h2so4alkylationprocesscomparison

H2SO4 Alkylation Process Comparison - Stratford Engineering

The two major H2SO4 alkylation processes are the auto-refrigerated process licensed by ExxonResearch and Engineering and STRATCO's Effluent Refrigerated process. The key differencebetween the two processes is in the reaction zone. The STRATCO process, see Figure 1,utilizes a liquid-full reactor system where the heat of reaction is removed with an internal heatexchanger.

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Figure 1 A Typical STRATCO Contactor and Acid Settler Arrangement

Vaporization is prevented by maintaining the reactor system at sufficient pressure. Theauto-refrigerated reactors are not liquid-full. The heat of reaction is removed by vaporization of aportion of the reaction mass, mainly isobutane. The obvious advantage of the liquid-full system(STRATCO ) is that the isobutane remains in the liquid state continuously available for reaction.For a constant deisobutanizer recycle rate and purity, the STRATCO system will have a higherconcentration of isobutane available for reaction in the reaction zone.

An additional benefit of the liquid-full reactor system is the ease of reactor operation. There areno acid or hydrocarbon levels that need to be maintained in the reactor system. Reactortemperature control for the STRATCO unit is accomplished with one automatic processcontroller regardless of unit size. The auto-refrigerated system requires five to seven locallymounted process controllers per reactor, to control reactor temperature.

The results of the different reaction zone designs are quite significant. For instance, at a U.S.Gulf Coast refinery with auto-refrigerated and STRATCO alkylation units side-by-side, underidentical feeds, extensive plant tests revealed a 1.5 octane number advantage with theSTRATCO unit. Another refiner's in-plant, side-by-side comparison showed that considerablyfewer side reactions occurred, less heavy alkylate was produced and less acid was consumedin the STRATCO unit than in the auto-refrigerated unit.

This result became further evident to us this summer. As part of research and licensor supportefforts, we have been analyzing the effluent stream from the reaction zones of operating units to

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determine if we could improve the operability and product quality currently being obtained. Aspart of these efforts, we have been able to analyze the effluent streams from both STRATCOContactors and auto-refrigerated reactors operating on identical feedstocks at comparablereaction zone conditions. The results of these analyses indicate that, at a minimum, a 0.5-1.0number octane advantage exists utilizing a STRATCO Contactor versus an auto-refrigeratedreactor. Also, the distribution of the alkylate components indicates an increased T90 andendpoint for the alkylate product from the auto-refrigerated process.

Another difference between the two processes is the energy input to the reaction zone. TheSTRATCO process utilizes a higher horsepower input per barrel of alkylate. However, thishigher mixing energy provides rapid dispersion of the olefins in the acid emulsion, high internalcirculation rates for even heat dissipation and a large interfacial area for mass transfer. Thelower horsepower input to the reaction zones of the auto- refrigerated system results in thenon-uniform distribution of acid and hydrocarbon. Unlike the STRATCO system, the desirablefinely dispersed hydrocarbon in acid emulsion cannot be controlled throughout the reactionzones of the auto-refrigerated systems. The lower circulation rates of the auto-refrigeratedreactors also result in uneven temperature distribution within the reactor.

The third difference in the reaction zone design is in the method of contacting the olefins withacid. In STRATCO's Effluent Refrigerated process, the isobutane and olefin feeds are premixedand then rapidly dispersed into the acid catalyst. The ratios of isobutane to olefin and olefin toacid are controlled at near optimum levels, producing higher quality product with lower acidconsumption.

Also, if there are seal or impeller shaft problems on the auto-refrigerated reactors, the entirevessel must be shut down for maintenance. This can result in lost product quality if the reactoris kept running until a planned shutdown, or lost production while the entire unit is down forrepairs. The STRATCO Contactors can be taken off line individually if any maintenance isrequired. Typical single seal life for a Contactor is approximately 18-24 months, while reliabilityis greatly extended with a double seal. If repair is required during normal operation, theContactor can be isolated, repaired, and back in service in less than 24 hours.

Another important difference between the two processes is the energy cost and energydistribution. A major energy consumer for both processes is the refrigeration compressor whichcompresses and recycles the isobutane that had been flashed to maintain the desired reactiontemperature. The compressor horsepower for STRATCO's Effluent Refrigerated process ishigher because more isobutane must be vaporized at a lower pressure, 2-5 psi, to maintain agiven reaction temperature. On the other hand, as previously discussed, the fractionationenergy costs will be higher for the auto-refrigerated process. Usually the net effect of these twoitems is a slight advantage to STRATCO's Effluent Refrigerated process.Trends in the alkylation industry in recent years provide evidence that STRATCO's EffluentRefrigerated process is the predominant H2SO4 alkylation technology. In the last ten years, inexcess of 90% of the H2SO4 alkylation added worldwide has been STRATCO's EffluentRefrigerated H2SO4 process. Revamp and expansion activity in H2SO4 alkylation also istestimony to the popularity of STRATCO's Effluent Refrigerated process. The first replacementof an auto-refrigerated unit with a STRATCO Effluent Refrigerated unit took place over 30 years

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ago. Since 1990, three major U.S. refiners have expanded or replaced their existingauto-refrigerated alkylation units with STRATCO's design.

SummaryIn summary, the STRATCO process offers the following advantages when compared toauto-refrigeration processes:• Isobutane is not vaporized in the reaction zone• High internal circulation rates for even heat dissipation• Highly dispersed hydrocarbon in acid emulsion• Increased interfacial catalyst area provided by mixing• Reduced acid consumption• Superior quality alkylate• Ease of reactor operation

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h2so4alkylationprocesscomparison

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