Abstract:
Processes for the production of tetrachloromethane are provided. The present processes involve catalyzing the chlorination of a feedstream comprising partially chlorinated methanes with a free radical initiator. Cost savings are thus provided relative to conventional processes that require the use of high temperatures and/or pressures, and safety concerns are alleviated or eliminated.

Description:
FIELD 
       [0001]    The present invention relates to processes for the production of tetrachloromethane. 
       BACKGROUND 
       [0002]    Hydrofluorocarbon (HFC) products are widely utilized in many applications, including refrigeration, air conditioning, foam expansion, and as propellants for aerosol products including medical aerosol devices. Although HFC&#39;s have proven to be more climate friendly than the chlorofluorocarbon and hydrochlorofluorocarbon products that they replaced, it has now been discovered that they exhibit an appreciable global warming potential (GWP). 
         [0003]    The search for more acceptable alternatives to current fluorocarbon products has led to the emergence of hydrofluoroolefin (HFO) products. Relative to their predecessors, HFOs are expected to exert less impact on the atmosphere in the form their much lower GWP. Advantageously, HFO&#39;s also exhibit low flammability and low toxicity. 
         [0004]    As the environmental, and thus, economic importance of HFO&#39;s has developed, so has the demand for precursors utilized in their production. Many desirable HFO compounds, e.g., such as 2,3,3,3-tetrafluoroprop-1-ene, may typically be produced utilizing feedstocks of chlorocarbons, and in particular, chlorinated propanes and/or propenes, which may also find use as feedstocks for the manufacture of polyurethane blowing agents, biocides and polymers. 
         [0005]    Unfortunately, many chlorinated propenes may have limited commercial availability, and/or may only be available at prohibitively high cost. This may be due at least in part to the fact that conventional processes for their manufacture may require the use of raw materials and/or starting materials that are prohibitively expensive, or otherwise too limited in the throughputs that can be achieved, to be economically produced by manufacturers on the large scale required to be useful as feedstocks. 
         [0006]    For example, some conventional processes may require highly chlorinated propanes or propenes as starting materials that are, in turn, prepared from raw materials that are not generally readily available. Such raw materials may be produced in limited quantities as by-products of other processes, or, may be produced by processes that may be less than optimal in terms of selectivity and/or yield, process operating and/or capital cost, safety, and/or environmental acceptability. 
         [0007]    It would thus be desirable to provide improved processes for the production of raw materials useful in the synthesis of chlorocarbon precursors that in turn, are useful as feedstocks in the synthesis of refrigerants and other commercial products. More particularly, such processes would provide an improvement over the current state of the art if they provided a commercially useful yield and/or selectivity, were operable under lower intensity, and thus safer, conditions. 
       BRIEF DESCRIPTION 
       [0008]    The present invention provides processes for the production of tetrachloromethane. Advantageously, the processes make use of partially chlorinated methanes as starting material, and, catalyze the chlorination of the same with a free radical catalyst. As a result, lower intensity process conditions than conventional processes for the production of tetrachloromethane, utilizing methane as a starting material, can be used. Although lower temperatures and pressures are used, and cost savings thus provided, chloroform and tetrachloromethane are produced in higher yields than provided by conventional processes. By maintaining conversion rates of less than 90%, greater reaction selectivity to tetrachloromethane may be seen, along with production of anhydrous HCl as a reaction byproduct. Recycling of reactants can increase the reaction yield and overall conversion, and provide even further cost savings. 
         [0009]    In one aspect, the present invention provides a process for the production of tetrachloromethane. The process comprises catalyzing the chlorination of a feed stream comprising partially chlorinated methanes with a free radical catalyst. The process may be conducted in the liquid phase, in the presence of a solvent. In some embodiments, the solvent may be tetrachloromethane produced by the process. In some embodiments, the feedstream does not comprise methane, and in such embodiments, or other embodiments, the feedstream may comprise chloroform, either alone or in combination with methyl chloride and/or methylene chloride. The free radical catalyst may comprise UV-light, azobisisobutyronitrile, 1,1′-azobis(cyclohexanecarbonitrile), di-tert-butyl peroxide, benzoyl peroxide, methyl ethyl ketone peroxide, acetone peroxide or combinations of any number of these. The temperature of the process may be less than 100° C., and the pressure is desirably less than 100 psig. In some embodiments, anhydrous HCl may be recovered from the process. 
         [0010]    The advantages provided by the present processes may be carried forward by utilizing the tetrachloromethane to produce further downstream products, such as, e.g., 1,1,1,2,3-pentachloroproprane and/or 1,1,2,3-tetrachloropropene. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0011]      FIG. 1  shows a schematic representation of a process for the production of tetrachloromethane according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The present specification provides certain definitions and methods to better define the present invention and to guide those of ordinary skill in the art in the practice of the present invention. Provision, or lack of the provision, of a definition for a particular term or phrase is not meant to imply any particular importance, or lack thereof. Rather, and unless otherwise noted, terms are to be understood according to conventional usage by those of ordinary skill in the relevant art. 
         [0013]    The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item, and the terms “front”, “back”, “bottom”, and/or “top”, unless otherwise noted, are merely used for convenience of description, and are not limited to any one position or spatial orientation. 
         [0014]    If ranges are disclosed, the endpoints of all ranges directed to the same component or property are inclusive and independently combinable (e.g., ranges of “up to 25 wt. %, or, more specifically, 5 wt. % to 20 wt. %,” is inclusive of the endpoints and all intermediate values of the ranges of “5 wt. % to 25 wt. %,” etc.). As used herein, percent (%) conversion is meant to indicate change in molar or mass flow of reactant in a reactor in ratio to the incoming flow, while percent (%) selectivity means the change in molar flow rate of product in a reactor in ratio to the change of molar flow rate of a reactant. 
         [0015]    Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
         [0016]    Further, “M1” may be used as an abbreviation for chloromethane or methyl chloride (CH 3 Cl), “M2” may be used as an abbreviation for dichloromethane or methylene chloride (CH 2 Cl 2 ), “M3” may be used as an abbreviation for trichloromethane or chloroform (CHCl 3 ) and “M4” may be used as an abbreviation for tetrachloromethane or carbon tetrachloride (CCl 4 ). 
         [0017]    The present invention provides efficient processes for the production of tetrachloromethane. Tetrachloromethane is an important raw material desirably utilized in the production of, e.g., 1,1,1,2,3-pentachloropropane and/or 1,1,2,3-tetrachloropropene. Prior to the present invention, tetrachloromethane was produced mainly as a byproduct from processes for the production of perchloroethylene, and in quantities insufficient for use as a feedstock in many processes. Although processes for the direct production of tetrachloromethane are known, these conventional processes may typically require the use of high intensity process conditions, e.g., high temperatures and pressures, and yet provided poor yields and selectivities to tetrachloromethane. Furthermore, processes employing such conditions are known by the art to be volatile, and often, explosive. And, the use of high intensity process conditions adds cost to a process, not only in the form of utility costs, but of the specialized equipment that may be necessary to achieve and/or house such conditions. 
         [0018]    The present processes make use of a feedstream comprising partially chlorinated methanes. In some embodiments, the feedstream may comprise chloroform, either alone or in combination with methyl chloride and/or methylene chloride. In these, or other, embodiments, the feedstream may be devoid of methane. The absence of methane from the feedstream is advantageous because methane is not very soluble in tetrachloromethane, and so, in its presence, high pressures would be required to keep methane in solution in the reaction mixture. Since the present processes do not make use of methane as a reactant, lower pressures may be used, and less capital and energy costs incurred. 
         [0019]    The chlorination of the feedstream is desirably catalyzed with one or more free radical initiators. The use of one or more free radical initiators not only provides the reaction with an acceptable rate, but can also increase the yield of tetrachloromethane, as well as the selectivity to chloromethane, particularly when conversions of the feedstream are limited to less than 90%, or less than 80%, or less than 70% or even to 60%. More specifically, at a feedstream conversion of 60%, chloroform and tetrachloromethane may be produced at ratios of 4:1, or1:1 or even 1:2, with very little production of methyl chloride or methylene chloride. 
         [0020]    Many free radical initiators are known, and any of these may be used in the present processes. Examples of suitable free radical initiators include, but are not limited to, compounds comprising one or more azo-groups (R—N═N—R′) such as azobisisobutyronitrile (AIBN) or 1,1′-azobis(cyclohexanecarbonitrile) (ABCN) and organic peroxides such as di-tert-butyl peroxide, benzoyl peroxide, methyl ethyl ketone peroxide, and acetone peroxide. Combinations of any number of these may also be utilized. In some embodiments, the use of AIBN may be preferred, either alone or in combination with UV or visible light or heat. 
         [0021]    The desired free radical initiator(s) can be provided either in bulk or in connection with a substrate, such as activated carbon, graphite, silica, alumina, zeolites, fluorinated graphite and fluorinated alumina 
         [0022]    The amount of the desired free radical initiator will depend upon the particular initiator chosen as well as the other reaction conditions. Generally speaking, enough of the initiator should be utilized to provide some improvement to reaction process conditions (e.g., a reduction in required temperature) or realized products, but yet not be more than will provide any additional benefit, if only for reasons of economic practicality. 
         [0023]    For purposes of illustration only, useful concentrations of free radical initiators will range from 0.0001% to 10% by weight each with respect to, or from 0.001% to 1%, or preferably from 0.01% to 0.1 wt %, inclusive of all subranges therebetween. 
         [0024]    Due at least in part to the use of at least one free radical initiator, as well as perhaps, at least in some embodiments, the exclusion of methane from the feedstream, the present processes may be carried out at lower intensity conditions, e.g., lower pressures and/or temperatures, than conventional processes. More particularly, the present processes may desirably be carried out at pressures of less than or equal to 140 psig, or less than or equal to 120 psig, or even less than or equal to 100 psig. Further, temperatures of less than or equal to 150° C., or less than or equal to 120° C., or less than or equal to 100° C., are appropriate. In some embodiments, unreacted reactants may be recycled, or other solvents may be utilized, to assist with heat management within the reactor. The process may be conducted in the liquid phase, in the presence of a solvent. In some embodiments, tetrachloromethane produced by the process may act as a solvent. 
         [0025]    The use of both a low temperature and a low pressure is also contemplated, but not required, and in embodiments wherein the use of both is desired, any combination of any temperature of less than or equal to 120° C. and any pressure less than or equal to 100 psig may be utilized. For example, if the pressure is desirably less than or equal to 140 psig, the temperature may be ambient, or less than or equal to 120° C., or less than or equal to 100° C. Similarly, if the pressure is desirably less than or equal to 120 psig, the temperature may be ambient, or less than or equal to 140° C., or less than or equal to 120° C., or less than or equal to 100° C., and so on. 
         [0026]    In some embodiments, the present processes are desirably conducted in the liquid phase. Liquid phase processes for the production of tetrachloromethane may provide advantages as compared to conventional methods for producing tetrachloromethane using gas-phase reactions at least because the production utility cost is lower for liquid phase processes, where evaporation of reactants is not required. In addition, the lower reaction temperatures used in the present liquid phase processes tend to result in lower fouling rates than the higher temperatures used in connection with gas phase processes. Higher fouling rates, in turn, tend to limit reactor lifetime and can lead to undesirable byproduct formation. 
         [0027]    The chlorination steps of the process may be carried out using any chlorination agent, and several of these are known in the art. Exemplary chlorination agents include, but are not limited to chlorine, and/or sulfuryl chloride (SO 2 Cl 2 ). If sulfuryl chloride is used, the by-product SO 2  may be catalytically recombined with Cl 2  to regenerate sulfuryl chloride that may then be recycled to the process. 
         [0028]    The present processes may be conducted in any suitable reactor, and are desirably conducted using reactors that are capable of continuous operation. In some embodiments, the processes may advantageously be conducted in a continuous stirred tank reactor. Stirring of the reaction mixture may lead to enhanced reaction rate, and thus can be utilized in some embodiments. 
         [0029]    Economics of the process, e.g., as witnessed by yield and/or selectivity, may be enhanced by recycling of unreacted reactants to the reactor. Such recycling may also assist in heat regulation of the process. Economics of the process may further be enhanced by allowing for the recovery of one or more usable byproducts, such as hydrogen chloride. And so, in some embodiments, provisions are made for the same. For example, hydrogen chloride may be recovered from the process via implementation of a distillation column, wherein the feedstream to the same, and from which hydrogen chloride is desirably recovered, is condensed at a temperature of from −40° C. to 0° C. prior to introduction to the distillation column. 
         [0030]    In additional embodiments, one or more reaction conditions of the process may be optimized, in order to provide even further advantages, i.e., improvements in selectivity, conversion or production of reaction by-products. In certain embodiments, multiple reaction conditions are optimized and even further improvements in selectivity, conversion and production of reaction by-products produced can be seen. 
         [0031]    Reaction conditions of the process that may be optimized include any reaction condition conveniently adjusted, e.g., that may be adjusted via utilization of equipment and/or materials already present in the manufacturing footprint, or that may be obtained at low resource cost. Examples of such conditions may include, but are not limited to, adjustments to flow rates, molar ratios of reactants, etc. 
         [0032]    That being said, the particular conditions employed at each step described herein are not critical, and are readily determined by those of ordinary skill in the art. What is important is that a feedstream comprising partially chlorinated methanes is catalyzed with a free radical catalyst to provide tetrachloromethane. The feedstream may comprise either or both chloroform and methylene chloride, and may further comprise methyl chloride and desirably does not comprise methane. It is also advantageous that anhydrous HCl is produced. Further advantages may be provided in those embodiments in which the process is conducted in the liquid phase. Those of ordinary skill in the art will readily be able to determine suitable equipment for each step, as well as the particular conditions at which the steps are desirably performed. 
         [0033]    A schematic illustration of such a process is shown in  FIG. 1 . As shown in  FIG. 1 , in process  100 , a feedstream comprising a mixture of chloromethane and methylene chloride is chlorinated in the liquid phase in reactor  102  to produce chloroform and tetrachloromethane. The overhead stream from reactor  102 , comprising excess chlorine, HCl, methyl chloride and methylene chloride, is fed to a separation column  104  where HCl is purified in the overhead stream. The bottom stream of separation column  104  comprising unreacted chlorine, methyl chloride, and methylene chloride is recycled back to reactor  102 . The organic liquid product of reactor  102 , comprising methyl chloride, methylene chloride, chloroform and tetrachloromethane, is sent to a separation column  110 , which provides an overhead stream comprising methyl chloride, methylene chloride and chloroform that is recycled back to reactor  102 . The bottom stream of separation column  110  comprising tetrachloromethane and heavier byproducts is provided to separation column  112 . In column  112 , tetrachloromethane is purified and provided as an overhead product stream, and the heavier byproducts are disposed of through a bottom stream. 
         [0034]    The tetrachloromethane produced by the present process may typically be processed to provide further downstream products including hydrofluoroolefins, such as, for example, 1,1,1,2,3-pentachloroproprane and/or 1,1,2,3-tetrachloropropene. Since the present invention provides an improved process for the production of tetrachloromethane, it is contemplated that the improvements provided will carry forward to provide improvements to these downstream processes and/or products. Improved processes for the production of tetra- and penta-chloropropanes and/or chloropropenes are thus also provided herein. 
         [0035]    The conversion of tetrachloromethane to tetra- and penta-chloropropanes and/or chloropropenes may broadly comprise the catalyzed reaction of tetrachloromethane and ethylene. A more specific example might involve a process wherein a feedstream of tetrachloromethane is reacted with ethylene_in the presence of less than 2 mole % of one or more catalysts comprising iron, such as FeCl3, and optionally, from 0.1 to 5 mole % a phosphours containing promoter. The reaction is generally carried out at temperatures of from 50° C. to 150° C. and pressure of from 1 atm to 14 atm. At such conditions, conversions of tetrachloromethane of from 80% to 100% are expected, with the main product being 1,1,1,2,3-pentachloropropane. 
         [0036]    Some embodiments of the invention will now be described in the following Examples. 
       EXAMPLE 1  
     Conversion of Methylene Chloride to Chloroform and Tetrachloromethane 
       [0037]    Methylene chloride (M2) is reacted with chlorine in the liquid phase at 82° C. and 70 psig in the presence of a 40 watt UV black light in a 1 inch ID tube reactor jacketed with circulating water from a 15° C. temperature-regulated water bath at ambient pressure. The organic phase is analyzed on a Varian 6000 gas chromatograph equipped with a 30 meter DB-5 fused-silica capillary column. Using 69-70 minute residence time and a methylene chloride/chlorine molar feed ratio of 1.32, liquid product analysis shows 22.72 wt %, 53.3 wt %, and 24 wt % of the methylene chloride, chloroform, and tetrachloromethane, respectively. In other words, a 3/1 chloroform/tetrachloromethane molar product ratio is obtained at 66% methylene chloride conversion. 
       EXAMPLE 2  
     Conversion of Methyl Chloride and Methylene Chloride to Chloroform and Tetrachloromethane 
       [0038]    Methyl chloride and methylene chloride, at a molar ratio of 1/4, are reacted with chlorine in the liquid phase in the presence of 100 ppm of AIBN at 70 psig and 84° C. in a ½ inch ID and 18 inch long tube. At flow rates of 1, 4, and 2.5 grmole/hr of methyl chloride, methylene chloride and chlorine, respectively, methyl chloride and methylene chloride conversions of 61.4 and 27.5%, respectively, are obtained. The product mixture comprises 4.1 wt. % methyl chloride, 48.4 wt. % methylene chloride, 38.0 wt. % chloroform, and 9.5 wt. % tetrachloromethane. The ratio of chloroform to tetrachloromethane is found to be 5.2. 
       EXAMPLE 3  
     Chlorination of Chloroform to Tetrachloromethane 
       [0039]    Forty five to 55 gallons of liquid chloroform was chlorinated at a temperature of from 35° C. to 40° C. using 400 watt H1 mercury vapor lamp with a wavelength of from 300 to 500 millimicrons. The reaction is conducted in a 30 inch ID nickel tank equipped with triangular chlorine bubbler and three-light well. The percent tetrachloromethane in the liquid product is determined using specific gravity. After adding 300 lbs of Cl 2 , 95mole % of tetrachloromethane is obtained in the product mixture.