Kinetics isobutane alkylation

In this work, the goal is to design a control function in such a manner that neither the reaction heat nor kinetic nor mass transfer terms are required for stabilizing temperature. The scheme provides an estimated value of the heat generation from energy balance. Alkylation isobutane/propylene using sulfuric... 

M.F. Simpson, J. Wei, and S. Sudaresan. Kinetic analysis of isobutane/butene alkylation over ultrastable H-Y zeoUte. Ind. Eng. Chem. Res., 35 3861-3873,... 

Carlier fundamental studies of autoxidations of hydrocarbons have concentrated on liquid-phase oxidations below 100 °C., gas-phase oxidations above 200°C., and reactions of alkyl radicals with oxygen in the gas phase at 25°C. To investigate the transitions between these three regions, we have studied the oxidation of isobutane (2-methylpropane) between 50° and 155°C., emphasizing the kinetics and products. Isobutane was chosen because its oxidation has been studied in both the gas and liquid phases (9, 34, 36), and both the products and intermediate radicals are simple and known. Its physical properties make both gas- and liquid -phase studies feasible at 100°C. where primary oxidation products are stable and initiation and oxidation rates are convenient. 

Figure 4-13. Liquid-liquid heterogeneous tubular flow reactor (e.g., alkylation of olefins and isobutane). (Source J. M. Smith, Chemical Engineering Kinetics, 3rd ed., McGraw-Hill, Inc., 1981.)...

Table 9.3 Kinetic parameters and heat of reaction for isobutane/1 -butene alkylation.

The major products of the commercial alkylation of Isobutane with butenes are trlmethylpentanes. This Indicates that the products of alkylation are kinetically controlled because thermodynamics would predict a minor proportion of trlmethylpentanes If the octanes were to Isomerlze to equilibrium. 

This theory was proposed by Knox [39] following a series of careful kinetic and analytical studies of the oxidation of ethane [40], propane [41], and isobutane [42] in the early stages of reaction (<1% fuel consumption). For these lower alkanes, he found that at this stage of the reaction 75—80 % of the alkane consumed appeared in the products as the conjugate alkene both at low temperature (ca. 300 °C) and at high temperature (ca. 450 °C). He concluded, therefore, that the primary oxidation process for alkyl radicals is the same at both temperatures, viz. 

Baldwin and Walker [99] have pointed out that, from kinetic considerations, surface reactions of alkylperoxy radicals cannot play a significant role except at very low overall rates of reaction and conclude that it is more likely that surface destruction of relatively stable intermediates such as the alkyl hydroperoxides or hydrogen peroxide are the main cause of surface effects in hydrocarbon oxidation. Luckett and Pollard [68, 134] have provided evidence, which suggests that the surface destruction of tert-butylhydroperoxide is indeed important during the oxidation of isobutane below ca. 320 °C. Since isobutene and acetone are known products of the decomposition of tert-butylhydroperoxide, it is clear that many of the foregoing results can be explained in these terms, but if this is the predominant heterogeneous reaction the yield of acetone would be... 

Acid strength and composition In H2SO4 processes, the optimal acid concentration is about 95-97%. At low levels (e.g., below 90%) catalyst activity is significantly diminished. At high levels (e.g., above 99%) isobutane reacts with SO3. Acid level is dictated by consumption and fresh catalyst make-up rates. Hence, add concentration affeds kinetics, alkylate yield and quality, and catalyst life. While HF plants are similar, a primary difference is that HF needs to be water-free because any water will rapidly deactivate the H F catalyst and can lead to severe corrosion problems. 

Simpson, M.F., J. Wei, and S. Sundaresan, Kinetic Analysis of Isobutane/Butene Alkylation over Ultrastable H-Y Zeolite. Industrial Engineering and Chemistry Research, 1996.35 p. 3861-3873. 

Alkylation of organic compounds with olefins is very important industrially (30-34). It appears that most acid-catalysed alkylations are very slow, hence kinetically controlled. However, Lee and Harriot (33) found that H2S04-catalysed alkylation of isobutane with butenes to be rather fast. Dixon and Saunders (34) studied the H2S04-catalysed alkylation of o-xylene with acetaldehyde and found that the reaction may be too fast to be kinetically controlled. 

For the alkylation of isobutane and aromatics, the phenomena in the reactors are complicated involving numerous consecutive and simultaneous reaction steps variable and unknown kinetics for the different reactions and numerous mass transfer or diffusion steps between phases or in a specific phase (2,5). In this article, comparative processes are evaluated. Methods to improve current processes are proposed. 

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