Results of kinetics studies and their use for one of
the most significant RSPs are illustrating considered approach to raising
ecological efficiency a chemist-technological objects.
1.4
- dioxane syntheses by dehydration of diethylene glycol (DEG)
is one of the most representative objects for demonstrations of bubble
RSP influence on chemical process. On its mechanism this reaction is similar
reactions an alcohol dehydration and can be realized by warming diethylene
glycol (DEG) up 130 to 170 °C in presence of different catalysts, for instance,
strong mineral acids.
When
these reactions are realized both in laboratory and in industrial conditions
significant asphaltization is observed because of main reaction product 1.4 -
dioxane polymerization. Studies have shown that diethylene glycol at conditions
of reactions is not polymerizated. Asphaltization brings to essential reducing a
target product (before 30% in industrial conditions). It's necessary to unload
the resin from the reactor occasionally and to burn it on special operating
platforms that greatly pollutes a surrounding because of black smoke formation,
containing not only smut and carbon compounds, as well as sulfur-containing
matters (resin is kept considerable proportion of perfecting catalyst - a
sulfuric acid).
For
increase of 1.4 - dioxane manufacture cleanliness the above-stated algorithm was
used. The system analysis has shown, that ecologization of this object by
improvement of quality of burning of the resin results in significant
complication and rise in price of manufacture. It was not possible to utilize
the resin with the rest of perfecting catalyst - a sulfuric acid.
The
maximal success expected the experts at a molecular stage. It was necessary to
regulate the speeds of two
parallel-proceeding reactions - dehydration of diethylene glycol (DEG)
and 1.4 - dioxane polymerization. The influence of a sulfuric acid as catalyst
on both processes is well known. It was necessary to find conditions of the
first reaction acceleration and to absence of the second process. Only possible
variant has appeared transformation homogeneous liquid process, where both
reactions went in a liquid phase, to bubble heterogeneous process, at which the
basic reaction, as well as in initial process, was carried out in a liquid
phase, but the products of reaction were removed in a gas phase (in bubbles) at
the moment of their formation by including in liquid of the gas desorptive agent
and by imposing of high-speed bubble process. As the catalyst - sulfuric acid is
practically non- volatile component of system, in gas phase there were no
conditions for 1.4 - dioxane
polymerization process.
In
connection with the initial product
in conditions of reaction is practically nonvolatile ones, the considered
reaction represents not only practical interest, but also it is interesting by
way of definition of influence of speed of reaction products removal on kinetics
of the combined RSP. In the quality the
desorptive agent we used the nitrogen, and also benzol, forming binary
azeotropic solutions with products of reaction and three components azeotropic
solution: benzol – 1.4-dioxane - water.
The
kinetics research in capacitor laboratory reactor with both mixer and bubblier
for desorption agent submission was carried out at constant sulfuric acid
concentration (catalyst) equal 5 % from DEG weight, in an interval of
temperatures 130-1750C. For the not combined process (without
desorption agent submission) in periodic action reactor are received kinetics
dependencies, which processing testifies to the first reaction order and gives
meaning of a reaction rate constant: K0
== 3,2 . 10-3 min-1 (at temperature 1500C).
The
researches for a quantitative estimation of influence of nitrogen or benzol
input, bubbled under a DEG layer, were
carried out in RIM. Is established, that the benzol vapour
input as desorption agent
increases in 1,5-6 times a speed of reaction of 1,4-dioxane synthesis. The
dependence of an observable constant of speed of chemical reaction on the vapour
benzol rate and
results of laboratory researches can be presented as:
K0 = (1,05 + 0,65 . 105Gd)
exp (6,9 - 1093,3/T),
(19)
where
Gd- the desorption agent – benzol rate, kg/sec (submitted in 100 ml volume
reactor);
T
- temperature.
Heterogeneous
factor in a considered case depends from Gd as follows:
c = 1,0 + 0,62 .
105 Gd
( 20)
It
is necessary to notice, that last dependencies keep linear character not in all
range of change Gd, and at rather high meanings Gd it is necessary to
expect reduction K0 and c.
The
research of process in periodic action reactor is complicated in connection with
necessity of creation of rather intensive mode of mixing and products removal
from a zone of chemical reaction. Besides on a products desorption measure the
concentration of the catalyst in system grows, that results in resinification
increase. Therefore kinetic of process researches was carried out also with
laboratory installation of continuous action including temperature-controlled
reactor of the flowing type executed as a bubble glass column in height 0,15 m
and diameter 0,05 m with a mechanical mixing
and a fixed overflow level.
The
initial mix consisting from DEG and the catalyst H2SO4,
continuously acted in reactor on screen
plate and was kept in it by an ascending flow of the desorption agent -
nitrogen. The reacted mass through overflow was removed in the measuring vessel.
DSc., Prof. William Zadorsky,
Academician of the Ukrainian Ecological Academy,
Ukrainian State University of Chemical Engineering.
Pridneprovie Cleaner Production Center
Tel: +(380) 567 440210
Tel/fax: +(380) 562 470813
http://www.crosswinds.net/~usuce/index.html
http://www.incubator.f2s.com
http://zadorsky.com