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MeOH + Hcl
- Thread starter chemman99
- Start date
bchoate
It is unlikely that chloromethane will form in that mixture. The reaction of HCl and methanol to form chloromethane also forms water. The presence of water inhibits the reaction. Typically chloromethane is made commercially by bubbling anhydrous HCl gas through 'dry' methanol. Chloromethane and water vapor are stripped and condensed.
Bill Choate
It is unlikely that chloromethane will form in that mixture. The reaction of HCl and methanol to form chloromethane also forms water. The presence of water inhibits the reaction. Typically chloromethane is made commercially by bubbling anhydrous HCl gas through 'dry' methanol. Chloromethane and water vapor are stripped and condensed.
Bill Choate
bchoate
The reaction between methanol and water can proceed in the liquid phase. The question posed is how much and how fast.
The methanol / HCl reaction is SN2(bimolecular nucleophlic substitution)not SN1 (unimolecular nucleophilic substitution). The Cl(-) nucleophile is weak. The reaction proceeds in two steps; 1) protonation of the methanol oxygen to form OH2 which is a much better leaving group and 2) simultaneous attack of chloride and loss of OH2. The second reaction is rate limiting and very slow. The Lucas test is a test to distinguish among alcohols. In that test con HCl and a sample of the alcohol are mixed with a small amount of zinc chloride. The amount of reaction distinguishes tertiary, secondary, and primary alcohols (positive test = second layer or emulsion; tertiary 2-3 minutes, secondary 5-10 minutes, primary no reaction). Methanol is similar to primary alcohols. Yes, there is reaction but it is very very slow.
The reaction between methanol and water can proceed in the liquid phase. The question posed is how much and how fast.
The methanol / HCl reaction is SN2(bimolecular nucleophlic substitution)not SN1 (unimolecular nucleophilic substitution). The Cl(-) nucleophile is weak. The reaction proceeds in two steps; 1) protonation of the methanol oxygen to form OH2 which is a much better leaving group and 2) simultaneous attack of chloride and loss of OH2. The second reaction is rate limiting and very slow. The Lucas test is a test to distinguish among alcohols. In that test con HCl and a sample of the alcohol are mixed with a small amount of zinc chloride. The amount of reaction distinguishes tertiary, secondary, and primary alcohols (positive test = second layer or emulsion; tertiary 2-3 minutes, secondary 5-10 minutes, primary no reaction). Methanol is similar to primary alcohols. Yes, there is reaction but it is very very slow.
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bchoate
25362, thanks for the interesting patent. The original post poses an issue that I've seen with most posts involving chemistry or reaction issues. It would be most helpful if those posting a question would also give some background into why the question is raised. In the initial post of this thread, it would be most helpful if one knew whether the author was concerned about a) a potential side reaction and byproduct from a process stream or b) if the author has genuine interest in finding better technology for producing methyl chloride (CH3Cl) from methanol and HCl.
My take on the author's question was that the interest was in side reactions and byproducts. The patent seems to indicate your interest in the other point of view.
The patent is not inconsistent with answers I have provided previously. The reaction between aqueous, concentrate HCl and methanol (MeOH)is very slow. I never said it was non-existent but that it was v-e-r-y slow. The patent author based his work on the fact that conventional, liquid phase, non-catalytic reaction between MeOH and HCl is s-l-o-w and that commercial application would require a very large reaction space. The work described in the patent was the effort to develop an alternative incarnation of the method that would use smaller reactors and give higher conversion.
The patent author succeeded by controlling composition within the reactor, by higher temperatures and pressures in the reactor, and by a recovery system designed to return reactants to the reactor and minimize their loss to waste streams. That recovery system was a two column, azeotropic distillation operated at pressure in one column and at reduced pressure in the second. That system, to achieve its goals, is not trivial nor low cost.
The results supporting the patent can be extrapolated to a commercial size to provide some measure of its basis. If one considers a 100 MPY plant based on the patent results, a reactor with a total volume of 8,000-10,000 gal. is needed (reaction holdup volume of 5,000 gal.). This is not excessively large, but one can wonder how large a reactor would be necessary without the authors claims to achieve the same.
If one is worried about methyl chloride formation in the process stream of the initial post, that reaction is slow. Small quanitites of methyl chloride are probably an environmental issue. Methyl chloride is likely to wind up in a vapor or vent stream somewhere.
Bill Choate
25362, thanks for the interesting patent. The original post poses an issue that I've seen with most posts involving chemistry or reaction issues. It would be most helpful if those posting a question would also give some background into why the question is raised. In the initial post of this thread, it would be most helpful if one knew whether the author was concerned about a) a potential side reaction and byproduct from a process stream or b) if the author has genuine interest in finding better technology for producing methyl chloride (CH3Cl) from methanol and HCl.
My take on the author's question was that the interest was in side reactions and byproducts. The patent seems to indicate your interest in the other point of view.
The patent is not inconsistent with answers I have provided previously. The reaction between aqueous, concentrate HCl and methanol (MeOH)is very slow. I never said it was non-existent but that it was v-e-r-y slow. The patent author based his work on the fact that conventional, liquid phase, non-catalytic reaction between MeOH and HCl is s-l-o-w and that commercial application would require a very large reaction space. The work described in the patent was the effort to develop an alternative incarnation of the method that would use smaller reactors and give higher conversion.
The patent author succeeded by controlling composition within the reactor, by higher temperatures and pressures in the reactor, and by a recovery system designed to return reactants to the reactor and minimize their loss to waste streams. That recovery system was a two column, azeotropic distillation operated at pressure in one column and at reduced pressure in the second. That system, to achieve its goals, is not trivial nor low cost.
The results supporting the patent can be extrapolated to a commercial size to provide some measure of its basis. If one considers a 100 MPY plant based on the patent results, a reactor with a total volume of 8,000-10,000 gal. is needed (reaction holdup volume of 5,000 gal.). This is not excessively large, but one can wonder how large a reactor would be necessary without the authors claims to achieve the same.
If one is worried about methyl chloride formation in the process stream of the initial post, that reaction is slow. Small quanitites of methyl chloride are probably an environmental issue. Methyl chloride is likely to wind up in a vapor or vent stream somewhere.
Bill Choate
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