656
ROZANOV, TREGER
approximately in the same way as the reaction rate. by empirical relationships. The dimethyl ether formaꢀ
Thus, the rate of methyl chloride formation also tion rate decreases and, accordingly, the rate of methyl
depends on the partial pressure of HCl over hydroꢀ chloride formation increases with a decreasing methꢀ
chloric acid to the first power within
±
10% accuracy.
anol concentration and an increasing hydrogen chloꢀ
To explain the unusual dependence of the reaction ride concentration.
rate on the hydrochloric acid concentration, we used
We attempted to describe the experimental dimeꢀ
data on the partial pressures of hydrogen chloride over thyl ether evolution rate data as a function of the
hydrochloric acid [8] and also on the activity of hydroꢀ methanol concentration and of the partial pressure of
gen chloride in its solutions [9]. Since measurement of hydrogen chloride over hydrochloric acid in terms of
partial pressures over solutions is one of the methods the different equations
for finding the activity of solutes [9], the experimental
−
1
w = k C
P
,
1
1
CH OH HCl
3
results can satisfactorily be described in terms of both
partial pressures and activities.
The data obtained agree well with one of the main
concepts of catalysis science, according to which
medium strength binding, not strong binding (such as
strong adsorption on a heterogeneous catalyst), is
optimal for a catalytic process. In our case, hydrogen
2
−1
w = k C
P
,
,
.
2
2
CH3OH HCl
2
−2
w = k C P
3 CH3OH HCl
3
−
2
w = k C P
3
4 CH OH HCl
4
It turned out that these data are best described by
chloride strongly bound to water does not contribute the first equation (maximum deviations of
to the partial pressure of HCl over hydrochloric acid
±
40%):
−
1
and, at the same time, does no react with methanol.
Weakly bound HCl participates in both processes.
Table 1 lists the rate constants of liquidꢀphase nonꢀ
catalytic methanol hydrochlorination calculated from
the dependences of the methyl chloride formation rate
on the methanol concentration and on the partial
pressure of hydrogen chloride over hydrochloric acid:
w(
= k(
OCCH3OHP .
CH3 2
HCl
CH3 2
)
O
)
The activation energy of dimethyl ether formation
is 8 kcal/mol (33 kJ/mol), and the preexponential facꢀ
tor is 2.3 atm/h. Thus, the equation for calculation of
w(
has the following form:
)
CH3 2
O
wCH3Cl = kCH3ClCCH3OHPHCl
.
33000
RT
−1
HCl
−1 −1
w(CH3)2O = 2.3exp −
CCH3OH
P
mol l h .
(
)
The average values of the rate constant kCH3Cl at 70, 80,
–
1
–1
From the data obtained, we infer that an increase in
9
0, and 100
respectively. Data processing in the ln
nates leads to an activation energy of 27 kcal/mol
113 kJ/mol) for liquidꢀphase noncatalytic methanol
hydrochlorination. This value is close to the earlier
reported value [1]. The preexponential factor is 1.1
°
С
are 0.696, 2.13, 6.66, and 15.8 h atm ,
the rate of methyl chloride synthesis is favored to the
greatest extent by an increase in the hydrochloric acid
concentration. An increase in pressure also accelerates
the process by raising the acid concentration at a fixed
temperature. The reaction temperature also exerts a
significant effect on the reaction rate. Our experimenꢀ
tal results make it possible to perform necessary calcuꢀ
lations for designing an industrial synthesis unit.
k
–1/ coordiꢀ
Т
(
×
17
–1 –1
10
atm h .
Thus, the rate of liquidꢀphase noncatalytic methaꢀ
nol hydrochlorination in hydrochloric acid is
described by the equation
INDUSTRIAL IMPLEMENTATION
OF THE PROCESS
1
7
wCH3Cl = 1.1×10
A scheme of the industrial setup for methyl chloꢀ
ride synthesis from methanol and hydrochloric acid
with a production capacity of about 4000 t/yr is preꢀ
sented in the figure. Concentrated hydrochloric acid
1
13000
RT
−1 −1
×
exp −
CCH3OHPHCl mol l h .
)
(
An analysis of the dependences of the apparent rate and methanol are fed to the first reactor stage 11, from
which they flow via an overflow pipe to the second
constant of dimethyl ether evolution (w(CH3)2O) on the
stage 12. The reacted mixture is directed to column
where unreacted methanol and HCl are stripped off
and are then directed to condenser . The reaction gas
from reactors 11 and 12 comes to condenser as well.
The hydrochloric acid condensed in condenser 12 with
3,
methanol and hydrogen chloride concentrations and
on the partial pressures of HCl or the activity of soluꢀ
tion is rather difficult to carry out. The matter is that
2
2
three processes contribute to the value of w(
O:
CH3 2
)
dimethyl ether formation from methanol, the conꢀ dissolved methanol returns to reactor 11. For preparaꢀ
sumption of dimethyl ether through its hydrochlorinaꢀ tion of a commercialꢀgrade product, methyl chloride
tion into methyl chloride, and dimethyl ether carryꢀ is subjected to neutralization, drying, and purification.
over from the reactor. The overall process is described The hydrochloric acid azeotrope in apparatus
4 is
KINETICS AND CATALYSIS Vol. 52
No. 5
2011