Process for producing pulverulent silylated cellulose

Abstract

A process for preparing powdered silylated cellulose is disclosed. The method includes preparing a reaction product in the form of a powder that can be mixed and processed with conventional powder processing equipment.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 432,715, filed Dec. 15, 2022, under 35 U.S.C. § 119(e). The U.S. Provisional Patent Application Serial No. 63 / 432,715 is hereby incorporated by reference. Technical field

[0003] Provided is a method for producing powdered silylated cellulose. More specifically, the method for producing powdered silylated cellulose can be utilized on a commercial production scale. Background art

[0004] Current techniques for producing silylated cellulose are based on slurry or solution processes with low volume yields. Some of these processes utilize high pressure where cellulose is suspended in a liquefied ammonia slurry. Others utilize an atmospheric pressure process for production in a large - volume swelling solvent. These processes have significant drawbacks, not only requiring a huge volume of swelling solvent and recrystallization solvent, but also generating a large amount of waste liquid. In addition, due to the large amount of solvent used, the space - time yield of these processes is extremely low. Therefore, these methods are not commercially viable for large - scale use.

[0005] U.S. Patent No. 4,320,692 to Green discloses a method for preparing trimethylsilyl cellulose ether, which includes reacting cellulose with hexamethyldisilazane in the presence of a small amount of catalyst. In a preferred method of implementing this process, the reaction temperature is maintained between about 100°C and about 135°C. When the temperature is below 100°C, the reaction is found to be too slow to be of practical use; when the temperature is above 135°C, the reaction is found to become extremely unstable.

[0006] There is an urgent need in the industry for a process with higher volume efficiency for preparing silylated cellulose. Ideally, the process should also operate at atmospheric pressure and / or consume less solvent than existing processes. Summary of the invention

[0007] Provided herein is a method for preparing silylated cellulose. The method comprises:

[0008] 1) Mixing starting materials, the starting materials comprising: A) cellulose, B) a polar aprotic swelling solvent, C) a catalyst, and optionally D) a first portion of a silylating agent, thereby preparing E) a powdered intermediate; and

[0009] 2) Adding D) the silylating agent to E) the powdered intermediate continuously or intermittently. Detailed description

[0010] More specifically, the method for preparing silylated cellulose described above includes:

[0011] 1) Mixing starting materials, the starting materials comprising

[0012] A) cellulose, the cellulose comprising repeating monomer units and each monomer unit having >2.5 hydroxyl groups,

[0013] B) a polar aprotic swelling agent,

[0014] C) a catalyst, and

[0015] optionally D) a silylating agent, the silylating agent comprising a silylamine having a silicon-nitrogen moiety;

[0016] wherein the amount of D) the silylating agent added is sufficient to provide an amount of silyl groups for 0 mol% to <50 mol% of the hydroxyl groups of A) the cellulose, thereby forming E) a powdery intermediate; and

[0017] 2) Adding a certain amount of D) the silylating agent continuously or intermittently to E) the powdery intermediate over a period of >2 hours; wherein the total amount of D) the silylating agent added in steps 1) and 2) is >80 mol% to <200 mol%, alternatively >80 mol% to <150 mol% based on the amount of the hydroxyl groups of starting material A) the cellulose; thereby forming a powdery reaction product comprising the silylated cellulose.

[0018] In step 1), the amount of D) silylating agent added in step 1) can be 0. Alternatively, in step 1), a first portion of D) silylating agent in an amount sufficient to provide silyl groups for >0 mol% to <50 mol%, alternatively 0.01 mol% to 49 mol%, alternatively 30 mol% to 45 mol% of the hydroxyl groups of A) cellulose can be used. In this case, the powdery intermediate prepared in step 1) is a powdery reaction product comprising partially silylated cellulose. Without wishing to be bound by theory, it is believed that if 50 mol% or more of D) silylating agent is added in one go in step 1), the reaction product comprising partially silylated cellulose will be difficult to handle. However, it may be beneficial to add at least 30 mol% of D) silylating agent in step 1) to minimize the total processing time. Alternatively, the amount of silylating agent added in step 1) can be at least 30 mol%, alternatively at least 34 mol%, alternatively at least 35 mol%; at the same time, relative to the hydroxyl groups of A) cellulose, the amount of silylating agent can be <50 mol%, alternatively at most 45 mol%, alternatively at most 42 mol%, and alternatively at most 40 mol%. (For example, the molar ratio of the silyl groups of starting material D) to the COH groups of starting material A), the Si / COH ratio can be >0 to <0.50, alternatively 0.30 to 0.45, alternatively 0.34 to 0.42, alternatively 0.35 to 0.40.)

[0019] Steps 1) and 2) can be carried out in a reactor, such as a batch vessel having a jacket for heating and cooling and a stirrer for mixing. The type of reactor is not critical and can be any reactor suitable for mixing liquids and powders. The temperature in steps 1) and 2) can be 30 °C to 150 °C, alternatively 50 °C to 85 °C, alternatively 50 °C to 80 °C, and alternatively 55 °C to 80 °C. The pressure in steps 1) and 2) can be 730 mmHg (97 kPa) to 790 mmHg (105 kPa), alternatively 750 mmHg (100 kPa) to 770 mmHg (103 kPa).

[0020] In step 2), D) the feeding rate of the silylating agent can be defined as any aliquot or continuous flow control, i.e., the stoichiometry of the silylating agent loaded within a period of > 24 min to 500 min is > 0 mol% to < 20 mol% based on the moving average of any two aliquots. Those skilled in the art will understand how to use aliquots or continuous flow to feed at this rate based on the description herein and the examples below. Without wishing to be bound by theory, it is believed that using this feeding rate in step 2) causes the reaction product containing silylated cellulose to form a powder, which can be processed with conventional solid handling equipment and avoids the formation of pastes or solids that cannot be mixed or removed from the reactor. Without wishing to be bound by theory, it is believed that if all of the remaining amount (e.g., ≥ 50 mol%) of D) the silylating agent is added at once in step 2), the reaction product containing silylated cellulose will be difficult to process. Therefore, the above continuous or intermittent feeding rate is used in step 2) to keep the reaction product as a powder. In step 2), the total amount of D) the silylating agent added in steps 1) and 2) is > 80 mol% to < 200 mol% based on the amount of the hydroxyl groups of starting material A) cellulose.

[0021] The method may also optionally include one or more additional steps. For example, the method may also include drying A) cellulose before step 1). Commercially available cellulose may contain adsorbed water. To minimize the formation of by-products, the cellulose can be dried to remove at least part of the moisture. Drying can be carried out by any convenient means, such as heating the cellulose and / or subjecting it to a reduced pressure environment, or exposing it to a stream of inert gas.

[0022] The method may optionally also include adding F) a solvent, which is different from B) the polar aprotic swelling agent, for example, added during or before step 1). Alternatively, the method may also include an additional step, which includes: before step 1), dissolving C) the catalyst in one or both of B) the polar aprotic swelling agent and F) the solvent to form a catalyst solution. The resulting catalyst solution can be mixed with A) cellulose before step 1) (e.g., before adding any silylating agent to the reactor). For example, the catalyst solution can be mixed with A) cellulose for at least 10 minutes, alternatively at least 15 minutes; meanwhile, the catalyst solution can be mixed with A) cellulose for at most 1 hour before adding the first portion of D) the silylating agent. When used, F) the solvent can be present in an amount of > 0 times to 15 times the weight of C) the catalyst, alternatively > 0 times to 12 times the weight of the catalyst. Alternatively, the method can be solvent-free, where F) the solvent is not used.

[0023] Alternatively, the method may further include an additional step, which includes forming C) a catalyst by a method including non-in-situ reaction of a part of D) a silylating agent with an acid. Optionally, F) a solvent may be used to facilitate mixing of D) the silylating agent with the acid. When this step is added to the method, the silylating agent used to form the catalyst may be (but is not limited to) a silazane as described below as starting material D). The silazane selected for forming the catalyst may be the same as or different from the starting material D) used in step 1) for the silylation reaction. This step may be carried out in any convenient manner, such as by mixing at room temperature and atmospheric pressure.

[0024] The method may optionally further include an additional step, which includes reducing the pressure on the powdered intermediate after step 1) and before step 2). The pressure may be, for example, ≤400 mmHg, alternatively ≤200 mmHg, and alternatively >0 mmHg to 100 mmHg. Alternatively, when adding D) the silylating agent in step 1), the pressure may be reduced on the powdered reaction product containing partially silylated cellulose, for example, to remove by-products.

[0025] The method may optionally further include step 4): washing the powdered silylated cellulose by mixing the powdered silylated cellulose with G) a washing solvent to remove any possible residual polar aprotic swelling agent, catalyst, and / or solvent, and / or by-products. The selection of the washing solvent is not particularly limited; however, the washing solvent may be a low-boiling polar solvent that can dissolve the residual starting material and / or by-products but does not significantly solubilize the silylated cellulose, and the washing solvent can be conveniently evaporated from the silylated cellulose product. The washing in step 4) may be carried out in any convenient manner, such as by mixing the washing solvent with the powdered silylated cellulose produced as described above in the reactor used in step 1) or in a stirred slurry container, and then discharging the solvent after a sufficient time. The washing step may be repeated as needed, such as 1 to 10 times.

[0026] The method may optionally further include step 5): removing G) the washing solvent by any convenient means, such as filtration, heating, reducing pressure, and / or by purging with a gas (such as air or an inert gas (such as nitrogen)).

[0027] The resulting product is a pure silylated cellulose with low waste emissions and high volume efficiency in the production process. The DS (degree of substitution) of the silylated cellulose produced by this method is alternatively 2.0 to 3.0, alternatively 2.2 to 3.0, alternatively 2.5 to 3.0, alternatively 2.6 to 3.0, and alternatively 2.8 to 3.0.

[0028] The starting materials used in this article will be described in further detail below.

[0029] A) Cellulose

[0030] Starting material A), namely the cellulose used in the above method, has > 2.5 to 3 hydroxyl groups, alternatively 3 hydroxyl groups, in each repeating monomer unit of its molecule. Cellulose is a polymer of β(1→4)-linked D-glucose repeating monomer units. Cellulose can have 200 or more repeating monomer units per molecule. Alternatively, cellulose can have at least 200, alternatively at least 300, alternatively at least 400, alternatively at least 500, alternatively at least 600, alternatively at least 700 repeating monomer units; meanwhile, cellulose can have at most 10,000, alternatively at most 9,000, alternatively at most 8,000, alternatively at most 7,000, alternatively at most 6,000, alternatively at most 5,000, alternatively at most 4,000 repeating monomer units per molecule. Alternatively, cellulose can have 200 to 10,000, alternatively 400 to 8,000 repeating monomer units per molecule.

[0031] The type of cellulose can be, for example, microcrystalline cellulose or pulp cellulose. Sources of cellulose include but are not limited to cotton linters, pine wood, and tunicin (animal-derived cellulose). Cellulose is commercially available from various sources.

[0032] B) Polar aprotic swelling agent

[0033] The starting material B) used in the above method is a polar aprotic swelling agent. Examples of suitable polar aprotic swelling agents include N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), dimethyl sulfone, propylene carbonate, pyridazine, dimethylformamide (DMF), ethylene carbonate, sulfolane, tetrahydrothiophene-1-oxide, and hexamethylphosphoric triamide (HMPA).

[0034] The amounts of starting materials A) and B) are such that the weight ratio of B) the polar aprotic swelling agent to A) cellulose is < 3:1, alternatively < 1:1, alternatively < 0.3:1 (B:A ratio). Alternatively, the B:A ratio can be at least 0.1:1, alternatively 0.11:1, alternatively 0.12:1, alternatively 0.13:1, alternatively 0.14:1, alternatively 0.15:1, while the B:A ratio can be at most < 0.3:1, alternatively 0.29:1, alternatively 0.28:1, alternatively 0.27:1, alternatively 0.26:1.

[0035] C) Catalyst

[0036] Starting material C) in the above method is a catalyst that can catalyze the reaction between the hydroxyl groups of A) cellulose and the silicon-nitrogen (Si-N) moiety of D) a silylating agent. Examples of suitable catalysts include ammonium salts such as ammonium chloride, ammonium trifluoroacetate, or ammonium trifluoromethanesulfonate; saccharin; sulfonic acids such as methanesulfonic acid, p-toluenesulfonic acid, or trifluoromethanesulfonic acid (triflic acid); trifluoroacetic acid; trimethylchlorosilane; or combinations thereof. Alternatively, the catalyst can be selected from the group consisting of ammonium chloride, ammonium trifluoroacetate, or saccharin. Alternatively, the catalyst can be selected from the group consisting of ammonium chloride or ammonium trifluoroacetate. Alternatively, the catalyst can include (or can be) ammonium trifluoroacetate.

[0037] Those skilled in the art should understand that the catalyst can be used by various methods. These methods can be to directly add C) the catalyst (such as ammonium trifluoroacetate) to the reactor, or to dissolve C) the catalyst in B) a polar aprotic swelling agent or F) a solvent, and then add the resulting catalyst solution to the reactor. Alternatively, C) the catalyst can be formed by pre-mixing a specific silylating agent (such as a silazane or other silylamine (as described below for starting material D)) with an acid (such as trifluoroacetic acid or triflic acid), and then loading the resulting mixture containing the silylammonium salt catalyst into the reactor.

[0038] The amount of the catalyst depends on various factors, including the type of the catalyst and the selected temperature. However, based on the combined weight of starting materials A), B), C), D) used in the method, the amount of the catalyst can be at least 0.01 wt%, alternatively at least 0.1 wt%, alternatively at least 0.3 wt%, while the amount of the catalyst can be at most 5 wt%, alternatively at most 4 wt%, alternatively at most 3 wt%, alternatively at most 2 wt%; alternatively, the amount of the catalyst can be from 0.1 wt% to 5 wt%, alternatively from 0.3 wt% to 2 wt%.

[0039] D) Silylating agent having Si-N moiety

[0040] Starting material D) in the above method is a silylating agent having a silicon-nitrogen (Si-N) moiety, including silylamines. The Si-N moiety can react with the hydroxyl groups of A) cellulose. The silylating agent can be selected from silazanes, aminosilanes, or combinations thereof. For example, the silazane can be a disilazane of the following formula: where R 1 、R 2 、R 3 、R 4 、R 5 、R 6 and R 7Each is independently selected from the group consisting of H, an alkyl group having 1 to 18 carbon atoms, and an alkenyl group having 2 to 18 carbon atoms. Suitable alkyl groups include methyl, ethyl, propyl, and butyl; alternatively, methyl, ethyl, and propyl. Suitable alkenyl groups include vinyl, allyl, and hexenyl. Examples of suitable disilazanes include 1,1,1,3,3,3 - hexamethyldisilazane (HMDZ), 1,3 - ethyl - 1,1,3,3 - tetramethyldisilazane, 1,3 - dipropyl - 1,1,3,3 - tetramethyldisilazane, 1,3 - dibutyl - 1,1,3,3 - tetramethyldisilazane, 1,3 - divinyl - 1,1,3,3 - tetramethyldisilazane, 1,3 - diallyl - 1,1,3,3 - tetramethyldisilazane, 1,3 - dibutenyl - 1,1,3,3 - tetramethyldisilazane, and 1,3 - hydro - 1,1,3,3 - tetramethyldisilazane.

[0041] Alternatively, the silylating agent can be an aminosilane, which can have the structural formula: R N x SiR 8 4-x , where each R N is an amino functional group bonded to silicon via a nitrogen atom; and each R 8 is independently selected from the group consisting of H, an alkyl having 1 to 18 carbon atoms, and an alkenyl having 2 to 18 carbon atoms, as described above for R 1 , where the subscript x is from 1 to 3. R N can have the structural formula -NR 9 2, where each R 9 is independently selected from the group consisting of H, an alkyl having 1 to 18 carbon atoms, or an aryl having 6 to 18 carbon atoms.

[0042] Examples of aminosilanes include tris(dimethylamino)silane, bis(diisopropylamino)silane, (N,N - dimethylamino)trimethylsilane, trimethyl(amino)silane {H2N - Si(CH3)3}, triethyl(amino)silane {H2N - Si(CH2 - CH3)3}, tripropyl(amino)silane {H2N - Si(C3H7)3}, tributyl(amino)silane {H2N - Si(C4H9)3}, dimethylethyl(amino)silane, dimethylbutyl(amino)silane, trivinyl(amino)silane, dibutylethyl(amino)silane, tris(1 - butenyl)(amino)silane, or triaryl(amino)silane. Suitable aminosilanes are known in the art and are commercially available from, for example, Sigma - Aldrich, Inc. (St. Louis, Missouri, USA) or Gelest Inc. (Morrisville, Pennsylvania, USA).

[0043] Starting material D) The silylating agent can be any one of the above-mentioned silazanes and / or aminosilanes. Alternatively, D) the silylating agent can be two or more silazanes, two or more aminosilanes, or a combination of silazanes and aminosilanes. The amount of starting material D) the silylating agent is sufficient to maintain the molar ratio of the Si-N moiety of the D) silylating agent to the hydroxyl groups of A) cellulose in the range of >0.67:1 to 4:1 (D Si :A OH ratio). Alternatively, D Si :A OH ratio can be 0.7:1 to 3.5:1, alternatively 0.8:1 to 3.0:1, alternatively 0.9:2.5:1, alternatively 1:1 to 2.0:1, alternatively 1.15:1 to 1.98:1, and alternatively 1.3:1 to 1.4:1.

[0044] F) Solvent

[0045] The starting material F) used in the above method is an optional solvent, which is different from B) the polar aprotic swelling agent. The solvent is not particularly limited and can be any solvent capable of dissolving or dispersing C) the catalyst and one or more other starting materials. For example, the solvent can include aliphatic hydrocarbons (such as hexane), aromatic hydrocarbons (such as toluene or xylene), halogenated hydrocarbons (such as carbon tetrachloride), or ethers (such as tetrahydrofuran).

[0046] The amount of the solvent depends on various factors, including the type and amount of the selected catalyst. However, the amount of the solvent can be ≥0 times to 15 times the weight of C) the catalyst, alternatively at most 12 times the weight of the catalyst. Without wishing to be bound by theory, it is believed that for volume efficiency, it is desirable to minimize the amount of the solvent.

[0047] G) Washing solvent

[0048] The starting material G) in the method described herein is an optional washing solvent, which can be used to remove the residual starting materials and / or by-products in the silylated cellulose produced by the method. The washing solvent can be different from the above-mentioned starting materials B) and F). Examples of suitable washing solvents include water, ketones (such as acetone), monohydric alcohols (such as methanol or ethanol); alternatively acetone. Without wishing to be bound by theory, it is believed that ketones (such as acetone) can effectively remove polar and non-polar residues while being easily removed from the silylated cellulose under reduced pressure.

[0049] Method of use

[0050] The silylated cellulose prepared as described herein can be used in a variety of end applications. For example, the silylated cellulose can replace the cellulose derivatives described in U.S. Patent No. 10,851,180 and be used in the optical films of image display devices. Alternatively, the silylated cellulose prepared as described above can be used as a thickening polymer in personal care applications such as cosmetic formulations or sunscreen formulations. For example, as a supplement to the silylated cellulose polymer disclosed in PCT Patent Publication WO / 2022 / 066591, or in place of that polymer.

[0051] Examples

[0052] These examples are provided to illustrate the invention to those skilled in the art and should not be construed as limiting the scope of the invention as recited in the claims. The starting materials used in these examples are summarized in Table 1 below.

[0053] Table 1 - Starting materials

[0054] Starting materials Description Source A1 Microcrystalline cellulose Avicel PH-101 from IFF A2 Pulped cellulose Ground E60 from Georgia Pacific B1 DMSO Dimethyl sulfoxide Sigma-Aldrich <![CDATA[C1 NH4Cl]]> Ammonium chloride Sigma-Aldrich D1 HMDZ Hexamethyldisilazane Dow F1 Acetone Oakwood Chemicals

[0055] Example 1 .

[0056] In this Example 1, the cellulose was silylated in a Sigma paddle mixer (reactor) by loading 236.2 grams of microcrystalline cellulose, then loading a pre-dissolved solution of 65.4 grams of DMSO and 5.7 grams of NH4Cl and mixing for 30 minutes. 130.3 grams of HMDZ (0.37 moles Si:COH) was loaded into the reactor at ambient temperature and heated to 53 °C and then held at that temperature for one hour. At this point, the mixture maintained a consistency like that of a wet powder. The reactor was then evacuated to <200 mmHg and held for 15 minutes until condensate ceased in the dry ice vacuum trap. The vacuum was then broken with nitrogen and, over time, the reaction was continued with aliquots of the HMDZ loaded. 182.7 grams of HMDZ (moles Si:COH of 0.52) was loaded in aliquots of approximately 60 grams every 30 minutes. Throughout this time, the material in the reactor maintained a free-flowing consistency like that of a wet powder. The reactor was then evacuated to <200 mmHg and held for 30 minutes. The vacuum was then broken with nitrogen and, over time, the reaction was continued with aliquots of the HMDZ loaded. An additional 135.1 g of HMDZ (moles Si:COH of 0.38) was loaded in four approximately equal aliquots every 40 minutes for a total moles Si:COH ratio of 1.27. At each addition, the material would assume the consistency of a free-flowing wet powder and slowly convert to a free-flowing dry powder over about 20 minutes. After the last addition, the reactor was held at that temperature for one hour. The reactor was then evacuated to <200 mmHg and held for approximately 45 minutes. The reactor was cooled and 527.2 grams of the resulting crude product was recovered. The DS of the resulting silylated cellulose powder was 3.0.

[0057] Example 2 .

[0058] In this Example 2, the cellulose was silylated in a Sigma paddle mixer by loading 235 g of pulped cellulose, then loading a pre-dissolved solution of 64.7 g of DMSO and 5.68 g of NH4Cl and mixing for 30 minutes. 140 g of HMDZ (molar Si:COH of 0.4) was loaded into the reactor, which was then heated to 50 °C and held for one hour. At this time, the vacuum was drawn down to <200 mmHg to strip the liquid from the reactor. Then an additional 217 g of HMDZ (molar Si:COH of 0.62) was loaded in seven equal increments, with a 15-minute interval between each addition. At this time, the vacuum was drawn down to <200 mmHg to strip the liquid from the reactor. Then an additional 85 g of HMDZ (molar Si:COH of 0.24) was loaded in six equal increments, with a 20-minute interval between each addition, for a total molar Si:COH ratio of 1.26. The reactor was then held at 50 °C for one hour. The material in the reactor was a free-flowing powder throughout the feed and vacuum stripping. After holding at this temperature, the reactor was evacuated to <200 mmHg. After achieving the vacuum, the reactor was heated at 90 °C for 30 minutes, ensuring that no more liquid dripped into the vacuum flask. 513.27 g of the crude product was recovered. The crude product was washed with acetone in a Buchner funnel and then dried overnight in a dish. The DS of the resulting silylated cellulose powder was 2.0.

[0059] Example 3 – Commercial scale run

[0060] In this Example 3, the cellulose was silylated in a Littleford plowshare mixer by loading 1735 grams of microcrystalline cellulose, then loading a pre-dissolved solution of 467.5 grams of DMSO and 41.3 grams of NH4Cl and mixing for 30 minutes. 870 grams of HMDZ (molar Si:COH = 0.34) were continuously fed through a spray nozzle using a pressure tank and a needle valve over 34 minutes while maintaining the reactor at 65 °C. The mixture was then held at this temperature and mixed for one hour. At this point, the vacuum was pulled <50 mmHg and held for 15 minutes. Then, an additional 894.6 grams of HMDZ (molar Si:COH = 0.34) were continuously fed through a spray nozzle using a pressure tank and a needle valve over 126 minutes while maintaining the reactor at 65 °C. The rate of HMDZ was then slowed, and an additional 1,490 grams of HMDZ (molar Si:COH = 0.58) were continuously fed through a spray nozzle using a pressure tank and a needle valve over 317 minutes while maintaining the reactor at 65 °C, for a total molar Si:COH ratio of 1.26. The reactor was then held at 65 °C for 29 minutes. The material in the reactor was a fine flowing powder throughout the reaction and feed. After being held at this temperature, the reactor was pulled to a vacuum <50 mmHg. After achieving the vacuum, the reactor was heated to 90 °C for 60 minutes, ensuring that no liquid dripped from the vacuum flask.

[0061] After vacuum stripping the crude product, a portion of the resulting material (1055 grams) was removed from the reactor. Then 8000 grams of cold acetone (3 °C) were loaded into the reactor with the remaining crude silylated cellulose, and the slurry was mixed occasionally (mixed three times at 60 RPM for 2 minutes - 5 minutes each over 33 minutes) while maintaining a slurry temperature of 25 °C. Then the bottom port was opened, and the material was drained through a bag filter to capture the solids. The solids were loaded back into the reactor and washed a second time. 6000 grams of acetone were loaded into the reactor and mixed with the plow at 60 RPM and the reactor at 25 °C for 31 minutes. Then the bottom port was opened, and the material was drained through a bag filter to capture the solids. In this step, 1350 grams of silylated cellulose were removed and set aside. The residue of the solids was loaded back into the reactor. 4000 grams of acetone were loaded into the reactor and mixed with the plow at 60 RPM for 31 minutes. Then the bottom port was opened, and the material was drained through the filter. The collected solids were loaded back into the reactor one last time. Then the remaining powder was mixed at 120 RPM while heating to 90 °C and pulling a vacuum to -22 inHg. The vacuum drying step was held for 72 minutes. The product was then cooled and discharged from the plowshare mixer as a fine dry powder. The final dried product collected was 1300 grams of powdered silylated cellulose with a DS of 2.5.

[0062] Example 4 – Silylated cellulose using TFAA.NH3 catalyst

[0063] In this Example 4, the cellulose was silylated in a Sigma paddle mixer by loading 249 grams of microcrystalline cellulose, then loading a pre-dissolved solution of 68 grams of DMSO and 10.43 grams of ammonium trifluoroacetate and mixing for 15 minutes. 157 grams of HMDZ (molar Si:COH = 0.42) was loaded into the reactor, which was then heated to 65 °C and held for one hour. At this time, the vacuum was drawn down to <200 Torr to strip the liquid from the reactor. The vacuum was then broken with nitrogen. Then an additional 188 grams of HMDZ (molar Si:COH = 0.51) was loaded in six equal increments, with a 10-minute interval between each addition. The material in the reactor remained a fine dry powder at all times. Then an additional 140.5 grams of HMDZ (molar Si:COH = 0.38) was loaded in seven equal increments, with a 20-minute interval between each addition, for a total molar Si:COH ratio of 1.31. The material in the reactor remained a fine dry powder at all times. The reactor was then held at 65 °C for one hour. After holding at this temperature, the reactor was evacuated to <200 Torr. After achieving the vacuum, the reactor was heated to 90 °C for 30 minutes, ensuring that no more liquid was dripping into the vacuum flask. 579.02 grams of crude product was recovered. The material was washed three times with acetone in a pressure filter and then dried overnight by purging with nitrogen. The DS of the resulting silylated cellulose powder was 2.6.

[0064] Example 5

[0065] In this Example 5, the cellulose was silylated in a Littleford plowshare mixer by loading 1440 g of microcrystalline cellulose, then loading a pre-dissolved solution of 404 g of DMSO and 35.6 g of NH4Cl and mixing for 35 minutes. 955 g of HMDZ (molar Si:COH = 0.44) was fed continuously through a nozzle using a pressure vessel and a needle valve over 50 minutes while maintaining the reactor at 70 °C. The mixture was then held at this temperature and mixed for twenty minutes. At this point, the vacuum was pulled <50 mmHg and held for 20 minutes. Then, an additional 870 g of HMDZ (molar Si:COH = 0.40) was fed continuously through a nozzle using a pressure vessel and a needle valve over 147 minutes while maintaining the reactor at 70 °C. At this point, the vacuum was pulled <50 mmHg and held for 10 minutes. Then an additional 910 g of HMDZ (molar Si:COH = 0.42) was fed continuously through a nozzle using a pressure vessel and a needle valve over 127 minutes while maintaining the reactor at 70 °C, for a total molar Si:COH ratio of 1.27. The reactor was then held at 65 °C for 30 minutes. The material in the reactor was a dry powder throughout the reaction and feed. After holding at this temperature, the reactor was pulled to a vacuum <50 mmHg. After achieving the vacuum, the reactor was heated to 80 °C and held for 13 minutes, ensuring that no liquid was dripping in the vacuum flask.

[0066] The 1.6 kg sample was divided into two equal portions. The two fractions were washed on a coarse fritted glass with acetone (1 L). For both fractions, the solids were ground to a powder using a laboratory blender, washed twice more with 1 L of acetone each, and filtered on the fritted glass. The samples were placed in a fume hood to dry for 24 h. The solids from the two fractions were combined and washed twice more with 1 L of acetone each, and filtered on the fritted glass. The samples were placed in a fume hood to dry for 72 h. The resulting silylated cellulose powder had a DS of 2.7.

[0067] Comparative Example 6 – Large initial loading of HMDZ, without step 2)

[0068] For Comparative Example 6, the cellulose was silylated in a horizontal plow mixer by loading 2.64 kg of pulped cellulose, then loading a pre-dissolved solution of 740 g of DMSO and 65.4 g of NH4Cl and mixing for 30 minutes. The stirrer was heated to 90 °C. When the internal temperature reached 68 °C, 5.25 kg of HMDZ (molar ratio of Si:COH = 1.33) was loaded within 10 minutes. When the internal temperature reached 90 °C, the temperature of the hot oil system was reduced to prevent the internal temperature from exceeding 90 °C. The reactor was maintained at this temperature for about 1.5 hours; however, a high current was observed during this period. When the system was evacuated, the stirrer malfunctioned and could not be restarted. When the stirrer was turned on, it was observed that the entire internal space was completely filled with a hardened foam-like substance, which had to be manually cut and removed. This example shows that when the method of the present invention is not followed and the silylating agent (HMDZ) is added all at once, powdered silylated cellulose is not formed. The formed hardened solid cannot be practically processed, and the method for silylating cellulose in this comparative example is not suitable for producing silylated cellulose on a commercial scale.

[0069] The DS or degree of substitution is defined as the average number of hydroxyl groups silylated in each monomer unit of cellulose. The DS was determined by ATR-FTIR as follows. The degree of substitution (DS) of -SiR3 in the silylated cellulose prepared by the method described herein was determined using techniques known in the art: based on attenuated total reflection - Fourier transform infrared spectroscopy, using the spectral parameters provided in Table 2, the peak areas calculated by MATLAB were analyzed, and the measured DS values are reported in Table 3.

[0070] Table 2 .

[0071]

[0072] Table 3. DS values of the above examples 。

[0073] Sample SiMe CO OH [OH] / [Si] DS Si wt% OH wt% Ex.1(27) 3.2 24.2 0 0 3.0 22.2％ 0.0％ Ex.2(29) 2.8 22.7 1.8 0.32 2.0 18.2％ 5.8％ Ex.3(BP-6) 1.4 11.7 0.3 0.12 2.5 20.5％ 2.4％ Ex.4(38) 2.7 20.8 0.5 0.11 2.6 20.7％ 2.2％ EX.5(BP-5) 2.6 20.3 0.3 0.06 2.7 21.3％ 1.3％

[0074] Industrial applicability

[0075] Without wishing to be bound by theory, it is believed that the methods described herein can provide silylated celluloses having a DS ≥ 2, alternatively DS ≥ 2.5, alternatively ≥ 2.6, and alternatively DS ≥ 2 to 3.0. Examples 1 to 4 show that silylated celluloses having a degree of substitution of up to 3.0 are prepared by the method of the present invention. Examples 1 to 4 and Comparative Example 5 show that the method of the present invention provides the benefit of providing silylated cellulose in powder form, which is easy to transport in a method with good volume efficiency and which does not require the use of solvents during the silylation reaction. In addition, the method of the present invention is suitable for the production of silylated cellulose on a commercial scale. The above examples show that the method can produce silylated cellulose in batches of ≥ 500 g, alternatively ≥ 600 g, alternatively ≥ 1 kg, alternatively ≥ 3 kg.

[0076] Without wishing to be bound by theory, it is believed that the method of the present invention can provide the further benefit of minimizing or eliminating the yellowing of silylated cellulose produced by carrying out the silylation reaction at a temperature of ≤ 85°C.

[0077] Definition and usage of terms

[0078] Unless otherwise indicated, all amounts, ratios, and percentages herein are by weight. Unless otherwise indicated, each of the articles "a", "an", and "the" refers to one or more. Unless otherwise indicated, the singular includes the plural meaning. The Summary of the Invention and the Abstract of the Specification are hereby incorporated by reference. The transitional phrases "comprising", "consisting essentially of", and "consisting of" are used as described in Chapters §2111.03I., II., and III of the Ninth Edition of the Manual of Patent Examining Procedure, Revision 08.2017, last revised in January 2018.

[0079] The abbreviations used herein have the definitions in Table 4.

[0080] Table 4—Abbreviations

[0081] Abbreviation Definition ATR-FTIR Attenuated total reflection - Fourier transform infrared ℃ Degree Celsius DS Degree of substitution g Gram h Hour Kg or kg Kilogram min Minute RT Room temperature of 23°C ± 3°C

Claims

1. A method for preparing powdered silylated cellulose, wherein the method comprises: 1) Mixing starting materials, the starting materials comprising A) cellulose, the cellulose comprising repeating monomer units and each monomer unit having >2.5 to 3 hydroxyl groups, B) a polar aprotic swelling agent, C) a catalyst, and optionally D) a silylating agent, the silylating agent comprising a silylamine having a silicon-nitrogen moiety; wherein the amount of D) the silylating agent added in step 1) is sufficient to provide an amount of silyl groups for 0 mol% to <50 mol% of the hydroxyl groups of A) the cellulose, thereby forming E) a powdered product; and 2) Adding, over a period of >2 hours, a quantity of D) the silylating agent continuously or intermittently to E) the powdered product; wherein the total amount of D) the silylating agent added in steps 1) and 2) is >80 mol% to <200 mol% based on the amount of the hydroxyl groups of starting material A) the cellulose; thereby forming a powdered reaction product comprising the silylated cellulose.

2. The method according to claim 1, wherein in step 1), the amount of D) the silylating agent is sufficient to provide 30 mol% to 45 mol% of the hydroxyl groups of A) the cellulose, and the reaction product prepared in step 1) comprises partially silylated cellulose.

3. The method according to claim 2, the method further comprising reducing the pressure on the reaction product comprising the powdered partially silylated cellulose before step 2).

4. The method according to any one of claims 1 to 3, the method further comprising drying A) the cellulose before step 1).

5. The method according to any one of claims 1 to 4, wherein the amounts of B) the polar aprotic swelling agent and A) the cellulose are such that the weight ratio of B) the polar aprotic swelling agent to A) the cellulose is <3:1 (B:A ratio).

6. The method according to any one of claims 1 to 5, wherein C) the catalyst is selected from saccharin, ammonium trifluoroacetate, and ammonium chloride.

7. The method according to claim 6, wherein C) the catalyst is ammonium trifluoroacetate.

8. The method according to any one of claims 1 to 5, wherein the method further comprises: C) the catalyst is formed by a method comprising an ex-situ reaction of a silazane with an acid.

9. The method according to any one of claims 1 to 8, wherein steps 1) and 2) are carried out at a pressure of 730 mmHg (97 kPa) to 790 mmHg (105 kPa).

10. The method according to any one of claims 1 to 9, wherein steps 1) and 2) are carried out by heating at 50 °C to 85 °C.

11. The method according to any one of claims 1 to 10, the method further comprising step 3): heating the reaction product at a temperature of >50 °C to 90 °C at a pressure of >0 kPa to <101 kPa and pulverizing the reaction product, thereby forming powdered silylated cellulose.

12. The method according to claim 11, wherein the method further comprises step 4): washing the powdered silylated cellulose 1 to 10 times by mixing the powdered silylated cellulose with G) a washing solvent.

13. The method according to claim 12, wherein G) the washing solvent is removed by heating, reducing pressure, and / or by purging with a gas.

14. The method according to any one of claims 1 to 13, wherein the powdered silylated cellulose is produced in an amount of at least 500 g.

15. The method according to any one of claims 1 to 14, wherein in step 2), D) the feeding rate of the silylating agent is any aliquot or continuous flow control, i.e., the stoichiometry of the silylating agent loaded in a period of > 24 min to 500 minutes is > 0 mol% to < 20 mol% based on the moving average of any two aliquots.

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