Environmental Engineering Reference
In-Depth Information
Based on the analysis and comparison of the mentioned chemical reactions, it
can be known that:
In the main reaction, it is easy to produce methyl nitrite,
which makes it dif
cult to increase the total yield;
the product is not stable under
acidic conditions;
dimethyl sulfate is very easy to decompose into methanol
under acidic and basic conditions;
dimethyl sulfate reacts with sodium nitrite
through two steps, in which the
first step is the conversion of dimethyl sulfate into
the intermediate methyl sulfonate followed by the higher energy-required reaction
between methyl sulfonate and sodium nitrite, thus, in this step, the formation of
byproduct methanol should be minimized through the hydrolysis of acid and base.
In order to improve the yield of nitromethane, the
first step hydrolysis damage of
dimethyl sulfate should be avoided, and decreasing reaction temperature is favorable
to the reaction; because the hydrolysis of dimethyl sulfate is related to the pH value,
strict controlling on the pH can avoid the damage on dimethyl sulfate, sodium sul
de,
nitromethane; catalyst can further accelerate the reaction, reduce the side reaction
hydrolysis and signi
cantly improve the yield and quality of product. The reaction is:
Na 2 CO 3 aq
(CH 3 ) 2 SO 4 +2NaNO 2
CH 3 NO 2 (much) +CH 3 ONO(little
+Na 2 SO 4
pH6-9
According to this equation, the synthesis process of nitromethane is shown in
Fig. 4.2 .
As shown in Fig. 4.2 , when the ratio of dimethyl sulfate over sodium nitrite is
1:1.25, effects of various factors during the synthesis on yields is listed in
Tables 4.2 , 4.3 , 4.4 , 4.5 and 4.6 .
The systems to synthesize nitromethane is shown in Fig. 4.3 .
Based on these results, the optimum process controlling conditions and raw
material parameters are: Dimethyl sulfate: sodium nitrite is 1:1.29, the reaction
temperature is from room temperature to 53
57
°
C, distillation temperature is
-
Commin
ution
Sodium nitrite
Drying
Temperature rising to
40~60 Agitation
and refulx for 2-6 h
Discharge
Filtration
Crude
product
Dimethyl sulfate
Reactor
Cooling
Sodium sulphate
industrial product
Tetrabutyl
ammonium bromide
Sodium sulphate
crude product
Washing
Sodium carbonate
Nitrosomethane
Distillation at 115
degree
Cooling
Recovery Sodium
sulphate
Distillation
Washing
Collecting product beween
100.5 degree and 101.5 degree
Collecting
Nitrosomethane
Nitromethane
 
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