Method and device for continuously preparing plant fiber pulp using subcritical fluid

Abstract

The method and preparation device of continuously preparing plant fiber pulp using subcritical fluid, the original plant fiber obtained by grinding is put into a mixer and mixed with the subcritical fluid, and the slurry obtained by mixing enters the oil kettle through the first pipeline under the action of pressure, and the first pipeline is in a spiral state (i.e., a spiral tube) in the oil kettle, and the oil kettle is filled with heat transfer oil, and the heat transfer oil wraps the spiral tube. The slurry is 1.0MPa~20MPa in the spiral tube, and the external temperature is 97℃~300℃, and the continuous reaction is 2-3 hours to obtain plant fiber pulp, and the working pressure of the plant fiber pulp is reduced to normal pressure and distilled, and the subcritical fluid in the gas state volatilized is collected, and the plant fiber pulp after distillation is separated to obtain plant cellulose. This method and preparation device used in the present invention make lignin cleanly separated, subvert the traditional concept of preparing pulp, change the traditional acid-base cooking process for preparing pulp, and avoid the pollution of the papermaking industry to the environment.

Description

Technical Field

[0001] The invention relates to the field of papermaking, and in particular to a method and a preparation device for continuously preparing pulp by combining subcritical fluid with plant fibers. Background Art

[0002] Paper is the most commonly used item in daily life. Papermaking is an important invention of the working people in ancient China. It is generally made of a water suspension of plant fibers that has been pulped, that is, the pulp is diluted with water to a certain concentration, and initially dehydrated on the paper machine net or manually to form wet paper sheets, which are then squeezed and dehydrated, and then dried into paper.

[0003] Conventional pulp preparation processes include stock preparation, pulping, alkali recovery, bleaching, and papermaking, which result in serious water pollution, air pollution, and solid waste pollution in the papermaking industry, commonly known as the three major pollutions. Each ton of pulp and paper uses more than 300 tons of water, and the wastewater discharged contains high levels of organic matter, seriously exceeding the biochemical oxygen demand (BOD) and suspended solids (SS), and contains a large amount of toxic substances and odor, which is extremely harmful to the normal growth of aquatic organisms and affects the water use and environmental landscape of industry, agriculture, animal husbandry, and residents. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a method and a preparation device for continuously preparing plant fiber pulp using subcritical fluid, aiming to overcome the defects of the prior art and achieve the purpose of safe and environmentally friendly papermaking and pollution-free preparation of pulp. The technical solution adopted is:

[0005] A method for continuously preparing plant fiber pulp using subcritical fluid, wherein the original plant fiber obtained by grinding is mixed with the subcritical fluid, and the mixed slurry is continuously reacted for 2-3 hours under the condition of internal pressure of 1.0MPa-20MPa and external temperature of 97℃-300℃ to obtain plant fiber pulp, the working pressure of the plant fiber pulp is reduced to normal pressure and distilled, the volatilized subcritical fluid in gas state is collected, and the distilled plant fiber pulp is separated to obtain plant cellulose. Plant cellulose can be directly used to make original color paper, or to produce different types of paper with recycled pulp. In the whole process, no pollutants are generated, only water and subcritical fluid participate in the reaction, and after the plant fiber pulp is reduced in pressure and distilled, the collected volatilized subcritical fluid can be continuously used to form a cycle, which is beneficial to environmental protection. The internal pressure is the working pressure required by the slurry during the reaction, which is provided by the inside of the pipeline (i.e., the spiral tube mentioned later), and the external temperature is the working temperature required by the slurry during the reaction, which is provided by the outside of the pipeline (i.e., the spiral tube mentioned later).

[0006] The above method for continuously preparing plant fiber pulp using subcritical fluid, further comprises:

[0007] The specific steps are as follows:

[0008] S1: crushing the plant straw skin to no more than 100 mesh, drying at 105°C for 0.5h to 24h to obtain original plant fiber;

[0009] S2: Mix 10%-40% original plant fiber (mass fraction ratio), 50%-70% water, 10%-60% subcritical fluid, and 1%-10% additive;

[0010] S3: pressurizing the slurry obtained in S2, so that it reacts continuously for 2-3 hours at a pressure of 1.0 MPa to 20 MPa and a temperature of 97° C. to 300° C., to obtain plant fiber pulp;

[0011] S4: reducing the pressure of the plant fiber pulp to normal pressure and distilling the plant fiber pulp, volatilizing the gaseous subcritical fluid in the plant fiber pulp mixed liquid, and collecting and condensing the volatilized gaseous subcritical fluid;

[0012] S5: Separating the distilled plant fiber pulp through a centrifugal or extrusion device to obtain plant cellulose.

[0013] The present invention first mixes the original plant fiber with the subcritical fluid in proportion, and places the slurry at a specific pressure and temperature for continuous reaction, so that the lignin in the original plant fiber is dissolved and separated from the cellulose. The specific pressure and temperature are the subcritical working pressure and temperature required for the dissolution of lignin in different original plant fibers. After the lignin in the original plant fiber is dissolved, the obtained plant fiber pulp is separated to obtain plant cellulose. Plant cellulose can be directly used for papermaking without bleaching to produce original color paper. Plant cellulose can also be made into recycled pulp with native plant fibers or inorganic nanofibers, and can even be directly mixed with waste paper product fibers to obtain pulp, producing various types of paper and products. The inorganic nanofibers refer to nanoscale fibers, such as artificial or natural whiskers, nanofibers, nanoparticles, nanotubes, etc.

[0014] The above-mentioned method for continuously preparing plant fiber pulp using subcritical fluid, further, the subcritical fluid is one or more of water, methyl cellosolve, pyridine, dioxane, acetone, ethanol, butanol, propanol, ethylene glycol, CO2, n-hexane, propane, butane, hexane, dimethyl ether, 1.4-butanediol. Subcritical fluid refers to a substance that exists in the form of fluid under the conditions of temperature higher than its boiling point but lower than its critical temperature and pressure lower than its critical pressure. The present invention utilizes this characteristic of subcritical fluid, and according to the critical pressure of different original plant fibers, utilizes subcritical fluid to help the lignin in the original plant fiber to be better dissolved, and then better separated from cellulose.

[0015] In the above method for continuously preparing plant fiber pulp using subcritical fluid, the original plant fiber is agricultural straw fiber or wood fiber with a mesh size of no more than 100 obtained by grinding, or kneaded fiber with a mesh size of no more than 100 obtained by kneading. There can be many types of original plant fibers, all of which are processed to obtain fibers with a mesh size of no more than 100.

[0016] The above-mentioned method for continuously preparing plant fiber pulp using subcritical fluid, further, the auxiliary agent is one or more of urea, formic acid, acetic acid, sodium hydroxide, sodium carbonate, sodium sulfite, magnesium chloride, H2O2, sodium acetate, KHCO3, phenol, polyethylene glycol, diethylene glycol, dilute sulfuric acid, and glycerol.

[0017] A preparation device using the above method comprises a mixer, wherein an agitator is arranged in the mixer, wherein the agitator extends downward from the top of the mixer into the mixer, wherein a first pipeline extends from the bottom of the mixer and is connected to the bottom of an oil kettle, wherein the first pipeline enters the oil kettle from the bottom, wherein the first pipeline rises in a spiral state in the oil kettle to form a spiral tube, wherein the top of the spiral tube passes through the side wall of the oil kettle and is connected to a storage tank, wherein a second pipeline extends from the top of the storage tank, wherein a condenser tube is wound around the second pipeline. The oil kettle is filled with heat transfer oil, wherein the heat transfer oil wraps around the spiral tube, wherein a supercharger is arranged at the top of the mixer, wherein a first flow meter is arranged on the pipeline from the mixer into the oil kettle, wherein a second flow meter and a pressure reducer are arranged in sequence on the pipeline from the oil kettle into the storage tank. Valves are arranged upstream and downstream of the first flow meter, wherein a valve is arranged upstream of the second flow meter, and wherein a valve is arranged downstream of the pressure reducer.

[0018] All raw materials are put into the mixer in proportion, and the agitator in the mixer stirs them. After stirring evenly, the supercharger is turned on, the pressure in the mixer increases, and the slurry in the mixer is transported to the oil kettle through the first pipeline under the action of pressure (the valves upstream and downstream of the first flowmeter are opened, and the first flowmeter controls the flow of the slurry through the first pipeline). Therefore, the first pipeline and the spiral tube have the pressure required for the slurry reaction (usually 1-20MPa), and the slurry is slowly transported from bottom to top in the spiral tube in the oil kettle (the transportation time is 2-3 hours). The heat transfer oil wraps the spiral tube in the oil kettle to provide temperature for the reaction inside the spiral tube to ensure the critical temperature required for the slurry reaction. The slurry reacts fully during the bottom-up transportation process. The slurry starts to react from the bottom of the spiral tube. When it is transported to the top of the spiral tube, it reacts completely. Under the action of subcritical fluid and critical pressure and temperature, the lignin in the original fiber pulp is fully dissolved and separated from cellulose.

[0019] After the reaction is complete, the plant fiber pulp enters the storage tank. During the process of the plant fiber pulp entering the storage tank, the pressure of the plant fiber pulp entering the storage tank is reduced to normal pressure through a pressure reducer. At this time, the plant fiber pulp is still warm. After the plant fiber pulp enters the storage tank, subcritical fluid volatile gas is formed. The volatile subcritical fluid gas enters the second pipeline, is cooled and condensed by the condenser wrapped around the second pipeline, and re-forms a liquid subcritical fluid, which can be further recycled.

[0020] The combination of the mixer and the oil kettle creates a subcritical environment, and because the mixer is connected to the oil kettle, and the oil kettle is connected to the storage tank, it ensures that the process of "the original plant fiber is mixed with the subcritical fluid, reacts fully in the subcritical environment, and then enters the storage tank" can continue, thereby ensuring that the plant fiber pulp can be produced continuously.

[0021] In the above-mentioned device for continuously preparing plant fiber pulp using subcritical fluid, further, the mixer can provide pressure for the slurry from the inside of the spiral tube alone, and the oil kettle can ensure the working temperature of the slurry from the outside of the spiral tube alone. This device can provide the required working temperature and working pressure to the slurry inside the spiral tube respectively, ensuring that the slurry can fully react.

[0022] In the above-mentioned device for continuously preparing plant fiber pulp using subcritical fluid, further, the mixer and the top of the oil kettle are both provided with a temperature sensor and a pressure sensor. The temperature sensor and the pressure sensor monitor the temperature and pressure in the mixer and the oil kettle in real time to ensure that the mixer and the oil kettle are at the critical pressure and temperature required for the original plant fiber reaction.

[0023] In the above-mentioned device for continuously preparing plant fiber pulp using subcritical fluid, further, the working pressure inside the spiral tube is 1-20MPa, and the temperature of the heat transfer oil is 97°C to 300°C. The working pressure inside the spiral tube is transmitted through the mixer through the first pipeline, so that the pressure inside the spiral tube reaches the pressure required for the slurry reaction, and the heat transfer oil outside the spiral tube wraps the spiral tube, providing the temperature required for the slurry reaction from the outside of the spiral tube.

[0024] The above-mentioned preparation device for continuously preparing plant fiber pulp using subcritical fluid, further, the first pipeline enters the oil kettle from the bottom, and is in a curved or straight or spiral state from left to right in the oil kettle. The first pipeline is connected to the inside of the oil kettle, and it can be of any shape, aiming to form the longest path in the limited space inside the oil kettle, and then combining the slurry flow through the first pipeline and the plant fiber pulp flow to the storage tank (the pulp flow is adjusted by adjusting the size of the valve upstream of the second flowmeter and the valve downstream of the pressure reducing valve, and the slurry flow is adjusted by adjusting the size of the valve upstream and downstream of the first flowmeter. By observing the first flowmeter and the second flowmeter, the first flowmeter and the second flowmeter are kept at 10L / h), so that the slurry has sufficient reaction time (2-3 hours) when it is transported from bottom to top in the oil kettle.

[0025] The subcritical fluid used in the present invention refers to a liquid below the supercritical point (such as the supercritical point of water 374 ° C, 22.1MPa; the supercritical point of carbon dioxide 31.1 ° C, 7.38MPa; the supercritical point of ethanol 243 ° C, 6.38MPa; the supercritical point of ammonia 132.4 ° C, 11.2MPa, etc.), with strong dissolving power and decomposition characteristics, especially water substantially without or less organic or inorganic solvents, no pollution to the environment and zero emission. However, the supercritical state of carbon dioxide or ethanol is more gentle, with the same mass transfer as water and lower pressure requirements for equipment. Subcritical technology is energy-saving and less solvent residue, and can achieve large-scale production, less investment, and low production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the device of the present invention;

[0027] Among them: 1-mixer, 2-booster, 3-agitator, 4-feed port, 5-temperature sensor, 6-pressure sensor, 7-valve, 8-oil kettle, 9-first flow meter, 10-pressure reducer, 11-storage tank, 12-condenser, 13-second flow meter, 14-spiral tube, 15-first pipeline, 16-second pipeline. DETAILED DESCRIPTION

[0028] The present invention will be further described in conjunction with the accompanying drawings.

[0029] like Figure 1The device for continuously preparing plant fiber pulp using subcritical fluid shown in the figure comprises a mixer 1, an agitator 3 is arranged inside the mixer, and a supercharger 2, a feed port 4, a pressure sensor 6, and a temperature sensor 5 are arranged on the top of the mixer. A first pipeline extends from the bottom of the mixer to the bottom of the oil kettle 8, and a first pipeline 15 is inserted from the bottom of the oil kettle into the inside, spirals upward from the bottom of the oil kettle, and forms a spiral tube 14 inside the oil kettle. The oil kettle is filled with 195° heat transfer oil, and the heat transfer oil wraps the spiral tube to ensure the temperature of the spiral tube. The top of the spiral tube extends from the side wall of the oil kettle and enters the storage tank through the pipeline. The top of the oil kettle is provided with a temperature sensor and a pressure sensor. A second flowmeter 13 and a pressure reducer 10 are arranged in sequence on the pipeline from the oil kettle to the storage tank, a valve is arranged upstream of the second flowmeter, and a valve is arranged downstream of the pressure reducer. The top of the storage tank 11 is connected to the external second pipeline, and a condenser is wound on the outer surface of the second pipeline 16. A first flow meter 9 is provided on the first pipeline, and valves 7 are provided upstream and downstream of the first flow meter. The slurry flow rate passing through the first pipeline is adjusted by adjusting the first flow meter and the valves upstream and downstream of the first flow meter.

[0030] Example 1

[0031] A method for continuously preparing plant fiber pulp using subcritical fluid, the specific steps of which are:

[0032] S1: The corn straw is dusted and crushed to separate the straw skin fiber into 100 mesh size, and then dried at 105°C for 1 hour to obtain the original plant fiber.

[0033] S2: 150kg of original plant fiber, 800kg of ethanol (60% concentration) and 50kg of acetic acid are placed in a 1000L mixing tank through the feed port, stirred evenly to form a slurry, and the booster pump adjusts the pressure in the mixing tank to 1.5MPa (normal temperature); heat the heat transfer oil in the oil kettle to 195°, and the heat transfer oil is kept at this temperature.

[0034] S3: Open the upstream valve and downstream valve of the first flow meter, and the slurry enters the spiral tube through the first pipeline under pressure. When the spiral tube is filled with slurry, adjust the upstream valve of the second flow meter and the downstream valve of the pressure reducer to control the outflow rate at 10L / h to ensure that the slurry in the spiral tube can fully react for 2-3h. Since the mixer is connected to the spiral tube, the pressure in the spiral tube is also 1.5MPa at this time; since the outside of the spiral tube is wrapped with heat transfer oil, the temperature of the spiral tube is 195°. The pressure inside the spiral tube and the temperature outside form a subcritical state, ensuring that the slurry fully reacts in the spiral tube, dissolving the wood fiber in the original plant fiber and separating it from the cellulose.

[0035] S4: After the slurry in the spiral tube reacts completely, plant fiber pulp is obtained, and the plant fiber pulp enters the storage tank through the pipeline. During the process of passing through the pipeline, the plant fiber pulp is reduced to normal pressure by a pressure reducer; the plant fiber pulp after decompression still has temperature, and enters the storage tank at this time. The volatile subcritical fluid gas formed in the storage tank rises into the second pipeline, and passes through the condenser outside the second pipeline to form a subcritical fluid liquid. The subcritical fluid liquid is recovered and can be used again.

[0036] S5: The plant fiber pulp in the storage tank is separated by a centrifugal device, and the separated cellulose can be directly used for papermaking.

[0037] In the above process, the ethanol in step S2 can also be prepared from methyl cellosolve, pyridine, dioxane, acetone, butanol, propanol, ethylene glycol, citric acid, CO 2 , n-hexane, propane, butane, hexane, dimethyl ether, and 1,4-butanediol.

[0038] Example 2

[0039] S1: The corn straw is dusted and crushed to separate the straw skin fiber into 100 mesh size, and then dried at 105°C for 1 hour to obtain the original plant fiber.

[0040] S2: 195kg of original plant fiber, 800kg of ethanol (60% concentration), and 5kg of urea are placed in a 1000L mixing tank through the feed port and stirred evenly to form a slurry. The booster pump adjusts the pressure in the mixing tank to 1.5MPa (normal temperature); the heat transfer oil in the oil kettle is heated to 195°, and the heat transfer oil is kept at this temperature.

[0041] S3: Open the upstream valve and downstream valve of the first flow meter, and the slurry enters the spiral tube through the first pipeline under pressure. When the spiral tube is filled with slurry, adjust the upstream valve of the second flow meter and the downstream valve of the pressure reducer to control the outflow rate at 10L / h to ensure that the slurry in the spiral tube can fully react for 2-3h. Since the mixer is connected to the spiral tube, the pressure in the spiral tube is also 1.5MPa at this time; since the outside of the spiral tube is wrapped with heat transfer oil, the temperature of the spiral tube is 195°. The pressure inside the spiral tube and the temperature outside form a subcritical state, ensuring that the slurry fully reacts in the spiral tube, dissolving the wood fiber in the original plant fiber and separating it from the cellulose.

[0042] S4: After the slurry in the spiral tube reacts completely, plant fiber pulp is obtained, and the plant fiber pulp enters the storage tank through the pipeline. During the process of passing through the pipeline, the plant fiber pulp is reduced to normal pressure by a pressure reducer; the plant fiber pulp after decompression still has temperature, and enters the storage tank at this time. The volatile subcritical fluid gas formed in the storage tank rises into the second pipeline, and passes through the condenser outside the second pipeline to form a subcritical fluid liquid. The subcritical fluid liquid is recovered and can be used again.

[0043] S5: The plant fiber pulp in the storage tank is separated by a centrifugal device, and the separated cellulose can be directly used for papermaking.

[0044] The subcritical fluid technology used in the present invention has extremely strong dissolving ability and decomposition characteristics, which allows lignin to be cleanly separated, subverting the traditional concept of pulp preparation, changing the traditional acid-base cooking pulp preparation process, and avoiding the pollution of the environment by the papermaking industry.

[0045] The spiral tube is combined with the oil kettle. The high-pressure slurry is controlled to flow continuously in the spiral tube. The oil bath provided by the constant temperature heat transfer oil outside the spiral tube ensures that the slurry has sufficient chemical reaction temperature to achieve continuous preparation of plant fiber pulp.

[0046] All the additives used in the present invention are recycled, the cellulose is separated for papermaking, the lignin is used as a chemical raw material, and the remaining pulp can be recycled again for the preparation of plant fiber pulp. The entire process is clean, green, pollution-free and zero-emission.

[0047] The above specific implementation methods are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for continuously preparing plant fiber pulp using a subcritical fluid, characterized in that: The original plant fiber obtained by grinding is mixed with a subcritical fluid, and the slurry obtained by the mixture is continuously reacted for 2-3 hours under an internal pressure of 1.0MPa-20MPa and an external temperature of 97°C-300°C to obtain plant fiber pulp, and the working pressure of the plant fiber pulp is reduced to normal pressure and distilled, and the volatilized subcritical fluid in a gas state is collected, and the distilled plant fiber pulp is separated to obtain plant cellulose; The specific steps are as follows: S1: crushing the plant straw skin to no more than 100 mesh, drying at 105°C for 0.5h to 24h to obtain original plant fiber; S2: Mix 10%-40% of original plant fiber, 50%-70% of water, 10%-60% of subcritical fluid, and 1%-10% of additives in a mass fraction ratio, wherein the total mass fraction ratio of the above raw materials is 100%; S3: pressurizing the slurry obtained in S2, so that it reacts continuously for 2-3 hours at a pressure of 1.0 MPa to 20 MPa and a temperature of 97° C. to 300° C., to obtain a plant fiber pulp mixed liquid; S4: reducing the pressure of the plant fiber pulp mixed liquid to normal pressure and distilling it, volatilizing the gaseous subcritical fluid in the plant fiber pulp mixed liquid, and collecting and condensing the volatilized gaseous subcritical fluid; S5: separating the distilled plant fiber pulp mixed liquid through a centrifugal or extrusion device to obtain plant fiber pulp; The subcritical fluid is one or more of water, methyl cellosolve, pyridine, dioxane, acetone, ethanol, butanol, propanol, ethylene glycol, CO2, n-hexane, propane, butane, hexane, dimethyl ether, and 1.4-butanediol.

2. The method for continuously preparing plant fiber pulp using subcritical fluid according to claim 1, characterized in that: The original plant fiber is agricultural straw fiber or wood fiber with a mesh size of no more than 100 obtained by grinding, or kneaded fiber with a mesh size of no more than 100 obtained by kneading.

3. The method for continuously preparing plant fiber pulp using subcritical fluid according to claim 1, characterized in that: The auxiliary agent is one or more of urea, formic acid, acetic acid, sodium hydroxide, sodium carbonate, sodium sulfite, magnesium chloride, H2O2, sodium acetate, KHCO3, phenol, polyethylene glycol, diethylene glycol, dilute sulfuric acid, and glycerol.

4. A preparation device using the method of claim 1, characterized in that: The invention comprises a mixer (1), wherein an agitator (3) is arranged inside the mixer, wherein the agitator extends downward from the top of the mixer into the interior of the mixer, wherein a first pipeline (15) extends from the bottom of the mixer and is connected to the bottom of an oil kettle (8), wherein the first pipeline enters the oil kettle from the bottom, wherein the first pipeline spirally rises inside the oil kettle to form a spiral tube (14), wherein the top end of the spiral tube passes through the side wall of the oil kettle and is connected to a storage tank (11), wherein a second pipeline (16) extends from the top of the storage tank, wherein a condenser tube (12) is wound around the second pipeline; The oil kettle is filled with heat transfer oil, the heat transfer oil wraps the spiral tube, a supercharger (2) is arranged on the top of the mixer, a first flow meter (9) is arranged on the pipeline from the mixer to the oil kettle, and a second flow meter (13) and a pressure reducer (10) are arranged in sequence on the pipeline from the oil kettle to the storage tank; Valves (7) are provided upstream and downstream of the first flow meter, a valve (7) is provided upstream of the second flow meter, and a valve (7) is provided downstream of the pressure reducer; The mixer can provide pressure for the slurry from the inside of the spiral tube alone, and the oil kettle can ensure the working temperature of the slurry from the outside of the spiral tube alone; The mixer and the top of the oil kettle are both provided with a temperature sensor (5) and a pressure sensor (6); The working pressure inside the spiral tube is 1-20MPa, and the temperature of the heat transfer oil is 97°C-30°C; The first pipeline enters the oil kettle from the bottom and is in a curved, straight or spiral state in the oil kettle.

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