Alkylation Reactors

Vista, Huntsman, and other linear alkylben2ene (LAB) producers feed chlorinated paraffins to an alkylation reactor to produce detergent alkylate without prior separation of the unreacted paraffins. Large amounts of paraffins must be recycled in these processes. 

Fig. 3. Unocal—Lummus—UOP ethylbenzene process AR = alkylation reactor TR = transalkylation reactor BC = benzene column ...

A necessary feature of the alkylation reaction section is the use of two reactors the first-stage reactor completes the major part of the alkylation reaction, and in the second-stage reactor the last traces of unsaturated hydrocarbons react, and a sizable portion of the soluble polyaromatics is removed. Modem units with lower-diene-containing feeds employ a single alkylation reactor (79). 

The minimum number of trays necessary to debutanize the effluent from an alkylation reactor will be calculated. The feed, products, and vapor-liquid equilibrium costants of the key components at conditions of temperature and pressure corresponding to the top tray and reboiler are shown in Table 8-1. 

Alkylation of benzene with linear monoolefms is industrially preferred. The Detal process (Figure 10-9) combines the dehydrogenation of n-paraffins and the alkylation of benzene. Monoolefms from the dehydrogenation section are introduced to a fixed-bed alkylation reactor over a heterogeneous solid catalyst. Older processes use HF catalysts in a liquid phase process at a temperature range of 40-70°C. The general alkylation reaction of benzene using alpha olefins could be represented as ... 

Figure 10-9. The UOP (Detal) process for producing linear alkylbenzene (1) pacol dehydrogenation reactor, (2) gas-liquid separation, (3) reactor for converting diolefins to monoolefins, (4) stripper, (5) alkylation reactor, (6,7,8) fractionators.

The LAB production process (process 1) is mainly developed and licensed by UOP. The N-paraffins are partially converted to internal /z-olefins by a catalytic dehydrogenation. The resulting mixture of /z-paraffins and n-olefins is selectively hydrogenated to reduce diolefins and then fed into an alkylation reactor, together with an excess benzene and with concentrated hydrofluoric acid (HF) which acts as the catalyst in a Friedel-Crafts reaction. In successive sections of the plant the HF, benzene, and unconverted /z-paraffins are recovered and recycled to the previous reaction stages. In the final stage of distillation, the LAB is separated from the heavy alkylates. 

The general treatment of the hydrocarbon stream leaving the alkylation reactor is similar in all processes. First, the acid and hydrocarbon phases have to be separated in a settler. The hydrocarbon stream is fractionated in one or more columns to separate the alkylate from recycle isobutane as well as from propane, n-butane, and (sometimes) isopentane. Because HF processes operate at higher isobutane/alkene ratios than H2S04 processes, they require larger separation units. All hydrocarbon streams have to be treated to remove impurity acids and esters. 

Nonlinear programming Staged-Distillation column (12.1) < Liquid extraction column (12.2) Gas transmission network (13.4) Ammonia reactor (14.2) Alkylation reactor (14.3) CVD reactor (14.5) Refrigeration process (15.2) Extractive distillation (15.3) Operating margin (15.4) Reactor control (16.3)... 

A, Find the optimum liquid concentration of the propane isobutane mixture in an auto lefrigerated alkylation reactor. The exothermic heat (10 Btu/h) of the alkylation reaction is removed by vaporization of the liquid in the reactor. The vapor is com pressed, condensed, and flashed back into the reactor through a pressure letdown valve. The reactor must operate at 50°F, and the compressed vapors must be condensed at 110°F. 

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.

Alkylation Reactor Model Kinetics, Mass Transfer and Dynamics... 

In order to state the control problem, the following property of the alkylation reactor is presented. 

The major discharges from sulfuric acid alkylation are the spent caustics from the neutralization of hydrocarbon streams leaving the alkylation reactor. These wastewaters contain dissolved and suspended solids, sulfides, oils, and other contaminants. Water drawn off from the overhead accumulators contains varying amounts of oil, sulfides, and other contaminants, but is not a major source of waste. Most refineries process the waste sulfuric acid stream from the reactor to recover clean acids, use it to neutralize other waste streams, or sell it. 

Alkylation is an association reaction that is exothermic. Therefore, it has a favorable equilibrium only at low temperatures. The process is catalyzed by hquid acids of solid AICI3, and modem alkylation reactors use sulfuric acid or hquid HF as catalysts operating at 0°C in a refrigerated reactor that is stirred rapidly to dissolve and create bubbles of the hydrocarbons in the acid. 

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. 

The alkylation reactor or contactor serves to bring isobutane and olefin into intimate... 

Toluene and olefinic stock from storage are pumped (at 80°F) separately through individual driers and filters into the alkylation reactor. The streams combine just before they enter the reactor. The reactor is batch operated 4 hr/cycle it is equipped with a single impeller agitator and a feed hopper for solid aluminum chloride which is charged manually from small drams. The alkylation... 

HF alkylation reactors have undergone more drastic changes than H2S04 reactors. In the middle 1950 s a Stratco contactor similar to that for H2S04 alkylation was used. Later a vertical reactor was developed in which the reactants were bubbled up through liquid HF. Cooling was... 

The Stratford Engineering Company furnished many alkylation reactors and were therefore interested in efficient mixing and heat transfer in this equipment. They subsequently developed a very efficient reactor, which makes part of the recycle by a flashing operation and is applicable to both hydrofluoric acid and sulfuric acid alkylation. This flashing differs from autorefrigeration in that the effluent stream is flashed after the reaction zone instead of in the reaction zone. 

Addition of ZSM-5 to the PCC circulating inventory results in a slight reduction in gasoline yield but an enhancement of gasoline quality in terms of octane rating [1]. In addition, increased yields of L.P.G. components are observed, notably propene and butenes which, subsequently, can be fed to alkylation reactors. 

Reactors can operate at low temperature (e.g., C4 sulfuric acid alkylation reactors run at 10°C) and at high temperatures (hydrodealkylation of toluene reactors run at 600°C). Some reactors operate in a batch or fed-batch mode, others in a continuous mode, and still others in a periodic mode. Beer fermentation is conducted in batch reactors. Ammonia is produced in a continuous vapor-phase reactor with a solid promoted iron catalyst. 

Figure 9.11 Cooled alkylation reactor with feed-effluent heat exchanger.

The reactor-outlet stream contains a dispersion of hydrocarbons in sulfuric acid. The first separation step is therefore a liquid-liquid split The sulfuric-acid phase contains some amounts of sec-butyl acid sulfate, which decomposes at higher temperature (15 °C) to produce conjuct polymers dissolved in the acid and a mixture of C4-C1( isoparaffins with low octane number (pseudoalkylate) that separates as a second liquid phase. The hydrocarbon phase contains a small amount of di-isoalkyl sulfates. These need to be removed before entering the distillation units otherwise they will decompose and release sulfuric acid. The sulfates are removed by washing with either dilute caustic or sulfuric acid. In the first case, sulfates are converted to salts that are discarded. With sulfuric acid, sulfates are converted to isoalkyl acid sulfates that can be recycled to the alkylation reactor [15, 10]. 

First commercialized at Georgia Gulfs Pasadena, TX plant in 1994, the Mobil-Badger Cumene process consists of a fixed-bed alkylator, a fixed-bed transalkylator and a separation section (22, 23). Fresh and recycle benzene are combined with liquid propylene in the alkylation reactor where the propylene is completely reacted. Recycled polyisopropylbenzenes are mixed with benzene and sent to the transalkylation unit to produce additional cumene. Trace impurities are removed in the depropanizer column. Byproduct streams consist of LPG (mainly propane contained in the propylene feedstock) and a small residue stream, which can be used as fuel oil. 

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