Method for reducing release of alkoxy ethers from cellulose ethers

Abstract

Release of alkoxy ethers from a cellulose ether composition containing alkoxy ethers can be reduced by contacting the cellulose ether composition with a zeolite having a silica to alumina molar ratio (SiO2 / Al2O3) greater than 3 in an amount sufficient to adsorb at least some of the alkoxy ethers present.

Description

Technical Field

[0001] The present invention relates to the field of cellulose ethers. Background Art

[0002] It is known to produce cellulose ethers by reacting cellulose with various reagents. See, for example, US 4,845,206 and Harika K et al., Basic Concepts of Cellulose Polymers-A Comprehensive Review. 3(3) Archives of Pharmacy Practice (ArchivesofPharmacyPractice)》 202-216 (2012). In many cases, the reaction is a two-step process. In the first step, cellulose is contacted with an aqueous alkali metal hydroxide to form alkali cellulose. In the second step, the alkali cellulose is contacted with an etherifying agent suitable for producing a cellulose ether. For example, in the production of methyl cellulose, the etherifying agent is methyl chloride. In the production of ethyl cellulose, the etherifying agent is ethyl chloride. In the production of hydroxypropyl cellulose, the etherifying agent is propylene oxide. A mixture of etherifying agents can produce cellulose ethers with mixed ether substituents, such as ethyl methyl cellulose or hydroxypropyl methyl cellulose. After production, the cellulose ether is typically washed to remove impurities and dried. If it is not already in a suitable powder form, it can be ground into a powder. Summary of the invention

[0003] Side reactions during the production of cellulose ethers may produce trace amounts of alkoxy ethers, such as 2-methoxyethanol (2-ME). For example, a side reaction between an alkali metal hydroxide and an etherifying agent may produce an alkanol. Other side reactions may produce a diol. Reactions between an alkanol and a diol may produce an alkoxy ether. Unlike other byproducts, conventional procedures for removing impurities from cellulose ethers may leave a large amount of alkoxy ethers in the product. Subsequently, the alkoxy ethers may be slowly released from the cellulose ether, causing an undesirable odor.

[0004] We have found that appropriately selected zeolites can adsorb alkoxy ethers and prevent their release into the atmosphere.

[0005] One aspect of the present invention is a method of reducing the release of alkoxy ethers from a cellulose ether composition, the method comprising the step of contacting the cellulose ether composition with a zeolite having a silica to alumina molar ratio (SiO2 / Al2O3) greater than 3, the zeolite being in an amount sufficient to adsorb at least some of the alkoxy ether present.

[0006] A second aspect of the present invention is a cellulose ether composition comprising 0.5 to 5 wt % of a zeolite having a silica to alumina molar ratio (SiO2 / Al2O3) greater than 3, wherein the weight percentages are based on the dry weight of the cellulose ether powder.

[0007] The method of the present invention can significantly reduce the alkoxy ether gas released from the cellulose ether. DETAILED DESCRIPTION

[0008] The present invention starts from a cellulose ether composition containing a small amount of alkoxy ether. The cellulose ether composition comprises cellulose ether, alkoxy ether and optionally other components.

[0009] Cellulose ethers include cellulose macromolecules in which some hydroxyl groups have been substituted with alkoxy groups or substituted alkoxy groups. Some embodiments of alkoxy groups or substituted alkoxy groups contain no more than 6 carbon atoms or no more than 4 carbon atoms or no more than 2 carbon atoms. In some embodiments, the substituted alkoxy groups include hydroxyl groups or carboxylic acid groups.

[0010] Examples of suitable cellulose ethers include:

[0011] ●Alkyl cellulose ethers, such as methyl cellulose, ethyl cellulose and ethyl methyl cellulose;

[0012] ●Hydroxyalkyl cellulose ethers, such as hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose;

[0013] Carboxyalkyl cellulose ethers, such as carboxymethyl cellulose; and

[0014] - Cellulose ethers containing mixtures of different substituents, such as hydroxypropyl methylcellulose.

[0015] In some embodiments, the cellulose ether is an alkyl cellulose ether. In some embodiments, the cellulose ether is methyl cellulose or ethyl cellulose or ethyl methyl cellulose. In some embodiments, the cellulose ether is a hydroxyalkyl cellulose ether. In some embodiments, the cellulose ether is hydroxypropyl cellulose. In some embodiments, the cellulose ether is hydroxypropyl methyl cellulose.

[0016] In some embodiments, the cellulose ether has a number average molecular weight of at least 5000Da, or at least 7500Da, or at least 10,000Da. In some embodiments, the cellulose ether has a number average molecular weight of at most 2,000,000Da, or at most 1,200,000Da, or at most 1,000,000Da. For lower viscosity cellulose ethers, it may be desirable to have a number average molecular weight of no more than 110,000Da, or 86,000Da, or 70,000Da. For higher viscosity cellulose ethers, it may be desirable to have a molecular weight of at least 110,000Da, or at least 120,000Da, or at least 140,000Da.

[0017] In some embodiments, a 1% aqueous solution of the cellulose ether has a viscosity of at least 10 cP, or at least 100 cP, or at least 1000 cP, or at least 3000 cP, or at least 5000 cP, when measured as described in the Test Methods. In some embodiments, a 1% aqueous solution of the cellulose ether has a viscosity of at most 250,000 cP, or at most 150,000 cP, or at most 120,000 cP, or at most 80,000 cP, or at most 50,000 cP, when measured as described in the Test Methods.

[0018] In some embodiments, at least 10% (or at least 15% or at least 20% or at least 25%) of the hydroxyl groups in the cellulose are substituted by alkoxy groups or substituted alkoxy groups. In some embodiments, up to 60% (or up to 50% or up to 40% or up to 36%) of the hydroxyl groups in the cellulose are substituted by alkoxy groups or substituted alkoxy groups.

[0019] In some embodiments, the cellulose ether is the product of a process comprising the steps of:

[0020] 1. contacting cellulose with an aqueous solution of an alkali metal hydroxide to form alkali cellulose; and

[0021] 2. Contacting the alkali cellulose with an etherifying compound to form a cellulose ether.

[0022] In some embodiments, the method further comprises one or more of the following steps:

[0023] 3. Washing the cellulose ether to remove salt;

[0024] 4. drying the cellulose ether; and

[0025] 5. Grind the cellulose ether.

[0026] Examples of these steps are illustrated in US Pat. No. 4,845,206 and US Pat. No. 6,261,218.

[0027] In step (1), the example of alkali metal hydroxide is sodium hydroxide. In some embodiments, the aqueous solution contains 30% to 70% by weight of alkali metal hydroxide. In some embodiments, the temperature of step (1) is at least 10°C or at least 20°C or at least 30°C, and in some embodiments, the temperature of step (1) is at most 70°C or at most 60°C. In some embodiments, keep in contact for at least 5 minutes and / or at most 90 minutes. In some embodiments, the reaction is carried out under an inert atmosphere (such as nitrogen). In some embodiments, the reaction mixture is stirred. In some embodiments, an acid (such as hydrochloric acid or acetic acid) is utilized to neutralize the residual hydroxide in the alkali cellulose.

[0028] In step (2), examples of etherifying compounds include one or more of the following: alkyl halides such as methyl chloride or ethyl chloride and epoxides such as ethylene oxide, propylene oxide. In some embodiments, step (2) is carried out under elevated pressure (such as 100 psi to 300 psi). In some embodiments, step (2) is carried out at elevated temperature (such as at least 50° C. or at least 60° C.). In some embodiments, step (2) is carried out for at least 0.5 hours and / or at most 16 hours.

[0029] Any solvent capable of dissolving the residual salt in the cellulose ether may be used in step (3). In some embodiments, the solvent is water.

[0030] In some embodiments, step (4) is performed at an elevated temperature (such as 40° C. to 80° C.) and / or under an air flow. In some embodiments, the water content of the cellulose ether is reduced to at most 5 wt % or at most 3 wt %. In some embodiments, the water content of the cellulose ether is reduced to at least 0.5 wt % or at least 0.8 wt % or at least 1 wt %.

[0031] Step (5) can be performed using known grinding equipment such as a ball mill and a hammer mill. Grinding can be performed in the presence of a grinding aid such as a surfactant.

[0032] Alkoxy ethers comprise a first alkyl group (R) bonded to both a hydroxyl group and an alkoxy group or a substituted alkoxy group. 1 ), as shown in Formula 1.

[0033] (1)R 2 -OR 1 -OH

[0034] Where R 1 is an alkyl group, and R 2 is an alkyl group or a substituted alkyl group. 1 and R 2 Each independently contains at least 1 or at least 2 carbon atoms. 1 and R 2 Each independently contains up to 6, or up to 4, or up to 3 carbon atoms. In some embodiments, R 2 Also includes a hydroxyl substituent. In some embodiments, R 2 is unsubstituted. Examples of potential alkoxy ethers include methoxymethanol, ethoxyethanol, ethoxymethanol and methoxyethanol, such as 2-methoxyethanol.

[0035] In many cases, the alkoxy ether is a residual byproduct from the production of cellulose ether. In some embodiments, the concentration of the alkoxy ether in the cellulose ether is at least 100 μg / g or at least 250 μg / g or at least 400 μg / g based on the dry weight of the cellulose ether. In some embodiments, the concentration of the alkoxy ether is at most 800 μg / g or at most 600 μg / g or at most 500 μg / g based on the dry weight of the cellulose ether.

[0036] The cellulose ether composition may optionally contain other components. Examples of other components include residual salts (such as sodium chloride) and grinding aids. In many embodiments, based on the dry weight of the cellulose ether, the other components account for 0 wt % to 5 wt %, or 0 wt % to 2 wt %, or 0 wt % to 1 wt % of the cellulose ether composition. In many embodiments, the cellulose ether accounts for at least 95 wt %, or at least 98 wt %, or at least 99 wt % of the cellulose ether composition (excluding the solvent).

[0037] In some embodiments, the cellulose ether composition is substantially dry, comprising 0 to 5 wt % or 0 to 4 wt % or 0 to 3 wt % solvent.In the method of the present invention, the cellulose ether composition is contacted with a zeolite to adsorb the alkoxy ether in the cellulose ether composition.

[0038] Zeolites can be classified by the ratio of silicon to aluminum in the zeolite. This ratio is usually calculated and reported as the molar ratio of the two oxides of silicon and aluminum (silicon dioxide (SiO2) and aluminum oxide (Al2O3)) ("silicon dioxide to aluminum oxide molar ratio" or "SiO2 / Al2O3 molar ratio"). The zeolites used in the present invention have a silicon dioxide to aluminum oxide molar ratio (SiO2 / Al2O3) greater than 3. In some embodiments, the silicon dioxide to aluminum oxide molar ratio is at least 3.5, at least 4, at least 4.5, or at least 5. In some embodiments, the silicon dioxide to aluminum oxide molar ratio does not exceed 1000 or does not exceed 900 or does not exceed 8000 or does not exceed 700.

[0039] In some embodiments, the zeolite has at least or at least or at least or at least In some embodiments, the zeolite has an average pore size of at most or at most or at most or at most The average pore size.

[0040] In some embodiments, the zeolite has a diameter of at least 0.1 cm 3 / g or at least 0.15cm 3 / g or at least 0.17cm3 In some embodiments, the zeolite has an average pore volume of at most 0.6 cm 3 / g or at most 0.55cm 3 / g or at most 0.5cm 3 The average pore volume of / g.

[0041] In some embodiments, the zeolite has at least 250 m 2 / g or at least 350m 2 / g or at least 450m 2 In some embodiments, the zeolite has a surface area of ​​no more than 1000 m 2 / g or not more than 900m 2 / g of surface area.

[0042] In some embodiments, the zeolite has an average crystallite size of at least 1 μm, or at least 1.5 μm, or at least 2 μm, or at least 2.5 μm. In some embodiments, the zeolite has an average crystallite size of no more than 150 μm, or no more than 125 μm, or no more than 100 μm, or no more than 50 μm, or no more than 30 μm, or no more than 25 μm, or no more than 20 μm.

[0043] In some embodiments, the zeolite can be selected from the group consisting of MFI zeolite and Y zeolite. In some embodiments, the zeolite is MFI zeolite. In some embodiments, the zeolite is Y zeolite. In some embodiments, the MFI zeolite is a ZSM-type zeolite, and in some embodiments, it is a ZSM-Na zeolite or a ZSM-NH3 zeolite. In some embodiments, the Y zeolite is faujasite.

[0044] In some embodiments, the zeolite is calcined before use to remove adsorbed water, particularly for hydrophobic zeolites. For calcination, the zeolite may be maintained at a temperature of at least 200°C, or at least 400°C, or at least 500°C. The optimal calcination period depends on the temperature, but for temperatures of at least 500°C, examples of calcination periods are at least 1 hour, or at least 2 hours, or at least 3 hours. There is no maximum temperature for calcination, as long as the zeolite remains chemically stable, but temperatures above 700°C are rarely necessary. There is no maximum time for calcination, but for temperatures of at least 500°C, times exceeding 10 hours are rarely necessary.

[0045] The amount of zeolite should be sufficient to substantially adsorb the alkoxy ether in the cellulose ether composition. In some embodiments, the amount of zeolite is at least 0.1 wt%, or at least 0.3 wt%, or at least 0.5 wt%, or at least 1 wt%, based on the dry weight of the cellulose ether. In some embodiments, the amount of zeolite is at most 10 wt%, or at most 8 wt%, or at most 6 wt%, or at most 5 wt%, or at most 4 wt%, or at most 3 wt%, based on the dry weight of the cellulose ether.

[0046] In some embodiments, the zeolite is present during the reaction for preparing the cellulose ether. For example, the zeolite may be blended with the cellulose or may be added with other reagents. In some embodiments, the zeolite is mixed with the cellulose ether as part of the purification process after the cellulose ether is prepared. In some embodiments, the zeolite is mixed with the dry cellulose ether after the ordinary purification is completed. Regardless of when the zeolite is added, in some embodiments, the zeolite is substantially uniformly mixed throughout the cellulose ether.

[0047] In some embodiments, the contact between the zeolite and the cellulose ether composition is maintained for at least 10 seconds, or at least 20 seconds, or 30 seconds, or at least 1 minute, or at least 5 minutes, or at least 10 minutes, or at least 30 minutes, or at least 1 hour. In some embodiments, the zeolite and cellulose ether are stirred or tumbled during contact to ensure good mixing and good contact of all parts of the zeolite and the cellulose ether.

[0048] Optionally, the zeolite can be extracted from the cellulose ether after it has adsorbed the alkoxy ether. Alternatively, the zeolite can remain in place in the cellulose ether. The adsorbed alkoxy ether desorbs only slowly or not at all at normal temperatures of storage and use of the cellulose ether, so that measurable off-gassing of the alkoxy ether rarely occurs.

[0049] After treatment with zeolite, in some embodiments, the cellulose ether composition contains no more than 120 μg / g (or no more than 100 μg / g or no more than 80 μg / g or no more than 60 μg / g) of free alkoxy ether (alkoxy ether not adsorbed on zeolite). There is no minimum desired amount of free alkoxy ether, but in some cases, it may not be practical to reduce the free alkoxy ether level to less than 10 μg / g.

[0050] In some embodiments, the process of the present invention reduces the concentration of free alkoxy ethers in the cellulose ether composition to no more than 50 wt % or no more than 40 wt % or no more than 30 wt % or no more than 20 wt % or no more than 15 wt % or no more than 10 wt % of the pretreatment concentration. There is no minimum desired amount of free alkoxy ethers, but in some cases, at least 1 wt % of free alkoxy ethers may remain.

[0051] Some embodiments of the invention are further illustrated in the following examples, which are not intended to limit the broad scope of the invention.

[0052] Example

[0053] Test Method

[0054] The following test methods are used to measure the quantities described in this application:

[0055]

[0056] Zeolite

[0057] The zeolites listed in Table 1 were calcined by heating in an oven at 600°C for four hours, and then cooled to room temperature and stored in sealed containers until use.

[0058] Table 1

[0059]

[0060] The commercial cellulose ether product contains approximately 80% hydroxyethyl methylcellulose and 20% starch ether modifier. A series of samples were prepared by mixing 1 g of the cellulose ether with each of the zeolites listed in Table 1 in the amounts shown in Table 2 in a 20 mL headspace vial. The vials were capped and mixed on a vortex mixer for 30 seconds. The unadsorbed 2-ME content of each sample was measured as described in the test method.

[0061] Table 2

[0062] Example No. Zeolite Zeolite weight% 2-ME(μg / g) 2-ME reduction (%) Comparison A none 0 165 0 IE 1 Abscents 3000 1.0 102 38 Internet Explorer 2 Abscents 3000 2.0 65 61 Internet Explorer 3 Abscents 3000 2.5 59 64 Internet Explorer 4 Abscents 3000 4.0 34 79 Internet Explorer 5 CBV400 2.5 74 55 Internet Explorer 6 CBV901 2.5 100 39 Internet Explorer 7 CBV 15014G 2.5 62 63 IE 8(1) CBV5524G 2 4 93 IE 9(1) CBV5524G 2 4 93 IE 10(2) CBV5524G 2 25 92 IE 11 Abscents 3000 7.0 23 86 IE 12 Abscents 3000 10 19 88 Comparative Example CE 1 Abscents 3000 0.5 134 19 Control B none 0 445 0 CE 2 Siolite 3AH 2 447 <5 CE 3 Siolite 5AH 2 435 <5 CE 4 Zeolite 4A 2 460 <5 CE 5 Siolite 13X 2 395 11 CE 6 Natural Z 2 390 11 CE 7 Zeoflair 810 2 387 11

[0063] (1) Using different basic cellulose ether samples. The recovery rate of the control sample is 55.

[0064] (2) Using different basic cellulose ether samples. The recovery rate of the control sample was 310.

Claims

1. A method for reducing the release of alkoxy ethers from a cellulose ether composition containing an alkoxy ether, the method comprising the step of contacting the cellulose ether composition with a zeolite having a silica to alumina molar ratio (SiO2 / Al2O3) greater than 3, the zeolite being in an amount sufficient to adsorb at least some of the alkoxy ether present.

2. The process according to claim 1, wherein the weight ratio of zeolite to the dry weight of cellulose ether exceeds 0.5% and does not exceed 10%.

3. The process according to any one of claims 2, wherein the weight ratio of zeolite to dry weight of cellulose ether is from 1% to 5%.

4. The method of claim 3, wherein the zeolite has a silica to alumina molar ratio (SiO2 / Al2O3) greater than 4.

5. The method of claim 3, wherein the zeolite has a silica to alumina molar ratio (SiO2 / Al2O3) greater than 5.

6. The method according to claim 3, wherein the zeolite has to The average pore size.

7. The method according to claim 3, wherein the zeolite has to The average pore size.

8. The method according to claim 3, wherein the zeolite has a 0.1 cm 3 / g to 0.6cm 3 / g pore volume.

9. The method of claim 3, wherein the zeolite comprises Y zeolite.

10. The method of claim 3, wherein the zeolite comprises MFI zeolite.

11. The method of claim 3, wherein the zeolite comprises ZSM-5 zeolite.

12. The method of claim 3, wherein the cellulose ether composition comprises methyl cellulose, ethyl cellulose, ethyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, or hydroxypropyl methyl cellulose.

13. The method of claim 3, wherein the alkoxy ether is 2-methoxyethanol.

14. The method of claim 3, wherein the method of the present invention reduces the concentration of free alkoxy ether in the cellulose ether composition to no more than 40 weight percent of the pretreatment concentration.

15. A cellulose ether composition comprising 0.5 wt% to 5 wt% of a zeolite having a silica to alumina molar ratio (SiO2 / Al2O3) greater than 3, wherein the weight percentages are based on the dry weight of the cellulose ether powder.

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