Propylene oxide chlorohydrin process

Figure 102. Typical arrangement for a propylene oxide chlorohydrin process...

Butylene Oxide. Butylene oxides are prepared on a small scale by Dow by chlorohydrin technology. There appears to be no technical reason why they could not be prepared by the propylene oxide Oxirane process (see Chlorohydrins). 

Propylene Chlorohydrin. Propylene chlorohydrin is synthesized with the aim of producing propylene oxide. Although the latter is manufactured commercially mainly by the direct oxidation of propylene, the chlorohydrination process is still in limited use. 

Aside from EB dehydrogenation, the only other commercial-scale production of styrene is through a propylene oxide/styrene process that produces roughly 15% of worldwide styrene. This technology was developed as an alternative to the chlorohydrin method for producing propylene oxide. 

A variant of the chlorohydrin method consists in causing chlorine and caustic soda to react simultaneously with r-butyl alcohol to form t-butyl hypochlorite, which can act on propylene to regenerate t-butyl alcohol and produce chlorohydrin. This is then hydrolysed in the presence of caustic soda to produce the final propylene oxide (Lummus process). 

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. 

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. 

Dehydrochlorination to Epoxides. The most useful chemical reaction of chlorohydrins is dehydrochlotination to form epoxides (oxkanes). This reaction was first described by Wurtz in 1859 (12) in which ethylene chlorohydria and propylene chlorohydria were treated with aqueous potassium hydroxide [1310-58-3] to form ethylene oxide and propylene oxide, respectively. For many years both of these epoxides were produced industrially by the dehydrochlotination reaction. In the past 40 years, the ethylene oxide process based on chlorohydria has been replaced by the dkect oxidation of ethylene over silver catalysts. However, such epoxides as propylene oxide (qv) and epichl orohydrin are stiU manufactured by processes that involve chlorohydria intermediates. 

For many years ethylene chlorohydrin was manufactured on a large iadustrial scale as a precursor to ethylene oxide, but this process has been almost completely displaced by the direct oxidation of ethylene to ethylene oxide over silver catalysts. However, siace other commercially important epoxides such as propylene oxide and epichlorohydrin cannot be made by direct oxidation of the parent olefin, chlorohydrin iatermediates are stiU important ia the manufacture of these products. 

The most important chemical reaction of chi orohydrin s is dehydrochloriaation to produce epoxides. In the case of propylene oxide. The Dow Chemical Company is the only manufacturer ia the United States that still uses the chlorohydrin technology. In 1990 the U.S. propylene oxide production capacity was hsted as 1.43 x 10 t/yr, shared almost equally by Dow and Arco Chemical Co., which uses a process based on hydroperoxide iatermediates (69,70). More recentiy, Dow Europe SA, aimounced a decision to expand its propylene oxide capacity by 160,000 metric tons per year at the Stade, Germany site. This represents about a 40% iacrease over the current capacity (71). 

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. 

CH2=CH2 + Cl2 + h2o = CH20H-CH2C1 + HC1 Chloroalcohols are important intermediates. Propylene chlorohydrin is made similarly and is used for making propylene oxide by hydrolysis with either calcium hydroxide or sodium hydroxide. If calcium hydroxide is used, the byproduct calcium chloride is useless and must be dumped. If sodium hydroxide is used, the byproduct sodium chloride can be recycled to the Castner-Kellner process. 

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... 

The process was commercially so superior to the chlorohydrin route, that by the 1970s, the new chemistry had completely replaced the old. Adding some momentum to this transition was the fact that the obsolete and abandoned chlorohydrin plants could be readily converted to propylene oxide plants. The silver bullet for that process has yet to be found. 

You have to talk about propylene oxide and propylene glycol after ethylene oxide and glycol. Its not that the chemical configurations are so similar (they are), or that the process chemistry is about the same (it is). The Fact is that much of the propylene oxide is now made in plants originally designed and constructed to produce EO, not PO. As you read in the last chapter, the chlorohydrin route to EO was abandoned by the 1970s in favor of direct oxidation. At the same time, the EO producers found that the old EO plants were suitable for the production of PO and certainly the cheapest hardware available to satisfy growing PO demands. 

Three equations describe the process. The first involves making the hypochlorous acid by reacting chlorine and water. In the second, the acid reacts with propylene to make chlorohydrin. The dehydirochlorination takes place in the third to give propylene oxide. 

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. 

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. 

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. 

Propylene oxide is produced from the chlorohydrination of propene similar to the process used to make ethylene oxide (see Ethene). A major use of propylene oxide involves hydrating propylene oxide to produces propylene glycol, propylene polyglycols, and other polyether polyols. These products are used to produce both rigid and flexible polyurethane foams, but they are also used to produce polyurethane elastomers, sealants, and adhesives. 

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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