Chlorohydrin process

Direct oxidation of propylene with air or pure oxygen (equivalent to ethylene oxide manufacturing) is not efficient, since the silver catalysts used in the direct ethylene oxidation are not suitable for the reaction of alkenes with allylic hydrogen atoms (like propylene). Direct oxidation of propylene results mainly in acrolein formation and total oxidation. Some 3% of the world capacity of PO is produced by very recently developed processes, for example, hydroperoxidation of cumene and propylene and catalytic epoxidation of propylene using H2O2. 

The chlorohydrin process for the manufacture of propylene oxide is similar to the process used for many years for the production of ethylene oxide. The chlorohydrin process is divided into two reaction steps the chlorohydrination and the dehydrochlorination  

In the chlorohydrination step, the reactants propylene and hypochlorous acid (chlorine and water) are converted into two propylene chlorohydrin isomers (90% l-chloro-2-propanol and 10% 2-chloro-l-propanol). Yields of up to 94% can be achieved in modern commercial plants. The main by-products formed in this reaction step are dichloropropane (3-10%), dichloropropanol (0.3-1.2%), and dichlorodiisopropyl ether (0.2-1.7%). In the second step (dehydrochlorination, also called epoxidation or saponification ) the aqueous propylene chlorohydrin solution is treated with slaked lime or caustic soda. Propylene oxide and calcium or sodium chloride are formed. In a commercial process 1.4-1.5 units of chlorine are consumed to produce one unit of propylene oxide. Typical by-products are monopropylene glycol, epichlorohydrin, glycerol monochlorohydrin, glycerol, propanal, and acetone. In dehydrochlorination, propylene oxide yields of up to 96% can be obtained. 

In the chlorohydrin reactor, gaseous propylene and chlorine (equimolar amount) are mixed with an excess of water. Propylene chlorohydrin is formed at 35-50 °C and 2-3 bar. The water plays an important role in this reaction step. The reaction products remain in aqueous solution and water, acting as diluent, minimizes the formation of by-products. Water is also a reactant [Eq. (6.12.8)] and direct cooling medium. In the separator the vent gas (mixture of propane, propylene, CI2, O2, N2, H2, and CO2) is removed from the propylene chlorohydrin solution and sent to the 

Only industrial producers (e.g. Dow) with a highly integrated and cost competitive supply chain of chlorine-caustic soda (through production from caustic soda by NaCl electrolysis) to provide chlorine for the chlorohydrin reactor and sodium hydroxide for the dehydrochlorination step can operate chlorohydrin units for propylene oxide production competitively with indirect oxidation units. 

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Propylene oxide [75-56-9] is manufactured by either the chlorohydrin process or the peroxidation (coproduct) process. In the chlorohydrin process, chlorine, propylene, and water are combined to make propylene chlorohydrin, which then reacts with inorganic base to yield the oxide. The peroxidation process converts either isobutane or ethylbenzene direcdy to an alkyl hydroperoxide which then reacts with propylene to make propylene oxide, and /-butyl alcohol or methylbenzyl alcohol, respectively. Table 1 Hsts producers of propylene glycols in the United States. 

Synthesis. The total aimual production of PO in the United States in 1993 was 1.77 biUion kg (57) and is expected to climb to 1.95 biUion kg with the addition of the Texaco plant (Table 1). There are two principal processes for producing PO, the chlorohydrin process favored by The Dow Chemical Company and indirect oxidation used by Arco and soon Texaco. Molybdenum catalysts are used commercially in indirect oxidation (58—61). Capacity data for PO production are shown in Table 1 (see Propylene oxide). 

Propylene oxide [75-56-9] (methyloxirane, 1,2-epoxypropane) is a significant organic chemical used primarily as a reaction intermediate for production of polyether polyols, propylene glycol, alkanolamines (qv), glycol ethers, and many other useful products (see Glycols). Propylene oxide was first prepared in 1861 by Oser and first polymerized by Levene and Walti in 1927 (1). Propylene oxide is manufactured by two basic processes the traditional chlorohydrin process (see Chlorohydrins) and the hydroperoxide process, where either / fZ-butanol (see Butyl alcohols) or styrene (qv) is a co-product. Research continues in an effort to develop a direct oxidation process to be used commercially. 

Propyleae oxide is produced by oae of two commercial processes the chlorohydrin process or the hydroperoxide process. The 1995 global propyleae oxide capacity was estimated at about 4.36 x 10 t/yr. About half came from each of the two processes. Table 3 summari2es the global productioa capacities for each of the processes. 

The chlorohydrin process involves reaction of propylene and chlorine in the presence of water to produce the two isomers of propylene chlorohydrin. This is followed by dehydrochlorination using caustic or lime to propylene oxide and salt. The Dow Chemical Company is the only practitioner of the chlorohydrin process in North America. However, several companies practice the chlorohydrin process at more than 20 locations in Germany, Italy, Bra2il, Japan, Eastern Europe, and Asia. 

Process flow sheets and process descriptions given herein are estimates of the various commercial processes. There are also several potential commercial processes, including variations on the chlorohydrin process, variations on the hydroperoxide process, and direct oxidation of propylene. 

Fig. 2. The chlorohydrin process via tert-huty hypochlorite (114—rll6,rl27—rl33).

Ethylene oxide (qv) was once produced by the chlorohydrin process, but this process was slowly abandoned starting in 1937 when Union Carbide Corp. developed and commercialized the silver-catalyzed air oxidation of ethylene process patented in 1931 (67). Union Carbide Corp. is stiU. the world s largest ethylene oxide producer, but most other manufacturers Hcense either the Shell or Scientific Design process. Shell has the dominant patent position in ethylene oxide catalysts, which is the result of the development of highly effective methods of silver deposition on alumina (29), and the discovery of the importance of estabUshing precise parts per million levels of the higher alkaU metal elements on the catalyst surface (68). The most recent patents describe the addition of trace amounts of rhenium and various Group (VI) elements (69). 

The chlorohydrin process (24) has been used for the preparation of acetyl-P-alkylcholine chloride (25). The preparation of salts may be carried out mote economically by the neutralization of choline produced by the chlorohydrin synthesis. A modification produces choline carbonate as an intermediate that is converted to the desired salt (26). The most practical production procedure is that in which 300 parts of a 20% solution of trimethyl amine is neutralized with 100 parts of concentrated hydrochloric acid, and the solution is treated for 3 h with 50 parts of ethylene oxide under pressure at 60°C (27). 

Ethylene oxide [75-21-8] was first prepared in 1859 by Wurt2 from 2-chloroethanol (ethylene chlorohydrin) and aqueous potassium hydroxide (1). He later attempted to produce ethylene oxide by direct oxidation but did not succeed (2). Many other researchers were also unsuccesshil (3—6). In 1931, Lefort achieved direct oxidation of ethylene to ethylene oxide using a silver catalyst (7,8). Although early manufacture of ethylene oxide was accompHshed by the chlorohydrin process, the direct oxidation process has been used almost exclusively since 1940. Today about 9.6 x 10 t of ethylene oxide are produced each year worldwide. The primary use for ethylene oxide is in the manufacture of derivatives such as ethylene glycol, surfactants, and ethanolamines. 

Ethylene oxide has been produced commercially by two basic routes the ethylene chlorohydrin and direct oxidation processes. The chlorohydrin process was first iatroduced dufing World War I ia Germany by Badische Anilin-und Soda-Eabfik (BASE) and others (95). The process iavolves the reaction of ethylene with hypochlorous acid followed by dehydrochlofination of the resulting chlorohydrin with lime to produce ethylene oxide and calcium chloride. Union Carbide Corp. was the first to commercialize this process ia the United States ia 1925. The chlorohydrin process is not economically competitive, and was quickly replaced by the direct oxidation process as the dominant technology. At the present time, all the ethylene oxide production ia the world is achieved by the direct oxidation process. 

Chlorohydrin Process. Ethylene oxide is produced from ethylene chlorohydrin by dehydrochlorination using either sodium or calcium hydroxide (160). The by-products include calcium chloride, dichloroethane, bis(2-chloroethyl) ether, and acetaldehyde. Although the chlorohydrin process appears simpler, its capital costs are higher, largely due to material of constmction considerations (197). 

The Teijin oxychlorination, on the other hand, is considered a modern version of the obsolete chlorohydrin process for the production of ethylene oxide. In this process, ethylene chlorohydrin is obtained by the catalytic reaction of ethylene with hydrochloric acid in presence of thallium(III) chloride catalyst ... 

Propylene oxide is purified by steam stripping and then distillation. Byproduct propylene dichloride may be purified for use as a solvent or as a feed to the perchloroethylene process. The main disadvantage of the chlorohydrination process is the waste disposal of CaCl2. Figure 8-3 is a flow diagram of a typical chlorohydrin process. 

Figure 8-3. A flow diagram of a typical chlorohydrin process for producing propylene oxide.

Propylene oxide (PO) is an important intermediate in the manufacture of a wide range of valuable products propylene glycol, ethers, isopropanolamines, and various propoxylated products for polyurethanes (1). The current processes for the large scale synthesis of PO include (i) the chlorohydrin process and (ii) the peroxide process (1, 2). 

The disadvantage of the chlorohydrin process is the use of toxic, corrosive, and expensive chlorine the major drawback of the peroxide process is the formation of co-oxidates in larger amounts than the desired PO. The direct epoxidation of propylene using 02 (i.e., partial oxidation of propylene) from air has been recognized as a promising route. 

Lefort A process for making ethylene oxide by oxidizing ethylene in the presence of a silver catalyst. Invented and developed in the 1930s by T. E. Lefort at the Societe Frangaisc de Catalyse. For maty years, refinements of this basic process were operated in competition with the ethylene chlorohydrin process, but by 1980 it was the sole process in use. 

Chlorohydantoin moiety, 73 113 Chlorohydrin, 72 649—650 Chlorohydrination, in the chlorohydrin process, 20 799-800 Chlorohydrin processes, 70 655 24 172 for propylene oxide manufacture, 20 796, 798-801... 

Ethylene carbonate, 10 640, 665 in lithium cells, 3 459 molecular formula, 6 305t physical properties, 6 306t transesterification of, 13 651-652 Ethylene-carbon monoxide (ethylene-CO) copolymers, 5 9 10 197 Ethylene chlorohydrin process, 10 640 Ethylene-chlorotrifluoroethylene (E-CTFE) alternating copolymer (ECTFE), 15 248... 

One ocher reaction noc shown is the formation of propylene dichloride. The demand for this compound is generally insufficient to absorb all the coproduction, so it also ends up on the list of things to be disposed of coming from the PO-chlorohydrin process, But despite this and all the ocher problems already mentioned about the chlorohydrin route, the process remains economically healthy—breathing heavily, but healthy. Indeed, 40 to 50% of the PO produced in the United States comes from this route. 

Early routes to AA were complex and expensive. In 1927 the ethylene chlorohydrin process was introduced, but it was also still expensive, and not much commercial interest was stimulated in AA. In 1940 a process came literally right off the farm—pyrolysis of lactic acid, a waste product of the dairy industry found in sour milk. 

The epoxidation of propylene to propylene oxide is a high-volume process, using about 10% of the propylene produced in the world via one of two processes [127]. The oldest technology is called the chlorohydrin process and uses propylene, chlorine and water as its feedstocks. Due to the environmental costs of chlorine and the development of the more-efficient direct epoxidation over Ti02/Si02 catalysts, new plants all use the hydroperoxide route. The disadvantage here is the co-production of stoichiometric amounts of styrene or butyl alcohol, which means that the process economics are dependent on finding markets not only for the product of interest, but also for the co-product The hydroperoxide route has been practiced commercially since 1979 to co-produce propylene oxide and styrene [128], so when TS-1 was developed, epoxidation was looked at extensively [129]. 

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. 

A new variation of the chlorohydrin process uses t-butyl hypochlorite as chlorinating agent. The waste brine solution can be converted back to chlorine and caustic by a special electrolytic cell to avoid the waste of chlorine. 

As an aside to the manufacture of propylene oxide via the chlorohydrin process let us mention use of this type of chemistry to make epichlorohydrin. 

Ethylene oxide was formerly made in a two-stage process by first adding HOCl to ethylene and then removing HCl. However, in the 1960s Scientific Design, Union Carbide, and Shell Oil developed a one-step direct oxidation process that has largely replaced the old chlorohydrin process. 

The direct oxidation of ethylene to EO by O2 has now replaced the chlorohydrin process entirely because it is cheaper and involves less byproducts, but propylene oxide (a monomer in polyurethanes) is still made by the chlorohydrin route. 

Ethylene and Propylene Oxides. Ethylene oxide (26) and its derivatives are among the important aliphatic chemicals the 1950 production amounted to between 400,000,000 and 500,000,000 pounds. The chlorohydrin process was introduced in the early 1920 s and the direct oxidation process in the 1930 s, both based on ethylene. In the older process, the one most used today, the ethylene reacts in solution with hypo-chlorous acid at room temperature. 

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