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Hydrofluoric 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- , the existing horizon- concerns around the rise lising the novel reactor . 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 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 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 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. side streams. The first side stream Combined pump Effluent from the two acid settlers was drawn off high in the stripping feed was routed to the isostripper as section and, being rich in isobutane, feed to the column. The isobutane was routed back to the reactor feed Figure 2 Typical pumped-flow HF reactor and propane rich isostripper over- to supply the remaining 70% of the

22 PTQ Q4 2018 www.eptq.com recycle isobutane to the reaction sec- Proprietary tion. The second side stream was Flashed vapour internals drawn off lower in the stripping sec- to compressor tion as the n-butane product stream. Olefin feed and Olefin feed and The isostripper bottoms stream was recycle isobutane recycle isobutane the alkylate product stream. Refrigerant Refrigerant The conversion solution for this recycle recycle case study involved converting the existing acid settlers to novel sul- Acid emulsion Acid emulsion recycle pumps recycle pumps phuric acid alkylation reactors by Fresh acid retrofitting them with DuPont’s Net effluent Spent acid proprietary internals and adding product acid emulsion recycle pumps (see Figure 4). Since sulphuric acid alkylation Figure 4 Novel reactor retrofit design reactions are optimised at a much lower temperature than HF acid a refrigerant recycle stream. Table Dry alumina adsorption alkylation reactions, a new refriger- 3 provides a summary of feed and In sulphuric acid alkylation units, ation section and new feed/effluent product streams for the conversion stable droplets (or colloidal suspen- heat exchangers were added to the solution offered for this case study, sions) of sulphuric acid and other system. Other existing equipment while Table 4 provides a summary acidic compounds exist in the net was repurposed for use as the acid of predicted alkylate properties. effluent. These droplets are formed coalescer, dry alumina adsorption, propane product treatment, and Case study: major equipment list acid blowdown. Figure 5 illustrates a simplified process flow diagram of the conversion solution for this Existing equipment New equipment required Existing equipment not reused or repurposed for conversion used for conversion HF alkylation unit. Acid blowdown drum (remote) Acid emulsion recycle pumps Acid circulation pump Most modern HF alkylation units Acid neutralisation pit Compressor K/O drum Acid regenerator also have remote HF acid storage Acid settlers Feed/effluent exchangers Acid regenerator condenser Acid storage drums Fresh acid pumps Acid regenerator IC superheater vessels and remote HF acid blow- 4 Alkylate cooler Net effluent pumps Acid regenerator overhead pump down drums. Depending on the Alkylate flush pump Propane purge pumps HF reactors location of these vessels and the Alkylate product coolers Refrigerant condensers HF stripper requirements of the conversion Depropaniser Refrigeration compressor Settled acid pump solution offered, these may be uti- Depropaniser accumulator Spent acid pumps Depropaniser bottoms cooler lised as spent acid after-settlers, Depropaniser charge pumps acid blowdown drums, or they Depropaniser condensers may be converted to novel sulphu- Depropaniser feed/bottoms exchangers ric acid alkylation reactors to take Depropaniser reboiler Depropaniser reflux pumps full advantage of the additional Feed coalescer capacity available through conver- Feed dryers sion to sulphuric acid. Potential Isobutane recycle pumps opportunities to reuse these vessels Isostripper Isostripper accumulator will be determined on a case-by- Isostripper condensers case basis. Table 2 provides a list of Isostripper feed/bottoms exchangers existing and new major equipment Isostripper feed/IC4 recycle exchangers in the alkylation unit. Isostripper reboiler Isostripper receiver To maximise product quality Isostripper reflux pumps and to minimise acid consumption, Isostripper side stream cooler DuPont applied patented designs to KOH pumps stage acid flows between the -reac n-Butane condensers n-Butane defluorinators tion sections. n-Butane draw vapour/liquid separator Since the isostripper and depro- n-Butane KOH treaters paniser were designed to pro- n-Butane product trim cooler vide 100% of the isobutane recycle Polymer surge drums Propane defluorinators stream, a significant capacity Propane KOH treaters increase of nearly 100% was possible Relief gas scrubber with the addition of a new refriger- Relief gas scrubber circulation pump ation section. The new refrigeration Tar neutraliser section provides approximately 50% of the required isobutane recycle as Table 2

www.eptq.com PTQ Q4 2018 23 Refrigeration compressor Original equipment New equipment Propane Refrigerant accumulator Compressor K/O drum Propane treaters

Depropaniser Feed dryers

2nd stage Makeup isobutane Olefin feed Feed coalescer 1st stage

Fresh acid

Acid storage drums

Acid coalescer Isostripper

Dry alumina adsorption n-butane

HC relief Spent acid header aftersettler

Acid relief header Acid blowdown drum Relief gas scrubber Alkylate Recovered hydrocarbons Spent acid

Figure 5 Converted alkylation unit

by the chemistry of the alkylation treating was the standard for caustic based system. Because the reactions and cannot be avoided, removal of acidic components from vessels in this technology are ver- regardless of the technology used. the net effluent stream. While this tical, plot space requirements are Additionally, these droplets exhibit system is a very effective means of reduced. Finally, by not contacting the characteristics of Brownian effluent treating, a recent change the effluent stream with caustic or motion and are not able to be effec- was made in the standard design water, this stream and the recycle tively removed by coalescing. If not of Stratco alkylation units. Instead isobutane stream from the deisobu- removed, these acidic components of a caustic based treating sys- taniser overhead is also completely will result in fouling and corrosion tem, dry alumina adsorption was dry. in the downstream fractionation adopted. Dry alumina adsorption Because the recycle isobutane equipment. provides both a capital and operat- stream is completely dry, water For many years, caustic based ing expense benefit compared to the removal is not required in the feed

24 PTQ Q4 2018 www.eptq.com Case study: feed and product stream summary Case study: product alkylate properties

Olefin feed, Isobutane Propane n-Butane Alkylate % Propylene/total olefins (feed) 42.1 % feed product product product % Isobutylene/total olefins (feed) 18.4 Volume flow, b/d 19 795 9564 2334 1,270 20,569 RON 93.5 Composition, vol% (R+M)/2 92.7 Ethane 0.03% 0.23% D-86 T90, °F (°C) <290 (143) Propane 9.51% 1.99% 97.50% D-86 EP, °F (°C) <400 (204) i-Butane 21.78% 95.00% 2.26% 16.71% 0.20% Acid consumption, n-Butane 6.98% 3.01% 0.02% 82.29% 3.03% lbs acid/gal alkylate 0.45-0.55 i-Pentane 2.60% 0.98% 7.11% Alkylate Reid vapour pressure n-Pentane 0.72% 0.02% 0.70% (RVP), psia 6.0 Propylene 24.61% Alkylate sulphur, ppm <2 Butylene 33.07% Amylene 0.71%

C6+ 0.00% 88.96% Table 4

Table 3 offline mode, and the spent alumina from the offline treater can either preparation section of the alkyla- as part of the reaction mechanism be removed and replaced or regen- tion unit. HF alkylation technol- mentioned above) forms a ‘crust’ on erated in place once the alumina ogy is very sensitive to water, so the alumina beads that hinders fur- is deactivated. While DuPont has feed dryers are required to remove ther reaction and removal of acidic done significant research to opti- nearly all the water from the feed. components. Acidic components mise the selection of alumina prod- This is not the case in sulphuric acid are still able to diffuse through this ucts for this service, even the most alkylation units. While water does crust for some period, but eventu- effective alumina products used dilute the sulphuric acid, resulting ally the diffusion rate is such that are very inexpensive, which is why in higher acid consumption rates, the alumina is no longer effective. some refiners choose not to regener- larger amounts of water in the feed Figure 6 provides an illustration ate the alumina and simply replace are acceptable, so feed coalescers of a typical dry alumina adsorption it once it becomes spent. For those are typically used instead of feed treater. refiners that do choose to regen- dryers. Additionally, if dry alumina Parallel treating vessels are erate, this is done by washing the adsorption is used for effluent treat- required so that the treating vessels alumina with water and then dry- ing and the recycle isobutane stream can be switched between online and ing it before placing it back in ser- is completely dry, feed coalescing vice. Regeneration or replacement is not required. When converting frequency is a function of treater Untreated from HF alkylation to sulphuric acid effluent size, so refiners can choose a- pre alkylation, no changes are required ferred frequency by selecting the in the feed preparation section. appropriate size if new vessels are Refiners have the option of -contin used. When converting an HF unit uing to use the existing feed dryers to a sulphuric acid alkylation unit, for removal of water from the olefin it is common to repurpose existing feed stream if they are sized appro- vessels in the plant for the alumina priately. However, the olefin feed treaters. In this case, the frequency stream is very small compared to of regeneration or replacement the recycle isobutane stream, so the is determined by the size of the impact on acid consumption would repurposed vessel. While regener- be negligible if this equipment was ation and replacement frequency abandoned instead. can vary, it is common for regen- Dry alumina adsorption technol- erations to occur every 2-6 weeks ogy works by flowing the effluent and replacement to occur every 6-9 stream across a packed bed of acti- months. Regenerated alumina can vated alumina. Acidic components typically withstand 40-60 regen- react in the pores of the alumina eration cycles before the alumina beads through a process called requires complete replacement. chemisorption. The basic reaction mechanism is: Conclusion Treated Community and regulatory pres- Al O + 3H SO ➝ Al (SO ) + 3H O 2 3 2 4 2 4 3 2 effluent to sure surrounding HF alkylation fractionation units is currently at an all-time high, The mechanism for alumina so refiners are being forced to con- deactivation in this service is that Figure 6 Typical dry alumina adsorption sider alternatives such as conver- the aluminum sulphate (produced treater sion or replacement of their existing

26 PTQ Q4 2018 www.eptq.com HF alkylation units. Demolishing regardless of which technology is ing global alkylation technology and replacing existing assets can used. However, by value engineer- have been incorporated into these be extremely expensive and result ing unique to reuse as conversion solutions. The resulting in lost opportunity costs due to the much existing HF alkylation equip- product includes proven technology downtime required for construc- ment as possible, the conversion applications, a robust design, and tion. The DuPont ConvEx technol- solutions now offered by DuPont equipment that is familiar to refin- ogy seeks to make conversion of offer step-change reductions in cost ery operators. HF alkylation units more feasible in comparison to other solutions for refiners by introducing -solu available on the market. tions that not only solve the prob- • Create value for the refiner ConvEx and STRATCO are marks of DuPont. lem around safety in HF alkylation through unit expansion. An increase units, but also provide an economic in throughput of 100% or more is Shane Presley is the Technical Service and justification for conversion projects. possible when converting from HF Development Manager for the alkylation and This technology was developed alkylation to sulphuric acid alkyla- hydroprocessing businesses with DuPont Clean with four key objectives in mind: tion by taking advantage of some of Technologies. With approximately 20 years of • Develop solutions that are safe the key design differences between refining and technology licensing experience, alternatives to HF. In addition to these two alkylation technologies. and roles at Chevron and ExxonMobil prior the safer chemical and physical Even if conversion from HF catalyst to joining DuPont, he holds a BS degree in properties of sulphuric acid com- is not a key driver, refiners have an chemical engineering from Mississippi State University. pared to HF, the alkylation designs opportunity to complete the expan- Jason Nunez is a Senior Technical Service by DuPont have a long history of sion and be left with a safer technol- Engineer for the alkylation and hydroprocessing incorporating the highest safety ogy that has long term viability. businesses with DuPont Clean Technologies. standards. This is reflected by the • Ensure the conversion technol- With over 14 years of experience in the refining positive safety record of refiners ogy is proven, robust and opera- and petrochemical industries, and roles with operating Stratco alkylation units. ble. Although many aspects of the Citgo Petroleum Corporation and the Saudi • Develop cost-effective conver- DuPont ConvEx technology are Aramco Mobil refinery prior to joining DuPont, sion solutions. A conversion from unique and innovative, the design he holds BS degrees in chemical engineering an HF alkylation unit to a sulphuric elements and know-how that have and environmental science from McNeese acid alkylation unit is no small feat, made Stratco alkylation the lead- State University.

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