Dehydrochlorination of chlorinated paraffins

This offers an indirect means of dehydrogenating paraffins. In the first step the parafiin is chlorinated, and in the second the monochlorinated derivative form is dechlorinated. This yields linear olefins with an internal double bond. This process was developed by Chemische Werke Huls. 

Chlorination is carried out in the liquid phase at 120 with a conversion rate of 40 per cent to limit the formation of polychlorinated compounds. Chlorination takes place mainly at the middle of the chain. The mixture of mono-, di- and polychlorinated derivatives and unconverted paraffin is sent to the dehydrochlorination reactor, which operates between 300 and 350 C in the presence of siiico-alumina. The monochlorinated derivatives are converted with a conversion yield of more than 99 per cent to mono-olefins with an internal double bond. The dehydrochlorination of di- and polychlorinated paraffins yields diolefms and polyolefins. 

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Cataldo, F. Synthesis of polyynes by dehydrochlorination of chlorinated paraffins. Angew. Makromol. Chem. 1999, 264, 65. 

Chlorination and Chlorination—Dehydrochlorination of Paraffins. Linear internal olefins were produced by Shell at Geismar from 1968 to 1988, using the dehydrochlorination of chlorinated linear paraffins, a process that also yields hydrogen chloride as a by-product. To avoid the production of dichloroparaffins, which are converted to diolefins by dehydrochlorination, chlorination of paraffins is typically limited to 10% conversion. 

Apart from the UOP Pacol process, today s only other meaningful economic process is the Shell higher olefin process (SHOP) in which /z-olefins are produced by ethylene oligomerization. Until 1992 Hiils AG used its own technology to produce -60,000 t/year of /z-olefins by the chlorination of /z-paraffins (from Molex plant) and subsequent dehydrochlorination [13]. In the past, the wax cracking process (Shell, Chevron) played a certain role. In the Pacol and Hiils processes, olefins are obtained as diluted solutions in paraffin (Pacol to max. 20%, Hiils about 30%) without further processing these are then used for alkylation. In contrast, the SHOP process produces pure olefins. 

Both monomeric and polymeric plasticizers are suitable for plasticization. Practically all monomeric plasticizers for PVC can be used. Suitable polymeric plasticizers include polyadipates, chlorinated paraffins, carbamide resins, and epoxides. Vinyl chloride copolymers are compatible with most conventional pigments and extenders. Despite their high intrinsic stability, paints based on vinyl chloride copolymers have to be stabilized against dehydrochlorination in the presence of heat and/or UV radiation for some applications. Epoxy compounds are often sufficient for thermal stabilization. 

More recent processes use olefine mixtures which are obtained either by thermal dehydrogenation or by chlorination and dehydrochlorination of paraffins [10]. The subsequent alkylation can be carried out not only with AICI3, but also with HF [11, 12]. 

The third route to detergent olefins is from paraffins of the same chain length. In principle, it is necessary only to remove two hydrogen atoms from an adjacent pair of carbons along the chain to produce the desired olefin, but the difficulties of dehydrogenation are such that a two-step process of chlorination and dehydrochlorination has been developed. In either process the reaction easily proceeds past the desired stage to give polychlorinated paraffins and polyolefins, all undesirable byproducts. 

This process seems much simpler than the Ziegler process, and you may wonder why it has not crowded Ziegler out. The problem is the olefin feed. Where do you get a ready supply of olefins the right size to feed to the process The answer is you have to malce them, and therein lies the rub. Normal paraffins from petroleum waxes or other chemical processes provide the feedstock to a two-step process, chlorination and dehydrochlorination, which produces an olefin corresponding to the paraffin. 

Use of halogens for the dehydrogenation of paraffins has been proposed in different ways. For example, heavy paraffins were first chlorinated and then dehydrochlorinated to heavy olefins commercially in... 

Normal Paraffin-Based Olefins, Detergent range -paraffins are currently isolated from refinery streams by molecular sieve processes (see ADSORPTION, LIQUID separation) and converted to olefins by two methods. In the process developed by Universal Oil Products and practiced by Enichem and Mitsubishi Petrochemical, a -paraffin of the desired chain length is dehydrogenated using the Pacol process in a catalytic fixed-bed reactor in the presence of excess hydrogen at low pressure and moderately high temperature. The product after adsorptive separation is a linear, random, primarily internal olefin. Shell formedy produced olefins by chlorination—dehydrochlorination. Typically, C —C14 -paraffins are chlorinated in a fluidized bed at 300°C with low conversion (10—15%) to limit dichloroalkane and trichloroalkane formation. Unreacted paraffin is recycled after distillation and the predominant monochloroalkane is dehydrochlorinated at 300°C over a catalyst such as nickel acetate [373-02-4]. The product is a linear, random, primarily internal olefin. 

The chlorination of paraffins first produces a so-called chloro-oil , which contains around 30% alkyl chlorides and 70% paraffins. The chloro-oil is dehydro-chlorinated in a dehydrochlorination column, with a bottom temperature of around 300 °C. The resulting olefin/paraffin mixture is mixed with a larg molar excess of benzene and fed into the reactor, which is fitted with a powerful stirrer and cooling pipes. Here, the benzene is alkylated in the presence of hydrogen fluoride at a temperature below 50 °C. The reaction product is then separated into two layers in a separation vessel the upper layer, the crude alkylate, is split by distillation into benzene, an inter-cut, paraffin, alkylbenzene and a higher-boiling tail product. The hydrogen fluoride, which is present in the lower layer, is recirculated. 

Three basic processes have been practiced for linear alkylbenzene manufacture. The most prevalent route of alkylbenzene manufacture is by partial dehydrogenation of paraffins, followed by alkylation of benzene with a mixed olefin/paraffin feedstock, using liquid hydrogen fluoride catalyst. A second route is via partial chlorination of paraffins, followed by alkylation of the chloroparaffin/paraffin feedstock in the presence of an aluminium chloride catalyst. The third process uses partial chlorination, but includes a dehydrochlorination to olefin step prior to alkylation with aluminium chloride or hydrogen fluoride. 

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