CA2315507A1 - Process for the production of cellulose derivatives - Google Patents

Abstract

A process is described for the production of cellulose derivatives in which a) cellulose is activated and b) is reacted with one or more reagents, optionally in the presence of a suspending agent, reaction step b) being carried out in an electromagnetic field having a frequency in the range from 10 MHz to 23 GHz.

Description

Process for the production of cellulose derivatives The invention relates to a process for the production of cellulose derivatives 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 are versatilely used substances from renewable raw materials that are increasingly used in different sectors because of their properties.
0 Thus, cellulose derivatives play an ever growing role as intermediates and auxiliary substances in biotechnology, pharmacy, the building, paper and foodstuffs industries, cosmetics, medical engineering and chromatography.
Normally, the cellulose derivatives discussed here are produced by heating a 5 preactivated cellulose with the required reagents (for example, chloroacetic acid or its sodium salt, methylchloride or propylchloride, vinylsulfonic acid or chloroethane-sulfonic acid) in the presence of aqueous alkali hydroxide solution and a suitable slurry medium (for example, a low alcohol). A review of the existing methods is to be found, for example, in "Comprehensive Cellulose Chemistry", D. Klemm, 0 B. Philipp, Th. Heinze, U. Heinze and W. Wagenknecht, Wiley-VCH, Weinheim, 1998. Not all the processes cited here have an economic significance.
Mixtures having various degrees of substitution on the individual glucose units (referred to below as AGU = anhydroglucose unit) are produced in the etherification 5 of cellulose at temperatures of 50°C to 150°C and with long reaction times ( 1-10 h).
In addition to relatively high energy demand, the discontinuous processes require a high process-engineering and also time expenditure. The reaction and the reaction product can barely be influenced by the long reaction times and the formation of by-0 products is promoted, as a result of which additional purification steps are necessary that increase the process expenditure further.

The object of the invention was to provide a process for the production of cellulose derivatives with which the reaction can be influenced with the purpose of influencing the reaction products and in which the process expenditure is reduced.
The invention therefore provides a process for the production of cellulose derivatives in which:
a) cellulose is activated and b) reacted with one or more reagents, optionally in the presence of a suspending agent, characterized in that reaction step b) is carried out in an electromagnetic field having 5 a frequency in the range 10 MHz to 23 GHz.
According to the invention, it was found that cellulose can be reacted under the influence of the high-frequency field in a short time to form cellulose derivatives having various substituents and various DS values.

It is surprising that cellulose can be converted under the influence of said high-frequency field into cellulose derivatives having various substituents and also 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 a 5 depolymerization of the cellulose being detectable. On the contrary, the DS
values and the substituents of the cellulose derivatives can be influenced and, consequently, varied through the choice of the very efficient energy input, which drastically reduces the energy demand, and through a suitable selection of reaction conditions, such as, for example, the magnitude of said energy input, pressure and temperature.

_ J
The reaction can be carned 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 resulted in unexpectedly short reaction times and, consequently, reaction products having a low accumulation of undesirable by-products so that the cellulose derivatives already produced immediately in the production process with the necessary purity are not subjected to subsequent purification steps or are subjected to subsequent purification steps only 0 insignificantly for the process expenditure.
At the same time, both a batch process and a continuous process can be employed.
The activation takes place by mixing with alkali solution in reaction step a).
Aqueous 5 potassium hydroxide solution or sodium hydroxide solution, in particular 10 to 70%
aqueous sodium hydroxide solution, preferably 50% aqueous hydroxide solution or solid sodium hydroxide, is used. The alkalization is normally carried out for 1 to 150 minutes, in particular for 100 minutes.
0 Reaction step b) is normally carried out at an elevated temperature of 20 to 150°C, in particular 50 to 100°C. Normally etherification reagents are used as reagents.
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 5 2.45 GHz is used for the induction in the reaction step b). The irradiation time is normally in the range from one to 120, in particular, one to 60 minutes.
The electromagnetic field can be produced in a manner known per se by a magnetron. A commercially available microwave oven can be used in carrying out 0 the batch process.

In a continuous process 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 process is suitable for the synthesis of nonionic, cationic and also anionic cellulose derivatives, such as cellulose ethers, cellulose esters and cellulose ether esters. Suitable cellulose ethers are carboxymethylcellulose (CMC) or alkyl-celluloses, for example methylcellulose (MC) or ethylcellulose (EC), hydroxyalkyl-celluloses, for example hydroxyethylcellulose (HEC) or hydroxypropylcellulose 0 (HPC) or their mixed ethers, such as alkylhydroxyalkylcellulose ethers, for example methylhydroxyethylcellulose or methylhydroxypropylcellulose (MHPC'.) butyl-hydroxyethylcellulose (BHEC), ethylhydroxyethylcellulose (EHEC), methyl-hydroxybutylcellulose (MHBC), alkylhydroxyalkylhydroxyalkylcellulose ethers, for example methylhydroxyethylhydroxypropylcellulose (MHEHPC), alkylcarboxy-5 alkylcellulose ethers, for example methylcarboxymethylcellulose (MCMC), alkyl-hydroxyalkylcarboxyalkylcellulose ethers, for example methylhydroxy-ethylcarboxy-methylcellulose (MHECMC) or methylhydroxypropylcarboxy-methylcellulose (MHPCMC), alkylhydroxyalkylhydroxyalkylcarboxyalkylcellulose ethers, for example methylhydroxyethylhydroxypropylcarboxymethylcellulose (MHEHPCMC) 0 or the respective sulfoalkyl-group-containing derivatives of the compounds mentioned, for example sulfoethylcellulose (SEC), methylsulfoethylcellulose (MSEC), ethylsulfoethylcellulose (ESEC), hydroxyethylsulfoethylcellulose (HESEC), hydroxypropylsulfoethylcellulose (HPSEC) or corresponding mixed forms, such as, for example, carboxymethylsulfoethylcellulose (CMSEC) or methyl-5 carboxymethylsulfoethylcellulose (MCMSEC). The process is also suitable for the production of hydrophobically modified forms of the cellulose ethers enumerated above, such as hexadecylcarboxymethylcellulose or hexadecylhydroxyethylcellulose or for cellulose esters, such as cellulose acetate (CA), cellulose lactate (CL), cellulose butyrate (CB), cellulose acetobutyrate (CAB), cellulose capronate (CCP).
Virtually 0 all mixed forms, for example hydroxypropylcellulose lactate (HPLC) are conceivable as cellulose ether esters.

The following examples are intended to explain the subject matter of the invention in greater detail.

Examples Example 1 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 carried 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 0 the standard methods for isolating carboxymethylcellulose. Some examples of reactions under various conditions are cited in Table 1.
Table 1:
5 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 ~~ AGU = anhydroglucose unit ''~ CMR = carboxymethylation reagent 0 ~~ DS = degree of substitution ~~ Sodium chloroacetate '~ Chloroacetic acid '~ Viscosity of a 2% aqueous solution, D = 2.55 s~' _7_ 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 I S% 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 5 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 0 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 stirring. The 5 reaction mixture is worked up by the standard methods for isolating carboxy-methylcellulose. DS = 2.1.
Example 5 0 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 _g_ 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 5 carboxymethylcellulose 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 0 174 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 r12_ss.S-' = 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 :0 min at room temperature. After adding 0.8 g of 75% chloroacetic acid, homogenization was carried out for approximately one minute and reaction was then carried 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:

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 ''~ DS = degree of substitution b~ Viscosity of a 2% aqueous solution, D = 2.55 s~' 0 Example 8 0.5 g of solid sodium hydroxide and corresponding amounts of vinylsulfonic acid (VSSNa, 30%) are added to a suspension of 1 g of pulp in 17 g of isopropanol and water and alkization is carried out for 80 min at room temperature.
Homogenization 5 is then carried out for approximately one minute and reaction is carried out for eight minutes at a power of 240 watt in a standard domestic microwave. After standard working-up, the products shown in Table 3 were obtained.

Table 3:
Synthesis of SEC in a high-frequency field under various conditions VSSNa Water DSa~ Viscosity ~
fig] fig] [-] [mPas]

1.1 0.81 0.21 2108 1.6 0.48 0.25 555 2.2 0.14 0.32 497 ~~DS = degree of substitution ''Viscosity of a 2% aqueous solution, D = 2.55 s' Example 9 (CMSEC) 4,8 g of sodium hydroxide and 12,7 g of the sodium salt of vinylsulfonic acid (30%
aqueous solution) are added to a suspension of 8,7 g of cellulose in 131 g isopropanol and 4,5 g water. After intertization, the mixture is stirred for 90 min at room tempera-ture. The reaction mixture is heated to 80°C by microwave irradiation (2,45 GHz) 5 and etherified for approx. 10 min at 80°C. After cooling to 50°C, 5,9 g of chloro-acetic acid (80% aqueous solution) are added and the mixture is reheated to 87°C and stirred for 10 min. After standard working-up (cooling, neutralization and puri-fication with aqueous methanol), carboxymethylsulfoethylcellulose is obtained with DS(CM) = 0,56, DS(SE) = 0,25 and viscosity V ~ = 1480 mPas (measued at '.0 D = 2,55 s-~) Example 10 (HESEC from SEC) 3 g of sodium hydroxide are added to a suspension of 30,8 g of sulfoethylcellulose '_5 (DS(SE) = 0,23) in 350 g of tert.-butanol and 36 ml water. After inertization, the mixture is stirred for 30 min at room temperature. After addition of 26,4 g of ethylene oxide, the reaction mixture is heated to 80 - 90°C by microwave irradiation (2,45 GHz, 500 W) and etherified for approx. 20 min at 80°C. After cooling and standard working-up, hydroxyethylsulfoethylcellulose is obtained with DS(SE) _ ~ 0,23, MS(HE) = 0,75 and viscosity V2 = 1003 mPas (measured at D = 2,55 s-~).
Example 11 (HEC) 9 g of sodium hydroxide are added to a suspension of 26 g of cellulose in 253 ml 0 tert.-butanol and 36 ml water.After interization, the mixture is stirred for 20 min at room temperature. After addition of 40 g of ethylene oxide, the mixture is heated to 110°C by microwave irradiation (2,45 GHz, 500 W) and etherified for approx.
25 min at 100°C. After cooling, neutralization and standard working-up, hydroxyeth ylcellulose is obtained with MS(HE) = 3,23 and viscosity V2 = 1032 mPas (measured S at D = 2,55 s-~).
Example 12 (HEC) 9 g of sodium hydroxide are added to a suspension of 26 g of cellulose in 350 ml '.0 tert.-butanol and 36 ml water. After inertization, the mixture is stirred for 20 min at room temperature. After addition of 40 g of ethylene oxide, the mixture is heated to 100°C by microwave irradiation (2,45 GHz, 500 W) and etherified for approx. 20 min at 100°C. After cooling, neutralization and standard working-up, hydroxyethyl cellulose is obtained with MS(HE) = 2,93 and viscosity V2 = 1133 mPas (measured :5 at D = 2,55 su).
Example 13 (SEC) 6 g of sodium hydroxide and 26,2 g of the sodium salt of vinylsulfonic acid (30%
.0 aqueous solution) are added to a suspension of 17,3 g of cellulose in 335 ml iso-propanol and 3,35 ml water. After intertization, the mixture is stirred for 75 min at room temperature . The reaction mixture is heated to 80°C by microwave irradiation (2,45 GHz) and etherified for approx. 10 min at 80°C. After cooling and standard working-up (neutralization and purification with aqueous methanol, sulfoethyl-cellulose is obtained with DS(SE) = 0,32 and viscosity V ~ = 576 mPas (measured at D = 2,55 s-~)

Claims (7)

1. Process for the production of cellulose derivatives in which a) cellulose is activated and b) reacted with one or more reagents, optionally in the presence of suspending agent, characterized in that reaction step b) is carried out in an electromagnetic field having a frequency in the range 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 carned out continuously.

7. Process according to claim 1, characterized in that the cellulose derivatives are isolated after reaction step b) and freed from salts and by-products.