Heavies phenol hydrogenation

Figure 5.1 illustrates the key reactions implied in the manufacturing of cyclohexanone by phenol hydrogenation. The reactions are of consecutive type, in which the desired product is an intermediate. Small amounts of cyclohexene might appear at higher temperature by cyclohexanol dehydration. Additional reactions can lead to heavies by polymerization or benzene and cyclohexane by disproportionation. 

The impurities can be grouped into two categories lights (water, cyclohexene, cyclohexadiene) and heavies (phenol, dicyclohexyl-ether, cyclohexenyl- cyclohexanone). To limit their amount, the conversion is kept around 80% with a selectivity of about 98%. The hot reactor effluent is cooled in countercurrent with the feed in FEHE, and finally for phase separation in the heat exchanger (E-2) at 33 °C. The simple flash (S-2) can ensure a sharp split between hydrogen, recycled to hydrogenation reactor, and a liquid phase sent to separation. 

After closing the material and heat balances, we will examine the potential environmental impact (PEI) of the design. The basic information is the stream report. Table 5.16 shows material- and heat-balance data for a fresh feed of 150kmol/h phenol and 350kmol/h hydrogen, in total 14822.5kg/h. The products are cyclohexanone 9618.9 and 5017.9 cyclohexanol in the molar ratio 2 1. After simulation it is found that the amount of waste is 150.6 kg/h lights and 80 kg/h heavies. These data lead to a global yield of raw materials of 98.75%. 

The hydrodeoxygenation reaction (HDO) is carried out in the gas phase in a fixed bed reactor (400 °C, 25 bar of hydrogen), using commercial nickel and molybdenum oxides supported on alumina as catalysts. The HDO allows a quantitative transformation of dioxygenated compounds into phenol with a selectivity of 96% [24]. Main by-products are heavy condensed polycyclic aromatic hydrocarbons. 

Toxic substances in wastewaters come either from products of man s activity (heavy metals, cyanides, phenols, pesticides, detergents) or from natural anaerobic processes (formation of ammonia, hydrogen sulphide, etc.) [33-39]. 

With AMS hydrogenation, 1.31 tons of cumene will produce 1 ton of phenol and 0.616 tons of acetone. This high-yield process produces very high-quality phenol and acetone products with very little heavy and light-end byproducts. With over 40 years of continuous technological development, the Kellogg Brown Root (KBR) phenol process features low cumene and energy consumptions, coupled with unsurpassed safety and environmental systems. 

---