March, 2010

2. Alkylation ALkylation process was developed in late 1930s and during World War II due to the increasing demand in high-octane blending stock for aviation gasoline. The first commercial unit was built in 1938 followed by rapid commercialization during the World War. Many of these plants were shut down after the end of the war. In late 1950s, refineries shifted to production of motor fuel by alkylation using different olefins as the feed. Nowadays, Alkylation is an integrated process in petroleum refineries.

3. Alkylation In general, Alkylation is the combination of olefins with paraffins to form larger molecules (transfer of an alkyl group from one molecule to another). In oil refining, alkylation refers to a particular alkylation of isobutane with olefins. It is a major aspect of the Petroleum upgrading. Olefins are reactive due to the presence of a double bond between two carbon atoms in a molecule.

4. Alkylation In refinery practice, Alkylation of iso-butane with iso/normal butane is of main concern due to the production of iso-octane which is the main constituent of gasoline. Alkylation is possible with out catalyst , but commercial processes use different catalyst to operate at lower temperature and minimize side reactions and polymerization. Butylene produces higher octane number fuel and propylene the lowest, however in all cases the octane number is larger than 87.

5. Alkylation processes Ethylene, propylene, butylene, and amylene are the most common olefins used in alkylation processes. Olefin feedstock is derived from hydrotreating processes. In thermal alkylation processes (in the absence of aluminum chloride as catalyst) olefins and iso-butane undergo reactions at temperatures between 50 � 280 C and pressures between 300 � 1000 psi. New catalytic processes operate at lower temperatures (30-100 F) and pressures (1-150 psi) depending on the type of catalyst used.

6. Sulfuric acid process In this process, concentrated sulfuric acid is used as the catalyst to produce high octane gasoline or motor fuel blend stock. The reactants and catalyst are completely mixed in the reactor which operates at 2-7 C and 5-15 psig. Vapors may form which are collected and processed. Sulfuric acid and the products form two layers which are separated for further processing Sulfuric acid is partially recycled back to the reactor while the products are sent to a caustic scrubber to neutralize the remaining acid.

7. Sulfuric acid process The neutralized product stream is sent to a deiso-butanizer where the alkylates are collected as the bottom product and the unreacted iso-butane is recycled back to the reactor. Since the operation is at relatively low temperatures a refrigerant is used to control the temperature in the reactor. In a special reactor (cascade type), Iso-butane and sulfuric acid are sent through the reactor and olefin is added at each level. Spent acid and the products are separated in the last two stages.

8. Sulfuric acid process Sulfuric acid is used for propylene and higher olefins, but not for ethylene as it forms ethyl hydrogen sulfate. Acid concentration should be minimum 85% wt. or higher. The rate of deactivation varies with the olefin and isobutane charge. Since concentrated sulfuric acid is hygroscopic the moisture content of the feed should be negligible. Heat generated due to dilution of sulfuric acid may increase the operation temperature and results in the formation of side products.

9. Sulfuric acid process

10. Hydrogen fluoride process In this process HF is used as a catalyst to unite olefins with iso-butane. The operation is carried out at 20-40 C and 1-150 psig. The ratio of iso-butane to olefins is kept high (15:1). The catalyst and feed are thoroughly mixed in the reactor. The acid is separated from products and unreacted feed in a settler tank. The top layer in the settler is sent to deisobutanizer and depropanizer for separation of products as shown in the block diagram.

11. Hydrogen fluoride process Hydrogen fluoride is used for alkylation of higher boiling olefins. Hydrogen fluoride consumption is lower than sulfuric acid as it is more readily separated and recovered from the products. The minimum concentration of HF is 85% wt (up to 92%). Hydrogen fluoride is very corrosive and health hazard. The product layer separated in the settler is also send to a caustic scrubber to neutralize the remaining acid.

12. Hydrogen fluoride process

13. Polymerization Polymerization is a process in which relatively small molecules, called monomers, combine chemically to produce a very large chainlike or network molecule. The monomer molecules may be all alike, or they may represent two, three, or more different compounds. Usually at least 100 monomer molecules must be combined to make a product that has certain unique physical properties�such as elasticity, high tensile strength, or the ability to form fibres.

14. Polymerization In the petroleum industry, polymerization is a process by which olefin gases are combined to form liquids that can be used in fuels or other products. The feedstock usually consists of propylenes and butylenes obtained from cracking processes (mainly hydrocracking and FCC). Polymerization may be accomplished thermally or in the presence of a catalyst. Thermal polymerization (500-600 C, and 1200 � 2000 psi) is preferred if saturated molecules are involved in the process.

15. Polymerization Olefins are conveniently polymerized by means of an acid catalyst. Sulfuric acid, Phosphoric acid, and copper pyrophosphats are common catalysts in olefin polymerization. Catalytic polymerization is carried out at 105-220 C and 150-1200 psi depending on the feedstock and product requirements. The reaction is exothermic and heat exchangers are used to control the temperature. The unreacted feed is separated from the products in a fractionation system and is recycled back to the reactor.

16. Polymerization The feed needs pretreatment if sulfur and nitrogen are present. (separation of sulfur and nitrogen compounds) In thermal polymerization, olefins are produced by thermal decomposition followed by polymerization. In catalytic polymerization, pelleted kieselguhr (diatomaceous earth) impregnated with acid solution is used as a catalyst in tubular reactor. The temperature is controlled by circulating water or oil around the tubes. Fractionation is used to separate feed from products.

17. Bulk Acid Polymerization In this process olefins are contacted by liquid phosphoric acid in a small reactor. The phosphoric acid and products are separated in a settler. The products are washed with caustic solution to neutralize the remaining acid. Acid is recycled back to the reactor. In order to keep the activity of the catalyst, fresh acid is mixed with the feed and a part of the spent acid is withdrawn form the system. This process is very effective with light olefins feedstock.