CA2315505A1

CA2315505A1 - Process for the production of carboxymethylcellulose

Info

Publication number: CA2315505A1
Application number: CA002315505A
Authority: CA
Inventors: Heiko Thielking; Wolfgang Koch; Klaus Nachtkamp; Bernd Ondruschka; Matthias Nuchter; Ute Heinze; Dieter Klemm
Original assignee: FRIEDRICH-SCHILLER-UNIVERSITAT JENA; Wolff Walsrode AG
Current assignee: FRIEDRICH-SCHILLER-UNIVERSITAT JENA; Dow Produktions und Vertriebs GmbH and Co OHG
Priority date: 1999-08-13
Filing date: 2000-08-09
Publication date: 2001-02-13
Also published as: DE19938501A1; JP2001048901A; NO20004037L; EP1083182B1; NO20004037D0; DE50001841D1; BR0003502B1; ATE238350T1; MXPA00007822A; KR20010050064A; EP1083182A1; KR100650097B1; BR0003502A

Abstract

A process is described for the production of carboxymethylcellulose in which a) cellulose is activated and b) is reacted with a carboxymethylation reagent, reaction step b) being carried out in an electromagnetic field having a frequency in the range from 10 MHz to 23 GHz.

Description

WW 5534- Foreign Countries Pt/by/NT

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-WW 5534- Foreign Countries 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.

WW SS34- Foreign Countries 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 WW 5534- Foreign Countries 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.

WW 5534- Foreign Countries -S-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-~

WW 5534- Foreign Countries 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.

WW 5534- Foreign Countries -7_ 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:

WW 5534- Foreign Countries _g_ 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).

WW 5534- Foreign Countries 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

Claims

1. Process for the production of carboxymethylcellulose 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.

2. Process according to claim 1, characterized in that reaction step b) is carried out in an electromagnetic field having a frequency of from 2 to 3 GHz.

3. Process according to claim 1, characterized in that a temperature range of 20°C to 150°C is employed in reaction step b).

4. Process according to claim 1, characterized in that reaction step b) is carried out in the electromagnetic field for a reaction time of 1 to 120 minutes.

5. Process according to claim 1, characterized in that the process is carried out discontinuously.

6. Process according to claim 1, characterized in that the process is carried out continuously.

7. Process according to claim 1, characterized in that the carboxymethyl-cellulose is isolated after the reaction and is freed from the salts and by-products.