Cyclohexanol production methods are mainly phenol hydrogenation and cyclohexane oxidation.

Phenol hydrogenation

In 1906, Β.Н. Ipadyev made cyclohexanol by hydrogenation of phenol and first industrialized it in aniline soda ash company in Baden, Germany. Nickel catalysts are generally used for phenol hydrogenation. The reaction temperature is 150°C and the pressure is 2.5MPa. The yield is close to the theoretical value. The purity of the product is high and the reaction is stable. In the 1960s, the cyclohexane oxidation method gradually replaced the phenol hydrogenation method in view of the price of raw materials.

Cyclohexane oxidation

Cyclohexane oxidation is more complex. It first produces cyclohexyl hydroperoxide and then decomposes into cyclohexanol and cyclohexanone (Figure 1). The rate constant ratio of each reaction process: k1/k2=3.7; k3/k4=1.4; k3/k1=24; k4/k2=66. These ratios are barely affected by temperature. It shows that: 1 Cyclohexanol and cyclohexanone are more easily oxidized than cyclohexane. 2 Most of cyclohexanone is produced by oxidation of cyclohexanol, and cyclohexanone generates various oxidation by-products. The reaction can be carried out in the presence of a catalyst or without a catalyst. The commonly used catalysts include: cobalt salts (cobalt naphthenate, cobalt oleate, etc.) and boric acid. When a cobalt salt catalyst is used, the resulting ketone-alcohol mixture (commonly known as ketoalcohol oil, KA oil) has a ketone to alcohol ratio of 1:1 to 2: When boric acid is catalyzed, it is 1:9, but boric acid recovery system must be added. In the absence of a catalyst process, a catalytic decomposition system of cyclohexyl hydroperoxide is provided. The cobalt salt method is the most widely used in industry.

Fresh cyclohexane containing 100 ppm of cobalt naphthenate mixed with recycled cyclohexane, oxidized with air in a three-stage reactor, temperature 150-160°C, pressure 0.8-1.0 MPa, reaction time 10-15 min, single-pass conversion The rate is 4% to 6%. The reaction tail gas was evacuated after the cyclohexane and high boilers were recovered by condensation. After the liquid-phase oxidation product is alkali-washed and saponified to remove impurities, more than 90% of the cyclohexane is recovered by distillation and recycled. After further removal of the light and heavy components, a mixture of alcohols and ketones is obtained. After rectification, cyclohexanol and cyclohexanone are separated.