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Comment Processing & Handling

Lower costs for converting alkylation units from hydrofluoric to sulfuric acid

By Scott Jenkins |

For petroleum refineries, the cost of converting hydrofluoric-acid-based alkylation units to the relatively safer sulfuric-acid-based alkylation process (diagram) has been cost-prohibitive and has lacked specific economic benefits. Now, DuPont (Wilmington, Del.; www.dupont.com) has developed a low-cost approach to converting existing HF alkylation units to use sulfuric acid that simultaneously allows an expansion of production capacity. Known as the ConvEx technology, the suite of DuPont conversion capabilities takes advantage of existing equipment to keep the capital expense low, says Shane Presley, technical service and development manager for DuPont Clean Technologies.

Changes to the reaction stage can take two forms. One option involves the installation of the DuPont Stratco Contactor reactor for sulfuric acid alkylation. This allows the highest product quality, but involves more capital expense. Another option involves retrofitting existing reactors.

alkylation

The DuPont ConvEx technology becomes particularly attractive economically when additional capacity is desired. The differences in how isobutane is recycled in HF compared to H2SO4 alkylation units is the key to the expansion opportunity provided by the ConvEx technology (see diagram). By taking advantage of these differences in the conversion protocol, ConvEx technology enables refiners to gain significantly more alkylation capacity.

“HF alky units are typically run at temperatures of 100°F, while sulfuric acid units are typically designed to run at 45°F,” Presley explains, “so the addition of a new refrigeration section for the H2SO4 alkylation process is required, but the ability to recycle some isobutane from the refrigeration section frees up space in the fractionation stage.” This allows refiners to generate an additional 100% or more alkylate when converting from HF to sulfuric using ConvEx, Presley notes.

DuPont currently runs a pilot facility to show the capacity expansion capabilities of the ConvEx process and is looking for opportunities for conversion of commercial-scale operations.

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