Alphabutol process

The Alphabutol process [23] selectively dimerizes ethylene into 1-butene by means of a titanium based catalyst (Table VUI). Hexenes, the only by-products of the reaction, represent 5 to 8% of the converted ethylene. 

The reaction (50 °C 1 to 3 MPa) takes place without solvent in a one stage well stirred reactor. A gaseous phase insures a steady concentration of ethylene in the liquid phase. There is no catalyst recycling and the effluent of the reactor, after deactivation of the catalyst by an amine, is directly fractionated into ethylene (recycled to the reactor) and 1-butene. The bottom fraction contains the catalyst residues. 

The common usage of 1-butene is as comonomer in linear low density polyethylene. 

Of these three processes the first is the most sophisticated and affords high added value chemicals. The two other processes are simpler and particularly convenient for more common olefins. It can be expected that other processes will appear in the near future. 

Wilke The Organic Chemistry of Nickel v. 2, 1. Academic Press (1975). 

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IFP Process for 1-Butene from Ethylene. 1-Butene is widely used as a comonomer in the production of polyethylene, accounting for over 107,000 t in 1992 and 40% of the total comonomer used. About 60% of the 1-butene produced comes from steam cracking and fluid catalytic cracker effluents (10). This 1-butene is typically produced from by-product raffinate from methyl tert-huty ether production. The recovery of 1-butene from these streams is typically expensive and requires the use of large plants to be economical. Institut Francais du Petrole (IFP) has developed and patented the Alphabutol process which produces 1-butene by selectively dimerizing ethylene. 

Similar to IFP s Dimersol process, the Alphabutol process uses a Ziegler-Natta type soluble catalyst based on a titanium complex, with triethyl aluminum as a co-catalyst. This soluble catalyst system avoids the isomerization of 1-butene to 2-butene and thus eliminates the need for removing the isomers from the 1-butene. The process is composed of four sections reaction, co-catalyst injection, catalyst removal, and distillation. Reaction takes place at 50—55°C and 2.4—2.8 MPa (350—400 psig) for 5—6 h. The catalyst is continuously fed to the reactor ethylene conversion is about 80—85% per pass with a selectivity to 1-butene of 93%. The catalyst is removed by vaporizing Hquid withdrawn from the reactor in two steps classical exchanger and thin-film evaporator. The purity of the butene produced with this technology is 99.90%. IFP has Hcensed this technology in areas where there is no local supply of 1-butene from other sources, such as Saudi Arabia and the Far East. 

The Alphabutol process (Figure 7-8) operates at low temperatures (50-55°C) and relatively low pressures (22-27 atm). The reaction occurs in the liquid phase without a solvent. The process scheme includes four sections the reactor, the co-catalyst injection, catalyst removal, and distillation. The continuous co-catalyst injection of an organo-hasic compound deactivates the catalyst downstream of the reactor withdrawal valve to limit isomerization of 1-hutene to 2-hutene. Table 7-2 shows the feed and product quality from the dimerization process. 

The simplest possible alkene oligomerization reaction, the dimerization of ethylene to butenes, is a well-studied reaction, and an industrial process was also developed for the selective formation of 1-butene42 (IFP Alphabutol process). 

Practical Applications. IFP s Alphabutol process is used to dimerize ethylene selectively to 1-butene.43,85 The significance of this technology is the use of 1-butene as a comonomer in the polymerization of ethylene to produce linear low-density polyethylene (see Section 13.2.6). Under the reaction conditions applied in industry (50-60°C, 22-27 atm), the selectivity of 1-butene formation is higher than 90% at the conversion of 80-85%. Since no metal hydride is involved in this system, isomerization does not take place and only a small amount of higher-molecular-weight terminal alkenes is formed. 

Commercial plants The AlphaSelect process is strongly backed by extensive Axens industrial experience in homogeneous catalysis, in particular, the Alphabutol process for producing butene-1 for which there are 19 units producing 312,000 tpy. 

The Alphabutol process features are simple processing, high turndown, ease of operation, low operating pressure and temperature, liquid-phase operation and carbon steel equipment. The technology has advantages over other production or supply sources uniformly high-quality product, low impurities, reliable feedstock source, low capital costs, high turndown and ease of production. 

This reaction has been developed commercially by IFF (Alphabutol process). The flow diagram for this process is given in Figure 5. 

Normally, the efficiency of a dimerization process is determined by (i) the selectivity to butene-1, (ii) the yield of butene-1 per unit weight of the catalyst, and (iii) the required process equipment [3]. So far, the only commercial process is the EFP-SABIC Alphabutol process, which is an indication of its technical advantages and economic potential. There are other processes which have not as yet reached commercial stage. These processes are offered by Phillips, MIT and Dow. 

The IFP-SABIC Alphabutol process utilizes a proprietary homogeneous titanium based catalyst which demonstrates high dimerization activity coupled with excellent selectivity to butene-1 at moderate pressures and temperatures. This performance is influenced by the catalyst composition and reaction parameters. 

The catalytic ethylene dimerization to butene-1 is widely regarded as a degenerate ethylene polymerization reaction and therefore the formation of higher molecular weight byproducts (oligomer and/or polymer) is expected [1]. However, in IFP-SABIC process, the Judicious choice of the titanium based catalyst [11-13] (Ti(OR)4 compound activated by an alkyl aluminum AIR3) and the reaction conditions [14] (20-30 atm. pressure and 50-60 °C temperature) lead to the selective generation of butene-1 (93 %wt.) at a conversion of (80-85%). Small amounts of by-products such as hexenes, cis/trans butene-2 and butane are formed. Typical analysis of the butene-1 produced by IFP-SABIC Alphabutol process is presented in Table 2. 

Figure 1. IFP-SABIC Alphabutol Process Scheme Influence of Reaction Conditions...

We have reviewed the processes for dimerization of ethylene to butene-1. IFP-SABIC Alphabutol process as yet remains the only commercially proven process. A plant based on this technology has been in operation since 1987. This plant has achieved targeted capacity of 50,000 metric tons/year and has met design requirements. 

IFP Industrial Department, Alphabutol Process for Butene-1 Manufacturing, IFP Publications Paris, 1988. 

ROH-hn C2H4O R(0C2H4) 0H Dimerization yielding 1-butene (IFP-SABIC alphabutol process)... 

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