 PetroStrategies, Inc. |
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HF Alkylation TopicsABC News Report on Dangers of HF Alkylation UnitsAccording to ABC News "Oil industry documents filed with the federal government reveal that an accidental release of a lethal chemical used in 50 aging refineries across the country could prove devastating, with 16 million Americans living within range of toxic plumes that could spread for miles. Los Angeles, Philadelphia, Minneapolis, New Orleans, and the stretch of Texas coastline known as "Refinery Row" are among the at-risk areas cited in the documents".
The Alkylation ProcessAlkylation is an important component of the modern day refinery. According to the Oil & Gas Journal there were 129 U.S. refineries with a capacity of 17,869,189 B/CD as of January 1, 2011. These refineries had 1,140,077 B/CD of alkylation capacity. The alkylation process involves the reaction of isobutane with either propylene or butylene to produce C3 or C4 alkylate. The reaction is performed in the presence of a strong acid catalyst, either sulfuric acid or hydrofluoric acid. In an oil refinery it is referred to as a sulfuric acid alkylation unit (SAAU) or a hydrofluoric alkylation unit, (HFAU). Refinery workers may simply refer to it as the alky or alky unit. The reaction is performed out at mild temperatures (0 and 30 �C). The reaction produces heat and cooling is required. SAAU plants require lower temperatures so the cooling medium needs to be chilled. The HFAU can be cooled with normal refinery cooling water. It is important to keep a high ratio of isobutane to alkene at the point of reaction to prevent side reactions which produces a lower octane product, so the plants have a high recycle of isobutane back to feed. The product is called alkylate and is composed of a mixture of high-octane, branched-chain paraffinic hydrocarbons (mostly isopentane and isooctane). C3 alkylate has an research octane of 90-92 and C4 alkylate an octane of 95-96. Alkylate's high octane, low vapor pressure, and low sulfur content makes it a premium gasoline blending stock. The octane number of the alkylate depends mainly upon the kind of alkenes used and upon operating conditions. For example, isooctane results from combining butylene with isobutane and has a research octane rating of 100. Since raw crude oil generally contains only 10 to 25 percent of hydrocarbon constituents in the gasoline range, refineries use the fluid catalytic cracking process to convert high molecular weight hydrocarbons into smaller molecules in the gasoline range. The catalytic cracked gasoline is added to the gasoline blending components. The catalytic cracking process also produces propylenes and butylenes. The alkylation process transforms these molecules, in combination with isobutane, into larger iso-paraffins with a high octane number. Thus alkylation also increases the yield of gasoline. Refineries examine whether it makes sense economically to install alkylation units. Alkylation units are complex, with substantial economy of scale. In addition to a suitable quantity of feedstock, the price spread between the value of alkylate product and alternate feedstock disposition value must be large enough to justify the installation. Alternative outlets for refinery alkylation feedstocks include sales as LPG, blending of C4 streams directly into gasoline and feedstocks for chemical plants. Local market conditions vary widely between plants. Variation in the RVP specification for gasoline between countries and between seasons dramatically impacts the amount of butane streams that can be blended directly into gasoline. The transportation of specific types of LPG streams can be expensive so local disparities in economic conditions are often not fully mitigated by cross market movements of alkylation feedstocks. The availability of a suitable catalyst is also an important factor in deciding whether to build an alkylation plant. If sulfuric acid is used, significant volumes are needed. Access to a suitable plant is required for the supply of fresh acid and the disposition of spent acid. If a sulfuric acid plant must be constructed specifically to support an alkylation unit, such construction will have a significant impact on both the initial requirements for capital and ongoing costs of operation. The second main catalyst option is hydrofluoric acid. Rates of consumption for HF acid in alkylation plants are much lower than for sulfuric acid. HF acid plants can process a wider range of feedstock mix with propylenes and butylenes. HF plants also produce alkylate with better octane rating than sulfuric plants. However, the hazardous nature of the material limits the use of HF acid limits its use.
U.S. Refineries with HF Alkylation UnitsUnited States Refining Capacity as of January 1, 2010
Three companies account for 52% of HF alkylation capacity: Valero (104,512 B/CD & 19.2%), Conoco Phillips (97,200 B/CD & 17.8%), and Marathon (82,300 B/CD & 15.1%). The refineries with HF alkylation units are in the Refinery Triangle Area (Port Arthur-Pasadena-Texas City) with 74,900 B/CD or 13.7% of capacity, Corpus Christi with 52,260 B/CD or 9.6% of capacity, and Belle Chase, LA with 38,000 B/CD or 7.0% of capacity. Other communities with large HF alkylation units are Garyville, LA; Joliet, IL; Catlettsburg, KY; Sweeny, OK; Philadelphia, PA; and Salt Lake City, UT.
The Dangers of Hydrogen FluorideHydrogen fluoride converts immediately to hydrofluoric acid upon contact with liquid water. Hydrofluoric acid is a highly corrosive liquid and contact poison. It should be handled with extreme care. HF penetrates tissue rapidly and poisoning can occur readily through exposure of skin or eyes, or when inhaled or swallowed. Symptoms of exposure to hydrofluoric acid may not be immediately evident. HF interferes with nerve function, meaning that burns may not initially be painful. Accidental exposures can go unnoticed, delaying treatment and increasing the extent and seriousness of the injury. Once absorbed into blood through the skin, it reacts with blood calcium and may cause cardiac arrest. Burns with areas larger than 25 square inches have the potential to cause serious systemic toxicity from interference with blood and tissue calcium levels. In the body, hydrofluoric acid reacts with the important calcium and manganese ions. Formation of insoluble calcium fluoride is proposed as the etiology for both precipitous fall in serum calcium and the severe pain associated with tissue toxicity. In some cases, exposures can lead to hypocalcemia. Thus, hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca2+ that sequesters the fluoride ions. HF chemical burns can be treated with a water wash and 2.5% calcium gluconate gel. or special rinsing solutions. However, because it is absorbed, medical treatment is necessary; rinsing off is not enough. Intra-arterial infusions of calcium chloride have also shown great effectiveness in treating burns. In some cases, amputation may be required.
Maintenance IssuesMaintenance problems at many refineries raise alarms about potential HF disasters. Common Ground II: Why Cooperation to Reduce Accidents at Louisiana Refineries is Needed Now � released in February 2011 by the Louisiana Bucket Brigade, refinery neighbors, United Steelworkers and the Environmental Working Group � examines 2,607 accident reports refineries submitted to the Louisiana Department of Environmental Quality from 2005-2009. During this five-year period, the reports show the state�s 17 refineries averaged 10 accidents per week. These accidents are especially dangerous for workers and those who live nearby. Maintenance issues account for a significant portion of refinery accidents and emissions as well. For six years, ExxonMobil�s Chalmette Refining ignored nine Occupational Health and Safety Administration recommendations on piping. In October, a contract worker died while trying to repair a leaking pipe. The refinery�s data shows 38 percent of accident emissions are sent to the flare. The EPA stated in 2000 that �frequent, routine flaring may cause excessive, uncontrolled sulfur dioxide releases,� burdening our public health system. Sulfur dioxide is the most released chemical during accidents at Louisiana refineries, totaling more than 8 million pounds from 2005-2009. (Source: Refinery Accident Reports Highlight Poor Maintenance, Inadequate Storm Preparation And Excessive Flaring, USW Local 13-2001.) In 2007, the Occupational Safety and Health Administration (OSHA) found many refinery violations. OSHA inspectors conducting an unprecedented national audit of U.S. refineries have found 146 violations, many described as potentially life-threatening, after reviewing just 17 refineries in a dozen states. OSHA inspectors have uncovered 11 proposed violations at Total Petrochemicals USA's refinery in Port Arthur; 45 at a refinery in Canton, Ohio; and 19 at a Kansas refinery, among others. In another report issued in May 2010 by the Center for Public Integrity Analysis, two refineries owned by BP accounted for 97 percent of all flagrant violations found in the refining industry by government safety inspectors over the past three years. Most of BP's citations were classified as "egregious willful" by the Occupational Safety and Health Administration and reflect alleged violations of a rule designed to prevent catastrophic events at refineries.
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