The RHT-Alkylation process is an improved method to react C3– C5 olefins with isobutane using the classical sulfuric acid alkylation process. This process uses a unique mixing device — eductor(s) — that provides low-temperature (25°F – 30°F) operations at isothermal conditions. This eductor mixing device is more cost-effective than other devices being used or proposed. It is maintenance free and does not require replacement every two to three years. This mixing device can be a retrofit replacement for existing contactors. In addition, the auto refrigeration vapor can be condensed by enhancing pressure and then easily absorbed in hydrocarbon liquid, without revamping the compressor.
In the RHT-Alkylation, C3 – C5 feed from FCC or any other source including steam cracker, etc., with isobutane make-up, recycle isobutene, and recovered hydrocarbons from the depropanizer bottom and refrigeration vapors are collected in a surge drum — the C4 system (5). The mixture is pumped to the reactor (1) to the eductor suction port. The motive fluid is sent to the eductor nozzle from the bottom of reactor, which is essentially sulfuric acid, through pumps to mix the reactants with the sulfuric-acid catalyst.
The mixing is vigorous to move the reaction to completion. The makeup acid and acid-soluble oil (ASO) is removed from the pump discharge. The process has provisions to install a static mixer at the pump discharge. Some feed can be injected here to provide higher OSV, which is required for C3 alkylation. Reactor effluent is withdrawn from the reactor as a side draw and is sent to acid/ hydrocarbon coalescer (2) where most of the acid is removed and recycled to the reactor (1). The coalescers are being used by conventional process to reduce the acid in the hydrocarbon phase to 7–15 wppm. The enhanced coalescer design RHT can reduce the sulfuric acid content in the hydrocarbon phase to negligible levels (below <1 wppm).
After the coalescer, the hydrocarbon phase is heated and flashed increasing the alkylate concentration in the hydrocarbon, which is sent through the finishing coalescer (4) where essentially all of the remaining acid is removed.
The hydrocarbon is sent to distillation column(s) (7), to separate alkylate product and isobutane, which is recycled. The butane is sent to offsites or can be converted back to isobutane for processing units requirements. The auto refrigeration occurs in the reactor at temperatures 25 –30°F. The isothermal condition lowers acid consumption and yields higher octane product due to improved selectivity of 2,4,4 trimethylpentane.
The auto-refrigeration vapor is first enhanced by the ejector and then absorbed in a heavy liquid — alkylate, which provides a low-cost option and then condensed. Some liquid is sent to depropanizer (6); propane and light ends are removed. The bottoms are recycled to C4 system and sent to the reactor.
The major advances of RHT process are threefold: eductor mixing device, advance coalescer system to remove acid from hydrocarbon (dry system), and C4 autorefrigeration vapors recovery by absorption, making compressor redundant.
Product properties: Octane (R+M) / 2:94.8 – 95.4
Licensor: Refining Hydrocarbon Technologies LLC.
