Refinery catalysts polymerization

Polypropylene is made by polymerizing high-purity propylene gas recovered from cracked gas streams in olefin plants and oil refineries. The polymerization reaction is a low-pressure process that utilizes Ziegler-Natta catalysts (aluminum alkyls and titanium halides). The catalyst may be slumed in a hydrocarbon mixture to facihtate heat transfer. The reaction is carried out in batch or continuous reactors operating at temperatures between 50 and 80 C and pressure in the range of 5 to 25 atm. 

Polygas Olefins. Refinery propylene and butenes are polymerized with a phosphoric acid catalyst at 200°C and 3040—6080 kPa (30—60 atm) to give a mixture of branched olefins up to used primarily in producing plasticizer alcohols (isooctyl, isononyl, and isodecyl alcohol). Since the olefins are branched (75% have two or more CH groups) the alcohols are also branched. Exxon, BASE, Ruhrchemie (now Hoechst), ICl, Nissan, Getty Oil, U.S. Steel Chemicals (now Aristech), and others have all used this olefin source. 

Washing light hydrocarbons with water is a common refinery practice. It finds application on the feed to catalytic polymerization plants. It is used to remove any entrained caustic from the mercaptan removal facilities as well as any other impurities such as amines which tend to poison the polymerization catalyst. Another use for water wash is in alkylation plants to remove salts from streams, where heating would tend to deposit them out and plug up heat exchanger surfaces. Water washing can be carried out in a mixer- settler, or in a tower if more intimate contacting is necessary. 

Alco An early process for thermally polymerizing refinery gases (mainly C3 and C4 hydrocarbons) to yield liquid hydrocarbon mixtures, suitable for blending with gasoline. The process was operated without a catalyst, at 480 to 540°C, and 50 atm. Developed by the Pure Oil Company, Chicago, and licensed to Alco Products, United States. 

Polymerization is a rather dirty process in terms of pounds of pollutants per barrel of charge, but because of the small polymerization capacity in most refineries, the total waste production from the process is small. Even though the process makes use of acid catalysts, the waste stream is alkaline because the acid catalyst in most subprocesses is recycled, and any remaining acid is removed by caustic washing. Most of the waste material comes from the pretreatment of feedstock, which removes sulfides, mercaptans, and ammonia from the feedstock in caustic and acid wastes. 

Solution polymerization of refinery C4 streams in the presence of AICI3 or BF3 catalyst yields liquid polymers called polybutenes. Because of the large difference in stability of tertiary and secondary carbocations involved, isobutylene cannot be effectively copolymerized with butenes. As a result, the majority of the product formed is polyisobutylene. 

Examples of catalytic reactions and processes relevant to hydrocarbon chemistry are numerous. The technologies of the oil refinery with extremely low (<0.1) E factors are excellent examples demonstrating the possibilities that can be achieved by the development of selective catalytic methods, particularly by the use of various solid acids (see detailed discussions in Chapter 2). Further examples of commercially highly successful processes are the oxidation catalyst TS-1 developed by Enichem researchers160 161 (see Sections 9.1.1, 9.2.1, and 9.4.1), the homogeneous aqueous-phase Rh-catalyzed hydroformylation (see Sections 7.1.3 and 7.4.1), and single-site metallocene polymerization catalysts, which allow the preparation of tailored polymers with new properties (see Sections 13.3.2).162-164... 

Polymer Gasoline. Refinery trends tend to favor alkylation over polymerization. Unlike the alkylation process, polymerization does not require isobutane. The catalyst is usually phosphoric acid impregnated on kieselghur pellets. Polymerization of butylenes is not an attractive alternative to alkylation unless isobutane is unavailable. The motor octane number of polymer gasoline is also low, and there is considerable shrinkage in product volume. The only commercial unit to be built in recent years is at Sasol in South Africa. The commercial process was developed by UOP in the 1940s (104). 

In charging gas to the polymerization unit, either a one- or two-stage compressor is required to take the gas up to the catalyst-chamber pressure. Units charging the total gas from a refinery usually in the first compression stage take the absorber or receiver gas from about 70 lb. pressure up to the stabilizer pressure, which is about 150 lb. The gas is then... 

Approximate reaction networks have become customary for modeling reactions in which the species are too numerous for a full accounting or chemical analysis. Lumped components or continuous distributions commonly take the place of single components in process models for refinery streams (Wei and Kuo 1969 Weekman 1969 Krambeck 1984 Astarita 1989 Chou and Ho 1989 Froment and Bischoff 1990). Polymerization processes are described in terms of moments of the distributions of molecular weight or other properties (Zeman and Amundson 1965 Ray 1972, 1983 Ray and Laurence 1977). Lumped components, or even hypothetical ones, are also prevalent in models of catalyst deactivation (Szepe and Levenspiel 1968 Butt 1984 Pacheco and Petersen 1984 Schipper et al. 1984 Froment and Bischoff 1990). 

As we saw previously, polypropylene was first made in June 1951, unintentionally as a solid polymer, by Phillips Petroleum, who were at that time seeking to convert excess refinery gases, ethylene and propylene, to high-octane fuel. Phillips developed their chromium olefin polymerization catalyst for linear polyethylene, but in fact, Phillips never entered the polypropylene manufacturing business. Paul Hogan and Robert Banks recorded the invention of the process by which they produced crystalline polypropylene about an hour after their discovery. As we shall see in more detail below, their January 1953 patent application was issued in March 1983 (32 years after their discovery) [11]. 

One can calculate that the annual consumption of crude oil would be more than 400 Mio per year higher, due solely to the lower efficiency of our refineries without the catalysts used today (for comparison, annual crude oil consumption was about 3 X lO tons per year in 2005). Materials would be very different as many plastics cannot be produced without catalysts that promote the polymerization process or that are needed for the production of monomers. Incidentally, we should not forget that nature is also full of biocatalysts that accelerate important processes like photosynthesis or the metabolism in our bodies and thus provide the fundamentals of life on earth. 

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