the solvent as it enters the unpressurized slurry mix tank. These gases can contain hazardous volatile organics and acid gases. Control techniques proposed for this source include scrubbing, incineration, or venting to the combustion air supply for either a power plant or a process heater. 

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