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Hydrofluoric Acid Alkylation Conversion and Expansion

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Hydrofluoric Acid Alkylation Conversion and Expansion Hydrofluoric acid alkylation conversion and expansion Much of the cost of switching from hydrofluoric acid to sulphuric acid alkylation can be avoided by using existing equipment SHANE PRESLEY and JASON NUNEZ DuPont Clean Technologies t a time when refiners face includes an in-depth case study uti- alkylation unit, the existing horizon- concerns around the rise lising the novel reactor solution. tal HF acid settler will be reused as Aof electric vehicles and the a sulphuric acid settler. eventual peak in global gasoline DuPont ConvEx HF conversion and The second conversion option demand, alkylate as a gasoline expansion technology using a novel reactor design is also blend component is more popular DuPont Clean Technologies devel- suitable for both gravity-flow and than ever. The unique properties oped the ConvEx HF conversion pumped-flow HF alkylation units. of alkylate, including high octane, and expansion technology for both For the conversion of a gravity-flow lack of olefins and aromatics, and gravity-flow and pumped-flow HF HF alkylation unit, the existing ver- extremely low sulphur, make it the alkylation units to utilise sulphu- tical acid settler will be retrofitted only blending component that truly ric acid as catalyst for the alkylation with proprietary internals for mix- enhances all aspects of the gasoline reactions. The conversion options for ing and will perform the function pool, helping refiners meet tight- the reaction section include: tradi- of an alkylation reactor, acid settler, ening specifications. Due to these tional Stratco Contactor reactors and and compressor suction vessel. For blend qualities, a transformation a novel reactor design. The Stratco the conversion of a pumped-flow has occurred in the last few years HF alkylation unit, the existing hori- whereby alkylate is sought out The unique properties zontal acid settler will be retrofitted worldwide and is now sold and with proprietary internals for mix- exported as a stand-alone product of alkylate make it ing and will perform the function of to serve those regions of the world alkylation reactor, acid settler, and where refining technology is not the only blending compressor suction vessel. In both able to keep up with changing fuel bases, the reaction zone modifica- specifications. component that truly tions are limited to vessel retrofits, The commercially adopted alky- new piping and new pumps. The lation processes in refineries utilise enhances all aspects novel reactor design incorporates two main catalyst types: sulphuric of the gasoline pool innovations developed through acid and hydrofluoric acid (HF). extensive research while utilising Refiners that use HF in their alkyla- proven design elements that are tion units are burdened with safety Contactor reactor option was dis- familiar to refinery operators. Due to and environmental concerns, lead- cussed extensively in the 2017 article, the fact that no new reaction vessels ing to tremendous pressure from so this article will focus primarily on are required, this conversion solu- both regulatory agencies and com- the novel reactor approach. tion can be very economical, while munity activists. This has led to a The first conversion option using still providing acid consumption and recent resurgence in the interest in Stratco Contactor reactors is suitable alkylate product properties similar to conversion or replacement of HF for both gravity-flow and pumped- grassroots Stratco alkylation units. alkylation units with alternative flow HF alkylation units and will technologies. match the performance of a grass- Expansion through conversion As part of the 2017 Revamps edition roots Stratco alkylation unit. For In both HF and sulphuric acid alky- of PTQ, an article titled ‘Advances the conversion of a gravity-flow HF lation units, the ratio of isobutane to in HF alkylation conversion and alkylation unit, the acid coolers will olefins in the reaction zone must be expansion’ was published, pro- be replaced by Contactor reactors, maintained adequately high to pre- viding an overview of the DuPont and the existing vertical acid settler vent unfavourable olefin-to-olefin ConvEx technology for converting will be retrofitted to perform as an reactions from occurring that can HF alkylation units to sulphuric acid settler for the converted sul- result in low quality alkylate and acid alkylation. This article explores phuric acid alkylation unit. For the higher acid consumption. How this the technology in greater detail and conversion of a pumped-flow HF ratio is achieved in these processes www.eptq.com PTQ Q4 2018 19 from the fractionation section. As a HF alkylation result, the fractionation equipment in HF alkylation units is signifi- Olefins 100% isobutane recycle cantly larger than in sulphuric acid Isobutane alkylation units. A comparison of isobutane flows Feed Reaction Fractionation Product in HF and sulphuric acid alkylation pre-treatment post-treatment units is shown in Figure 1. Propane This difference between the isobu- ASO Butane tane recycle streams in HF and sul- extraction phuric acid alkylation units is the Alkylate basis for unit expansion capabili- ties at the same time as conversion Sulphuric acid alkylation with minimal additional cost. The Olefins fractionation equipment and efflu- ~50% isobutane recycle Isobutane ent piping in HF alkylation units is approximately twice the size of that Feed Reaction Dry alumina Fractionation of a sulphuric acid alkylation unit preparation adsorption of similar size. As part of any HF conversion to sulphuric acid alky- Butane lation, a new refrigeration section Alkylate is required to reduce reaction tem- ~50% isobutane Refrigeration recycle Propane peratures. This refrigeration section will provide additional isobutane (refrigerant recycle) flow to the reac- tion zone, unloading the fractiona- Figure 1 Comparison of isobutane recycle streams in the HF and sulphuric acid alkylation tion equipment. Instead of operating processes the unit in a very unloaded fashion, it may be beneficial to utilise this Capacity expansion case studies additional capacity to expand the throughput of the unit. Customer Feed type Design capacity, bpd Expansion capacity, bpd Capacity increase DuPont has evaluated many HF A MTBE C =/C = 13 500 22 601 +67% 3 4 alkylation units for conversion to B FCC C3=/C4= 10 000 27 810 +178% C MTBE C = 13 500 24 435 +81% sulphuric acid alkylation using the 4 Table 1 D FCC C3=/C4= 10 500 20 569 +96% ConvEx technology. shows E FCC C4= 20 500 43 865 +114% the extent to which expansion was F FCC C =/C = 10 000 24 309 +143% 3 4 possible as part of this evaluation. In each of these examples, the units Table 1 were expanded up to the limits of the fractionation equipment or other is quite different, however. This refrigeration section. In sulphuric major unit constraints. Of the six difference is leveraged as part of acid alkylation units, isobutane is examples shown in this table, three the ConvEx technology to achieve flashed in the reaction zone to pro- of these resulted in an expansion a significant increase in throughput vide cooling for the reactors, which potential that more than doubled by converting an HF alkylation unit typically operate at around 45-60°F the capacity of the existing HF alky- to one using sulphuric acid as the (7-15°C). This flashed isobutane is lation unit. Doubling unit capacity catalyst. then compressed, condensed and may not always be possible as part For sulphuric acid alkylation cooled in the refrigeration section of a conversion of an HF alkylation units, there are two sources of before being routed back to the unit, but in all the cases examined, isobutane that circulate back to the reaction zone as refrigerant recycle. considerable expansion was possi- reaction zone. The first source is The refrigerant recycle stream pro- ble, providing an economic incen- the fractionation section, where net vides the remainder of the isobu- tive for refiners to consider HF effluent is separated into its com- tane required in the reaction zone. conversion. ponents (isobutane, normal butane In HF alkylation units, the reac- and alkylate). The isobutane stream tion zone is operated at much Case study from the top of the deisobutaniser higher temperatures, so no refriger- The case study presented here uti- tower provides recycle isobutane ation section is required. Since there lises DuPont’s novel reactor design to the reaction zone. This stream is no refrigeration section providing to retrofit an existing pumped-flow makes up about one half of the total refrigerant recycle back to the reac- HF alkylation unit (see Figure 2) for isobutane required for the reaction tion zone, all the isobutane required conversion to a sulphuric acid alky- zone. The second source is from the in the reaction zone must come lation unit. 20 PTQ Q4 2018 www.eptq.com Reuse Abandon/demo Isostripper Repurpose receiver HF stripper 1st stage reactor Depropaniser Feed dryers Alumina 1st stage treaters acid settler Makeup isobutane KOH treaters Olefin feed Feed coalescer 2nd stage Propane reactor 2nd stage acid settler Fresh acid Acid storage drums Isostripper Acid Tar regenerator Alumina Tar Polymer treaters neutraliser surge drums HC relief header KOH treaters Acid relief header n-butane Relief gas scrubber Alkylate Figure 3 Original HF alkylation unit This HF alkylation unit was orig- head stream was then routed to the inally designed to produce 10 500 depropaniser as feed to the column. Settler b/d of alkylate product using two The depropaniser overhead stream effluent HF reactors, acid settlers, and acid was the propane product and the HF circulation pumps with a feed con- bottoms product was routed back Cooling reactor water sisting of FCC butylene and propyl- to the reactor feed streams to sup- supply Figure 3 Acid ene (see ). ply approximately 30% of the recy- Cooling settler The fractionation equipment for cle isobutane to the reaction section. water this unit included an isostripper col- The isostripper also included two Acid return circulation umn and a depropaniser column.
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