Process collaboration Hydrofluoric acid alkylation ABB and ConocoPhillips develop a critical new process analysis tool Michael B. Simpson, Michael Kester
The ABB Process Fourier Transform Infrared (FTIR) Analyzer for HF (Hydrofluoric Acid) Alkylation Refinery Process Unit Optimization, jointly developed with ConocoPhillips, helps petroleum refineries to operate their HF alkylation units more efficiently and safely, while making a signifi- cant contribution to operational and environmental risk mitigation.
22 ABB Review 3/2007 Hydrofluoric acid alkylation
Process collaboration
n the early days of petroleum refin- be produced that are of limited use. sharpened. Requirements for lower Iing, back in the 1920’s and 30’s, N-butane can easily be converted to sulfur, lower benzene, lower aromat- most of the pool of gasoline blending iso-butane, and in this form it joins ics, lower RVP and lower Driveability components was made up of straight- the FCC c3 or c4 olefins (butene or Index (a combination of fuel distilla- run material taken directly from the propene) as the combined feeds to tion properties) severely restrict the crude oil distillation unit. Refineries the HF alkylation unit. options for refiners in their final prod- were essentially rather simple oil boil- uct gasoline blending operations. ers. The first conversion units were The HF alkylation unit performs the uncomplicated and aimed at thermal important role of upgrading these The two most recent changes that reforming of straight-run naphthas to byproducts to high-value alkylate, have probably had the biggest impact yield higher octane blending compo- which is used as a gasoline blending on the gasoline pool are the removal nents for improved product quality. component. This economically invalu- of MTBE (methyl tertiary-butyl ether), able task of sweeping up the c4 ole- because of its contaminating impact The situation was given a significant fins from the FCC and the c4 isoal- on groundwater, and the addition of boost during World War II when there kanes from the crude oil distillation bio-ethanol for its carbon-neutral sta- arose, for obvious reasons, a desper- unit and converting them, through tus. MTBE is a lower vapor pressure ate need for high-octane aviation the catalytic HF alkylation process (a high-octane blending component for gasoline (military aircraft at that time modified Friedel-Crafts reaction), to gasoline. Although ethanol is equally were mainly equipped with recipro- iso-octanes, continues to be of major high-octane it makes a substantial cating piston engines fuelled by importance in petroleum refining. contribution to RVP, which essentially high-octane gasoline, rather than jet prevents straight butane from being engines fed on kerosene). Iso-octanes (alkylates) are the gold- used to any large extent in the same standard of gasoline blending feed- blend recipe. Thus, alkylate produced One of the responses to this need for stocks in today’s context of clean fuels by the HFU is of exceptional value to high-octane gasoline was the develop- and environmental concerns. They refineries in their struggle to meet ment of a refinery conversion unit – have high RON and MON (Research environmental and other legal con- the hydrofluoric acid (HF) alkylation and Motor Octane Numbers), low-sul- straints on their operations 1 . unit. fur, low Reid Vapour Pressure (RVP) and near zero aromatics. They are the HF alkylation operating issues Iso-octanes (alkylates) are perfect gasoline component. Consequently, refiners operating HF alkylation units are under increasing the gold-standard of gas- Over the past 15 years, gasoline for- pressure to maximize unit throughput, oline blending feedstocks mulation requirements, as driven by improve product quality and yields government environmental agencies while operating safely and with low in today’s context of clean in most regions of the world (but led environmental impact. Ever tightening fuels and environmental by the European Union and the Unit- legislation on gasoline quality and in- concerns. ed States), have been significantly creasing public and regulatory scruti-
1 The HF alkylation unit operational objectives The HF alkylation unit (HFU) remains of key importance to this day. It plays Ensure safety a critical role in providing one of the c/w Maintain Maximize reactor most important feeds to the final pro d- thoughput temperature uct gasoline blending pool. Its signifi- RX cance has grown side by side with Olefin Acid acid feed Settler acid recycle Maintain the increasing number of fluid cata- recycle acid acid lytic cracking (FCC) units in refineries. strength The FCC adds value to the heavy end recycle make-up HF of crude distillation by catalytically acid I DC3 acid regen Minimize Minimize Strip S cracking heavy feeds into lighter prod- Minimize ASO Minimize energy energy make- saturates O formation acid usage ucts such as light cycle oil and FCC up iC4 feed S gasoline, which can be used either Maintain optimal iC4 recycle T directly or after hydrotreating in final product quality R iC4 recycle Propane I Maintain optimal Butane product blending operations. The P product quality downside of this process is that light P Minimize E energy olefins, typically butene and propene, R R E are also produced in FCC operations. C Increase alkylate production These are essentially worthless as T Improve octane number feedstock. Similarly, in any crude dis- Alkylate tillation process an excess of light end products such as butane tend to
ABB Review 3/2007 23 Hydrofluoric acid alkylation
Process collaboration
ny of the use of hydrofluoric acid cy and alkylate quality. The ideal cations, and a productive partnership combine to make reliable and efficient blending characteristics of alkylate between ABB and ConocoPhillips operation of HFUs of critical impor- make it a critical element in meeting Factbox was formed to jointly develop tance to the overall reputation and refinery profit targets and complying an analytical solution. profitability of petroleum refineries. with fuel quality legislation. At the time, monitoring the key pro- The efficient operation of an HFU is a Operational targets cess parameters of HF alkylation units difficult task and subject to the most Alkylate quality optimization: the was not straightforward. It relied on testing of operating regimes. This is RON, RVP and distillation properties expensive, slow and potentially haz- due to a number of industry-specific of the alkylate product of the HFU ardous manual sampling of the recir- constraints and operating issues that are critical for its use in downstream culating hydrofluoric acid catalyst for stretch the processing capability of the gasoline blending. These parameters laboratory assessment of its strength plant. are influenced by HF catalyst purity, and the level of critical contaminants and specifically by water content, such as water and fluorination by- Operating issues which must be optimized within a products (known as acid soluble oils). HFUs must be able to deal with suitable operating window. The feedstocks that routinely vary in water content of the HF acid recycle HF acid purity determination is the contaminant levels, hydrocarbon stream is vulnerable to feed contam- key control parameter for HFU control composition and volume due to ination events, and these must be and optimization, provided it can be upstream operating complexities. picked up and acted upon promptly. delivered quickly enough to detect Operators have the difficult chal- Corrosion mitigation: corrosion miti- process unit upsets, such as transient lenge of minimizing iC4 recycling gation places severe lower limits on shifts in acid strength and contamina- and associated utility costs while HF acid purity and upper limits on tion events caused by upstream distur- producing alkylate of the desired water content. Keeping within de- bances in, for example, FCC opera- quality with minimum acid con- fined operational windows extends tion. sumption. HFU turnaround times, significantly The units must be operated in a reduces maintenance costs and lim- As of December 2006, safe manner despite the ever-pres- its the risk of HF release into the ent potential for acid runaway, ac- environment. the online acid analysis celerated equipment corrosion and HF acid consumption: correct oper- system is installed in associated HF release. ation of the HFU depends on the successful separation of hydrocar- almost 20 HF alkylation The demands on HF alkylation units bon product from the acid catalyst units worldwide and has are further increased by ongoing in the acid settler. If there is a build a combined operating trends within the petroleum refining up of acid soluble oil (ASO) by- industry. product and HF acid is consumed history of more than (thereby reducing acid strength), the 40 years. Industry trends process can fail, with the resulting The ongoing expansion of FCC units rapid consumption of the remaining ABB began working with the Cono- and the introduction of new crack- acid – a so-called acid runaway coPhillips R&D laboratory at Bartles- ing catalysts to satisfy gasoline event. Such an event is extremely ville, Oklahoma in 1996 to develop an growth also result in the production costly, but is an inevitable risk of online acid analysis system. Two years of more alkylation feedstock. HFU operation. A close watch on of testing and development followed The continuing trend of increased acid strength and the percentage on HF alkylation pilot scale units. residue cracking and upgrading ca- of ASO byproduct can significantly This included sample system design, pacity produces more complex and reduce the likelihood of this hap- metallurgy considerations and model problematic alkylation feedstock. pening. development. The analyzer was then There is an increasing interest in installed at the Phillips Petroleum re- C5 olefin processing as a means to The ABB-ConocoPhillips partnership finery in Sweeny, Texas in May 1998. return volatile components to the Recognizing the need for improved Two more years of successful onsite gasoline pool while increasing online HFU process monitoring and testing ensured the technology was product volumes. control in the mid-1990’s, Phillips Pe- ready for industry-wide implementa- The continual tightening of legisla- troleum (now ConocoPhillips) sought tion. The online acid analyzer was tion concerning gasoline quality a process analytical instrumentation then launched for the HF alkylation further restricts the use of some partner to jointly develop a solution market at the 2000 Phillips licensee current blend components. that would improve the monitoring symposium. and optimization of these complex Each of the above requires the HF process units. ABB was an established As of December 2006, the online acid alkylation unit to be more flexible in supplier of online process FTIR ana- analysis system is installed in almost handling increased and varying feed- lytical solutions in gasoline blending 20 HF alkylation units worldwide and stocks while maintaining unit efficien- and downstream petrochemical appli- has a combined operating history of
24 ABB Review 3/2007 Hydrofluoric acid alkylation
Process collaboration
more than 40 years. The systems are dard and run it in a laboratory scale minimal field intervention inside the installed in both ConocoPhillips and pilot alkylation reactor under real-life acid area (which in an HFU requires UOP licensed units in North and process conditions – but without any full C-suit personal safety equipment). South America, Europe and the Middle olefin feed in order to maintain exact East, and in sites operated by other acid composition during the run. FTIR analyzer technology major refining companies. ABB’s fiber-optic-based multichannel The successful devel- process FTIR analyzer is ideally suited The ABB–ConocoPhillips solution for this type of application. It allows a The key breakthrough in the creation opment and market remote field-based acid-area sample of a robust and useful process FTIR introduction of the ABB flow cell and associated safety and analytical solution for HFU monitoring sample conditioning system to be and optimization came with the devel- process FTIR HF acid physically separate from the analyzer opment of an accurate and precise analyzer is the result of optics station (which is normally lo- pre-calibrated chemometric model for a very fruitful cooperation cated in a control room or similar safe the required process variables (HF area). This arrangement is essential acid strength, water % and ASO %) 2 . between ABB and when dealing with the online analysis ConocoPhillips. of an exceptionally hazardous process The traditional laboratory reference stream such as HF acid. techniques for these measurements The data obtained were essential and are poor, and in contrast to the usual subsequently formed the basis for a An additional benefit of ABB’s FTIR methods of analyzer calibration, do successful patent registration under technology is its ability to monitor not provide a reliable basis for the which ABB offers the HF process FTIR multiple process streams with a single development of a precise calibration alkylation analyzer solution under analyzer. In HFUs this enables two model. Fortunately, the HF acid recy- license. acid streams to be monitored (for cle stream is of relatively simple com- example, the main acid recycle and position. This allowed ConocoPhillips A major part of ABB’s contribution to the acid regeneration overhead) in to develop the required universal cali- the project was the development of a real time, which significantly improves bration model on the basis of a gravi- safety-engineered field sample panel HF acid purity control and regenera- metrically prepared calibration stan- that is low maintenance and requires tion efficiency 3 .
2 Run-time data from ABB's Process FTIR HF Acid Analyzer a b
Hydrofluoric acid concentration Water %
86.2 1.5 86.0 1.3 85.8
85.6 1.1
Vol (%) 85.4
Water (%) 0.9 85.2 0.7 85.0
84.8 0.5 3 Days 2 Days
c d
Hydrofluoric acid strength Acid Soluble Oil (ASO) %
88.8 9.0
88.6 8.5 88.4 8.0 88.2 88.0 7.5 HF (%) 87.8 ASO (%) 7.0 87.6 6.5 87.4 87.2 6.0
2 Days 2 Days
ABB Review 3/2007 25 Hydrofluoric acid alkylation
Process collaboration
In addition to these benefits An extended portfolio 3 Real-time process monitoring with APC there are other exciting pro- The successful development cess control options for the and market introduction of HFU process FTIR analyzer. the ABB process FTIR HF Besides the HF acid catalyst acid analyzer is the result of monitoring role, there are Reduce variance a very fruitful cooperation many important hydrocarbon between ABB and Cono- streams in the HFU that bene- coPhillips. fit from reliable, low-mainte- Shift target nance and rapid composition- As one of the principal HF al analysis. The olefin feed process licensors, Cono- stream and the iC4 recycle coPhillips brought to the stream from the iso-stripper Actual constraint partnership a key under- are the most important. No Analyzer / APC standing of real-life process Together, these two streams monitoring requirements and directly influence the feed critical process variables. purity to the HFU, which in Through their R&D depart- turn has a direct impact on HF acid Lower acid inventory, as acid make- ment they also brought the capability consumption. Real-time process data up requirements are reduced to develop the crucial universal ana- on these streams, along with the HF Alkylate octane enhancements are lyzer pre-calibration necessary for suc- acid purity measurement, provide a possible as the water content of the cessful commercial exploitation. significant improvement in unit opera- catalyst can be increased in a con- tional stability. trolled manner. One of the major ABB was able to contribute state-of- licensors reports that an increase in the-art process FTIR technology and ConocoPhillips brought a water content from 1.0 – 2.0 wt% expert field sample system design en- can deliver more than $1 million gineering. Together, these inputs have key understanding of real- in benefits for a 10,000 bpd unit produced a result of significant bene- life process monitoring operating at the typical I:O ratio fit to both parties. ConocoPhillips is of 10 able to offer a key process analytical requirements and critical Less aggressive regenerator opera- tool to its many HF process licensees, process variables to the tion and lower acid losses as well as benefiting from the direct partnership. Higher quality alkylate and yields implementation of the technology in Acid:hydrocarbon ratios and reactor its own refining operations. ABB has temperature are controlled to im- been able to add a significant and In summary, the ABB–ConocoPhillips prove product quality and suppress unique building block to its portfolio solution for HFU reactor optimization ASO production of refinery process FTIR analytical offers ABB multivariable control tech- Reactor conditions are optimized to solutions. nology underpinned by a unique manage variations in fresh feed capability for rapid online character- compositions. ization of HF acid, recycle iC4, olefin/ iC4 makeup feeds and alkylate. The solution delivers the following signifi- Factbox ConocoPhillips cant operating improvements to HF alkylation reactors: Feed rates, alkylate yield, and alkyl- Headquartered in Houston, Texas, Cono- ate octane are maximized to an coPhillips is the third-largest integrated economic optimum, subject to oper- energy company in the United States – ating constraints based on market capitalization, oil and Isobutane:olefin (I:O) ratio and en- gas proved reserves and production – and ergy consumption can be reduced the second-largest refiner in the United while meeting alkylate quality and States. The company operates in more yield targets with minimum acid than 40 countries, has 38,700 employees consumption. and is known worldwide for its technologi- Michael B. Simpson Isobutane makeup rate can be opti- cal expertise in deepwater exploration and ABB Analytical mized while respecting iC4 invento- production, reservoir management and Québec, Canada ry constraints exploitation, 3-D seismic technology, high- [email protected] Acid quality is maintained in the op- grade petroleum coke upgrading and sul- timum operating range for HF, ASO fur removal. For more information, please Michael Kester and water content. This leads to: refer to www.conocophillips.com ABB Inc., Less frequent approaches to run- Houston, Texas away conditions [email protected]
26 ABB Review 3/2007