Note: Descriptions are shown in the official language in which they were submitted.
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Process for the production of carboxymethylcellulose
The invention relates to a process for the production of
carboxymethylcellulose in
which the reaction is carried out in a discontinuous or continuous reaction
procedure
with exposure to a high-frequency field.
Refinement products of cellulose, such as carboxymethylcelluloses (referred to
as
CMCs below) are versatilely used substances from renewable raw materials that
are
increasingly used in different sectors because of their properties. Thus,
substances,
such as CMCs, play an ever growing role as intermediates and auxiliary
substances
in biotechnology, pharmacy, the paper and foodstuffs industries, cosmetics,
medical
engineering and chromatography. An important field of application for CMCs as
the
most important anionic cellulose ether is its use as drilling aid in petroleum
production and also generally in drilling technology.
Normally, the carboxymethylcelluloses discussed here are produced by heating a
preactivated cellulose with chloroacetic acid or its sodium salt in the
presence of
aqueous alkali hydroxide solution and a low alcohol. In addition, there also
exists a
number of further processes that are to be regarded as modifications of the
basic
syntheses, but do not play any economic role (c~ "Comprehensive Cellulose
Chemistry", D. Klemm, B. Philipp, Th. Heinze, U. Heinze and W. Wagenknecht,
Wiley-VCH, Weinheim, 1998).
During carboxymethylation, mixtures having various degrees of substitution at
the
individual glucose units (referred to below as AGU = anhydroglucose unit) are
produced at temperatures of 50°C to 150°C with long reaction
times (1 to 10 h).
In addition to a relatively high energy demand, the discontinuous processes
require a
high process-engineering and time expenditure. The reaction and the reaction
product
can barely be influenced by the long reaction times and the fornlation of by-
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products (glycolates) is promoted, as a result of which additional
purification steps
are necessary that further increase the process expenditure.
The object of the invention is to develop a process for the production of
carboxymethylcelluloses that make possible production with short reaction
times and
a low accumulation of by-products.
It has now been found that, if the carboxymethylation reaction is carried out
in an
electromagnetic field, products are obtained with short reaction times and
with a low
accumulation of by-products.
The invention therefore provides a process for the production of carboxymethyl-
cellulose in which
a) cellulose is activated and
b) reacted with a carboxymethylation reagent,
characterized in that reaction step b) is carried out in an electromagnetic
field having
a frequency in the range from 10 MHz to 23 GHz.
According to the invention, the reaction of the activated cellulose with a
carboxymethylation reagent known per se is carried out under the influence of
an
electromagnetic field having a frequency in the range from 10 MHz to 23 GHz,
and
preferably in the range from 2 to 3 GHz, particularly preferably 2.45 GHz. The
duration of the exposure to the electromagnetic field is, in this process, in
the range
from 1 minute to 120 minutes, preferably between 1 minute and 60 minutes.
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Surprisingly, it was found that cellulose can be reacted under the influence
of said
high-frequency field to form carboxymethylcelluloses having various DS values
in a
substantially shorter time without the reaction product being degraded by the
electromagnetic radiation in the specified frequency range, i.e. without
S depolymerization of the cellulose being detectable. On the contrary, the DS
values of
the carboxymethylcelluloses can be influenced and, consequently, varied
through the
choice of the very efficient energy input, which drastically reduces the
energy
demand, and through suitable selection of the reaction conditions, such as,
for
example, the magnitude of said energy input, pressure and reaction
temperature.
The reaction can be carried out in such a way that the reaction mixture is
exposed to
the high-frequency radiation in the equipment at atmospheric pressure or under
pressure with control of energy input, pressure and temperature.
Carrying out the process according to the invention unexpectedly resulted in
short
reaction times and, consequently, reaction products with a low accumulation of
undesirable by-products so that the carboxymethylcelluloses already produced
immediately in the production process with the required purity do not have to
be
subjected to subsequent purification steps or only have to be subjected to
subsequent
purification steps that are insignificant for the process expenditure.
At the same time both a batch process and a continuous process can be
employed.
The reaction steps are carned out in a mixture of an organic solvent and
water.
2S Alcohols, ethers or ketones, for example, can be used as organic solvents.
In this
connection, suitable alcohols are low C~-C4-alcohols or their mixtures, in
particular
isopropanol. Particularly preferred is an alcohol/water mixture containing S-
20 wt.%
of water.
The cellulose is activated for reaction step b) by mixing with, for example,
aqueous
alkali solution in reaction step a). Aqueous potassium hydroxide solution or
sodium
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hydroxide solution, in particular 10 to 70% aqueous sodium hydroxide solution,
preferably 15% aqueous sodium hydroxide solution or solid sodium hydroxide is
used. The alkalization is normally earned out for 1 to 150 minutes, in
particular for
100 minutes.
Normally, chloroacetic acid or its sodium salt is used as carboxymethylation
reagent
(referred to as CMR below). Preferred is 80% chloroacetic acid.
Reaction step b) is normally earned out at an elevated temperature of 20 to
150°C, in
particular 50 to 100°C.
According to the invention, an electromagnetic high-frequency field having a
frequency in the range from 10 MHz to 23 GHz, preferably 2 to 3 GHz, in
particular
2.45 GHz is used for the induction in reaction step b). The irradiation time
is
normally in the range from 1 to 120, in particular, 1 to 60 minutes.
The electromagnetic field is produced in a manner known per se by a magnetron.
A
commercially available microwave oven can be used for carrying out the batch
process.
In the case of the continuous procedure, it is also possible, inter alia, to
expose a
continuous-flow reactor (for example, Cont Flow° MLS Lautkirch) to the
influence
of the electromagnetic field.
The following examples are intended to explain the subject matter of the
invention in
more detail.
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Examples
Example 1
S A suspension of 1 g of pine sulfite pulp in 30 ml of isopropanol is
preactivated with
aqueous sodium hydroxide solution while stirring. Mixing is carned out at room
temperature for one hour and the carboxymethylation reagent is then added. The
reaction mixture is irradiated in a pressure vessel with a power of 500 W
(2.45 GHz)
under the specified conditions while stirring. The reaction mixture is worked
up by
the standard methods for isolating carboxymethylcellulose. Some examples of
reactions under various conditions are cited in Table l .
Table 1:
Synthesis of CMCs in a high-frequency field under various conditions
Molar ratio Temperature Time DS~ Viscosity
AGUa~:CMRb~:NaOH[C] [min] [mPas]
1 : 2d~ : 2 70 30 1.2 1580
1 : 3d~ : 2 70 60 1.3 456
1 : 2~ : 4 70 30 0.85 164
a~ AGU = anhydroglucose unit
b~ CMR = carboxymethylation reagent
'~ DS = degree of substitution
d~ Sodium chloroacetate
e~ Chloroacetic acid
~ Viscosity of a 2% aqueous solution, D = 2.SS s-~
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Example 2
A mixture of 15 g of pine sulfite pulp and 400 ml of isopropanol is
preactivated for
one hour with 40 ml of a 15% aqueous sodium hydroxide solution. 18 g of sodium
monochloroacetate is added and the reaction mixture is irradiated in a
pressure vessel
for 20 min with a power of 500 W (2.45 GHz) at not more than 55°C.
After cooling
and working-up, carboxymethylcellulose is obtained that has a DS of 1.1.
Example 3
A suspension of 1 g of pine sulfite pulp in 30 ml isopropanol is preactivated
while
stirring with 2.66 ml of a 15% aqueous sodium hydroxide solution. Mixing is
carried
out for one hour at room temperature and then 1.2 g of sodium
monochloroacetate is
added. The mixture is irradiated in a reactor with a power of 500 W at a
frequency of
13.65 MHz at not more than 70°C while stirring. The reaction mixture is
worked up
by the standard methods for isolating carboxymethylcellulose. DS = 1.2.
Example 4
A suspension of 1 g of carboxymethylcellulose (DS = 1.3) in 30 ml of
isopropanol is
preactivated with 2.66 ml of a 15% aqueous sodium hydroxide solution while
stirring. Mixing is carried out for one hour at room temperature and 1.2 g of
sodium
monochloroacetate is then added. The mixture is irradiated in a reactor with a
power
of 500 W at a frequency of 2.45 GHz at not more than 70°C while
stirnng. The
reaction mixture is worked up by the standard methods for isolating
carboxymethylcellulose. DS = 2.1.
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Example 5
A preactivated mixture of 100 g of pearl cellulose, 3000 ml of isopropanol,
270 ml of
a 15% aqueous sodium hydroxide solution and 120 g of sodium monochloroacetate
is
pumped through a continuous flow reactor at a maximum temperature of
100°C, a
pressure of 20 bar, a power of 350 W (2.45 GHz) and at a mean dwell time of
about
min. The reaction solution is quenched at the end of the reactor, cooled to
room
temperature and worked up as normally. The reaction is quantitative. The
carboxy-
methylcellulose produced has a DS of 1.3.
Example 6
5.2 g of sodium hydroxide are added to a suspension of 10 g of pine sulfite
pulp in
174 ml of isopropanol and 26 ml of water and the mixture is stirred for 30 min
at
room temperature. 9.9 g of monochloroacetic acid are added and the reaction
mixture
is irradiated for 20 min with a power of 500 W (2.45 GHz) at 55°C.
After cooling
and standard working-up, carboxymethylcellulose is obtained that has a DS of
0.64
and a viscosity of rl2.sss' - 1880 [mPas].
Example 7
0.6 g of solid sodium hydroxide is added to a suspension of 1 g of pulp in 16
g of
isopropanol, 1 g of methanol and 1.7 g of water and alkalization is carried
out for 80
min at room temperature. After adding 0.8 g of 75% chloroacetic acid, homo-
genization was carried out for approximately one minute and reaction was then
earned out for four to eight minutes at a power of 240-500 watt in a standard
domestic microwave. After standard working-up, the products shown in Table 2
were
obtained:
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Example 8
10,8 g of sodium hydroxide and 31,45 g of sodium monochloroacetate are added
to a
suspension of 25,9 g of cellulose of 450 ml isopropanol, 31 ml methanol and 36
ml
water. After inertization, the mixture is stirred for 30 min at room
temperature. The
reaction mixture is heated to 80°C by microwave irradiation (2,45 GHz)
and etheri-
fied for approx. 18 min at 80°C. After cooling and standard working-up
carboxy-
methylcellulose is obtained with DS = 1,13 and viscosity r12,55s-1 = 17469mPas
(2%
aqueous solution).
Example 9
8,4 g of sodium hydroxide are added to a suspension of 25,2 g of cellulose in
490 ml
isopropanol, 34 ml methanol and 39 ml water. After interization, the mixture
is
stirred for 30 min at room temperature. After addition of 25 g of sodium mono-
chloroacetate, the reaction mixture is heated to 80°C by microwave
irradiation (2,45
GHz) and etherified for approx. 22 min at 80°C. After cooling and
standard working-
up carboxymethylcellulose is obtained with DS = 0,96 and viscosity q2 55s-1 -
6079 mPas (2% aqueous solution).
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Table 2:
Synthesis of CMCs in a high-frequency field under various conditions
Etherification Power DSa~ Viscosityb~
time [watt] [-] [mPas]
[min]
4 500 0.53 1730
8 240 0.73 3066
2x4 500 0.71 1406
a~ DS = degree of substitution
b~ Viscosity of a 2% aqueous solution, D = 2.55 s-1
