MXPA00004992A - Method of producing hydrofluorocarbons - Google Patents

Abstract

A process for producing fluorinated organic compounds comprising reacting an organic compound fluorination agent in the presence of a fluorination catalyst, while maintaining a pressure less than sufficient for high-temperature distillation, to produce the desired fluorinated carbon compound.

Description

METHOD OF PRODUCTION OF HYDROFLUOROCARBONS FIELD OF THE INVENTION The present invention relates, in general, to the preparation of hydrofluorocarbons and fluorocarbons. More specifically, the invention relates to the catalytic fluorination process which improves the performance of the desired hydrofluorocarbon / fluorocarbon and prolongs the activity of the fluorination catalyst used.

BACKGROUND OF THE INVENTION The production of hydrofluorocarbons (HFC) and fluorocarbons (FC) is well known in the art. In general, production methods include the fluorination of chlorinated organic compounds to produce the desired HFC or FC compounds, and then recovery of the desired compounds by distillation. Among the preferred fluorination methods is the catalytic vapor phase fluorination. For example, in the production of difluoromethane (HFC-32) a chlorinated organic compound, such as, for example, methylene chloride (CH 2 Cl 2) and a fluorinating agent, such as, for example, hydrogen fluoride (HF), preheat and react with each other in the presence of a fluorination catalyst to generate a product stream.

The desired HFC or FC compound is recovered by using distillation from the product stream which also contains other materials as by-products of the reaction. Distillation is well known in the art and usually includes the use of distillation media, such as a recycle column, which operates at specific pressures and temperatures to separate the desired compound from the product stream. The distillation pressure and temperature are interrelated so that higher operating pressures generally correspond to higher distillation temperatures. The distillation temperatures dictate cooling requirements of the column.

For purposes of the description herein, there are basically two types of cooling, high temperature and low temperature. Cooling at high temperature refers to cooling to a temperature of not less than about 0 ° C. Such cooling at high temperature can be achieved with relative ease and little cost using common equipment and refrigerants. On the other hand, cooling to low temperature refers to cooling to a temperature no greater than about -15 ° C. The equipment and refrigerants needed for low temperature cooling tend to be substantially more expensive than those required for high temperature cooling. Thus, in the industry it is highly preferable to operate the recycle column within a range of pressure that allows the use of cooling at high temperature, hereinafter referred to as "distillation at high temperature. To obtain the proper flow of the product stream, The recycle column is operated at a lower pressure than the reactor, so taking into account the pressure drop between the reactor and the recycling column, the usual practice is to carry out the reaction at a temperature that allows the use of distillation high temperature, a sufficient reaction pressure for high temperature distillation is easily determined by an expert in the distillation technique, it depends on different factors including, for example, the pressure difference between the reactor and the recycle column, the characteristics phase of the desired product and the other constituents of the product stream, for example a suitable pressure for The high temperature distillation of HFC-32 is above about 100 psig. Although widely used, prior art methods for producing HFC and FC through fluorination and distillation have some disadvantages. Among the most important drawbacks is deactivation of the catalyst during fluorination. This gives rise to lower yields. In an attempt to maintain the catalyst activity, a regenerative agent, as it can be chlorine, it is usually co-fed with the reactants in the reactor in a continuous mode. The continuous addition of chlorine, however, adds to the formation of generally undesirable by-products. The by-products complicate the distillation and can significantly reduce the yield of the product and decrease the quality of the product. For example, in the production of HFC-32, the formation of chlorofluoromethane (CFC-12) increases substantially with the use of increasing amounts of chlorine. Unfortunately, CFC-12 and HFC-32 form a low-boiling azeotropic mixture from which it is difficult to separate the desired HFC-32 product. Distillation claims approximately 10 parts of HFC-32 for each part of CFC-12 removed from the product. Even if the volume of commercial production is quite high to accommodate such a loss, the unwanted byproducts present waste problems. Therefore, there is a need to prepare HFC and FC by a process that does not have the aforementioned and other drawbacks. The present invention meets this need among others.

DESCRIPTION OF THE INVENTION AND PREFERRED MODALITIES The present invention identifies a range of reaction pressure to produce fluorinated organic compounds, such as hydrofluorocarbons and fluorocarbons, in a fluorination / distillation process that minimizes the deactivation of the catalyst and the formation of unwanted byproducts and that increases yields. The identified reaction pressure range is lower than that commonly practiced and, preferably, lower than the pressure conventionally used for high temperature distillation. Although relatively high reaction pressures are preferred in the prior art production of HFCs and FC due to the advantages of high temperature distillation, a significant and surprising reduction in catalyst deactivation has been achieved using relatively high reaction pressures. losses according to the present invention. Accordingly, the amount of the oxidizing agent (e.g., chlorine) necessary to regenerate the catalyst is reduced. The use of smaller amounts of the oxidizing agent in turn reduces the formation of undesirable by-products which are responsible for the low yields of the product, which complicates the distillation, and which presents waste problems. Therefore, the use of the "low pressure" process of the present invention results in the formation of a product stream that is more easily distillable than that produced by the use of a "high pressure" process of the prior art. Est provides higher product yields, simpler distillation and less byproduct formation. In a preferred embodiment, the present invention provides a process for the production of a fluorinated organic compound consisting of: (a) reacting the reaction medium, having at least one fluoridating agent and an organic compound, in the presence of u catalyst for fluorination, while maintaining a relatively low reaction pressure, to produce a product stream; and (b) recovering the desired fluorinated organic compound from the product stream by distillation. Each of these steps is described further in more detail. For purposes of illustration, the preparation of difluoromethane is specifically considered, although it should be understood that the process of the present invention can be applied to the preparation of a variety of HFC and FC, such as, for example, pentafluoroethane (HFC-125 ), 1,1,1,1-tetrafluoroethane (HFC 134a) and exafluoroethane (FC-116). The reaction medium used in the process of the present invention contains a fluorinating agent and an organic compound. A suitable fluorinating agent includes any material capable of providing fluorine in the reaction. The preferred fluorinating agent is hydrogen fluoride (HF) substantially anhydrous. The presence of water in the reaction tends to deactivate the fluorination catalyst. The term "substantially anhydrous", as used herein, means that the HF contains less than about 0.05% by weight of water and, preferably, contains less than about 0.02% by weight of water. However, it should be understood that the presence of water in the catalyst can be compensated by increasing the amount of the catalyst used. The organic compound can be any compound containing a chlorine attached to the carbon or another fluorine-replaceable atom and / or containing an unsaturated carbon-carbon bond that is saturable with fluorine. Suitable organic compounds include, for example, hydrochlorofluorocarbons (compounds containing carbon, chlorine, fluorine and hydrogen), hydrochlorocarbons (compounds containing carbon, chlorine and hydrogen) and chlorofluorocarbons (compounds containing carbon, chlorine and fluorine), chlorocarbons (carbon-containing compounds). and chlorine) or mixtures of two or more thereof In a preferred embodiment, the chlorinated organic is methylene chloride (HCC-30) The reaction medium preferably includes recycled material that is recovered from the product stream.

If a continuous recycle stream of a high boiling fraction obtained in the distillation is added to the reaction medium, a large excess of the fluorinating agent to the organic compound must be used. The use of higher molar ratios of the fluorinating agent to the organic compound will generally result in higher yields and selectivity. In addition, the use of a large excess of the fluorinating agent will decrease the deactivation rates of the catalyst and will cause less decomposition in the preheaters and vaporizers, especially when the reaction is carried out at pressures in excess of 3 atmospheres. In the production of HFC-32, a large excess of HF will also give rise to the reduction of hydrochlorofluoromethane (CFC-31) produced as well as the concentration of unreacted HCC-30. In general, the ratio of HF to HCFC-31 is used, when measured after the separation of HFC-32 from the product stream, from at least about 25.1 to at least about 300: 1, preferably at least about 50. : 1 to at least about 200: 1 and most preferably at least about 75: 1 to at least about 150: 1. Although the reaction medium preferably includes recycled material, it is possible to use new starting materials. When the process is run without continuous recycling, a sufficient amount of the fluorinating agent must be supplied to the reaction to provide at least a stoichiometric amount of the fluorine relative to the chlorine of the chlorinated organic compound. In the preferred embodiment, wherein HF and HCC-30 are used, the molar ratio of HF to HCC-30 is preferably from about 1: 1 to about 10: 1, and most preferably from about 1: 1 to about 4. :1. Optionally, it is possible to add HCFC-31 to the reaction medium. When desired, one or more of the reagents comprising the fluorinating agent and the chlorinated organic compound can be preheated in at least one vaporizer before being fed into the reactor. The term "preheated" refers to vaporizing and optionally superheating the reactants. Suitable temperatures for preheating are in the range from about 125 ° to about 400 ° C, preferably from about 150 ° to about 350 ° C, more preferably from about 175 ° C to about 275 ° C, and still more preferred from about 200 ° C to about 250 ° C. The vaporizer, as well as other containers used in this process, can be made of any suitable corrosion resistant material. The reactor is preferably charged with a catalyst for fluorination before feeding the reactants to the reactor. The term "fluorination catalyst", as used herein, refers to an inorganic metal catalyst that favors a reaction that includes a substitution of fluorine for chlorine in a chlorinated organic molecule. Fluoridation catalysts are well known to those skilled in the art. Exemplary catalysts include, without limitation, oxides, hydroxides, halides, chromium oxyhalides, copper, aluminum, cobalt, magnesium, manganese, zinc, nickel and iron and the inorganic salts thereof, Cr 2 3/12 2 3, Cr 2 ? 3 / lF3, CoCl2Cr? 3 / Al2? 3, NiCl2 / Cr02? 3 / l2? 3, C? Cl2AlF3 and NiCl2 / AlF3. In addition metal catalysts with support such as nickel, cobalt, zinc, iron and copper supported on chromia, magnesia, or alumina can be used. Such chromium oxide / aluminum oxide catalysts are known and described, for example, in U.S. Patent No. 5,155,082. Preferably, the chromium oxide, a commercially available catalyst, is used. The chromium oxide can be crystalline or amorphous. Preferably, amorphous chromium oxide is used. Before adding the reactants to the reactor, it may be preferable to pre-treat the catalyst chemically and / or physically to create active sites that facilitate a fluorination reaction. For example, the catalyst can be pre-treated by calcining it under a flow of inert gas such as nitrogen at a temperature comparable to or greater than that of the fluorination reaction. Next, the calcined catalyst is exposed to a fluorinating agent alone or in combination with up to about 5 to about 99% by weight of an inert gas at a temperature from about 200 ° C to about 450 ° C for at least about one hour. . Preferably, the catalyst is subjected to a third step in which an oxidation agent such as chlorine is contacted with the catalyst to improve its reactive properties even more. Preferably, the chlorine is diluted with from about 60 to about 75% HF and / or from about 20 to about 30% of an inert gas. The chlorine can be passed over the catalyst at a ratio of total chlorine volume to total catalyst volume of about 1: 3000, preferably about 10: 1000, more preferably about 50: 500. The exposure time can be from about 1 to about 200 hours, preferably from about 5 to about 70 hours, most preferably about 10 to about 30 hours. Exposure to chlorine can be carried out at any temperature and pressure suitable for the fluorination reaction. The reactants can be fed individually or as a mixture to the reactor to form a reaction medium. Once the reaction is under way, the reactants can be continuously added under pressure to supply the additional quantities of reactants needed to continue the process. The temperature at which the fluorination reaction is carried out and the reaction period will depend on the initial materials, the amounts used and the catalyst used. One skilled in the art can easily optimize the reaction conditions to obtain the desired results. Temperatures are generally between about 125 ° and about 425 ° C, preferably between about 150 ° and about 300 ° C, and still more preferably between about 200 ° and about 250 ° C. The contact times depend on several factors including, for example, the catalyst concentration, the type of catalyst and the temperature. The time required for the reactants to pass through the catalyst bed (assuming a 100% cavity catalyst bed) it is usually from about 1 to about 120 seconds, preferably from about 2 to 60 seconds, most preferably from about 4 to about 50 seconds, and still from greater preference from about 5 to about 30 seconds. As already mentioned, the process of the present invention is carried out at relatively low pressure in comparison with the usual practice which usually includes quite high pressures to guarantee distillation at high temperature. The minimum pressure required for high temperature distillation depends on the product stream, more specifically, the low boiling fraction of the product stream. The distillation pressure must be very high to partially condense the low-boiling fraction at a certain temperature. In the case of high temperature distillation, the temperature is greater than about 0 ° C. Preferably, the reaction pressure used in the process of the present invention is lower than that necessary to effect the high temperature distillation. For example, the minimum pressure required for high temperature distillation of HFC-32 is above 100 psig. According to the process of the present invention, the reaction pressure usually should not be greater than about 135 psig, more preferably between near atmospheric pressure and about 100 psig, still more preferably between about 20 psig and about 80 psig, and more preferably between about 40 psig and about 75 psig. The process of the present invention may comprise an optional step in which an oxidizing agent is added to the reaction to regenerate the catalyst. Suitable oxidizing agents are well known in the art. These include, for example, chlorine and elemental oxygen. The oxidizing agent can be added in any suitable form, for example, the oxidizing agent can be added continuously or intermittently, for example, by mixing it with the reactants and feeding it as necessary to maintain the activity of the catalyst. In the preferred form, the oxidizing agent is added periodically which reduces the need to monitor the reaction and oxidant feed continuously. Otherwise, according to the prior art, the activity of the catalyst can be maintained by regenerating the catalyst during periodic interruptions of the reaction. Since the catalyst is not deactivated so rapidly under the operating pressures of the present invention, the need for interruptions in the reactor is less frequent than under the operating conditions of the prior art. As mentioned in the foregoing, when performing the reaction at a pressure prescribed herein, the catalyst tends to maintain its activity for a longer period than if the reaction is carried out at higher pressures. Accordingly, it is possible to use small amounts of the oxidizing agent. This results in a reduction in the formation of undesirable byproducts, for example, under optimum conditions in high pressure production of HFC-32, the amount of CFC-12 commonly found in the low boiling fraction. greater than about 50 ppm. The corresponding amount of CFC-12 is significantly less when the process of the present invention is used. concentration of CFC-12, at the preferred pressures, less than about 250 ppm, at preferred pressures m less than about 100 ppm and at still more preferred pressures less than about 50 ppm. The desired HFC or FC compound is recovered from the reaction mixture using the apparatus and traditional techniques. In the preferred embodiment, the product stream is separated into the low and high boiling point fractions, and then the desired compound is recovered from the respective fraction. For example, in difluoromethane production, the product stream probably also includes CFC-31 and HCl, as well as unreacted feed stream, such as HF and HCC-30. This product stream is fed to the recycled column for separation. . The high boiling point fraction, or waste stream, of the separated one contains HF and unreacted HCC-30 and the intermediate reactant HCFC-31. Preferably, this mixture is recycled to the reactor as already mentioned. The fraction of low boiling point, or higher current, containing difluoromethane, HCl, HF and byproducts of the reaction, is recovered. Otherwise, the separation of the fractions can be carried out in two steps. In the first step, the product stream is extinguished, that is, the temperature of the product stream is reduced below its dew point. The extinction can be performed in a packed column containing any suitable corrosion resistant packing material and a suitable reflux liquid such as HF, HCC-30, and / or HCFC-31. The extinguished product is subsequently fed to a recycling column. The substantially pure product is recovered from the low boiling fraction by any suitable method. Preferably, the recovery is carried out by a series of sub-steps including the treatment of the gas mixture in an HCl distillation column or in an aqueous HCl absorption tower under suitable conditions to remove traces of HCl and HF. The crude product, such as difluoromethane, is then treated with a first caustic scrubber under conditions which neutralize the residual acidity and form a neutralized product. Usually, the caustic scrubber contains water, sodium hydroxide or potassium hydroxide. The neutralized product is then treated in a second caustic scrubber, preferably containing sodium hydroxide together with a sulphite, such as sodium sulphite under conditions which are effective for the removal of residual chlorine and in the formation of a product practically. without chlorine. The virtually chlorine-free product is then treated with a sulfuric acid scavenger followed by a solid desiccant, such as any commercially available, suitable molecular sieve that absorbs the residual moisture from the gas stream containing the product to form a product virtually free of charge. humidity. Lastly, the virtually moisture-free product is conducted through a plurality of distillation columns under conditions sufficient to remove residual impurities and produce a practically pure product, eg, greater than 99.97% by weight of difluoromethane. Any residual HCFC-31 removed in this last step can be recycled as mentioned above. In the case of the production of difluoromethane, the reduction of CFC-12 and, consequently, the azeotrope of CFC-12 / HFC-32 minimizes the previous distillation steps.

EXAMPLES The examples described below are illustrative of the practice of the invention. More specifically, the examples describe a process at low pressure to produce difluoromethane in which the deactivation of the catalyst and the formation of undesirable byproducts is reduced in relation to the results obtained in the use of a high pressure process.

Example 1 This example illustrates that keeping the reactor at relatively low pressures in the production of difluoromethane prolongs the activity of the fluorination catalyst. A 4-inch diameter Monel 400 reactor was charged with 4 liters of chromium oxide catalyst which was subjected to the following pre-treatment process. The catalyst was dried under 20 liters per minute standard (slpm) of nitrogen flow at a temperature of 30 ° C for 8 hours. The catalyst was conditioned by adding HF at a rate of 0.2 Ib / h for the flow of nitrogen at a reactor temperature of 250 ° C. The flow of HF was increased to one lb / h at a very low rate to avoid an exotherm of excessive catalyst, which would give rise to the well-known phenomenon of "incandescence". The temperature was then gradually increased to 350 ° C and maintained for 4 hours. The temperature of the catalyst bed was then lowered to 250 ° C and chlorine was introduced into the HF / N mixture at a rate of 500 standard cubic centimeters per minute (sccm) for a period of 24 hours.

After this pre-treatment procedures, chlorine and nitrogen flows were interrupted and HCC-30 was mixed with HF and passed through a preheater at 185 ° C. The mixture of HCC-30 and vaporized HF was fed to the reactor which was maintained at a predetermined pressure, as set forth in Table 1 below. The reactor effluent was extinguished using a heat exchanger and fed to a recycle column which was maintained at a pressure of 5-10 psig below the reactor pressure. The low-boiling distillation components, HCFC-31, HF and HCC-30, were recycled to mix with the fresh HF and HCC-30 feed stream and fed to the preheater and the reactor at a flow rate of Ib / in. The recent HF and HCC-30 feeding rates were maintained at 0.6 and 1.2 Ib / in, respectively.

The experimental procedure included carrying out the reactions at different pressures, as established in Table 1 below. For the 45 and 75 psig experiments, the chlorine was added to the feed mix at a flow rate of 200 sccm for a period of 6-8 hours as needed to maintain catalyst activity. At an operation at 135 psig, the chlorine was added in an amount necessary to bring the catalyst activity to the previous levels, typically 300-400 g over a period of 6 hours. The conversion of the resulting HCC-30 was 85-95%. A sudden drop in the conversion to 60% signaled the need for chlorine addition to bring the conversion back to the previous levels. Surprisingly, it was found that the time between the necessary additions of chlorine to maintain catalyst activity increased at lower pressures of the process of the present invention. This is shown in Table 1 below. - Table 1 - Addition of chlorine Reactor pressure (psig) Time between additions of Cl (hrs.) 45 100 75 60 135 20 Example 2 This example illustrates that keeping the reactor at relatively low pressures during the production of difluoromethane reduces the formation of low boiling byproducts. The different pressures used in the comparative tests are identified in Table 2 below. The other reaction conditions were as described in Example 1. The low boiling components separated in the distillation column, HCl and HFC-32, were passed through a caustic scrubber containing 10% KOH where it was removed the HCl. The HFC-32 product was dried and collected. The additional boiling byproducts that could be formed during the reaction are CFC-12, HCFC-22 and HFC-23. These byproducts represent significant yield losses, especially CFC-12 which forms an azeotrope with HFC-32. The rate of formation of these by-products was surprisingly increased with increasing reactor pressure, as shown in Table 2 below. The concentration of the by-products is shown as parts per million (ppm) of the difluoromethane (HFC-32) in the crude product. The time in the stream is expressed as the number of hours of operation at the specified pressure.Table 2 Low boiling point byproducts Pressure Time in CFC-12 (Fpirt) HCFC-22 (Fp) HFC-23 (F £ tn) (psig) current (h) 45 260 n.d. n.d. n.d. 75 240 n.d. n.d. n.d. 75 977 19 102 1497 135 577 654 2815 2816 n.d. = not detected, detection limit 1 ppm, As shown in Table 2 above, low-boiling byproducts are only observed at low pressure (45 and 75 psig) after an important time in the current, while at high pressure (135 psig) these are immediately observed at higher levels.

Example 3 This example illustrates * that keeping the reactor at relatively low pressures in the production of difluoromethane reduces the formation of high-boiling by-products. The different pressures used in the comparative tests are identified in Table 3 below. The other reaction conditions were as described in Example 1. The high-boiling by-products can be formed in the process. Examples of high-boiling byproducts are methyl chloride (HCC40) and HCFC-2 1. Although these materials are recycled to the reactor, together with HF, HCC-30 and unreacted HCFC-31, they nonetheless represent significant losses in performance. In addition, HCC-40 reacts very slowly to HFC-41 and thus accumulates in the recycle stream, requiring periodic interruptions to purge the system. The formation rate of these high-boiling byproducts was surprisingly increased with increasing reactor pressures, as shown in Table 3 below. The concentrations are given as a percentage by weight of the total organic concentration of the recycle stream Table 3 High boiling byproducts Pressure (psig) 'Time in HCC-40 (% in HCFC-21 (% in current (h) weight) weight) 45 260 n.d. n.d. 75 914 n.d. n.d. 135 180 0.23 n.d 135 582 0.64 n.d 135 703 0.97 1.34 As shown in Table 3 above, high-boiling byproducts are not detectable at low pressure (45 and 75 psig) after a significant time in the stream, while at high pressure (135 psig) HCC was observed. 40 after a relatively short time and HCFC-21 after a longer time.

Claims (20)

1. A process for producing a fluorinated organic compound comprising: reacting an organic compound with a fluorinating agent in the presence of a fluorination catalyst while maintaining a pressure less than sufficient for high temperature distillation to produce a current of the product; and recovering the fluorinated organic compound from the product stream by distillation at low temperature.

2. The process of claim 1, wherein the reaction pressure is maintained at no more than about 100 psig.

3. The process of claim 2, wherein the reaction pressure is maintained between about 20 and about 80 psig.

The process of claim 3, wherein the reaction pressure is maintained between about 40 and about 75 psig, and distillation at low temperature is performed at no greater than about -15 ° C.

5. The process of claim 1, further comprising: periodically contacting the catalyst with an oxidizing agent.

6. A process for producing a fluorinated organic compound comprises: reacting an organic compound with a fluorinating agent in the presence of a fluorination catalyst, while maintaining a pressure no greater than about 135 psig, to produce a product stream; and recovering the fluorinated organic compound from the product stream by distillation.

The process of claim 6, wherein the reaction pressure is maintained between near atmospheric and about 100 psig.

The process of claim 7, wherein the reaction pressure is maintained between about 20 and about 80 psig.

9. A process for producing difluoromethane comprises. reacting a methylene chloride vapor and steam of hydrogen fluoride in the presence of a fluorination catalyst, while maintaining less than the pressure sufficient for distillation at a temperature of ^ Lta, to produce a product stream; and recovering difluoromethane from the product stream by distillation at low temperature.

The process of claim 9, wherein the reaction pressure is maintained at no greater than about 100 psig.

11. The process of claim 10, wherein the reaction pressure is maintained between about 20 and about 80 psig.

12. The process of claim 11, wherein the reaction pressure is maintained between about 40 and about 75 psig.

13. The process of claim 9, further comprising: periodically contacting the catalyst with oxidizing agent.

14. A process for producing difluoromethane comprises the steps of: reacting methylene chloride with hydrogen fluoride in a reactor charged with fluorination catalyst to produce a product stream, while maintaining the reaction pressure so that the concentration of CFC-12 is not greater than about 500 ppm of the low boiling fraction; recovering by distillation of the product stream a high boiling fraction and a low boiling fraction, the low boiling fraction containing difluoromethane; and recovering difluoromethane from the low boiling fraction.

15. The process of. Claim 14, wherein the reactor pressure is maintained so that the concentration of CFC-12 is not greater than about 100 ppm of the low-boiling fraction.

16. The process of claim 15, wherein the pressure of the reactor is maintained so that the concentration of CF 12 is not greater than about 50 ppm of the low boiling fraction.

The process of claim 16, wherein the reagent is maintained at a pressure, not greater than about 1 psig and at a temperature no greater than about -15 ° C.

18. A process for maintaining the activity of a fluorination catalyst in a reaction in which fluorinated carbon compound is synthesized by reacting chlorinated organic compound with a fluorination agent in a reactor charged with fluorination catalyst to produce a product stream from which the fluorinated carbon compound is recovered by distillation; the process comprises: maintaining the reactor at a pressure less than sufficient for high temperature distillation.

19. The process of claim 14, wherein the pressure of the reactor is maintained between near atmospheric near 100 psig. The process of claim 15, wherein the pressure of the reactor is maintained between about 20 psig and about psig.