UOP HF Alkylation Process
Figure 8.8 shows a flow diagram for a UOP HF alkylation process . Olefin and iso-butane feed streams are dried to remove water before they are mixed with the iso-butane recycle stream. The mixture is fed to the reactor, where it is highly dispersed into an incoming stream of acid catalyst. Conversion of reactants to high-quality alkylate takes place quickly, and the mixture flows up to the settling zone. In the settler, the catalyst is separated out as a bottom phase and flows, by gravity, through the catalyst cooler and returns to the reactor. The hydrocarbon phase from the settler, which contains propane, recycled iso-butane, normal butane, and alkylate, is charged to the main fractionator. High-purity propane is sent overhead to pass through the HF- propane stripper, de-fluorinator, and potassium hydroxide (KOH) treater before it is recovered. Recycled iso-butane is drawn from the side of the fractionator and returned to the entrance of the reactor after it is mixed with the dried olefin and isobutane feed. The n-butane product is taken from the side of the fractionators as vapor, condensed and KOH- treated before recovery. The alkylate product is obtained from the bottom of the fractionator. The HF catalyst is regenerated onsite in the regeneration section, where heavy oils (tars) are removed from the catalyst.
Transporting and working with concentrated acids pose safety risks. In particular, HF tends to form a vapor cloud that is difficult to disperse. The major licensor of the HF alkylation processes is UOP, whereas ExxonMobil and Stratford Engineering Corporation license H2SO4 alkylation processes. A newly designed alkylation process by UOP uses a solid catalyst called Alkylene®. Advantages of this new process over traditional HF alkylation processes (liquid acid technology) include no acid transportation, no acid spills, no corrosion, and reduced maintenance cost. Efforts to develop alternative processes that use solid acid catalysts instead of concentrated HF and H2SO4 for alkylation are underway.