Manufacturing Process of Chloromethanes

• Chloromethanes are produced from methane by chlorination route.

Chloromethanes namely methyl chloride (CH₃Cl), methylene chloride (CH₃Cl₂), Chloroform (CHCl₃) and Carbon Tetrachloride (CCl₄) are produced by direct chlorination of Cl₂ in a gas phase reaction without any catalyst.

 Reactions

     CH₄ + Cl₂ → CH₃Cl + HCl 

     CH₃Cl + Cl₂ → CH₂Cl₂ + HCl

     CH₂Cl₂ + Cl₂ → CHCl₃ + HCl

     CHCl₃ + H₂ → CCl₄ + HCl

• • The reactions are very exothermic.
• The feed molar ratio affects the product distribution.  When CH₄/Cl₂ is about 1.8, then more CH₃Cl is produced.  On the other hand, when CH₄ is chosen as a limiting reactant, more of CCl₄ is produced. Therefore, depending upon the product demand, the feed ratio is adjusted.

Process Technology

• • Methane and Cl₂ are mixed and sent to a furnace
• The furnace has a jacket or shell and tube system to accommodate feed pre-heating to desired furnace inlet temperature (about 280 – 300°C).
• To control temperature, N₂ is used as a diluent at times.
• Depending on the product distribution desired, the CH₄/Cl₂ ratio is chosen.
• The product gases enter an integrated heat exchanger that receives separated CH₄ (or a mixture of CH₄ + N₂) and gets cooled from the furnace exit temperature (about 400°C).
• Eventually, the mixture enters an absorber where water is used as an absorbent and water absorbs the HCl to produce 32 % HCl.
• The trace amounts of HCl in the vapour phase are removed in a neutralizer fed with NaOH
• The gas eventually is compressed and sent to a partial condenser followed with a phase separator.  The phase separator produces two streams namely a liquid stream consisting of the chlorides and the unreacted CH₄/N₂.
• The gaseous product enters a dryer to remove H₂O from the vapour stream using 98% H₂SO₄ as the absorbent for water from the vapour.
• The chloromethanes enter a distillation sequence.  The distillation sequence consists of columns that sequentially separate CH₃Cl, CH₂Cl₂, CHCl₃ and CCl₄.





Figure. Flowsheet of Chloromethane production