CN113501971B - Method for preparing low-polymerization-degree water-soluble cellulose ether - Google Patents
Method for preparing low-polymerization-degree water-soluble cellulose ether Download PDFInfo
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- 229920003086 cellulose ether Polymers 0.000 title claims abstract description 116
- 238000000034 method Methods 0.000 title claims abstract description 27
- 238000006116 polymerization reaction Methods 0.000 claims abstract description 105
- 239000000047 product Substances 0.000 claims abstract description 34
- 239000007789 gas Substances 0.000 claims description 79
- 238000001035 drying Methods 0.000 claims description 33
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 28
- 239000007864 aqueous solution Substances 0.000 claims description 14
- 239000001866 hydroxypropyl methyl cellulose Substances 0.000 claims description 12
- 229920003088 hydroxypropyl methyl cellulose Polymers 0.000 claims description 12
- 235000010979 hydroxypropyl methyl cellulose Nutrition 0.000 claims description 12
- 229920002153 Hydroxypropyl cellulose Polymers 0.000 claims description 11
- 239000001863 hydroxypropyl cellulose Substances 0.000 claims description 11
- 235000010977 hydroxypropyl cellulose Nutrition 0.000 claims description 11
- 238000002156 mixing Methods 0.000 claims description 10
- 239000000203 mixture Substances 0.000 claims description 10
- 239000004354 Hydroxyethyl cellulose Substances 0.000 claims description 9
- 229920000663 Hydroxyethyl cellulose Polymers 0.000 claims description 9
- 235000019447 hydroxyethyl cellulose Nutrition 0.000 claims description 9
- 238000010926 purge Methods 0.000 claims description 9
- 159000000011 group IA salts Chemical class 0.000 claims description 6
- 229960003943 hypromellose Drugs 0.000 claims description 6
- 150000001447 alkali salts Chemical class 0.000 claims description 5
- 238000007599 discharging Methods 0.000 claims description 5
- 238000007873 sieving Methods 0.000 claims description 5
- UIIMBOGNXHQVGW-DEQYMQKBSA-M Sodium bicarbonate-14C Chemical compound [Na+].O[14C]([O-])=O UIIMBOGNXHQVGW-DEQYMQKBSA-M 0.000 claims description 4
- 238000005086 pumping Methods 0.000 claims description 4
- 239000012265 solid product Substances 0.000 claims description 4
- 239000012467 final product Substances 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 1
- 230000000694 effects Effects 0.000 abstract description 8
- 239000006227 byproduct Substances 0.000 abstract description 4
- 239000000546 pharmaceutical excipient Substances 0.000 abstract description 3
- 229940124531 pharmaceutical excipient Drugs 0.000 abstract description 3
- 239000002904 solvent Substances 0.000 abstract description 3
- 239000000126 substance Substances 0.000 abstract description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 22
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical group [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 description 14
- 239000002253 acid Substances 0.000 description 12
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
- 238000002360 preparation method Methods 0.000 description 9
- 238000006243 chemical reaction Methods 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 7
- 239000000843 powder Substances 0.000 description 7
- 229910000030 sodium bicarbonate Inorganic materials 0.000 description 7
- 235000017557 sodium bicarbonate Nutrition 0.000 description 7
- 229920002678 cellulose Polymers 0.000 description 6
- 239000001913 cellulose Substances 0.000 description 6
- 238000010438 heat treatment Methods 0.000 description 6
- UFVKGYZPFZQRLF-UHFFFAOYSA-N hydroxypropyl methyl cellulose Chemical compound OC1C(O)C(OC)OC(CO)C1OC1C(O)C(O)C(OC2C(C(O)C(OC3C(C(O)C(O)C(CO)O3)O)C(CO)O2)O)C(CO)O1 UFVKGYZPFZQRLF-UHFFFAOYSA-N 0.000 description 6
- 239000000463 material Substances 0.000 description 5
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- 239000003513 alkali Substances 0.000 description 4
- 239000002585 base Substances 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 4
- 238000000576 coating method Methods 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 238000005507 spraying Methods 0.000 description 3
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
- 238000004061 bleaching Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000006386 neutralization reaction Methods 0.000 description 2
- 230000003472 neutralizing effect Effects 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 238000004383 yellowing Methods 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 229920000742 Cotton Polymers 0.000 description 1
- 229920001131 Pulp (paper) Polymers 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 238000007405 data analysis Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000002845 discoloration Methods 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 238000010981 drying operation Methods 0.000 description 1
- 238000011010 flushing procedure Methods 0.000 description 1
- 239000008103 glucose Substances 0.000 description 1
- 150000004676 glycans Chemical class 0.000 description 1
- 230000003301 hydrolyzing effect Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 229920001282 polysaccharide Polymers 0.000 description 1
- 239000005017 polysaccharide Substances 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 239000002562 thickening agent Substances 0.000 description 1
- 238000002834 transmittance Methods 0.000 description 1
- 238000000870 ultraviolet spectroscopy Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2301/00—Characterised by the use of cellulose, modified cellulose or cellulose derivatives
- C08J2301/08—Cellulose derivatives
- C08J2301/26—Cellulose ethers
- C08J2301/28—Alkyl ethers
Abstract
The invention belongs to the technical field of pharmaceutical chemicals, and particularly relates to a method for preparing water-soluble cellulose ether with low polymerization degree. The invention uses HCl-ClO 2 And the mixed gas is used for depolymerizing the water-soluble cellulose ether with high polymerization degree by a dry method to finally obtain the water-soluble cellulose ether with low polymerization degree and low viscosity, which meets the use requirements of pharmaceutical excipients. The invention has the following advantages: first, use HCl-ClO 2 The mixed gas reduces the polymerization degree of the water-soluble cellulose ether with high polymerization degree, ensures obvious depolymerization effect, does not introduce a large amount of solvent, and can also improve the whiteness of the final water-soluble cellulose ether product with low polymerization degree; second, HCl-ClO 2 Residues or byproducts in the depolymerization process of the mixed gas can be effectively removed, and the final low-polymerization degree water-soluble cellulose ether product meets the requirements of Chinese pharmacopoeia on the viscosity standard; third, the method has no great limitation on the type of the water-soluble cellulose ether with high polymerization degree, and has higher applicability.
Description
Technical Field
The invention belongs to the technical field of preparation of pharmaceutical excipients, and particularly relates to a method for preparing water-soluble cellulose ether with low polymerization degree.
Background
The water-soluble cellulose ether can be used as a release retardant, a thickener and a coating material in the pharmaceutical industry, and the low-polymerization degree water-soluble cellulose ether is generally used as a film-forming coating material, so that the water solution of the water-soluble cellulose ether needs to have relatively low viscosity so as to ensure good spraying and smearing properties.
The aqueous solution of the high-polymerization-degree water-soluble cellulose ether has high viscosity, so that the spraying and smearing effects are poor, and more importantly, the coating prepared from the high-polymerization-degree water-soluble cellulose ether is slowly dissolved in water, and the release of the medicine is affected.
The conventional preparation methods of the existing low-polymerization-degree water-soluble cellulose ether are two methods: one method is to reduce the polymerization degree of raw materials (such as wood pulp and refined cotton) in the preparation process of the water-soluble cellulose ether, and then etherify the raw materials to obtain the water-soluble cellulose ether with low polymerization degree. Taking hydroxypropyl methylcellulose as an example, the cellulose is degraded in the alkalization process and etherified to obtain a product with the viscosity of 3-100mPa.s of a 2% aqueous solution, the yield is only about 60% of the theoretical yield, and a large amount of products with low polymerization degree are lost in the washing process. The other is that water-soluble cellulose ether with high polymerization degree is prepared firstly, then hydrochloric acid is added for acidic degradation, and the water-soluble cellulose ether with low polymerization degree obtained by the method is yellow in color, and particularly is used as a film forming material, so that the appearance quality is seriously influenced.
Therefore, in view of the above, there is an urgent need for a processing method that can greatly reduce the polymerization degree of water-soluble cellulose ether to obtain low viscosity water-soluble cellulose ether for use as film-forming and coating materials.
Chinese invention patent publication No. CN110945032a, publication No. 2020.03.31 discloses a controlled preparation method of low molecular weight cellulose ether, comprising: (a) Providing an initial cellulose ether powder comprising 0.5 to 10 weight percent water based on the total weight of the cellulose ether powder; (b) Heating the initial cellulose ether powder to a temperature of 30 to 130 degrees celsius; (c) Adding a solid base to the cellulose ether powder before, during and/or after heating in step (b) and mixing with the initial cellulose ether powder to form a cellulose ether/base mixture; (d) Adding a volatile acid to the cellulose ether/base mixture and mixing; and (e) hydrolyzing the initial cellulose ether with the volatile acid to form a final cellulose ether having a lower viscosity than the initial cellulose ether.
However, in the preparation method of the invention, the initial cellulose ether is hydrolyzed by the volatile acid to reduce the polymerization degree of the initial cellulose ether, and the disadvantage is that the volatile acid and the alkali mixed in the cellulose ether react immediately, the volatile acid is consumed quickly, the effect of reducing the polymerization degree of the cellulose ether is not obvious, and the low-viscosity cellulose ether which is difficult to obtain finally.
Disclosure of Invention
The invention aims to provide a method for preparing low-polymerization degree water-soluble cellulose ether, which can pass through HCl-ClO 2 And the mixed gas is used for depolymerizing the water-soluble cellulose ether with high polymerization degree by a dry method to finally obtain the water-soluble cellulose ether with low polymerization degree and low viscosity, which meets the use requirements of pharmaceutical excipients.
The invention adopts the technical proposal that: the preparation method of the water-soluble cellulose ether with low polymerization degree sequentially comprises the following steps:
s1, drying water-soluble cellulose ether with a polymerization degree of more than 200;
s2, carrying out HCl-ClO on the dried high-polymerization-degree water-soluble cellulose in a closed container 2 Depolymerizing the mixed gas to obtain a low-polymerization-degree water-soluble cellulose ether product;
s3, discharging redundant HCl-ClO in the closed container 2 Mixing the gases;
s4, adding alkaline salt into a closed container to neutralize residual trace HCl, wherein the alkaline salt can be added in a dry powder form or dissolved in water and added in a spray form;
and S5, crushing and sieving the product after the depolymerization operation to obtain a final low-polymerization degree water-soluble cellulose ether finished product.
In the prior art, the high polymerization degree water-soluble cellulose ether is depolymerized by using volatile acid, and the defects of the prior art are that: 1. the volatile acid is mixed with the water-soluble cellulose ether and the alkali simultaneously, and the volatile acid is easy to react with the alkali firstly, so that the aim of depolymerizing the water-soluble cellulose ether is not achieved; 2. the consumption of volatile acid is very large, and a large amount of salt generated after neutralization is remained in the product as residue; 3. the depolymerization process does not have a measure for inhibiting the discoloration of the water-soluble cellulose ether, and the obtained low-polymerization-degree water-soluble cellulose ether has poor self-shape, namely, the whiteness is insufficient in solid state, and the color of an aqueous solution is over-yellow after the aqueous solution is dissolved in water.
In the present invention, the degree of polymerization of the water-soluble cellulose ether is defined as follows: the cellulose molecule is macromolecular polysaccharide composed of D-glucose with beta-1, 4-glycosidic bond, and the number of glucose in cellulose ether molecule is the polymerization degree.
Therefore, in the present invention, the reaction is carried out by HCl-ClO 2 The principle or function of depolymerizing the water-soluble cellulose ether with high polymerization degree by the mixed gas is as follows.
The first HCl gas is contacted with the water-soluble cellulose ether with high polymerization degree, the basic effective depolymerization effect is ensured by the same principle as acid solution depolymerization, and no solvent is introduced, so that the subsequent drying work is avoided by the dry depolymerization operation.
Second, clO 2 The gas can perform proper bleaching operation on the low-polymerization degree water-soluble cellulose ether product, so that the final low-polymerization degree water-soluble cellulose ether product has higher whiteness and lighter color after being dissolved in water.
Third, the water still remained after the drying of the water-soluble cellulose ether with high polymerization degree can be mixed with ClO 2 The gas reaction or the use of the catalyst for dissolving HCl gas can form dilute hydrochloric acid in both modes and promote depolymerization, so that the drying operation does not need to ensure that the moisture content is extremely low, and the sufficient depolymerization effect can be obtained in a proper smaller range, and the subsequent drying and dewatering operation is avoided.
In addition, alkali carbonate is more alkaline than NaOH, ca (OH) 2 Has relatively mild acid-base neutralization capability and can fully neutralize residual HCl gasWhereas ClO 2 The gas does not react with the water-soluble cellulose ether, but only plays roles in bleaching and preventing materials from yellowing, and is removed by vacuum, nitrogen flushing and the like after depolymerization.
The further preferable technical scheme is as follows: in the step S1, the high-polymerization degree water-soluble cellulose ether is any one of hydroxypropyl methylcellulose, hydroxypropyl cellulose and hydroxyethyl cellulose with high polymerization degree, the water content of the high-polymerization degree water-soluble cellulose ether before drying is 1.0-5.0%, and the water content after drying is 0.1-1.0%.
In the present invention, if the water content after drying is too high, HCl-ClO is largely absorbed during depolymerization 2 The mixed gas causes uneven mixing, the depolymerization effect is poor, and a proper amount of water is kept in a small amount, so that HCl-ClO in the depolymerization process is maintained 2 Is always in a gaseous state, and achieves good contact effect.
The further preferable technical scheme is as follows: in step S2, the HCl-ClO 2 The composition of the mixed gas comprises ClO with the volume percentage of 0.1-5.0% 2 The gas, the rest is HCl gas. The HCl-ClO 2 The weight of the mixed gas accounts for 0.1 to 0.5 percent of the weight of the water-soluble cellulose ether with high polymerization degree before drying.
In the invention, a solid-gas two-phase contact reaction mode is adopted to ensure that the water-soluble cellulose ether with high polymerization degree can be effectively depolymerized so as to reduce the polymerization degree, wherein HCl gas is mainly used for depolymerization and ClO 2 The gas is mainly used for preventing the product from yellowing and ensuring that the water-soluble cellulose ether product with high appearance whiteness and low polymerization degree can be finally obtained. In the implementation process, clO must be strictly controlled 2 In terms of volume percent concentration of ClO 2 A volume percentage concentration of more than 5% is dangerous.
The further preferable technical scheme is as follows: in the step S2, the closed container is heated to 30-80 ℃ and kept at the temperature until the mixed gas is introduced into the container, and the polymerization process is continued for 1-40 h.
In the present invention, the solid-gas two-phase contact reaction needs to be matched with enough and proper temperature and enough reaction time to ensure the sufficient contact reaction, so that the solid-gas reaction condition of heating to 30-80 ℃ and heat preservation is determined.
The further preferable technical scheme is as follows: in step S3, HCl-ClO 2 The discharge of the mixed gas is accomplished by alternately performing a vacuum-purging operation.
In the present invention, HCl-ClO remained in the closed container 2 If a large amount of mixed gas leaks out, the mixed gas is dangerous, so that the HCl-ClO can not remain in the whole closed container when the low-polymerization degree water-soluble cellulose ether is finally taken out from the closed container by means of nitrogen purging and vacuumizing 2 And (3) mixing the gases.
The further preferable technical scheme is as follows: and when the vacuum pumping operation is performed, the vacuum degree in the closed container is not lower than-0.05 MPa.
The further preferable technical scheme is as follows: in step S4, the alkali salt is sodium bicarbonate in a powder form, and the added weight is 0.1 to 0.6% of the weight of the high-polymerization degree water-soluble cellulose ether before drying.
In the present invention, sodium bicarbonate can neutralize HCl-ClO 2 The mixed gas and water react to produce a very small amount of diluted hydrochloric acid, so that the final low-polymerization degree water-soluble cellulose ether product can not remain acidic substances, and more importantly, the use and appearance of the low-polymerization degree water-soluble cellulose ether can not be influenced by the residual very small amount of sodium bicarbonate.
The further preferable technical scheme is as follows: in the step S5, the final product of the low-polymerization degree water-soluble cellulose ether has the viscosity of 3-100mPa.s and the whiteness of 85-92 in a 2% aqueous solution at 20 ℃.
The further preferable technical scheme is as follows: in step S2, the HCl-ClO 2 The composition of the mixed gas comprises ClO with the volume percentage of 0.1-5.0% 2 The gas, the rest is HCl gas.
In the invention, clO with the volume percentage of 0.1 to 5.0 percent 2 After depolymerizing the high-polymerization degree water-soluble cellulose ether by gas and the rest HCl gas, the obtained low-polymerization degree water-soluble cellulose ether has higher whitenessAnd the color of the water solution is lighter, so that the performance of the low-polymerization degree water-soluble cellulose ether product is far superior to that of other similar products on the market.
The further preferable technical scheme is as follows: in step S2, the HCl-ClO 2 The composition of the mixed gas comprises ClO with the volume percentage of 0.1-1.0% 2 The gas, the rest is HCl gas.
The further preferable technical scheme is as follows: the closed container is a rotary vacuum dryer and is heated in a water bath mode.
The invention has the following advantages: first, use HCl-ClO 2 The mixed gas reduces the polymerization degree of the water-soluble cellulose ether with high polymerization degree, ensures obvious depolymerization effect, does not introduce a large amount of solvent, and can also improve the whiteness of the final water-soluble cellulose ether product with low polymerization degree; second, HCl-ClO 2 Residues or byproducts in the depolymerization process of the mixed gas can be effectively removed, and the final low-polymerization degree water-soluble cellulose ether product meets the requirements of Chinese pharmacopoeia on the viscosity standard; third, the method has no great limitation on the type of the water-soluble cellulose ether with high polymerization degree, and has higher applicability.
Drawings
FIG. 1 is a comparative table of performance parameters of the low degree of polymerization water-soluble cellulose ether products of 3 examples and 2 comparative examples of the present invention.
Wherein, ji Wei intelligent desk type handheld digital display whiteness instrument WSB-3 is used for whiteness test, and a sample is smoothed and compacted before the test; the transmittance test uses a double beam ultraviolet-visible spectrophotometer (TU-1901), the sample is dissolved in water to prepare a 2.0wt% aqueous solution, the aqueous solution is refrigerated in a refrigerator for 1-3 hours, then the temperature is kept constant to 20 ℃, and finally the detection is performed.
Detailed Description
The following description is of the preferred embodiments of the invention and is not intended to limit the scope of the invention.
Example 1
The preparation method of the water-soluble cellulose ether with low polymerization degree sequentially comprises the following steps:
s1, drying water-soluble cellulose ether with high polymerization degree;
s2, carrying out HCl-ClO on the dried high-polymerization-degree water-soluble cellulose in a closed container 2 Depolymerizing the mixed gas to obtain a low-polymerization-degree water-soluble cellulose ether product;
s3, discharging redundant HCl-ClO in the closed container 2 Mixing the gases;
s4, adding alkaline salt into the closed container, and neutralizing to remove acid liquor byproducts;
s5, crushing and sieving the solid product to obtain a final low-polymerization degree water-soluble cellulose ether finished product.
In step S1, the high-polymerization degree water-soluble cellulose ether is high-polymerization degree hypromellose, the water content of the high-polymerization degree hypromellose before drying is 2.6%, and the water content of the high-polymerization degree hypromellose after drying is 0.4%.
Specifically, the viscosity of the 2% aqueous solution of the hydroxypropyl methylcellulose with high polymerization degree at 20 ℃ is 4080mPa.s, the drying temperature is 70 ℃ by heating in a water bath, and the hydroxypropyl methylcellulose is carried out in a rotary vacuum dryer, wherein the rotary vacuum dryer is the closed container, and the subsequent operation is completed in the rotary vacuum dryer all the time.
In step S2, the HCl-ClO 2 The composition of the mixed gas comprises ClO with the volume percentage of 0.5 percent 2 The rest is HCl gas, the HCl-ClO 2 The weight of the mixed gas accounts for 0.3 percent of the weight of the hydroxypropyl methylcellulose with high polymerization degree before drying.
At this time, the closed vessel was heated to 75℃and kept at a constant temperature until the operation of introducing the mixed gas was completed, and after the mixed gas was introduced, the rotational speed of the rotary vacuum dryer was maintained at 25rpm for 8 hours.
In step S3, HCl-ClO 2 The discharge of the mixed gas is accomplished by alternating vacuum-purge operations.
And during the vacuumizing operation, the vacuum degree in the closed container is-0.07 MPa, and the purging time of the nitrogen is 30min.
In step S4, the alkali salt is powdered sodium bicarbonate, the added weight is 0.4% of the weight of the hypromellose with high polymerization degree before drying, and the time after the powdered sodium bicarbonate is added is 60min.
Finally, through the step S5, the performance of the finally obtained hydroxypropyl methylcellulose product with low polymerization degree is shown in the attached drawing.
Example 2
The preparation method of the water-soluble cellulose ether with low polymerization degree sequentially comprises the following steps:
s1, drying water-soluble cellulose ether with high polymerization degree;
s2, carrying out HCl-ClO on the dried high-polymerization-degree water-soluble cellulose in a closed container 2 Depolymerizing the mixed gas to obtain a low-polymerization-degree water-soluble cellulose ether product;
s3, discharging redundant HCl-ClO in the closed container 2 Mixing the gases;
s4, spraying an aqueous solution of alkaline salt into the closed container to neutralize residual HCl gas;
s5, crushing and sieving the solid product to obtain a final low-polymerization degree water-soluble cellulose ether finished product.
In step S1, the high-polymerization degree water-soluble cellulose ether is high-polymerization degree hydroxypropyl cellulose, the water content of the high-polymerization degree hydroxypropyl cellulose before drying is 3.5%, and the water content of the high-polymerization degree hydroxypropyl cellulose after drying is 0.5%.
Specifically, the viscosity of the 2% aqueous solution of the hydroxypropyl cellulose with high polymerization degree at 20 ℃ is 205mPa.s, the drying temperature is 75 ℃ by heating in a water bath, and the hydroxypropyl cellulose is carried out in a rotary vacuum dryer, wherein the rotary vacuum dryer is the closed container, and the subsequent operation is always completed in the rotary vacuum dryer.
In step S2, the HCl-ClO 2 The composition of the mixed gas comprises ClO with the volume percentage of 0.5 percent 2 The rest is HCl gas, the HCl-ClO 2 The weight of the mixed gas accounts for 0.4% of the weight of the hydroxypropyl cellulose with high polymerization degree before drying.
At this time, the closed vessel was heated to 80℃and kept at a constant temperature until the operation of introducing the mixed gas was completed, and after the mixed gas was introduced, the rotational speed of the rotary vacuum dryer was kept at 25rpm for 12 hours.
In step S3, HCl-ClO 2 The discharge of the mixed gas is accomplished by alternating vacuum-purge operations.
During the vacuum pumping operation, the vacuum degree in the closed container is-0.07 MPa, and the nitrogen purging time is 30min.
In step S4, the alkali salt is powdered sodium bicarbonate, the added weight is 0.3% of the weight of the high-polymerization-degree hydroxypropyl cellulose before drying, and the time for mixing after the powdered sodium bicarbonate is added is 60min.
Finally, through the step S5, the performance of the finally obtained hydroxypropyl cellulose product with low polymerization degree is shown in the attached drawing.
Example 3
The preparation method of the water-soluble cellulose ether with low polymerization degree sequentially comprises the following steps:
s1, drying water-soluble cellulose ether with high polymerization degree;
s2, carrying out HCl-ClO on the dried high-polymerization-degree water-soluble cellulose in a closed container 2 Depolymerizing the mixed gas to obtain a low-polymerization-degree water-soluble cellulose ether product;
s3, discharging redundant HCl-ClO in the closed container 2 Mixing the gases;
s4, adding alkaline salt into the closed container, and neutralizing to remove acid liquor byproducts;
s5, crushing and sieving the solid product to obtain a final low-polymerization degree water-soluble cellulose ether finished product.
In step S1, the high-polymerization-degree water-soluble cellulose ether is a high-polymerization-degree hydroxyethyl cellulose, the water content of the high-polymerization-degree hydroxyethyl cellulose before drying is 4.2%, and the water content of the high-polymerization-degree hydroxyethyl cellulose after drying is 0.4%.
Specifically, the viscosity of the 2% aqueous solution of the high-polymerization-degree hydroxyethyl cellulose at 20 ℃ is 2000mPa.s, the drying temperature is 60 ℃ by heating in a water bath, and the drying is carried out in a rotary vacuum dryer, wherein the rotary vacuum dryer is the closed container, and the subsequent operation is always completed in the rotary vacuum dryer.
In step S2, the HCl-ClO 2 The composition of the mixed gas comprises ClO with the volume percentage of 0.3 percent 2 The rest is HCl gas, the HCl-ClO 2 The weight of the mixed gas accounts for 0.3% of the weight of the hydroxyethyl cellulose with high polymerization degree before drying.
At this time, the closed vessel was heated to 70℃and kept at a constant temperature until the operation of introducing the mixed gas was completed, and after the mixed gas was introduced, the rotational speed of the rotary vacuum dryer was kept at 25rpm for 4 hours.
In step S3, HCl-ClO 2 The discharge of the mixed gas is accomplished by alternating vacuum-purge operations.
During the vacuum pumping operation, the vacuum degree in the closed container is-0.07 MPa, and the nitrogen purging time is 30min.
In step S4, the alkali salt is powdered sodium bicarbonate, the added weight is 0.34% of the weight of the high-polymerization-degree hydroxyethyl cellulose before drying, and the time for the powdered sodium bicarbonate to enter the post-reaction is 20min.
Finally, through step S5, the properties of the finally obtained hydroxyethyl cellulose product with low polymerization degree are shown in the attached drawing.
Comparative example 1
This comparative example 1 differs from example 1 only in that:
by reacting raw HCl-ClO 2 The mixed gas is changed into single HCl gas, so that the self addition amount of the HCl gas is ensured to be unchanged.
The properties of the finally obtained hypromellose product with a low degree of polymerization are shown in the accompanying drawings.
Comparative example 2
This comparative example 2 differs from example 2 only in that:
by reacting raw HCl-ClO 2 The mixed gas is changed into single HCl gas, so that the self addition amount of the HCl gas is ensured to be unchanged.
The properties of the finally obtained low-polymerization hydroxypropyl cellulose product are shown in the attached drawing.
Finally, by data analysis of the above examples 1, 2, 3 and comparative examples 1 and 2, the following conclusion was drawn.
First, HCl-ClO 2 The mixed gas synergistic effect can obviously reduce the polymerization degree of the water-soluble cellulose ether with high polymerization degree so as to obtain the water-soluble cellulose ether with low polymerization degree, which has relatively extremely low viscosity, and the whiteness of the water-soluble cellulose ether with low polymerization degree is greatly improved.
Second, clO 2 From HCl-ClO 2 After removal from the mixed gas, the appearance of the water-soluble cellulose ether product after the depolymerization is extremely poor, the aqueous solution thereof is yellow in color, and the color is darker as the concentration of the aqueous solution is higher.
Thirdly, the addition of sodium bicarbonate can well remove residual HCl gas in the final water-soluble cellulose ether product, and ensure that the water solution of the water-soluble cellulose ether product is neutral.
The embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is not limited to the above embodiments, and various modifications may be made within the knowledge of those skilled in the art without departing from the spirit of the present invention. These are all non-inventive modifications which are intended to be protected by the patent laws within the scope of the appended claims.
Claims (10)
1. A method for producing a water-soluble cellulose ether having a low degree of polymerization, comprising the steps of:
s1, drying high-polymerization degree water-soluble cellulose ether with a polymerization degree of more than 200;
s2, carrying out HCl-ClO on the dried high-polymerization-degree water-soluble cellulose ether in a closed container 2 Depolymerizing the mixed gas to obtain a low-polymerization-degree water-soluble cellulose ether product;
s3, discharging redundant HCl-ClO in the closed container 2 Mixing the gases;
s4, adding alkaline salt into the closed container to neutralize residual HCl gas;
s5, crushing and sieving the solid product to obtain a final water-soluble cellulose ether finished product with the polymerization degree of 30-150,
in step S2, the HCl-ClO 2 The composition of the mixed gas comprises ClO with the volume percentage of 0.1-5.0% 2 The rest is HCl gas, the HCl-ClO 2 The weight of the mixed gas accounts for 0.1 to 0.5 percent of the weight of the water-soluble cellulose ether with high polymerization degree before drying.
2. The process for producing a water-soluble cellulose ether having a low degree of polymerization according to claim 1, characterized by: in step S1, the water-soluble cellulose ether having a high degree of polymerization is any one of hypromellose, hydroxypropyl cellulose, and hydroxyethyl cellulose having a degree of polymerization of 200 or more.
3. The process for producing a water-soluble cellulose ether having a low degree of polymerization according to claim 1, characterized by: the water content of the high-polymerization degree water-soluble cellulose ether before drying is 1.0-5.0%, and the water content after drying is 0.1-1.0%.
4. The process for producing a water-soluble cellulose ether having a low degree of polymerization according to claim 1, characterized by: in the step S2, the closed container is heated to 30-80 ℃ and kept at the temperature for 1-40 h.
5. The process for producing a water-soluble cellulose ether having a low degree of polymerization according to claim 1, characterized by: in step S3, HCl-ClO 2 The discharge of the mixed gas is accomplished by alternating vacuum-purge operations.
6. The process for producing a water-soluble cellulose ether having a low degree of polymerization according to claim 5, characterized by: and when the vacuum pumping operation is performed, the vacuum degree in the closed container is not lower than-0.05 MPa.
7. The process for producing a water-soluble cellulose ether having a low degree of polymerization according to claim 1, characterized by: in the step S4, the alkali salt is powdery sodium bicarbonate, and the added weight is 0.1-0.6% of the weight of the high-polymerization degree water-soluble cellulose ether before drying.
8. The process for producing a water-soluble cellulose ether having a low degree of polymerization according to claim 1, characterized by: in the step S5, the final product of the low-polymerization degree water-soluble cellulose ether has the viscosity of 3-100mPa.s and the whiteness of 85-92 in a 2% aqueous solution at 20 ℃.
9. The process for producing a water-soluble cellulose ether having a low degree of polymerization according to claim 1, characterized by: in step S2, the HCl-ClO 2 The composition of the mixed gas comprises ClO with the volume percentage of 0.1-1.0% 2 The gas, the rest is HCl gas.
10. The process for producing a water-soluble cellulose ether having a low degree of polymerization according to claim 1, characterized by: the closed container is a rotary vacuum dryer and is heated in a water bath mode.
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| US7005514B2 (en) * | 2002-10-16 | 2006-02-28 | International Paper Company | Process for preparing microcrystalline cellulose |
| US9926385B2 (en) * | 2013-08-12 | 2018-03-27 | Shin-Etsu Chemical Co., Ltd. | Method for producing water-soluble cellulose ether having low degree of polymerization and method for producing film coating composition comprising same |
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