Kinetic relationships in synthesis of dimethoxymethane

Article abstract of DOI:10.1007/s11167-005-0206-2

The kinetics of formation of dimethoxymethane by acetalization of formaldehyde with methanol, catalyzed by silicotungstic heteropoly acid, were studied.

Full text of DOI:10.1007/s11167-005-0206-2

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Russian Journal of Applied Chemistry, Vol. 77, No. 12, 2004, pp. 1994 1996. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 12, 2004,
pp. 2018 2020.
Original Russian Text Copyright
2004 by Danov, Kolesnikov, Logutov.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Kinetic Relationships in Synthesis of Dimethoxymethane
S. M. Danov, V. A. Kolesnikov, and I. V. Logutov
Dzerzhinsk Branch, Nizhni Novgorod State Technical University, Dzerzhinsk, Nizhni Novgorod oblast, Russia
Received July 15, 2004
Abstract The kinetics of formation of dimethoxymethane by acetalization of formaldehyde with methanol,
catalyzed by silicotungstic heteropoly acid, were studied.
Dimethoxymethane (DMM) is a colorless solvent
with a low boiling point, low viscosity, and an excel-
lent dissolving power. It finds application in organic
and pharmaceutical syntheses, paint and varnish indus-
try, as a washing solvent, as component of cleaning and
degreasing solvents, in production of adhesives and
plastics, as a fuel additive, and as a component of in
technical aerosols and in household chemistry articles.
EXPERIMENTAL
In experiments, we used a water-methanol solution
of formalin containing 37 wt % FA; the amount of
FA was determined by the sodium sulfate technique,
and that of M, by gas chromatography. We used M
purified by distillation; gas chromatographic analysis
showed that it contained residual water only. Analyt-
ically pure silicotungstic heteroply acid was dried by
calcination at 250 C for 3 h.
The starting reagents for preparation of DMM are
formaldehyde (FA) and methanol (M). These are read-
ily accessible and cheap chemicals, which, combined
with their acceptable production costs, affords a cheap
commercial DMM. The overall reaction of DMM
formation can be represented schematically as
Cat.
The kinetic relationships were experimentally stud-
ied in a glass reactor (V = 100 ml) equipped with
a water jacket, two ground-glass joints connecting
the reactor with a reflux condenser and a thermometer,
and a sampler. To exclude hot spots, the reaction
mixture was stirred with a magnetic stirrer. A constant
temperature in the reactor was maintained by water
circulating between the thermostat and the reactor
jacket, with the temperature monitored within the lat-
ter. A water thermostat connected to the reactor case
was operated in the forced-circulation mode.
2CH3OH + HCHO
CH2(OCH3)2 + H2O.
Since recently, commercial plants have been using
as catalysts ion-exchange resins, which afford DMM
in high yields but degrade during the reaction into
small particles clogging the column, lose their activity
under exploitation, and need either regeneration or
replacement [1]. Also, inorganic acids such as sulfuric
acid have been tested as catalysts, but they cause
many nuisances like corrosion activity, environmental
pollution, the need for neutralization of wastewater,
and irreversible loss of the acid [2].
The reaction mixture was prepared by mixing M,
FA, and water to achieve the desired ratio of the re-
actants, whereupon the required amount of the result-
ing mixture was sampled, weighed on an analytical
balance, and placed in the reactor. When the desired
temperature was established in the reactor, the required
amount of STA was added, from which moment the
time of the process was measured. Samples (0.2 ml)
were taken at regular intervals; a sample was added to
5 ml of aqueous NaOH of the concentration required
for neutralizing the acid contained in the taken volume
of the reaction mixture, and the mixture contained in
the test tube was thoroughly stirred.
We believe that tungstic heteropoly acids and, in
particular, silicotungstic heteropoly acid H4SiW12O40
(STA), are suitable as catalysts. The trials on labora-
tory batch and continuous-operation units showed that
tungstic heteropoly acids can be successfully applied
as catalysts in synthesis of DMM.
In the context of development of the optimal pro-
cedure for isolation and purification of DMM, it is
necessary to analyze the kinetic aspects of its syn-
thesis, which constituted the aim of this study.
All the samples were analyzed chromatographical-
ly on a Tsvet 500 gas chromatograph with a flame-
1070-4272/04/7712-1994 2004 MAIK Nauka/Interperiodica

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KINETIC RELATIONSHIPS IN SYNTHESIS OF DIMETHOXYMETHANE
1995
ionization detector and a 2000 3 mm steel column
packed with Polysorb (0.16 0.2 mm grains). The car-
rier gas was nitrogen; the flow rate of nitrogen and
1
hydrogen was 30, and that of air, 300 cm3 min .
The temperatures of the column, detector, and vapor-
izer were 150 C. The relative error of analysis
was 3%.
As mentioned above, DMM is formed by a two-
stage reaction between M and FA:
k1
HCHO + CH3OH
HOCH2OCH3,
(1)
(2)
k
1
Fig. 1. Kinetic curves of DMM formation at (1) 303,
(2) 308.3, (3) 313.3, and (4) 318.3 K. M : FA molar ratio
2 : 1. (c ) DMM concentration, and ( ) time. (Solid
k1
HOCH2OCH3 + CH3OH
CH2(OCH3)2 + H2O.
k
2
DMM
line) Calculated values and (black squares) experimental
values at c = 0.1298 M.
The rate of formation of hemiacetal (HA) is very
high [3], with the equilibrium strongly shifted toward
its formation [4]. Since M was taken in excess in all
the experiments, we assumed that the whole amount
of FA was in the form of HA. Thus, we developed
a kinetic model taking into account reaction (2) only.
We described the DMM formation rate of by the dif-
ferential equation
cat
dcDMM/d = k2 cPA cM
k 2 cDMM cH O,
2
where k2 and k are the effective rate constants,
2
1
l min 1 mol ; cPA, cM, cDMM, and cH O, concentra-
2
tions (M) of PA, M, DMM, and water, respectively.
Fig. 2. Variation of the effective rate constants (1) k and
2
This equation was solved by the Runge-Kutta
method. The rate constants were calculated by the
least-squares method. Figure 1 shows the typical ki-
netic curves of DMM formation.
(2) k , of DMM formation with the catalyst concentration
2
c
at 313.3 K.
cat
The temperature dependence of the rate constant
is described by the Arrhenius equation (see table),
and it was used for determining the expressions for
The dependence of the effective rate constants k2
and k on the catalyst concentration was described
by the2 equation
1
k2 = f(T) and k = f(T) (activation energy, J mol ;
temperature, K):2
k2 = k2 ccnat
,
k
= k 2 ccmat
,
2
88 800/RT
k2 = 1.478 1013e
,
84 690/RT
2
where k2 and k 2 are true rate constants, l2 min 1 mol ;
ccat, catalyst concentration, M; and n and m, reaction
orders with respect to the catalyst.
k
2 = 6.798 1011
e
.
Rate constants k2 and k at different temperatures
2
Figure 2 shows that the logarithm of the effective
rate constants linearly varies with the logarithm of
the catalyst concentration. The orders with respect to
k2
k
2
T, K
2
l2 min 1 mol
the catalyst are identical for the constants k2 and k ,
2
namely, 1.43.
303
0.007421
0.01318
0.02226
0.03897
0.06679
0.001855
0.002784
0.005566
0.008165
0.01484
308.3
313.3
318.3
323.1
The constants k2 and k were calculated by the
equations
2
1.43
1.43
k2 = k2 /c
,
k
= k 2 /c
.
cat
cat
2
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1996
DANOV et al.
These dependences suggest that the rate constants
k2 and k are weakly dependent both on the initial
water con2centration in the system and, evidently, on
the composition of the reaction mixture as a whole.
CONCLUSION
A kinetic model was developed for synthesis of
dimethoxymethane from methanol and formalde-
hyde, catalyzed by silicotungstic heteropoly acid
H4SiW12O40. The dependences of the rate constants
of the process on the temperature and composition
of the medium were obtained.
Fig. 3. Variation of the rate constants (1) k and (2) k
,
2
2
of DMM formation with the initial water concentration
REFERENCES
0
c
at 313.3 K.
H O
2
1. Chinese Patent 688041.
2. UK Patent 1379444.
3. Walker, J.F., Formaldehyde, 2-nd ed., New York:
American Chem. Soc., 1953. Translated under the title
Formal’degid, Moscow: Goskhimizdat, 1957.
Using the dependences of k2 and k (T = 313.3 K)
on the initial concentration of water2 in the system
(Fig. 3), we derived the expressions
k2 = 0.02493
0.000161c0H O
,
2
4. Zhenghun Shan, Yanru Wang, Shouchang Qiu, et al.,
Fluid Phase Equil., 1995, vol. 111, no. 1, pp. 113 126.
k
= 0.0069
0.00008454c0H O
.
2
2
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 12 2004