Isobutane-to-olefin ratio

To form the process model, regression analysis was carried out. The alkylate yield x4 was a function of the olefin feed xx and the external isobutane-to-olefin ratio jc8. The relationship determined by nonlinear regression holding the reactor temperatures between 80-90°F and the reactor acid strength by weight percent at 85-93 was... 

The motor octane number jc7 was a function of the external isobutane-to-olefin ratio jc8 and the acid strength by weight percent x6 (for the same reactor temperatures and acid strengths as for the alkylate yield x4)... 

The external isobutane-to-olefin ratio jc8 was equal to the sum of the isobutane recycle x2 and the isobutane makeup x5 divided by the olefin feed xx... 

Another factor which contributes most to the high cost of the alkylation process is the necessity of having a large excess of isobutane in the reaction zone. This requirement results in increased capital costs for over-sized reactors, settlers, fractionators, and accessories, as well as in increased operating costs of this equipment. Process developments which would allow satisfactory operations at considerably lower isobutane-to-olefin ratios would help reduce these costs. Such developments might again involve improvements in reactors or in catalysts. 

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. 

Another way of indicating isobutane-to-olefin ratio is the per cent isobutane in the reactor effluent. This method of indicating the ratio takes... 

Most side reactions can be reduced by increasing the isobutane-to-olefin ratio, by providing more efficient contact between the acid and hydrocarbon, and by reducing the reaction temperature to the lowest practical point. 

The sulfuric acid alkylation process for making aviation or motor gasoline from isobutane and olefins from cracked gases requires a relatively high isobutane-to-olefin ratio in the reaction zone to insure high octanes, good yields, and low polymer formation in the acid. The sulfuric acid catalyst can make use not only of the relatively pure external isobutane... 

Because of the relatively high normal butane tolerance in HF units, all of the recycle isobutane can be made from the effluent stream with little rectification. The purity of the recycle under these conditions is 75 to 85 % isobutane. Even though such a relatively impure external isobutane recycle can be used without appreciably lowering the quality of the alkylate, an increase in the internal isobutane-to-olefin ratio does not improve the quality as is the case with sulfuric acid catalyst. When the external isobutane recycle is charged to the first of a series of reaction zones and the olefinic feed is divided between the individual reaction zones, there is no apparent improvement in quality. This indicates that any increase in the isobutane-to-olefin ratio over and above the external ratio which may be... 

A second question is what might be done to improve selectivity beyond the usual practice of refiners to maximize mixing, maximize the isobutane to olefin ratio, lower the temperature and reduce the olefin space velocity. One approach is to decide what s rate determining and then to develop a chemical solution. This paper will be concerned with developing evidence that hydride transfer from a tertiary paraffin is generally slow and may be considered to be the rate determining step. The fact that a cation abstracts from Isobutane relatively slowly compared to... 

I-Butene, propylene, the catalysts s low water content, and low isobutane-to-olefin ratio favor the production of residue. 

In studies with propylene. Increasing isobutane-to-olefin ratio suppressed the formation of high-molecular-weight residue, indicating a substantial reduction in the role of olefin polymerization to large ions. 

Polymer or residue formation is minimized by maintaining proper reaction conditions, i.e., good mass transfer, high isobutane-to-olefin ratio, proper catalyst activity, and minimum concentration of alkylate in the reaction zone. 

Isobutane-to-Olefin Ratio with Propylene Feed. The isobutane-to-olefin ratio has long been recognized as an important process variable in the alkylation of isobutane with either butenes or pxopylene (Phillips Petroleum Company, 1946). By maintaining a sufficiently high concentration of isobutane in the reaction zone, the abstraction of hydride ions from isobutane is favored over abstraction from product isoparaffins. 

Even with propylene feed, a high isobutane-to-olefin ratio influences the product toward predominantly Cg hydrocarbons which have the highest octane number and also Improves yields. Thus, both alkylate quality and yield are found to improve with increasing ratio and olefin dilution. In Table IX, detailed propylene-isobutane alkylate composition data are shown, where the volume ratio was increased from 4.6 to 126. For quick reference, composition data are summarized in Table IV. 

EFFECT OF ISOBUTANE-TO-OLEFIN RATIO ON ALKYLATE COMPOSITION... 

To control an operating plant for minimum acid make-up, the Isobutane concentration in the reactor must be maintained at the maximum possible level. This means operating both the depropanizer and the deisobutanizer under optimum conditions. The operator should adjust tower feed rates and operating conditions, always using the isobutane concentration in either the total effluent hydrocarbon or the net effluent hydrocarbon from the reactor as his primary reference. Isobutane-to-olefin ratio, deisobutanizer overhead purity, depropanizer recycle purity, and refrigerant recycle purity are significant only as they relate to reaction zone isobutane concentration. 

Typical results are summarized in Table 14-5. The higher the isobutahe concentration, isobutane to olefin ratio, acid to olefin ratio and acid strength, and the lower the reaction temperature, the higher the octane rating of the 338°F end-point material and the lower the acid consumption and the quantity of heavy polymer formed. As the sulfuric acid is contaminated, a portion is withdrawn and replaced by fresh acid. The effluent treater is to remove acidic material. 

From previous works, it becomes clear that, with the exception of the onedimensional ZSM-12 zeolite mentioned above, large-pore zeolites with three-dimensional pore structures such as faujasite (X and Y) and beta are more appropriate as solid alkylation catalysts because of the easiest formation and diffusion of the desired TMP products and improved lifetime. Among them, beta has been shown to outperform USY, particularly in terms of catalyst lifetime (117). At equivalent reaction conditions (T = 50°C, P = 20 bar, isobutane-to-olefin ratio (I/O) = 15, olefin WHSV = 1 h ), zeolite beta displays a lower deactivation... 

Isobutane concentration is generally expressed in terms of the isobutane-to-olefin ratio (I/O). This ratio is the most important process variable to control in terms of refinery alkylation productivity, yield, and quality of alkylate, as well as the add... 

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