Propylene and Butylene

As we learned in Chapter 8, the official production of propylene is usually about half that of ethylene, only because a large part of the propylene is used by petroleum refineries internally to alkylate gasolines. This captive use is not reported. Of the propylene used for chemical manufacture, nearly 40% is polymerized to polypropylene, to be discussed in a later chapter. Of the remaining amount of propylene, seven chemicals from the top 50 are manufactured. These are listed in Table 10.1. Their industrial manufacturing methods are summarized in Fig. 10.1. Note that four of these chemicals, cumene, phenol, acetone, and bisphenol A, are also derived from a second basic organic chemical, benzene. 

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LPG recovered from natural gas is essentially free of unsaturated hydrocarbons, such as propylene and butylenes (qv). Varying quantities of these olefins may be found in refinery production, and the concentrations are a function of the refinery s process design and operation. Much of the propylene and butylene are removed in the refinery to provide raw materials for plastic and mbber production and to produce high octane gasoline components. 

The Cg—0 2 branched, odd and even, linear and internal olefins are used to produce improved flexible poly(vinyl chloride) plastics. Demand for these branched olefins, which are produced from propylene and butylene, is estimated to be increasing at a rate of 2% per year. However, the growth of the linear a-olefins is expected to slow down to a rate of 5% per year from 1992 to 1997 (3), as opposed to growth rates of 7—10% in the 1980s. 

The feedstock, usuaHy consisting of propylene and butylenes (various isomers of C Hg) from cracking processes, may even consist of selective olefins for dimer, trimer, or tetramer production ... 

Deep C t lytic Crocking. This process is a variation of fluid catalytic cracking. It uses heavy petroleum fractions, such as heavy vacuum gas oil, to produce propylene- and butylene-rich gaseous products and an aromatic-rich Hquid product. The Hquid product contains predorninantiy ben2ene, toluene, and xylene (see BTX processing). This process is being developed by SINOPEC in China (42,73). SINOPEC is currentiy converting one of its fluid catalytic units into a demonstration unit with a capacity of 60,000 t/yr of vacuum gas oil feedstock. 

Superffex C t lytic Crocking. A new process called Superflex is being commercialized to produce predorninantiy propylene and butylenes from low valued hydrocarbon streams from an olefins complex (74). In this process, raffinates (from the aromatics recovery unit and the B—B stream after the recovery of isobutylene) and pyrolysis gasoline (after the removal of the C —Cg aromatics fraction) are catalyticaHy cracked to produce propylene, isobutylene, and a cmde C —Cg aromatics fraction. AH other by-products are recycled to extinction. 

Table 10. Utilization of Ethylene, Propylene, and Butylene for Produetion of Chemieals, 10 t...

When earbon atoms are linked by a double bond the eompounds are ealled olefins. Sinee these moleeules eontain less than the maximum quantity of hydrogen they are termed unsaturated. Examples inelude ethylene, propylene, and butylene. Note that the latter ean exist in several forms ... 

Light Ends Recovery, Fractionation, and Conversion Propylenes and butylenes may be recovered for feed to a polymerization plant for production of high octane... 

Polyethylene can be chlorinated in solution in carbon tetrachloride or in suspension in the piescnce ot a catalyst. Below 55-60% chlorine, it is more stable and more compatible with many polymers, especially polyvinyl chloride, to which it gives increased impact strength. The low pressure process copolymerizes polyethylene with propylene and butylene to increase its resistance to stress cracking. Copolymerization with vinyl acetate at high pressure increases flexibility, resistance to stress cracking, and seal ability of value to the food industry. 

Figure 11.4-2 shows process flows for an HF alkylation unit. The three sections are 1) reaction, 2). settling and 3) fractionation. In the reaction section isobutane feed is mixed with the olefin feed (usually propylene and butylene) in approximately a 10 or 15 to 1 ratio. In the presence of the HF acid catalyst the olefins react to form alkylate for gasoline blending. The exothermic reaction requires water cooling. The hydrocarbon/HF mixture goes to the settling... 

Propylene and butylenes Feed to alkylation or polymerization units... 

The olefins used are propylenes and butylenes ethylene is also produced from cracking operations but is not used in refinery processing. 

The first three members of the olefin series are ethylene, propylene, and butylene (or butene). Structural isomers exist when n > 4, as a consequence of the positioning of the double bond in normal alkenes as a result of branching in branched alkenes. In addition, geometric isomers may be possible owing to restricted rotation of atoms about the C=C bond. For instance, C H (butene) has four possible isomers instead of the expected three ... 

It seems that silver is a unique epoxidation catalyst for ethylene. All other catalysts are relatively ineffective, and the reaction to ethylene is limited among lower olefins. Propylene and butylenes do not form epoxides through this route. ... 

Cj s and C s include propane, propylene, normal butane, isobutane, and butylene. Propylene and butylene are used to make ethers and alkylate, which are blended to produce high-octane gasoline. Most gas plants also include treating facilities to remove sulfur from these products. 

The overhead stream from the debutanizer or stabilizer is a mix of C, s and C4 s, usually referred to as LPG (liquefied petroleum gas). It is rich in olefins, propylene, and butylene. These light olefins play an important role in the manufacture of reformulated gasoline (RFG). Depending on the refinery s configuration, the cat cracker s LPG is used in the following areas ... 

Sugar maple was reacted with propylene and butylene oxide (Rowell etal., 1982). The modulus of elasticity (MOE) and modulus of rupture (MOR), fibre stress at proportional limit, and maximum crushing strength all exhibited a reduction, compared to unmodified samples. Nilsson and Rowell (1983) reacted ponderosa pine with butylene oxide and exposed the wood in an unsterile soil decay test. At low WPGs, severe surface decay due to soft rot and tunnelling bacteria was observed. Such attack was reduced at 15 % WPG,... 

The resistance of propylene and butylene epoxide modified wood to subterranean termites was studied (Rowell etal., 1979). A threshold of 34 % WPG was found to give good protection. Giant ipil ipil (Leucaena leucocephala) was modified with acetic anhydride, maleic anhydride - glycerol or propylene oxide (Mallari etal., 1988, 1990). All modified samples showed good decay resistance to C. versicolor and Tyromyces palustris. 

Alkylation (Figure 4.11) combines low-molecular-weight olefins (primarily a mixture of propylene and butylene) with isobutene in the presence of a catalyst, either sulfuric acid or hydrofluoric acid. The product, called alkylate, consists of... 

Polymerization The process of producing higher-molecular-weight compounds by reacting two or more unsaturated molecules together. In the refinery, propylene and butylene are the primary polymerization feedstocks. 

Propylene and butylene require much milder conditions for their sulfation with sulfuric acid. Butylene is sulfated at 30—50°C and 300—600 kPa (ca 3—6 atm) with 30—60 wt % sulfuric acid, and propylene is sulfated at 10—30°C and 500 kPa (ca 5 atm) with 65—85 wt % sulfuric acid. The rate of sulfation of propylene increases sharply with increasing pressure (80). It can also be increased by the addition of kerosene, which raises the concentration of olefin in the liquid phase (81). 

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