Ethylene catalytic process

Most refinery/petrochemical processes produce ethylene that contains trace amounts of acetylene, which is difficult to remove even with cryogenic distillation. Frequently it is necessary to lower the acetylene concentration from several hundreds ppm to < 10 ppm in order to avoid poisoning catalysts used in subsequent ethylene consuming processes, such as polymeri2ation to polyethylene. This can be accompHshed with catalytic hydrogenation according to the equation. 

The RR developed by the author at UCC was the only one that had a high recycle rate with a reasonably known internal flow (Berty, 1969). This original reactor was named later after the author as the Berty Reactor . Over five hundred of these have been in use around the world over the last 30 years. The use of Berty reactors for ethylene oxide process improvement alone has resulted in 300 million pounds per year increase in production, without addition of new facilities (Mason, 1966). Similar improvements are possible with many other catalytic processes. In recent years a new blower design, a labyrinth seal between the blower and catalyst basket, and a better drive resulted in an even better reactor that has the registered trade name of ROTOBERTY . ... 

The situation has now changed and currently an area of considerable research interest is in heterogenizing homogeneous catalysts. One such instance is to be found in the ethylene based manufacture of vinyl acetate (11). A homogeneous catalytic process based on palladium and copper salts was first devised, but corrosion problems were made much less serious in a heterogeneous system based on the same chemical principles. 

Most small olefins produced in the chemical industry are used to make polymers, with a global production of the order of 100 million tons per year. Polymers are macromolecules with molecular weights of typically lO" to 10 and consist of linear or branched chains, or networks built up from small monomers such as ethylene, propylene, vinyl chloride, styrene, etc. The vast majority of polymers are made in catalytic processes. Here we concentrate on ethylene polymerization over chromium catalysts as an example [M.P. McDaniel, Adv. Catal. 33 (1985) 47]. 

The course of decomposition of confirmed or presumed metallocyclo-butane intermediates is important, but most results reported deal with stoichiometric rather than catalytic processes. Retention of the 3-carbon skeleton via pathways d or f in Eq. (26) occurs much more frequently than does cleavage to metathesis-related products. For example, thermolysis of phenyl-substituted platinocyclobutanes yields propenylben-zenes and phenyl-cyclopropane, but no styrene or ethylene (77). Similarly, the decomposition of tantalum carbene adducts (8) with olefins... 

Alkar [Alkylation of aromatics] Also (incorrectly) spelled Alcar. A catalytic process for making ethylbenzene by reacting ethylene with benzene. The ethylene stream can be of ary concentration down to 3 percent. The catalyst is boron trifluoride on alumina. Introduced by UOP in 1958 but no longer licensed by them. Replaced by the Ethylbenzene process. 

Borstar A catalytic process for polymerizing ethylene. Use of two reactors, a loop reactor and a gas-phase reactor, allows better control of molecular weight distribution. The loop reactor operates under super-critical conditions to avoid bubble formation. Either Ziegler-Natta or metallocene catalysts can be used. The first commercial unit was installed in Porvoo, Finland, in 1995. 

Ethoxene A catalytic process for dehydrogenating ethane to ethylene. Developed by Union Carbide. Acetic acid is a minor by product. 

Lovacat [Low valency catalyst] A catalytic process for making ethylene propylene and EPDM rubbers. Developed by DSM Elastomers in 1996. 

MTO [Methanol to olefins] A catalytic process for converting methanol to olefins, mainly propylenes and butenes. Developed by Mobil Research Development Corporation and first demonstrated in 1985. Another version of this process was developed by UOP and Norsk Hydro and has been ran at a demonstration unit at Porsgrunn, Norway, since June 1995. It is based on fluidized bed technology using a SAPO molecular sieve catalyst. It converts 80 percent of the carbon in the feed to ethylene and propylene. 

Obviously, in a relatively small work such as this it is not possible to be comprehensive. Preparations of bulk, achiral materials (e.g. simple oxiranes such as ethylene oxide) involving key catalytic processes will not be featured. Only a handful of representative examples of preparations of optically inactive compounds will be given, since the emphasis in the main body of this book, i.e. the experimental section, is on the preparation of chiral compounds. The focus on the preparation of compounds in single enantiomer form reflects the much increased importance of these compounds in the fine chemical industry (e.g. for pharmaceuticals, agrichemicals, fragrances, flavours and the suppliers of intermediates for these products). 

Alpha olefins are made either by oligomerization, growing them on an aluminum root by adding ethylene until the desire size is reached, or by catalytic processes, one favoring the shorter alpha olefins. 

A major part of the work described in this section has been carried out with the aim of applying these silsesquioxane complexes of Ti, Zr and Hf in catalytic processes such as ethylene polymerization, olefin epoxidation and Oppenauer oxidation. These catalytic aspects have been highlighted in several recent review articles. 

Another example of a famous organic chemical reaction being replaced by a catalytic process is furnished by the manufacture of ethylene oxide. For many years it was made by chlorohydrin formation followed by dehydrochlorination to the epoxide. Although the chlorohydrin route is still used to convert propylene to propylene oxide, a more efficient air epoxidation of ethylene is used and the chlorohydrin process for ethylene oxide manufacture has not been used since 1972. 

This chapter has focused on inorganic and heterogeneous catalysts, because historically these are the major systems with which chemical engineers have been concerned. There are number of important homogeneous catalytic processes such as the Wacker process to make vinyl acetate from ethylene and acetic acid, and there are many acid and base homogeneous catalyst systems. 

The search for a new epoxidation method that would be appropriate for organic synthesis should also, preferably, opt for a catalytic process. Industry has shown the way. It resorts to catalysis for epoxidations of olefins into key intermediates, such as ethylene oxide and propylene oxide. The former is prepared from ethylene and dioxygen with silver oxide supported on alumina as the catalyst, at 270°C (15-16). The latter is prepared from propylene and an alkyl hydroperoxide, with homogeneous catalysis by molybdenum comp e ts( 17) or better (with respect both to conversion and to selectivity) with an heterogeneous Ti(IV) catalyst (18), Mixtures of ethylene and propylene can be epoxidized too (19) by ten-butylhydroperoxide (20) (hereafter referred to as TBHP). 

Many homogeneous catalytic processes, in particular of anionic nature, are known, in which the polymerization takes place by stepwise addition (polymerization of ethylene oxide (34) of ethylene at low pressure and temperature with ALfia (7, 35), of styrene by Szwarc catalysts (36), for which the growth of the macromolecule can last for a very long time). This led some researchers to talk of a life of macromolecules and of living molecules (37). 

The third most crucial stage in the balanced process is the oxychlorination step.188-190,272,273 In this reaction ethylene and HC1 are converted to 1,2-dichloroethane in an oxidative, catalytic process. The reaction proceeds at temperatures of 225-325°C and pressures 1-15 atm. Pure oxygen or air is used as oxidant.276-278 Numerous, somewhat different industrial processes were developed independently.272-274 However, the reaction is generally carried out in the vapor phase, in fixed-bed or fluidized-bed reactors. 

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