Chlorinated hydrocarbon reaction

The kinetics of chlorinated hydrocarbon reactions exhibit several distinguishing features when compared to the reactions of analogous hydrocarbons. " First, as a consequence of the weaker C-Cl bond dissociation energies, CHCs decompose at temperatures that are significantly lower than the analogous hydrocarbons. This leads to the early production of Cl radicals, thereby establishing the requisite free radical chain reactions, which destroy the parent CHC and lead to gas phase polymerization, ultimately forming soot. 

In early designs, the reaction heat typically was removed by cooling water. Crude dichloroethane was withdrawn from the reactor as a liquid, acid-washed to remove ferric chloride, then neutralized with dilute caustic, and purified by distillation. The material used for separation of the ferric chloride can be recycled up to a point, but a purge must be done. This creates waste streams contaminated with chlorinated hydrocarbons which must be treated prior to disposal. 

The most abundant natural steroid is cholesterol. It can be obtained in large quantides from wool fat (15%) or from brain or spinal chord tissues of fat stock (2-4%) by extraction with chlorinated hydrocarbons. Its saturated side-chain can be removed by chromium trioxide oxidation, but the yield of such reactions could never be raised above 8% (see page 118f.). 

Chlorine reacts with saturated hydrocarbons either by substitution or by addition to form chlorinated hydrocarbons and HCl. Thus methanol or methane is chlorinated to produce CH Cl, which can be further chlorinated to form methylene chloride, chloroform, and carbon tetrachloride. Reaction of CI2 with unsaturated hydrocarbons results in the destmction of the double or triple bond. This is a very important reaction during the production of ethylene dichloride, which is an intermediate in the manufacture of vinyl chloride ... 

Hydrogen chloride is produced by the direct reaction of hydrogen and chlorine, by reaction of metal chlorides and acids, and as a by-product from many chemical manufacturing processes such as chlorinated hydrocarbons. 

Chlorinated C2> Perchloroethylene (PCE) and trichloroethylene (TCE) can be produced either separately or as a mixture in varying proportions by reaction of C2-chlorinated hydrocarbons, eg, C2-chlorinated waste streams or ethylene dichloride, with a mixture of oxygen and chlorine or HCl. 

Aluminum alkoxides are easily soluble in hydrocarbons and in chlorinated hydrocarbons, but sparingly soluble in alcohols. They are sensitive to moisture and dry storage is essential. Aluminum alkoxides are used extensively as intermediates, for example, in the Meerwein-Poimdorf reaction (94). 

Reaction vessels for supercritical water oxidation must be highly corrosion resistant because of the aggressive nature of supercritical water and oxidation reaction products at extreme temperatures and pressures. Supercritical oxidation of PCBs and some chlorinated hydrocarbons can be difficult... 

Acetjiene has found use as a feedstock for production of chlorinated solvents by reaction with hydrogen chloride or chlorine (6). However, because of safety concerns and the lower price of other feedstock hydrocarbons, very Htfle acetylene is used to produce chlorinated hydrocarbons in the United States (see Acetylene-derived chemicals). 

Many chlorinated hydrocarbons react readily with aluminum in the so-caHed bleeding reaction. A red aluminum chloride—chlorinated hydrocarbon complex is formed. Storage of uninhibited chlorinated solvents in aluminum vessels results in corrosion in a short period of time. Proprietary organic inhibitors permit commercial use of reactive solvents such as 1,1,1-trichloroethane and trichloroethylene for cleaning of aluminum. 

Methylene chloride is one of the more stable of the chlorinated hydrocarbon solvents. Its initial thermal degradation temperature is 120°C in dry air (1). This temperature decreases as the moisture content increases. The reaction produces mainly HCl with trace amounts of phosgene. Decomposition under these conditions can be inhibited by the addition of small quantities (0.0001—1.0%) of phenoHc compounds, eg, phenol, hydroquinone, -cresol, resorcinol, thymol, and 1-naphthol (2). Stabilization may also be effected by the addition of small amounts of amines (3) or a mixture of nitromethane and 1,4-dioxane. The latter diminishes attack on aluminum and inhibits kon-catalyzed reactions of methylene chloride (4). The addition of small amounts of epoxides can also inhibit aluminum reactions catalyzed by iron (5). On prolonged contact with water, methylene chloride hydrolyzes very slowly, forming HCl as the primary product. On prolonged heating with water in a sealed vessel at 140—170°C, methylene chloride yields formaldehyde and hydrochloric acid as shown by the following equation (6). 

Chlorination of Ethylene Dichloride. Tetrachloroethylene and trichloroethylene can be produced by the noncatalytic chlorination of ethylene dichloride [107-06-2] (EDC) or other two-carbon (C2) chlorinated hydrocarbons. This process is advantageous when there is a feedstock source of mixed C2 chlorinated hydrocarbons from other processes and an outlet for the by-product HCl stream. Product ratios of tri- and tetrachloroethylene are controlled by adjusting the CI2 type="subscript">2 EDC ratio to the reactor. Partially chlorinated by-products are recycled to the chlorinator. The primary reactions are... 

Oxychlorination of G2 Chlorinated Hydrocarbons. Tetrachloroethylene and trichloroethylene can be produced by reaction of EDC with chlorine or HCl and oxygen in the presence of a catalyst. When hydrochloric acid is used, additional oxygen is requked. Product distribution is varied by controlling reactant ratios. This process is advantageous in that no by-product HCl is produced, and it can be integrated with other processes as a net HCl consumer. The reactions may be represented as follows ... 

Reaction Conditions. Typical iadustrial practice of this reaction involves mixing vapor-phase propylene and vapor-phase chlorine in a static mixer, foEowed immediately by passing the admixed reactants into a reactor vessel that operates at 69—240 kPa (10—35 psig) and permits virtual complete chlorine conversion, which requires 1—4 s residence time. The overaE reactions are aE highly exothermic and as the reaction proceeds, usuaEy adiabaticaEy, the temperature rises. OptimaEy, the reaction temperature should not exceed 510°C since, above this temperature, pyrolysis of the chlorinated hydrocarbons results in decreased yield and excessive coke formation (27). 

Materials of Construction. GeneraHy, carbon steel is satisfactory as a material of construction when handling propylene, chlorine, HCl, and chlorinated hydrocarbons at low temperatures (below 100°C) in the absence of water. Nickel-based aHoys are chiefly used in the reaction area where resistance to chlorine and HCl at elevated temperatures is required (39). Elastomer-lined equipment, usuaHy PTFE or Kynar, is typicaHy used when water and HCl or chlorine are present together, such as adsorption of HCl in water, since corrosion of most metals is excessive. Stainless steels are to be avoided in locations exposed to inorganic chlorides, as stainless steels can be subject to chloride stress-corrosion cracking. Contact with aluminum should be avoided under aH circumstances because of potential undesirable reactivity problems. 

Catalytic Reaction. The desired reaction of the chlorine group on a chlorinated hydrocarbon is... 

Several other changes that are supposed to slow down the reaction can cause runaway. In the case of ethylene oxidation, chlorinated hydrocarbons are used as inhibitors. These slow down both the total and the epoxidation, although the latter somewhat less. When the reaction is running too high and the inhibitor feed is suddenly increased in an attempt to control it, a runaway may occur. The reason is similar to that for the feed temperature cut situation. Here the inhibitor that is in the ppm region reacts with the front of the catalytic bed and slowly moves down stream. The unconverted reactants reach the hotter zone before the increased inhibitor concentration does. 

Chlorinated rubber is usually prepared by bubbling chlorine into a solution of masticated rubber in a chlorinated hydrocarbon solvent such as carbon tetrachloride. Hydrochloric acid is removed during the reaction. The solvent may be removed by vacuum or steam distillation or by precipitation of the derivative by a non-solvent such as petroleum. 

While ethyl chloride is one of the least toxic of all chlorinated hydrocarbons, CE is a toxic pollutant. The off-gas from the reactor is scrubbed with water in two absoiption columns. The first column is intended to recover the majority of unreacted ethanol, hydrogen chloride, and CE. The second scrubber purifies the product fiom traces of unreacted materials and acts as a back-up column in case the first scrubber is out of operation. Each scrubber contains two sieve plates and has an overall column efficiency of 65% (i.e., NTP = 1.3). Following the scrubber, ethyl chloride is finished and sold. The aqueous streams leaving the scrubbers are mixed and recycled to the reactor. A fraction of the CE recycled to the reactor is reduced to ethyl chloride. This side reaction will be called the reduction reaction. The rate of CE depletion in the reactor due to this reaction can be approximated by the following pseudo first order expression ... 

Organic solvents have acute narcotic effects. Aromatic and chlorinated hydrocarbons seem to be especially effective. As stated, the combined effect of several organic solvents is usually considered to be additive. However, there is some evidence that the combined effect may in fact be synergistic. The symptoms caused by organic solvents, often called prenarcotic symptoms, resemble those caused by the use of alcohol. A decrease in reaction time and impairment in various psychological performances can be observed. Acute neurotoxicity can also be detected as abnormalities in the electroencephalogram (EEG i, which records the electrical activity of the brain. " ... 

Xylan sulphates, known also as pentosan polysulphates (PPS), are permanently studied with regard to their biological activities [3,419-422]. Usually, sulphuric acid, sulphur trioxide, or chlorsulphonic acid are employed as sul-phating agents alone or in combination with alcohols, amines or chlorinated hydrocarbons as reaction media [423]. 

Mere destruction of the original hazardous material is not, however, an adequate measure of the performance of an incinerator. Products of incomplete combustion can be as toxic as, or even more toxic than, the materials from which they evolve. Indeed, highly mutagenic PAHs are readily generated along with soot in fuel-rich regions of most hydrocarbon flames. Formation of dioxins in the combustion of chlorinated hydrocarbons has also been reported. We need to understand the entire sequence of reactions involved in incineration in order to assess the effectiveness and risks of hazardous waste incineration. 

The reaction of volatile chlorinated hydrocarbons with hydroxyl radicals is temperature dependent and thus varies with the seasons, although such variation in the atmospheric concentration of trichloroethylene may be minimal because of its brief residence time (EPA 1985c). The degradation products of this reaction include phosgene, dichloroacetyl chloride, and formyl chloride (Atkinson 1985 Gay et al. 1976 Kirchner et al. 1990). Reaction of trichloroethylene with ozone in the atmosphere is too slow to be an effective agent in trichloroethylene removal (Atkinson and Carter 1984). 

This concept meshes with another important environmental issue solvents for organic reactions. The use of chlorinated hydrocarbon solvents, traditionally the solvent of choice for a wide variety of organic reactions, has been severely curtailed. In fact, so many of the solvents favoured by organic chemists have been blacklisted that the whole question of solvents requires rethinking. The best solvent is no solvent and if a solvent (diluent) is needed then water is preferred. Water is non-toxic, non-inflammable, abundantly available, and inexpensive. Moreover, owing to its highly polar character, one can expect novel reactivities and selectivities for organometallic catalysis in water. 

R. Tauler, A.K. Smilde, J.M. Henshaw, L.W. Burgess and B.R. Kowalski, Multicomponent determination of chlorinated hydrocarbons using a reaction-based chemical sensor. 2 Chemical speciation using multivariate curve resolution. Anal. Chem., 66 (1994) 3337-3344. 

Methods based on color reactions have been published for several of the chlorinated hydrocarbon insecticides. Although most colorimetric methods are much more specific... 

More experimental work has been done with DDT than with all the other five chlorinated hydrocarbons combined, probably because DDT was the first of the group found to have insecticidal value. Carter (10) has summarized the several colorimetric methods for DDT. The one proposed by Stiff and Castillo (51), as modified by Claborn (14), and the one by Schechter and Haller (47) have probably been most widely used. In the Stiff and Castillo method, when the DDT is heated in pyridine solution containing xanthydrol and potassium hydroxide, a red color develops which is proportional to the quantity of DDT present. The reaction is sensitive to 10 micrograms. As TDE does not give a color with this reagent, Claborn (14) has proposed the reaction for the determination of DDT in the presence of TDE. He has also shown that for the development of the color the amount of water in the pyridine is critical. 

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