ADVANCES IN HYDROFLUORIC (HF) ACID CATALYZED ALKYLATION

Transcription

1 Annual Meeting March 23-25, 2003 Marriott Rivercenter Hotel San Antonio, TX ADVANCES IN HYDROFLUORIC (HF) ACID CATALYZED ALKYLATION Presented By: Franz-Marcus Nowak Technology Manager UOP LLC Des Plaines, IL J. Frank Himes Alkylation-Isomerization Senior Process Specialist UOP LLC Des Plaines, IL Robert L. Mehlberg FCC-Alky Senior Process Specialist UOP LLC Des Plaines, IL National Petrochemical & Refiners Association 1899 L Street, NW Suite 1000 Washington, DC voice fax

2 This paper has been reproduced for the author or authors as a courtesy by the National Petrochemical & Refiners Association. Publication of this paper does not signify that the contents necessarily reflect the opinions of the NPRA, its officers, directors, members, or staff. Requests for authorization to quote or use the contents should be addressed directly to the author(s)

3 PU ADVANCES IN HYDROFLUORIC (HF) ACID CATALYZED ALKYLATION J. Frank Himes, Robert L. Mehlberg PhD-ChE, Franz-Marcus Nowak UOP, LLC Des Plaines, Illinois INTRODUCTION For the last 50 years, HF alkylation has been a workhorse for the refining industry, producing clean-burning, high-octane gasoline. As the 21 st century begins, significant changes have been made to the requirements of the gasoline pool. These changes, which limit the refiner s flexibility, have only raised the importance of alkylate as a key blending component. As one of the leading licensor s in alkylation technology, UOP has responded to the market needs by continuous improvement of HF alkylation technology. In response to the issue of risk mitigation surrounding the use of HF, UOP has continued the development of the Alkad 1 process, an HF aerosol vapor suppression additive technology, and introduced the Alkylene process, a true solid catalyst alkylation technology. While the economic efficiency of solid catalyst alkylation technology continues to improve, industry activity related to the use of HF technology for both new and revamps continues at a high level. This paper will focus on recent developments in HF alkylation technology and how the UOP HF Alkylation and Alkad processes effectively meet the demands of the gasoline market in the 21 st century. Page 1

4 MARKET TRENDS There have been a number of changes in gasoline formulation that will increase the demand for alkylate. The changes with the largest impact are the phase-out of methyl tertiary butyl ether (MTBE) and the phase-in of ethanol. MTBE PHASE-OUT As of January 2003, seventeen states within the United States have banned the use of MTBE as a gasoline blending component. Many refiners are voluntarily removing MTBE from the gasoline pool before the ban is in effect. Removing MTBE from the U.S. market will result in a volumetric reduction of 3 to 4% in the U.S. gasoline supply. 2 In addition to the volumetric loss, removing MTBE adversely impacts both the octane and emissions of the blending gasoline pool. MTBE is a high-octane, non-aromatic, low sulfur blending stock with a moderate Reid Vapor Pressure (RVP) of 9 psi. Without MTBE, refiners will be hard pressed to meet the RVP requirements, octane or Driveability Index (DI) targets. DI = 1.5*T *T 50 + T 90 ETHANOL REQUIREMENT Ethanol is the only viable replacement for MTBE, where oxygenates are required. It is common for gasoline blends, especially those in the Midwestern states, to contain as much as 10 % ethanol by volume. Adding ethanol, with a blending octane of 113 3, provides both volume and octane to the gasoline pool. However, as a blending component, ethanol has a high RVP. A gasoline blend with 10 percent ethanol may have a RVP as high as 18 psi 4. This is much above the RVP requirement of many states. In order to meet a vapor pressure specification of 7.6 psi, a blend with 10 percent ethanol will require the removal of lighter components such as butane and pentane. The net impact of the pentane back-out phenomenon is subject to much debate. However, it is clear that using ethanol as a blending stock stresses the ability of the refiners to meet stringent RVP requirements of the existing gasoline pool. Page 2

5 ALKYLATE S ADVANTAGE Alkylate, produced by alkylation of C 3 to C 5 olefins with isobutane, is a high-octane, low-rvp blending stock. The low blending RVP of alkylate, between 2 and 4 psi, allows refiners to blend lighter materials, such as isomerate and pentanes, back into the gasoline pool. Unlike some other processes for producing gasoline blending components, the alkylation process does not contribute any additional aromatics, sulfur, or olefins into the gasoline pool. Alkylate is an ideal blending component. ALKYLATION TECHNOLOGIES The majority of alkylate produced today comes from two routes: sulfuric and hydrofluoric acid catalyzed alkylation. In time, the Alkylene process will join the other two as a significant source of high quality alkylate. SULFURIC ALKYLATION AND HYDROFLUORIC ALKYLATION On a fundamental basis sulfuric and hydrofluoric alkylation are quite similar. The major differences between the two processes stems from the difference in the ability of the acid to catalyze the reaction. Sulfuric acid is less effective at promoting alkylation. The major differences between sulfuric and hydrofluoric alkylation are temperature and acid consumption. Sulfuric alkylation requires refrigeration to maintain a low reactor temperature. The acid consumption rate for sulfuric alkylation is over a hundred times that of HF. SOLID CATALYST ALKYLATION: THE ALKYLENE PROCESS After developing the Detal process, which utilizes solid catalyst for detergent alkylation in 1995, UOP focused extensive research into a solid catalyst process for motor fuel alkylation. Many researchers, UOP included, initially based their solid alkylation technologies around a fixed-bed reactor scheme. Upon confronting the challenges posed by side reactions and catalyst regeneration, UOP soon recognized that a fixed-bed design would be inadequate. Instead, UOP chose a reactor design with short catalyst contact time and insitu regeneration capability. In 1997 the Alkylene process was introduced based on an innovative riser transport reactor technology. A key enabler was the development of the HAL solid catalyst. The Alkylene process is commercially available and in 2002 UOP delivered two engineering specification packages. The economic efficiency of the Alkylene process has steadily improved with continuing catalyst and process improvements, and today the overall economics are superior to sulfuric acid technology. Page 3

6 ECONOMIC COMPARISON As seen in Table 1, while the quality of alkylate produced by the three alkylation technologies are equivalent, there are significant yield advantages for the Alkylene and HF processes over sulfuric, and significant cost advantages for HF over the Alkylene process and sulfuric alkylation. The data presented in Table 1 indicate HF alkylation as the best economic choice. Table 1 Comparison of Alkylation Options Alkylene + Butamer* HF + Butamer* Onsite Regen H 2 SO 4 + Butamer* Total Feed from FCC, BPSD 7,064 7,064 7,064 + C 5 Alkylate 8,000 7,990 7,619 + C 5 Alkylate RON MON (R+M)/ C 5 Alkylate D-86, ºF 50% % Economics Variable Cost of Production, $/bbl** Fixed Cost of Production Total Cost of Production EEC, $MM *All cases include a Butamer to maximize feed utilization **Raw Materials are not included Simple economics is not always the key parameter for today s refiner, as the regulatory climate and/or other local factors can influence technology choices. Responding to these varying needs, UOP offers a variety of alkylation technologies to meet the needs of any refiner, from HF alkylation, HF alkylation with the Alkad process, and the Alkylene process. Page 4

7 HF ALKYLATION IN THE 21 ST CENTURY The flow scheme used in the UOP HF Alkylation process is shown in Figure 1. This design offers several advantages over the other HF alkylation technologies. The UOP design is a forced acid and water cooled system. The advantage of using water to directly remove the heat of reaction, as opposed to using circulating HF, is that it decouples the acid inventory from the unit capacity. Therefore, the acid inventory is not set by heat removal requirements. For large units, the water-cooled reactor design allows for a significant reduction in the acid inventory relative to the competing technologies. The pumped design maximizes the mixing between the hydrocarbon and the acid. The pump provides the necessary inlet pressure into specially designed feed nozzles, which produce droplets of an optimal size. The enhanced dispersion and contact of hydrocarbon and acid contributes an additional 0.2 to 0.7 octane to the alkylate product. Figure 1 UOP HF Alkylation Process Typical Flow Diagram Cooling Water Olefin Feed Saturate Feed Recycle i-c 4 n-c 4 Product Alkylate Propane Product Page 5

8 One of the most significant advances in HF design is the Split Feed Series Recycle (SFSR) reactor sections, shown in Figure 2. The SFSR design allows the refiner to set the conditions at the inlet to each reactor such that the effective Isobutane: Olefin ratio(i:o) is higher than the overall I:O ratio. The refiner has the flexibility to change from minimizing operating costs, by minimizing I:O ratio, to maximizing octane depending upon the market conditions. Figure 2 Split-Feed, Series Recycle Reactor System Olefin Feed Recycle i-c 4 Rx 2 Cooling Water Rx 2 Cooling Water Hydrocarbon to Isostripper Acid Settler 1 Acid Settler 2 Circulation Pump With its low acid inventory, maximum octane and minimum I:O ratio, the UOP design is well suited for today s alkylate. In the last 6 years UOP has licensed 6 new HF units. Furthermore, the SFSR design is a very effective revamp for octane and capacity. Either a forced acid single feed or a gravity flow system can be effectively converted to the SFSR design. HF RELEASE MITIGATION Over recent years, the industry has addressed the issue of the potential environmental impact of an acid leak, and has developed effective mitigation strategies to address this very low probability occurrence. Two general mitigation strategies have been employed, the first related to the installation of remotely operated isolation valves, water curtain/cannon systems and rapid acid dump systems. The effectiveness of any active mitigation system is predicated on the quick detection of the leak. The effectiveness of a water cannon system may also depend upon accurately locating the leak. Page 6

9 A second strategy relates to the use of a vapor suppression additive which offers the refiner an additional mitigation strategy that does not rely on rapid detection and greatly increases the effectiveness of all the traditional methods of risk mitigation. UOP s Alkad process integrates the use of an effective vapor suppression additive to the economic operation of an HF alkylation unit. Figure 3 demonstrates how the additive in the Alkad process reduces the dispersion distance of any level of HF concentration beyond the mitigation area 6. In conjunction with other mitigation techniques and hardware, the additive reduces the amount of HF aerosol by 90%. In the context of a Quantitative Risk Assessment, the additive significantly reduces the Societal Risk Index. Figure 3 Reactive Mitigation Release Scenario Relative HF Concentration beyond Mitigation Area Water Spray Activated Automated Water Spray System with additive* Acid Transfer Time *60-70% reduction in acid volatility In the Alkad process, alkylation reactions take place in the presence of liquid polyhydrogen complexes. The additive reacts with the HF to from a polyhydrogen fluoride complex. The complex contains a long chain of strongly associated HF molecules. It is the strong association that reduces the tendency of the HF molecules to form an aerosol upon release to the atmosphere. The low physical vapor pressure of the polyhydrogen complex also contributes to reduced aerosol formation. It has been established that the Alkad process additive can effectively mitigate as much as 90% of the risk of an HF release. Proper choice of an additive is key to effective mitigation while maintaining the economic efficiency of the alkylation unit. Significant disadvantages would be realized if the additive chosen increased the amount of HF required to produce an equivalent barrel of alkylate, actually increased the likelihood of a release, required high utility consumption, or contaminated the product alkylate. The additive used in the Alkad process has been specifically designed to avoid these problems and work synergistically with the HF alkylation process. Page 7

10 ALKAD TECHNOLOGY The Alkad process easily integrates into any HF alkylation unit. Based on commercial operating data from the former Texaco refinery at El Dorado, Kansas, the Alkad process additive can increase octane by about 1 RON. Of great importance with the new sulfur regulations, the aditive does not contaminate the alkylate product with sulfur. In fact, the Alkad process tolerates high sulfur in the feed and efficiently removes sulfur oils without contaminating the product(s). UOP's additive does not degrade the product and does not harm waste water treating. Fluorides in LPG do increase but these are readily managed without additional capital. Furthermore, calcium fluoride and other byproducts from the plant can be recycled or landfilled. The UOP additive does not decrease unit capacity. Table 2 summarizes the positive impact the additive had on the product quality in a commercial unit. The Alkad additive does not increase corrosion. After 4 years of operation at El Dorado, the HF unit, the Alkad unit and corrosion test coupons were thoroughly examined for signs of increased corrosion. The testing included detailed examination of the iron fluoride scale and ultrasonic thickness measurements. The inspection confirmed that the additive does not accelerate corrosion. Subsequently, the El Dorado plant has not had any corrosion-related failures. Table 2 Alkylate Product Additive No Yes ASTM RON Calculated C + 5 RON C + 5 Composition, lv-% (Normalized) C C C C C Calculated C + 9 RON DMP/MH TMP/DMH Based on Commercial Operating Conditions Page 8

11 The additive separates cleanly from hydrocarbons and is easily recovered and recycled to the alkylation unit. An additive recovery process module keeps additive consumption to a low level and facilitates the separation of polymer from the additive-hf complex. The recovery module generally consists of one column, a separator, and associated equipment. The additive stripper removes the complex and polymer from the HF, water and light acid soluble oil. The HF acid regenerator column is still used for the removal of water and light polymer from the process. The simplified flow scheme is shown in Figure 4. Figure 4 Alkad Process Recovery Section HF to Isostripper (Internal Regeneration) Additive Stripper i-c 4 Recycled HF from Rx Section i-c 4 Polymer to Neutralization HF to Rx Section Acid Regeneration Column i-c 4 HF - Additive to Rx Section Light Acid Soluble Oils and CBM to Neutralization Page 9

12 Finally, implementing the Alkad process is not prohibitively expensive or complex. The additive recovery facilities are compact and can be modularized. The additive recovery facilities add about 15% to the cost of a grass-roots HF alkylation unit, but the total cost remains less than that of a sulfuric acid unit. Table 3 summarizes the cost impact of installing and operating the UOP Alkad technology. Table 3 Cost Impact of the Alkad Process $/BBL Alkylate HF Alkylation HF with Alkad Unit Feedstock Base Base Utilities Catalyst and Additive Chemicals Labor/Maintenance Delta Production Cost, (Increase) (0.20) Delta Octane Value, Increase 0.12 HF Alkylation Unit (8800 BSD) $42.5 MM $49 MM Alkad Unit Add-on, EEC $7.9 MM In 2002, the first new HF alkylation unit incorporating UOP s Alkad technology was licensed. This UOP HF Alkylation/Alkad unit located in Europe will go on-stream in late These units represent state of the art in both risk mitigation and process design. The units will process field butanes and mixed C 4 olefins from a UOP MSCC unit. The Alkad unit will operate at an aerosol reduction factor in the range of 70%, before active mitigation. The unit will also include other mitigation systems, such as isolation valves, a rapid dump system and water sprays, driving the aerosol reduction factor into the 90% range. Page 10

13 REVAMP CASE STUDY ALKYLATE CAPACITY AND QUALITY In addition to new unit activity and investments in risk mitatigion strategies, UOP has also seen a high level of activity in revamps of HF Alkylation units to increase capacity and/or unit performance, often utilizing the Split-Feed, Series Recycle (SFSR) design feature. When revamping using the SFSR design, not only is the throughput increased, but also the acid inventory is reduced. This occurs when a new reactor section of the SFSR type replaces an existing gravity flow reactor section. UOP recently designed such a revamp with the target of increasing both the quality and quantity of the alkylate. The UOP design was to increase the octane by 1.5 RONC and alkylate production by 40%. CONSTRAINTS/ISSUES The existing reactor section, a gravity flow system, set the acid inventory. The existing major equipment within the fractionation section set the rate, temperature and composition of the isobutane recycle. The off-sites limited availability of cooling water. The existing acid regeneration equipment set the reactor design pressure. SOLUTION/EXECUTION The existing gravity flow reactor system was replaced with a new SFSR reactor system. The SFSR design allowed the refiner to produce the additional alkylate with only minor modifications to the fractionation section and without increasing the acid inventory. The water cooled system was able to remove the additional heat of reaction with the available cooling water. The acid inventory from the original gravity flow system provided enough acid to fill the circuit and catalyze the reaction to increase alkylate production by 40%. RESULTS The project met all performance expectations. The project schedule, from design basis to start-up, was 16 months. During the construction of the SFSR section, the existing gravity flow system maintained production. Downtime was brief and the restart went smoothly. The capital cost of this revamp would be between $10 MM and $15 MM in current dollars. This amount is roughly 30% of the cost of a new unit for the additional capacity. Page 11

14 SUMMARY AND CONCLUSION As the demand for alkylate increase, refiners will look to add alkylate capacity by building new units or expanding existing plants. HF alkylation remains the most economically viable method for the production of alkylate. In terms of octane, acid inventory, operating costs and capital cost, the SFSR design is a very attractive option for adding alkylate production to either a gravity flow system or a single stage pumped system. With either system, the revamp can produce additional alkylate at about 30% of the cost of a new unit. UOP continues to improve the economics of HF alkylation. In 2002 a cross functional Six Sigma team was formed to identify, rank and evaluate new opportunities. Several ideas have been slated for development. In the near future, UOP will make several advances in alkylation technology available to the refining industry. The scope of the advances covers the entire alkylation process from pre-treatment to acid neutralization. UOP will continue to build upon its expertise in alkylation to push the envelope of alkylation technology, both hydrofluoric alkylation and solid catalyst alkylation. The refiner can look to UOP as a partner in meeting the demands of producing tomorrow s gasoline. Page 12

15 REFERENCES 1. The Alkad process is a joint development between ChevronTexaco, UOP and Dr. George Olaf. 2. California Energy Commission, Report on the Current Oxygenate Market, October Octane Week, June 17, Gasoline Volatility: Environmental Interactions with Blending, by George II. Unzelman NPRA Annual Meeting, Solid Catalyst Alkylation Technology for Clean Fuels: The Alkylene Process, by Cara Moy Roeseler et al. 6. The Quest release test conducted by UOP and Texaco. uoptm UOP LLC 25 East Algonquin Road Des Plaines, IL UOP LLC. All rights reserved. Page 13 UOP 4141D