Produce high-purity cyclohexane by liquid-phase catalytic hydrogenation of benzene.
The main reactor (1) converts essentially all of the feed isothermally in the liquid phase at a thermodynamically favorable low temperature using a continuously injected soluble catalyst. The catalyst’s high activity allows using low-hydrogen partial pressure, which results in fewer side reactions, e.g., isomerization or hydrocracking.
The heat of reaction vaporizes cyclohexane product and, using pumparound circulation through an exchanger, also generates steam (2). With the heat of reaction being immediately removed by vaporization, accurate temperature control is assured. A vapor-phase fixed-bed finishing reactor (3) completes the catalytic hydrogenation of any residual benzene. This step reduces residual benzene in the cyclohexane product to very low levels. Depending on purity of the hydrogen makeup gas, the stabilization section includes either an LP separator (4) or a small stabilizer to remove light ends.
A prime advantage of the liquid-phase process is its substantially lower cost compared to vapor-phase processes: investment is particularly low because a single, inexpensive main reactor chamber is used as compared to multiple-bed or tubular reactors used in vapor-phase processes. Quench gas and unreacted benzene recycles are not necessary, and better heat recovery generates both cyclohexane vapor for the finishing step and a greater amount of steam. These advantages result in lower investment and operating costs.
Operational flexibility and reliability are excellent; changes in feedstock quality and flows are easily handled. If the catalyst is deactivated by feed quality upsets, then fresh catalyst can be injected without a shutdown.
Yield: 1.075 kg of cyclohexane is produced from 1 kg of benzene.