April 27, 1948. A. G. oBLAD 2440,414 PRODUCTION OF CYCLOHEXANE Filed Dec. 3, 1945 Alex G. Oelso/ or 24, 6,374//W/AW7OA Patented Apr. 27, 1948 2440414 UNITED STATES PATENT OFFICE PRODUCTION of CYCLOHEXANE Alex G. Oblad, Dallas, Tex, assignor, by mesne assignments, to Socony-Vacuum Oil Company, Incorporated, New York, N.Y., a corporation of New York Application December 3, 1945, Serial No. 632,546 4. Claims. (C. 260-667) 2 This invention relates to the manufacture of Cyclopentane which serves in the coordinated cyclohexane of high purity by the hydrogenation azeotropic distillation step as an agent for remov of benzene and more particularly to a novel. ing unconverted benzene from the cyclohexane process wherein benzene is catalytically hydro product. The methylcyclopentane-benzene aze genated at Only moderately high pressures to otrope is recycled to the hydrogenation reaction produce a substantially benzene-free cyclohexane Zone. I use an all hydrocarbon system in which product. the methylcyclopentane may be recycled from the In the preparation of cyclohexane by the hy distillation step through the hydrogenation zone drogenation of benzene it is difficult to hydro without adversely affecting the hydrogenation genate the benzene completely unless pressures O reaction therein, thus avoiding the loss of aze in excess of 2000 or 3000 pounds per Square inch . otropic agent incurred by the necessity of sepa are employed and unless the reactants are highly ration of recycle benzene therefrom. purified. Wery active cataylists which are rela Methylcyclopentane forms with benzene an tively sensitive to deactivation must be used to azeotrope which boils at 71.5 C, at atmospheric obtain complete conversion of benzene to cyclo 5 pressure, that is, about nine degrees centigrade hexane in a single pass. Hence, the more ad below the boiling point of benzene and of cyclo vantageous method of carrying out the hydro hexane. The composition of this azeotrope is genation has been to carry out the process by approximately 90 mole percent methylcyclopen taking a 90 to 95 percent conversion and sepa tane and 10 mole percent benzene. The composi rating unreacted benzene from the cyclohexane 20 tion of the azeotrope varies somewhat with the product by solvent extraction methods or by the pressure at which the distillation is carried out. use of an azeotropic agent in making this separa Thus, at about five pounds absolute pressure the tion by fractionation. Agents well known to the composition of the azeotrope is about 91 mole art are isopropyl alcohol, acetone, and methyl percent methylcyclopentane and 9 mole percent acetate. Solvents which may be used to separate 25 benzene while the azeotrope is richer with respect the benzene for recycle from the cyclohexane to benzene content at distillation pressures above product are liquid sulfur dioxide, furfural and atmospheric and may contain as much as 14 mole phenol. In general, the use of solvents has percent of benzene when the fractionation is proved to be unsatisfactory and not adaptable carried out at pressures of 100 to 150 pounds gage for continuous operation. Likewise, the use of 30 or about 12 mole percent benzene at preSSures of alcohols and other oxygen containing compounds 50 to 75 pounds gage. Hence, for the recovery as azeotropic agents has not been entirely satis of benzene from a hydrocarbon mixture the factory since these agents must be removed from amount of methylcyclopentane in the mixture the benzene by extraction with a solvent and the should fall within the range of from about 10.2 agent must then be reconcentrated, which step. 35 moles per mole of benzene in the mixture for adds to the cost of the process. sub-atmospheric pressure fractionation to about It is an object of this invention to Overcome 6 moles of methylcyclopentane per mole of ben the disadvantages of the prior art and produce zene at high fractionation pressures and about relatively pure cyclohexane from benzene by 7.4 or 7.5 moles of methylcyclopentane per mole means of catalytic hydrogenation. Another ob 40 of benzene for moderate pressure fractionation. ject of this invention is to provide a continuous In general, it is desirable to maintain a Small process for producing cyclohexane from benzene excess of methylcyclopentane Over that required by hydrogenation at moderate pressures. A fur to form the azeotropic mixture in Order to insure ther object of this invention is to obtain rela complete removal of benzene. The amount of tively pure cyclohexane substantially free of non 45 methylcyclopentane to be added may be readily hydrogenated benzene by an azetropic agent adjusted to correspond to the operating cond which can be recycled along with the associated tions of the azeotropic fractionation. benzene to the hydrogenation reactor, thus avoid Substantially all of the unconverted benzene ing the intermediate separation of azetropic can be removed from a 95 percent cyclohexane-5 agent from said benzene. Other objects and ad percent benzene hydrogenated benzene product vantages of the invention will be apparent from mixture by adding thereto from about 7.4 to 9.0 the following specification in which the preferred moles of methylcyclopentane per mole of benzene embodiment and details are described. in said product mixture and fractionating of the My improved process consists of catalytically azeotrope at pressures from atmospheric up to 55 50 or 75 pounds per square inch. The benzene of hydrogenating benzene in the presence of methyl f . 2,404. 3 4 this azeotrope fraction can be hydrogenated to 180 C-220 C, and at a pressure preferably in cyclohexane along with fresh benzene feed to the excess of 500 pounds per square inch. I prefer hydrogenation zone. The methylcyclopentane is to operate with space velocities such that at least inert to the hydrogenation reaction at the COn 90 percent of the benzene is converted to cyclo ditions employed although a part of this come hexane. The space velocity in tower f is prefer ponent may be isomerized to cyclohexane thus ably adjusted to give from about 95 to 98 percent producing an increased yield of the desired conversion. Conversions as high as 99.5% may product. be practicably obtained in which case the total In the hydrogenation step of my process, I amount of methylcyclopentane introduced as such subject the mixture of benzene and benzene 0. or as the benzene azeotrope through line 4 is methylcyclopentane azeotrope from previous much reduced since the amount of methylcyclo fractionations to a temperature within the range pentane required is directly proportional to the of from about 70° C. to about 250° C., preferably amount of benzene escaping conversion in tower about 180° C. to 220 C. in the presence of hydro . Thus, at 90 percent conversion of 100 moles of gen and a hydrogenation catalyst such as nickel 15 benzene, ten moles of benzene remain uncon supported on pumice or on other porous but rela verted which if the fractionation of the product tively inactive support. I may also use a catalyst is carried out at atmospheric pressure will re which is less sensitive to poisons. Thus, I may quire the addition of about 90 moles of methyl use molybdenum sulfide, molybdenum oxide Sup cyclopentane to remove said unconverted benzene ported On alumina, or supported on acid treated 90 from the cyclohexane product in fractionator 4. clay such as fuller's earth or attapulgus clay. On the other hand, if 99.5 moles of the benzene Somewhat higher temperatures are required for are converted only about 4.5 moles of methylcy these less active catalysts. The hydrogenation is clopentane per 100 moles of benzene feed to re carried out continuously, preferably in liquid actor need be used. Less methylcyclopentane phase, by passing the mixture of Carbocylic hy 25 will be required if the fractionation is carried out drocarbons and hydrogen over a bed of the cata at higher pressures. lyst in a tower at a space velocity within the The reaction mixture passes from reactor range of from about 1 to 10 volumes of liquid hy through line 25 to hot settler 2 without substan drocarbon per volume of free catalyst space per tial reduction in pressure or temperature. In hour. The hydrogenation reactor is maintained 30 settler 2 undissolved hydrogen separates from at a pressure within the range of from about 100 the liquid product and passes through line 26 to pounds to 1000 pounds gage, preferably from hydrogen recycle line 27. The liquid product about 500 to about 800 pounds per square inch. from settler 2 passes through line 28, cooler 29 The amount of hydrogen added to the hydrocar and line 30 to cold settler 3 which is operated at bons is at least three moles per mole of total ben 35 substantially the same pressure as hot settler 2. Zene including fresh benzene feed and benzene In cooler 29 the temperature of the liquid reac in the recycled azeotrope. I may use as much as tion product is lowered to the range of 100° C.- 12 Or 15 moles of hydrogen per mole of benzene in 125° C. and as a result of the lower temperature a the total feed passing to the hydrogenation zone. Substantial part of the hydrogen dissolved there One mode of conducting the process of my in 0 in at the higher temperature is freed from liquid vention continuously is illustrated diagrammati product which settles out as a separate layer in cally in the accompanying drawing of which the bottom of settler 3. The hydrogen thus numeral represents the catalyst packed hy freed passes through overhead line 3 which con drogenation reactor, 2 and 3 represent hot and nects with hydrogen recycle line 27.