Design alkylation reactors

Through this systematic study, Exelus was able to identify an optimal window of design parameter values that were then used to develop the catalyst. By judicious manipulation of the active material composition, researchers at Exelus developed a unique solid-acid catalytic system that has roughly 400% more active sites than a typical solid-acid catalyst. The catalyst activity was found to be higher than a typical liquid acid catalyst, which means that smaller amounts of catalyst are required, allowing one to design alkylation reactors with significantly lower volumes. 

Fig. 1. Configuration or alkylation reactors. The refrigeration system basically consists in compressor and depropanizer. The main contribution is the design of an approach to the robust control temperature via heat reaction compensation. Thus, dynamical behavior of the refrigeration system is not considered.

Thus this reactor requires mass transfer between the gas and hquid phases and between the organic and aqueous liquid phases. Stirring to mix phases, make small drops and bubbles, and increase inter-facial mass transfer is crucial in designing an alkylation reactor. 

Relatively low temperatures are required in alkylation reactors using sulfuric acid catalyst. They are necessary in order to slow down polymerization reactions and reduce the formation of undesirable acid soluble and hydrocarbon soluble by-products. Typically, most commercial units operate with reaction temperatures in the range of 35 F. to 65 F. Design temperatures are usually set at 50 F. For minimum acid make-up the reactor section should be operated as cold as possible. This means operating... 

In addition to the particular design of the alkylation reactor and the amount of horsepower going into the mixing, the mixing and alkylation results are usually improved by having 50% or more by volume of acid catalyst in the emulsion so that the acid is in the continuous phase. Recycle of emulsion containing... 

This isn t so serious if the used catalyst from alkylation is sent to the SARP recovery section. In some cases, the size of the reactor is determined by the amount of cooling surface required for the design temperature. With SARP not as much cooling is required in the alkylation reactor, since part of the heat of the alkylation reaction is evolved in the absorption section. It has been estimated that 50% or more of the heat of alkylation is in the absorption step. 

The yield loss in this process, depending on the alkylation system design and control, is between 0.6 and 0.9 lb flux oil per 100 lb ethylbenzene. Steam is generated by waste-heat boilers. These together with the alkylation reactor waste-heat boiler account for 90 percent of the energy required for the entire ethylbenzene unit. 

Design a reactor for the alkylation of benzene with propylene to maximize the selectivity of isopropylbenzene. [Prac. 2nd Joint China/USA Chem. Eng. Conf III, 51, (1997)]. 

Because the main alkylation reactions occur at the interface, both isobutane and olefins in the dispersed droplets are transferred to the interface, and the resulting C5-C16 isoparaffins are transferred from the interface back into the dropletJ Experimental data indicate that such transfer steps are in part at least rate controlling steps. In any case, each droplet acts as a different reaction zone (basically a separate minireactor). As droplets of different compositions and sizes occur in all commercial reactors, the alkylation results differ in various droplets, i.e., different alkylates, RONs, yields, amounts of by-products, etc. Improved results would occur if alkylation reactors could be designed and operated so that all the alkylate was produced only at optimal conditions. 

Cascade Reactors At least two types of these reactors and/or operating conditions are currently employed. Units designed by M.W. Kellogg were built until the mid-1960s, and some still produce about 8% of the total alkylate (P. Pyror, personal communication). Exxon-Mobil now designs units, as shown in Fig. 2, which account for about 6% of all alkylate produced worldwide. They refer to their units as stirred autorefrigerated alkylation reactors. At least one refinery claims their cascade reactors differ from the above two. 

Similar to the B/E in the alkylation reactor section, the first liquid phase plants were designed and operated with Bz/PEB close to 10 or higher. Over time, transalkylation catalyst system stability has been improved and the Bz/PEB has steadily decreased and in 2004 plants are typically designed with Bz/PEB in the range of 2.0-4.0. Generally, a commercial plant is operated at or very close to its design Bz/PEB and the operating Bz/PEB is not frequently adjusted. 

In the latest version of aluminum chloride plant designs, the alkylation reactions occur in a homogenous liquid phase at 160-180" C. The conditions of the alkylation reactor prohibit the recycle of PEB to the reactor. As a result, these plants have a separate transalkylation reaction zone. The recycle PEB stream is mixed with the alkylation reactor effluent and fed to the transalkylation reaction zone. The aluminum chloride present in the alkylation reactor effluent catalyzes the transalkylation reactions. 

The original vapor phase design accomplished the alkylation and transalkylation reactions in a single reactor. Subsequent designs performed the transalkylation reactions in a vapor phase, secondary reactor that was separate from the alkylation reactor. Fig. 3 shows a flow diagram for the latest publicly disclosed version of the process, sometimes referred to as the third-generation EB process. The alkylation and... 

The CDTECH EB process is based on a mixed liquid-vapor phase alkylation reactor section. The design of a commercial plant is similar to the liquid phase technologies except for the design of the alkylation reactor, which combines catalytic reaction with distillation into a single operation. ... 

Construction of an AlkyClean process demonstration unit at Fortum s facilities in Porvoo, Finland, was completed in 2002. Figure 12.14 shows the process flow schematic of the demo unit, which contains all of the key elements of our proposed commercial design. Three reactors are included - two under cyclic operation (i.e., alternating between alkylation and mild regeneration) allowfor continuous production... 

A brief discussion of the impact of these factors on reactor type along with a description of various reactor designs used in industry is given in the following. The two factors inherent in all alkylation reactor designs, however, are good mixing characteristics and excellent heat removal capability. 

Fig. 2. Autogenerated alkylation reactor with 10 reactor stages in series. Design of Exxon Research and Engineering Company. FI, flow indicator PC, pressure controller.

Propane and light ends are rejected by touting a portion of the compressor discharge to the depropanizer column. The reactor effluent is treated prior to debutanization to remove residual esters by means of acid and alkaline water washes. The deisobutanizer is designed to provide a high purity isobutane stream for recycle to the reactor, a sidecut normal butane stream, and a low vapor pressure alkylate product. 

The choice of appropriate reaction conditions is crucial for optimized performance in alkylation. The most important parameters are the reaction temperature, the feed alkane/alkene ratio, the alkene space velocity, the alkene feed composition, and the reactor design. Changing these parameters will induce similar effects for any alkylation catalyst, but the sensitivity to changes varies from catalyst to catalyst. Table II is a summary of the most important parameters employed in industrial operations for different acids. The values given for zeolites represent best estimates of data available from laboratory and pilot-scale experiments. 

Here, a control law for chemical reactors had been proposed. The controller was designed from compensation/estimation of the heat reaction in exothermic reactor. In particular, the paper is focused on the isoparafhn/olefin alkylation in STRATCO reactors. It should be noted that control design from heat compensation leads to controllers with same structure than nonlinear feedback. This fact can allow to exploit formal mathematical tools from nonlinear control theory. Moreover, the estimation scheme yields in a linear controller. Thus, the interpretation for heat compensation/estimation is simple in the context of process control. 

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