Cumene operating conditions

Overhead vapor from the CD column (1) is condensed and returned as reflux after removing propane and lights (P). The CD column bottom section strips benzene from cumene and heavies. The distillation train separates cumene product and recovers polyisopropylbenzenes (PIPB) and some heavy aromatics (H) from the net bottoms. PIPB reacts with benzene in the transalkylator (2) for maximum cumene yield. Operating conditions are mild and noncorrosive standard carbon steel can be used for all equipment. 

In a new process for making phenol, cumene (isopropylbenzene) is oxidized with air to form cumene hydroperoxide, which is then changed to phenol and acetone. The cumene is made by the direct alkylation of gaseous benzene, using a phosphoric acid-kieselguhr catalyst and operating conditions of 500 K. 

On its face value, the cumene conversion and benzene selectivity seem to be better at Cp = 50 than 5. This is only because more catalyst has been used. In fact, it is 10 times more. The normalized benzene selectivities given in columns 3 and 5 with respect to Cp = 5 and 50 provide clearer indication. The physical structures of the catalyst pores and zeolites obtmned from electronic scanning microscope analysis are also important. However, they are not reported here since this is out of the scope of the present contribution and can be found elsewhere[ 15]. To achieve the optimal catalyst effectiveness and obtain the maximum product selectivity, the preferable operation conditions, in the present case, are at a catalyst to feed ratio of 5 while the conversion level is at 60%. 

Excellent monoalkylation selectivity has also been observed over many years of service in the JLM operation as shown in Fig. 10. Under the normal operating conditions of the unit, an equilibrium cumene selectivity of about 91 mol% is predicted. Thus, results clearly show that the beta zeolite catalyst is active enough to achieve near-equilibrium selectivity. This is an important feature of the catalyst as the amount of dialkylate that must be processed in the transalkylator and the subsequent cost of processing this material are minimized. 

The Japanese company Showa Denka has, for several years already, proposed a catalyst capable of iransalkylating diisopropylbenzene and benzene to two molecules of cumene. The operating conditions are as follows temperature between 180 and 250°C, benzene/dhsopropylbenzene molar ratio between 5 and 10,. LHSV between 1 and 2, pressure about 2.106Pa absolute. Diisopropylbenzene (nice-through conversion is 53 per cent, and the cumene yield is 93 molar per cent This process thus enhances the total alkylation yield and reduces the amount of excess benzene required. 

The total yield of the oxidation of toluene to phenol varies according to the technology and operating conditions, from between 75 and 80 molar per cent in the liquid phase to between SO and 85 per cent in the vapor phase. Its economics in comparison with competing methods, including the cumene method, which is the most widespread and shows the highest performance, depends closely on the price differential existing between the raw materials employed (benzene and toluene). 

Cumene Processes. Current processes now used to produce cumene are similar to those that produce ethylbenzene. Monsanto found that its ethylbenzene process was also applicable to produce cumene but with slightly different operating condition. The modified conditions are temperatures less than 135°C and pressure of about 50 psig (46). Monsanto-type processes are used at several plants. Unreacted benzene and poly-isopropyl benzenes are separated from the reaction products and then recycled to the reactor. Eventually, all of polyisopropyl benzenes react to give cumene, so overall yields are typically 97-98%. 

Oxidation of cumene to cumene hydroperoxide is usually achieved in three to four oxidizers in series, where the fractional conversion is about the same for each reactor. Fresh cumene and recycled cumene are fed to the first reactor. Air is bubbled in at the bottom of the reactor and leaves at the top of each reactor. The oxidizers are operated at low to moderate pressure. Due to the exothermic nature of the oxidation reaction, heat is generated and must be removed by external cooling. A portion of cumene reacts to form dimethylbenzyl alcohol and acetophenone. Methanol is formed in the acetophenone reaction and is further oxidized to formaldehyde and formic acid. A small amount of water is also formed by the various reactions. The selectivity of the oxidation reaction is a function of oxidation conditions temperature, conversion level, residence time, and oxygen partial pressure. Typical commercial yield of cumene hydroperoxide is about 95 mol % in the oxidizers. The reaction effluent is stripped off unreacted cumene which is then recycled as feedstock. Spent air from the oxidizers is treated to recover 99.99% of the cumene and other volatile organic compounds. 

As before, if the pure cumene used contains cumene hydroperoxide. Equation (17) does not give the correct value of Kp. If, however, either the pure cumene constant kiBa obtained from differential reactor studies or the conversion of pure cumene in the integral reactor operated under the same conditions is known, the correct value can be found. Let Kp be the value of Kp determined from Equation (17) when impure cumene is used. Furthermore, let... 

A commercial cumene cracking catalyst is in the form of pellets with a diameter of 0.35 cm which have a surface area. Am, of 420 m g and a void volume, Vm, of 0.42cm g. The pellet density is 1.14g cm. The measured l -order rate constant for this reaction at 685K was 1.49cm s g . Assume that Knudsen diffusion dominates and the path length is determined by the pore diameter, dp. An average pore radius can be estimated from the relationship fp = 2Vm/Am if the pores are modeled as noninterconnected cylinders (see equation 4.94). Assuming isothermal operation, calculate the Thiele modulus and determine the effectiveness factor, tti, vmder these conditions. 

By material balance, the concentration of solute in the extract will be 14,1 lb solute per 1,000 lb cumene. We now have established the condition at the top of the extractor that can be located on the equilibrium diagram. The operating line will join the compositions at the top of the tower with the compositions at the bottom of the tower on this diagram,... 

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