Environmental Engineering Reference
In-Depth Information
4CH
4
þ
3N
2
O
4
!
4CH
3
NO
2
þ
2NO
þ
2H
2
O
2H
2
O
þ
3N
2
O
4
!
4HNO
3
þ
2NO
When there is dehydrating agent in the reaction mixture, the formation of nitric
acid can be prevented. Therefore, increasing the reaction temperature, shortening
the reaction time and increasing oxygen can increase the conversion rate of nitra-
tion. In the preparation of nitromethane from sodium nitrite and alkyl halide,
sodium sul
te is added into an autoclave with a mixture of water and acetonitrile as
the solvent and ammonium chloride as catalyst, and methyl chloride is pressed into
the autoclave. After 4
6 h at room temperature, nitromethane is prepared, and this
process has advantages of relatively low temperature and good production safety;
but the large investment in equipment, very low conversion of sodium nitrite or
chlorine methane (usually only of 15
-
36 %) and dif
cult separation of the crude
-
product from the solvent are its drawbacks.
In sodium nitrite and acid salt replacement method [
29
,
30
], ammonium chlo-
roacetate as a raw material reacts with sodium nitrite mainly through the following
reactions.
ClCH
2
CO
2
NH
4
þ
NaNO
2
!
NO
2
CH
2
CO
2
NH
4
þ
NaCl
NO
2
CH
2
CO
2
NH
4
þ
H
2
O
!
CH
3
NO
2
þ
NH
4
HCO
3
The advantages of this process include the following: The byproducts can be
used as industrial raw materials and agriculture fertilizer, therefore the production
process does not have industrial pollution, the investment in production equipment
is low, there is no security risk, and the product purity is high. Its disadvantages are
the high production costs and the reduced yield of nitromethane. In China, this
technology method is generally adopted, but some European and American coun-
tries have this preparation process with product yield of 40
70 %.
However, the replacement reaction between sodium nitrite and dimethyl sul
-
de
to prepare nitromethane is very moderate and the reaction principle is:
ð
CH
3
Þ
2
SO
4
þ
2NaNO
2
!
CH
3
NO
2
much
ð
Þþ
CH
3
ONO little
ð
Þ"þ
NaSO
4
78 %. Its advantages
are: raw materials are cheap with wide source, equipment investment is low,
operation is simple, production cost is low, and it is easy to implement industrial
production. However, the toxicity of dimethyl sulfate in this production process is
high, and the produced methyl nitrite should be absorbed with basic solution, etc.
The disadvantage of lye. Nevertheless, in China and most Asian countries, this
process route has been adopted to produce nitromethane.
Therefore, the important and urgent issues are: how to optimize nitromethane
process to reduce pollution, improve product yield, reduce production costs, sim-
plify the operation, and achieve the environmental and friendly green process.
In this reaction, the yield of nitromethane can be up to 55
-
