1
64
MAKHIN et al.
10 , L mol s–1
6
–1
equipped with a stirrer, bubbler, reflux condenser,
k
×
thermocouple, and electric heater. The rotational
speed of the stirrer was 1500 rpm, which ensured the
absence of reactant concentration and temperature
gradients throughout the reaction volume. The temꢀ
perature in the reactor was measured using the therꢀ
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
γ
= 0.5
5
mocouple with an accuracy of 0.1°С. Methanol (or a
±
methanol–water mixture) was pumped continuously
into the reactor at a rate of 15–20 g/h. The concentraꢀ
tion of water in methanol was varied between 5 and
4
3
2
3
5 wt %. Hydrogen chloride was continuously fed into
the reactor through the bubbler at a rate of 16–20 g/h.
The hydrogen chloride flow rate was controlled using
a system consisting of a rheometer and a manostat.
The liquid reaction mixture was removed from the
reactor when it reached a certain level using a side outꢀ
let with a hydraulic seal. Excess hydrogen chloride was
adsorbed in a water column, and the methyl chloride
formation rate was measured with a soap bubble flowꢀ
meter. The results of experiments in which the temꢀ
1
0
0.4
0.8
γ
1.2
1.6
Fig. 2. Methyl chloride formation rate constant as a funcꢀ
tion of the degree of hydration of hydrogen chloride at
(1) 40, (2) 50, (3) 55, (4) 60, and (5) 65°C.
perature variations did not exceed
in mass balance was no larger than
by interacting with the solvent and acquiring solvate into account.
shells. The released thermal energy heats the solution.
Organic products were analyzed by gas–liquid
When hydrogen chloride is dissolved in water, the chromatography using a Tsvetꢀ800 chromatograph
dipoles of water polarize the polar H–Cl bond to a still (Tsvet, Russia, 3 m
3 mm column, PEGꢀ40 phase on
greater extent and then break the molecule completely Chromaton NꢀAW) with a flame ionization detector.
into ions, forming a hydration shell around them.
The hydrochloric acid content was determined by
±
1
°
C
and the error
±
5% were taken
×
The smaller the size of a molecule being hydrated titration in the presence of an indicator.
and the higher its polarity, the stronger its bond with
the hydration shell, i.e., in other words, the higher the
energy of hydration. Thus, the energy of hydration of
RESULTS AND DISCUSSION
the chloride anion is –347 kJ/mol [14], which is comꢀ
parable to the energy of a chemical bond.
In order to describe the rate of methanol hydroꢀ
chlorination, the coefficient , which characterizes the
γ
degree of hydration of the chloride anion and is the
ratio of the water concentration to the hydrogen chloꢀ
ride concentration, was introduced into the kinetic
equation. This approach has already proved applicable
to the study of the glycerol hydrochlorination kinetics
It is because of the formation of hydration shells
that it is necessary to consider the solvent as an agent
participating directly in the reaction. The higher the
concentration of water in the reaction mixture, the
larger the number of its molecules that interact with
the chloride anion and the stronger the hydration shell
of the latter, and, consequently, the higher the energy
of activation and the lower the rate of the reaction.
Our experiments on the hydrochlorination of polyꢀ
[
13], makeing it possible to adequately describe the
rates of the reactions proceeding in the system.
The kinetics of the liquidꢀphase hydrochlorination
of methanol was studied at 40–65
atomic alcohols, such as glycerol [13], confirmed this centrations of 0.5 to 13 mol/L, so the coefficient
°
С
and water conꢀ
varꢀ
assumption and made it possible to determine the ied from 0.5 to 1.5. The methyl chloride formation rate
dependence of the rate of the reaction on the water constants were calculated, and their dependence on
Fig. 2) was determined from Eq. (1) using the calcuꢀ
γ
γ
(
concentration. It is likely that a similar dependence
will be observed in the hydrochlorination of many lated values of the methyl chloride formation rate and
alcohols of various structures.
The purpose of this work was to determine the
kinetics of the liquidꢀphase noncatalytic hydrochloriꢀ
data on the concentrations of the reactants in the reacꢀ
tion mixture.
This dependence makes it possible to determine
nation of methanol and to confirm the conclusion the rate constant of the reaction at any temperature
about the influence of the degree of solvation of hydroꢀ and any value of
γ
. When
stants obey the Arrhenius equation. A typical example
for = 0.5 is presented in Fig. 3.
The mathematical processing of the data presented
in Fig. 3 made it possible to calculate the activation
γ
is constant, the rate conꢀ
gen chloride on the rate of the reaction.
γ
EXPERIMENTAL
Methanol hydrochlorination was performed in a energy and preexponential factor. The rate equation
continuous mode using a 45ꢀmL glass reactor for the methyl chloride formation reaction at
γ
= 0.5 is
KINETICS AND CATALYSIS Vol. 55
No. 2
2014