STRATCO® Alkylation Technology
DuPont Clean Technologies has invested heavily into the research and development of sulfuric acid alkylation with recent breakthroughs bringing even more flexibility to the STRATCO® Alkylation Technology.
With the popularization of hydraulic fracturing in the upstream oil & gas industry, large volumes of propane and butane (NGL) are flooding the market and will remain in oversupply for the foreseeable future. As such, several refiners and petrochemical processors have considered plans to build butane-to-alkylate (BTA) or propane-to-alkylate (PTA) complexes in the United States and other countries around the world. These complexes convert otherwise low value NGL to high value alkylate, which is in chronic undersupply. In the Northeast region of the USA alone, a considerable volume of alkylate is currently being imported in order to meet Tier 3, NAAQS and CAFE standards. Thus, alkylate will increasingly become a more important part of the gasoline pool.
BTA complexes involve converting butanes to olefins in a dehydrogenation unit and then upgrading the resulting stream in an alkylation unit. A number of BTA complexes have considered first isomerizing the butanes to isobutane in an isomerization unit prior to the dehydrogenation unit, but this step is not required. Similarly, PTA complexes include a dehydrogenation unit to convert the propane to propylene with the resultant propylene mix then upgraded in an alkylation unit.
For decades, DuPont has successfully proven alkylation with high purity olefin feed stocks in the pilot plant. To determine commercial viability of alkylating a 100% iC4= feed stream, DuPont partnered with a U.S. refiner to test this feed in its existing STRATCO® alkylation unit. In the spring of 2016, this refiner purchased several rail cars of 99+% isobutylene and processed it for more than two days in the STRATCO® alkylation unit. This test run was very successful, producing a high quality alkylate product with no operational issues.
A traditional Butane-to-Alkylate complex consists of field butanes that are isomerized to form isobutane. This isobutane is then sent to a dehydrogenation unit to create isobutylene. The isobutylene serves as the primary olefin feed stock to the STRATCO® sulfuric acid alkylation unit.
Using typical operating conditions for this type of complex, it is estimated that a feedstock of 25,500 BPD of field butanes will yield 20,000 BPD of high quality alkylate with a RON of approximately 95.5. During the commercial test run, the alkylate produced matched this case study’s result.
A Propane-to-Alkylate complex operates in similar fashion to a BTA complex by taking low cost propane and dehydrogenating it to propylene. This propylene serves as the primary olefin feedstock to the STRATCO® sulfuric acid alkylation unit.
In a PTA case study 12,950 BPSD of propane and 12,900 BPSD of isobutane yielded 20,000 BPSD of alkylate product. This alkylate product would have minimum value of 90 RON depending on the quantity and quality of C4 olefins that are processed with the propylene.