GB843632A - Process for starting an installation for the pressure refining of crude benzene - Google Patents

Abstract

<PICT:0843632/IV(b)/1> In the catalytic refining of benzene by hydrogenation the circulating gas and the reaction chamber are brought to reaction temperature by circulating town gas or coke oven gas charged with steam but without benzene and heated to a temperature not above 200 DEG C. and increasing the quantity of one or more constituents of the gas which react exothermically at temperatures below the refining temperature beyond that necessary for normal refining until the heat generated has heated the apparatus to the temperature of about 320 DEG C. required for refining. In normal operation crude benzene is heated in heater 3 to about 180 DEG C. and introduced to the polymerisation stage 4 where it remains for 15-80 minutes and polymerisable impurities form non-volatile products. The benzene passes into the evaporator 6 into which recycle hydrogencontaining gas at about 280 DEG C. is fed by line 7; additional heat is also supplied. Hydrogen containing gas and benzene vapours at about 190 DEG C. leave by line 9 and unevaporated liquid is removed by line 8. In heat exchanger 10 the benzene vapour feed is heated to about 310-320 DEG C. by reaction products; if an excess of heat is supplied part of the feed may be caused to by-pass the heater through line 11. Coke oven gas or town gas from line 15 is heated in heater 17 to about 150 DEG C. and saturated with steam in saturator 18 before being fed by line 14 to the reactor 13 along with the benzene feed from line 12. Under the conditions in the reactor, viz. about 320 DEG C. and about 45 atmospheres pressure in the presence as catalyst of an oxide or sulphide of a Group 5, 6 or 8 metal the steam reacts with carbon monoxide in the gas to give carbon dioxide and hydrogen, and hydrogen reacts with impurities in the benzene to give volatile products. The hot reactants pass through heat exchanger 10 and the benzene is then condensed and removed by line 22. A portion of the hydrogen-containing gas is removed by line 23 to avoid build up of impurities and the remainder is reheated to about 280 DEG C. and recycled to the evaporator 6. In starting-up operation no benzene is supplied. In order to raise the temperature of the circulating gas and the catalyst to about 320 DEG C. one or more of the following operations is performed:-Extra gas up to 2-3 times greater than normal may be supplied by line 15 thereby supplying extra oxygen; coke oven gas or town gas contains 0,5-1,0% free oxygen. Air or oxygen may be supplied by line 27. Steam saturation in saturator 18 may be suspended by by-passing through line 29. As a result exothermic oxidation reactions take place in the reactor and the highly exothermic hydrogenation of carbon monoxide to methane may take place instead of the formation of carbon dioxide by reaction with steam. Due to these exothermic reactions rapid heating of the system occurs and when the necessary temperature is reached normal operation including the supply of benzene vapour is commenced.