Industrial preparation of ethylene

Dehydrogenation (Section 5.1) Elimination in which H2 is lost from adjacent atoms. The term is most commonly encountered in the industrial preparation of ethylene from ethane, propene from propane, 1,3-butadiene from butane, and styrene from ethylbenzene. 

A third example is the industrial preparation of ethylene glycol (HOCH2CH2OH) by hydrolysis of ethylene oxide in dilute sulfuric acid. This reaction and its mechanism (Mechanism 16.3) illustrate the difference between the ring openings of ethylene oxide discussed in the preceding section and the acid-catalyzed ones described here. In acid, the species that is attacked by the nucleophile is not the epoxide itself, but rather its... 

Ethylene [74-85-1] is the monomer used to make LDPE [9002-88-4]. The predominant method of manufacture of ethylene is high temperature cracking of natural gas or crude oil. Some properties of ethylene are collected in Table 1. The principal method for the industrial preparation of ethylene is thermal cracking of hydrocarbons. Small amounts of comonomers, such as vinyl acetate [108-05-4], methyl acrylate [96-33-3], or ethyl aciylate [108-88-5], can be added to modify... 

ETHYLENE We discussed ethylene production in an earlier boxed essay (Section 5 1) where it was pointed out that the output of the U S petrochemi cal industry exceeds 5 x 10 ° Ib/year Approximately 90% of this material is used for the preparation of four compounds (polyethylene ethylene oxide vinyl chloride and styrene) with polymerization to poly ethylene accounting for half the total Both vinyl chloride and styrene are polymerized to give poly(vinyl chloride) and polystyrene respectively (see Table 6 5) Ethylene oxide is a starting material for the preparation of ethylene glycol for use as an an tifreeze in automobile radiators and in the produc tion of polyester fibers (see the boxed essay Condensation Polymers Polyamides and Polyesters in Chapter 20)... 

Alkenyl halides such as vinyl chloride (H2C=CHC1) do not form carbocations on treatment with aluminum chloride and so cannot be used m Friedel-Crafts reactions Thus the industrial preparation of styrene from benzene and ethylene does not involve vinyl chloride but proceeds by way of ethylbenzene... 

Not so for synthesis in the chemical industry where a compound must be prepared not only on a large scale but at low cost There is a pronounced bias toward reactants and reagents that are both abundant and inexpensive The oxidizing agent of choice for example in the chemical industry is O2 and extensive research has been devoted to develop mg catalysts for preparing various compounds by air oxidation of readily available starting materials To illustrate air and ethylene are the reactants for the industrial preparation of both acetaldehyde and ethylene oxide Which of the two products is ob tamed depends on the catalyst employed... 

Key intermediates in the industrial preparation of both nicotinamide and nicotinic acid are alkyl pyridines (Fig. 1). 2-Meth5l-5-ethylpyridine (6) is prepared in ahquid-phase process from acetaldehyde. Also, a synthesis starting from ethylene has been reported. Alternatively, 3-methylpyridine (7) can be used as starting material for the synthesis of nicotinamide and nicotinic acid and it is derived industrially from acetaldehyde, formaldehyde (qv), and ammonia. Pyridine is the principal product from this route and 3-methylpyridine is obtained as a by-product. Despite this and largely due to the large amount of pyridine produced by this technology, the majority of the 3-methylpyridine feedstock is prepared in this fashion. 

The conjugated diene 1,3-butadiene is used in the manufacture of synthetic rubber and is prepared on an industrial scale in vast quantities. Production in the United States is currently 4X10 Ib/yearc One industrial process is similar- to that used for the preparation of ethylene In the presence of a suitable catalyst, butane undergoes thermal dehydrogenation to yield 1,3-butadiene. 

A method of considerable industrial importance for the large-scale preparation of ethylene oxide is direct oxidation of ethylene at elevated temperatures over a suitably prepared metallic silver catalyst. Although the reaction may be written aa indicated in Eq. (09), in actual practice only about half the ethylene is converted into ethylene oxide, the remainder being oxidized further to carbon dioxide and water. In spite of this seeming disadvantage, catalytic oxidation appears at present to bo economically competitive with chlorohydrin formation aa a means for the commercial production of ethylene oxide.MM Unfortunately, other olefins, such as propylene and mo-butylene for example, apparently give only carbon dioxide and water under the usual oxidation conditions,1310 so that until now the patent hu balance ethylene oxide has been the only representative accessible by tins route. 

Vinyl chloride (H2C=CHC1), the starting material used in the industrial preparation of poly(vinyl chloride), is prepared by a two-step process that begins with the reaction of Cl2 with ethylene to yield 1,2-dichloroethane ... 

Epoxides are important intermediates in many industrial processes. For example, the reaction of the simplest epoxide, ethylene oxide, with water is employed to produce ethylene glycol, which is used in antifreeze and to prepare polymers such as Dacron. One method for the preparation of ethylene oxide employs an intramolecular nucleophilic substitution reaction of ethylene chlorohydrin ... 

Several addition reactions have been or are currently used on a large scale in industrial chemical plants. For example, an older method for the preparation of ethylene oxide employed the addition of chlorine to ethylene in water to form ethylene chlorohydrin or 2-chloroethanol. (In industry, ethene is almost always called ethylene.) Treatment of the chlorohydrin with calcium hydroxide results in the formation of ethylene oxide, which is an important intermediate in the manufacture of ethylene glycol and other products (see the Focus On box on page 375). However, this method is wasteful of... 

An efficient industrial process for the preparation of ethylene carbonate... 

Catalysts based on the Hf pyridyl amine complexes 126-128 have been used for the preparation of ethylene/ propylene co-polymers as well as of ethylene/propylene/l-octene terpolymers. These co-polymers are characterized by having at least 60 wt% propylene units, Mw around 300000, and Mw/Mn in the range 2.0-2.4. The NMR analysis of these co-polymers showed that the propylene sequences are remarkably isotactic mm > 90%) and showed the presence of regioirregularly inserted propylene units(<0.5% mol). The most interesting property of catalysts based on 126-128 is their high thermal stability.1119 Using modifications of isospecific bis(phenoxy-amine)-based catalysts, such as complex 164, the controlled synthesis of iPP- /orjf-poly/E-co-P) diblock co-poly-mers has been achieved. This is a remarkable result since iPP and PE are both polymeric materials of extreme industrial relevance.1206... 

Thus, the industrial preparation of styrene from benzene and ethylene does not involve vinyl chloride but proceeds by way of ethylbenzene. 

---