Optimization isobutane alkylation

Considerable effort has been put into minimizing the adverse effects of these olefins. It was found that alkylating propylene and pentylenes in a mixture with butylenes promoted the desired reactions and reduced the octane and acid consumption penalties. Furthermore, by optimizing temperature, isobutane-to-olefin ratio, acid strength, and other variables, the deleterious effects of propylene and pentylenes in the feed can be minimized (4, 8, 21). The decision as to how much of these olefins to include in the alkylation unit feed depends on many different factors, such as their value relative to alkylate, butylene and isobutane avails, alkylate volume and octane requirements, acid costs, etc. 

Model structure is shown in Figure 5. Process variables, unit constants (such as heat transfer coefficients), and feed streams are described on input or as selected by the optimization routine. Then, heat and material balances are performed using an assumed alkylate yield and isobutane consunq>tion. These results form a set of reaction conditions irtiich are used in correlations to calculate reactor performance. The heat and material balance calculations are repeated if reactor performance differs significantly from that used in the previous calculation. Operating incentives are then conqmted and may be used in the optimization routine to select new values of the optimization variables. 

Some normal butane is also produced from butylenes but this is estimated at only 4-6%. The higher octane isobutylene alkylate and a claimed yield increase must be contrasted with normal paraffin production from olefins and a higher isobutane requirement. The typical mixed 03 = 704= feed can be made to produce a high octane alkylate with either acid catalyst by the optimization of other variables. The highest alkylate octane numbers reported are produced with sulfuric acid catalyst, alkylating with a typical cat cracker butylene olefin. 

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. 

With HF, water should be completely removed. In the case of H2SO4, water and, to a lesser extent, hydrocarbons (acid soluble oUs) lower the acid strength. As excess acidity can cause unwanted by-products there is an optimal acid concentration for each set of conditions and feed mix. Since HF has higher isobutane solubility, it provides higher alkylate quality with less isomerization and oligomerization. 

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. 

The above problem will be referred to as Problem A in the following. The 7 inequality constraints in equations 1.4e to 1.4k are the bounds on the 7 variables (X4, xs, X2, Xe, Xio, Xg and X3) in the original problem, and they arise from the elimination of these variables from the 7 equality constraints in the model thus making them dependent variables. The cost coefficients in the profit are alkylate product value ( 0.063/octane-barrel), olefin feed cost ( 5.04 arrel), isobutane recycle cost ( 0.035/barrel), fresh acid cost ( 10.0/thousand pounds) and isobutane feed cost ( 3.36/barrel). The optimal solution for this SOO problem is also presented in Table 1.2. The reader can verify this using the Excel file Alkylation.xls in the folder Chapter 1 on the compact disk (CD) provided with the book. 

Alkylation process has been described in Sec. 1.4. Two optimization problems referred in Chap. 1 as Case A (Maximize Profit and Maximize Octane Number) and Case B (Maximize Profit and Minimize Isobutane Recycle) are solved using NSGA-II and SAEA to illustrate the benefits of SAEA. Variable bounds for optimization problem Case A is the same as those... 

The alkylation of isobutane with C4 olefins is currently carried out using liquid acids. In the last few years there was an increasing research effort in order to develop solid catalysts to replace the liquid acids. The major problem of the solid catalysts is a rapid deactivation due to coke deposition. Therefore, the development of a catalyst for this process requires the study of the regeneration and its optimization. 

The process variables temperature, acid strength, isobutane concentration, and mixing have to be carefully optimized in refinery alkylation to obtain high fuel quality. The optimum parameters differ for the H2SO4- and HF-catalyzed processes. 

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