Method for preparing dry ice by using carbon dioxide

Abstract

The invention discloses a method for manufacturing dry ice by using carbon dioxide. The method comprises the following steps: removing impurities from mineral processing byproduct carbon dioxide exhaust gas under a plasma catalysis condition; further purifying carbon dioxide in the carbon dioxide gas under a supercritical condition, and removing trace impurities; converting the carbon dioxide gas into a liquid state under a low-temperature condition; inputting the liquid carbon dioxide into a dry ice maker, and converting the liquid carbon dioxide into solid dry ice through rapid expansion under a low-temperature condition; and carrying out quality detection on the manufactured dry ice, including carbon dioxide purity, evaporation residue and microbiological indexes, and carrying out heat insulation packaging after the detection is qualified. According to the method, the waste heat generated in the low-temperature liquefaction and dry ice manufacturing process is used for preheating the input gas, the overall energy consumption is greatly reduced, in addition, the energy utilization efficiency is further improved by accurately controlling the operation conditions of all the process steps, and compared with a traditional method, the energy consumption is remarkably reduced, and the production cost is correspondingly reduced.

Description

Technical Field

[0001] The present invention relates to the field of dry ice preparation, and specifically to a method for manufacturing dry ice using carbon dioxide. Background Art

[0002] Carbon dioxide is a common industrial waste gas and also an important chemical raw material. In recent years, with the enhancement of environmental awareness and the proposal of the carbon neutrality goal, the recovery and utilization of carbon dioxide have become the focus of global attention. Dry ice, as an important coolant and cleaning agent, is widely used in fields such as food preservation, medical cold chain, and industrial cleaning. However, traditional dry ice manufacturing methods have problems such as high energy consumption, high cost, and large environmental pollution, and it is difficult to meet the requirements of modern industry for efficient, environmentally friendly, and low-cost production.

[0003] In the prior art, the manufacturing of dry ice mainly adopts the following methods:

[0004] Compression liquefaction method: Compress and cool carbon dioxide gas to liquefy it, and then obtain dry ice through expansion. This method has high energy consumption, and impurities are easily introduced during the liquefaction process, affecting the purity of dry ice.

[0005] Direct freezing method: Directly freeze carbon dioxide gas to below -78.5 °C to obtain dry ice. This method has complex equipment, high operating costs, and low production efficiency.

[0006] Chemical absorption method: Use a chemical absorbent to absorb carbon dioxide, and then release and obtain dry ice through heating. This method has problems such as difficult regeneration of the absorbent and large environmental pollution.

[0007] Traditional methods consume a large amount of energy during liquefaction, freezing, and absorption processes, resulting in high production costs; and due to process limitations, the dry ice obtained by traditional methods may contain trace impurities (such as sulfides, nitrogen oxides, organic pollutants, etc.), making it difficult to meet food-grade standards. At the same time, the absorbents used in the chemical absorption method may cause environmental pollution, and the waste gas treatment is not thorough. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for manufacturing dry ice using carbon dioxide to solve the problems raised in the above background art.

[0009] To achieve the above purpose, the present invention provides the following technical solutions:

[0010] A method for manufacturing dry ice using carbon dioxide, comprising the following steps:

[0011] Step S1, introducing the carbon dioxide waste gas from mineral processing by-products into a plasma catalytic reactor, and removing impurity substances under plasma catalytic conditions. The impurity substances include sulfides, nitrogen oxides, and organic pollutants;

[0012] Step S2: Introduce the high-purity carbon dioxide gas after plasma catalysis into the supercritical fluid extraction device, and further purify carbon dioxide under supercritical conditions to remove trace impurities, so that the purity of carbon dioxide reaches the food-grade standard;

[0013] Step S3: Pass the carbon dioxide gas after supercritical fluid extraction through the cryogenic liquefaction device to convert the carbon dioxide gas into a liquid under low-temperature conditions, providing high-purity liquid carbon dioxide for subsequent dry ice production;

[0014] Step S4: Input the liquid carbon dioxide into the dry ice maker, and convert it into solid dry ice through rapid expansion under low-temperature conditions to ensure the particle uniformity and sublimation stability of the dry ice;

[0015] Step S5: Conduct quality inspection on the produced dry ice, including carbon dioxide purity, evaporation residue, and microbial indicators. After passing the inspection, perform heat-insulating packaging.

[0016] In the present invention, the plasma conditions of the plasma catalytic reactor are as follows:

[0017] The frequency is 13.56 MHz;

[0018] The power is 500 W to 1000 W;

[0019] The catalyst is nanoscale titanium dioxide, and its specific surface area ≥ 200 m 2 / g, and the pore diameter is 2 nm to 50 nm.

[0020] In the present invention, the supercritical conditions of the supercritical fluid extraction device are as follows:

[0021] The temperature is 31.1 °C;

[0022] The pressure is 7.39 MPa;

[0023] The extractant is supercritical carbon dioxide.

[0024] In the present invention, the liquefaction conditions of the cryogenic liquefaction device are as follows:

[0025] The temperature is -20 °C to -30 °C;

[0026] The pressure is 2.0 MPa to 3.0 MPa.

[0027] In the present invention, the production conditions of the dry ice maker are as follows:

[0028] The temperature is -78.5 °C;

[0029] The expansion pressure is 0.1 MPa to 0.5 MPa.

[0030] In the present invention, the quality inspection includes the following indicators:

[0031] The purity of carbon dioxide is detected by gas chromatography, and the purity is ≥99.9%;

[0032] The evaporation residue is detected by gravimetry, and the residue content is ≤0.01%;

[0033] The microbial index is detected by the microbial culture method.

[0034] In the present invention, the heat-insulating package uses a multi-layer composite heat-insulating material, including:

[0035] The outer layer is high-strength polyethylene;

[0036] The middle layer is a vacuum heat-insulating panel;

[0037] The inner layer is an aluminum foil composite material.

[0038] In the present invention, the gas flow rate of the plasma catalytic reactor is 10 L / min to 50 L / min, so that the residence time of the carbon dioxide waste gas in the reactor is 0.5 s to 2.0 s.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. In the present invention, the waste heat generated during the low-temperature liquefaction and dry ice manufacturing processes is used to preheat the input gas, resulting in a significant reduction in overall energy consumption. In addition, by precisely controlling the operating conditions of each process step, the energy utilization efficiency is further improved. Compared with traditional methods, the energy consumption of the present invention is significantly reduced, and the production cost is also correspondingly reduced.

[0041] 2. In the present invention, by using a plasma catalytic reactor and a supercritical fluid extraction device, trace impurities in carbon dioxide are effectively removed. The plasma catalytic reactor can efficiently remove sulfides, nitrogen oxides, and organic pollutants, while the supercritical fluid extraction device further removes heavy metals and particulate matter. Through these measures, the purity of the dry ice produced is significantly improved, fully meeting the food-grade standard. In addition, the size distribution of the dry ice particles is uniform, suitable for a variety of application scenarios. Description of the Drawings

[0042] Figure 1 It is a schematic flow chart of a method for manufacturing dry ice using carbon dioxide according to the present invention. Detailed Embodiments

[0043] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0044] Please refer to Figure 1 , the present invention provides a technical solution:

[0045] A method for manufacturing dry ice using carbon dioxide, comprising the following steps:

[0046] Step S1, introducing the carbon dioxide waste gas from mineral processing by-products into a plasma catalytic reactor to remove impurities under plasma catalytic conditions. The impurities include sulfides, nitrogen oxides, and organic pollutants;

[0047] Among them, the plasma conditions of the plasma catalytic reactor are:

[0048] The frequency is 13.56 MHz;

[0049] The power is 500 W to 1000 W;

[0050] The catalyst is nanoscale titanium dioxide, with a specific surface area ≥ 200 m 2 / g, pore diameter of 2 nm to 50 nm. The nanoscale titanium dioxide is prepared by the sol-gel method: mixing tetrabutyl titanate (Ti(OC4H9)4) with ethanol, adding nitric acid as a catalyst, stirring to form a sol, and obtaining nanoscale TiO2 through drying and calcination (450 °C, 2 hours); the used catalyst is calcined in air at 400 °C for 2 hours to remove the adsorbed impurities on the surface; after continuous operation for 1000 hours, the catalytic efficiency decreases by no more than 5%.

[0051] The gas flow rate of the plasma catalytic reactor is 10 L / min to 50 L / min, so that the residence time of the carbon dioxide waste gas in the reactor is 0.5 s to 2.0 s.

[0052] Preferably, the model of the plasma catalytic reactor is PCT-1000 (under the conditions of 800 W and 30 L / min, the sulfide removal rate is 99.7%, the nitrogen oxide removal rate is 99.6%, and the organic pollutant removal rate is 99.8%).

[0053] The plasma conditions are as follows:

[0054] Frequency: 13.56 MHz.

[0055] Power: 800 W.

[0056] Catalyst: nanoscale titanium dioxide, specific surface area: 250 m 2 / g, pore diameter: 10 nm.

[0057] Gas flow rate: 30 L / min.

[0058] Residence time: 1.0 s.

[0059] The operation process of step S1 is as follows:

[0060] Step S101, introducing the carbon dioxide waste gas from the by-products of magnesite processing into the plasma catalytic reactor.

[0061] Step S102, under the plasma catalytic condition, sulfides, nitrogen oxides and organic pollutants in the carbon dioxide waste gas are efficiently decomposed.

[0062] Step S103, outputting high-purity carbon dioxide gas, with the impurity removal rate ≥ 99.5%.

[0063] In this embodiment, the plasma conditions of 13.56 MHz and 800 W can efficiently activate carbon dioxide molecules and simultaneously catalytically decompose impurities; the nanoscale titanium dioxide has a high specific surface area and an appropriate pore diameter, which can enhance the catalytic effect of the plasma, and the optimized conditions of 30 L / min and 1.0 s ensure the full treatment of the carbon dioxide waste gas in the reactor.

[0064] Step S2, introducing the high-purity carbon dioxide gas after plasma catalysis into the supercritical fluid extraction device, further purifying carbon dioxide under supercritical conditions, removing trace impurities, and making the carbon dioxide purity reach the food-grade standard. The high-purity carbon dioxide gas output from the plasma catalytic reactor enters the supercritical fluid extraction device through a buffer tank (pressure 1.0 MPa, temperature 25°C);

[0065] Among them, the supercritical conditions of the supercritical fluid extraction device are:

[0066] Temperature is 31.1°C;

[0067] Pressure is 7.39 MPa;

[0068] The extractant is supercritical carbon dioxide. Supercritical carbon dioxide has the advantages of non-toxicity, no pollution, and easy recovery, and its critical temperature (31.1°C) and critical pressure (7.39 MPa) are relatively low, which is suitable for the purification of food-grade carbon dioxide; trace impurities include heavy metals (such as lead, mercury), volatile organic compounds (such as benzene, toluene) and particulate matter; the heavy metal removal rate ≥ 99.9%, the volatile organic compound removal rate ≥ 99.8%, and the particulate matter removal rate ≥ 99.5%.

[0069] Compared with supercritical water, supercritical CO2 has stronger selectivity for organic pollutants and does not introduce new impurities.

[0070] Preferably, the model of the supercritical fluid extraction device is SCF-2000 (under the conditions of 31.1 °C and 7.39 MPa, the purity of carbon dioxide is 99.95%).

[0071] The supercritical conditions are as follows:

[0072] Temperature: 31.1 °C.

[0073] Pressure: 7.39 MPa.

[0074] Extraction agent: supercritical carbon dioxide.

[0075] Gas flow rate: 20 L / min.

[0076] The operation process of step S2 is as follows:

[0077] Step S201, introducing the carbon dioxide gas after plasma catalysis into the supercritical fluid extraction device.

[0078] Step S202, under supercritical conditions, carbon dioxide exhibits unique solubility and selectively extracts trace impurities.

[0079] Step S203, outputting high-purity carbon dioxide gas with a purity ≥ 99.9%.

[0080] In this embodiment, the supercritical conditions of 31.1 °C and 7.39 MPa enable carbon dioxide to exhibit unique solubility and be able to selectively extract trace impurities; the optimized condition of 20 L / min ensures the efficient treatment of carbon dioxide gas in the extraction device.

[0081] Step S3, passing the carbon dioxide gas after supercritical fluid extraction through a low-temperature liquefaction device to convert the carbon dioxide gas into a liquid state under low-temperature conditions, providing high-purity liquid carbon dioxide for subsequent dry ice production. The carbon dioxide gas output from the supercritical fluid extraction device enters the low-temperature liquefaction device through a condenser (temperature -10 °C, pressure 2.0 MPa);

[0082] Among them, the liquefaction conditions of the low-temperature liquefaction device are:

[0083] Temperature is -20 °C to -30 °C;

[0084] Pressure is 2.0 MPa to 3.0 MPa.

[0085] Preferably, the model of the low-temperature liquefaction device is CL-3000 (under the conditions of -25 °C and 2.5 MPa, the liquefaction efficiency is 96.2%).

[0086] The liquefaction conditions are as follows:

[0087] Temperature: -25°C.

[0088] Pressure: 2.5 MPa.

[0089] Gas flow rate: 15 L / min.

[0090] The operation process of step S3 is as follows:

[0091] In step S301, the carbon dioxide gas after supercritical fluid extraction is introduced into the low-temperature liquefaction device.

[0092] In step S302, under low-temperature conditions, the carbon dioxide gas is converted into a liquid state.

[0093] In step S303, high-purity liquid carbon dioxide is output, and the liquefaction efficiency is ≥95%.

[0094] In this embodiment, the liquefaction conditions of -25°C and 2.5 MPa can efficiently convert carbon dioxide gas into a liquid state; the optimized condition of 15 L / min ensures the efficient treatment of carbon dioxide gas in the liquefaction device.

[0095] In step S3, the specific calculation method of the liquefaction efficiency:

[0096] The calculation formula for the liquefaction efficiency (η): Where m liquid is the mass of liquefied carbon dioxide, m total is the mass of input carbon dioxide. Under the conditions of -25°C and 2.5 MPa, the liquefaction efficiency is 96.2%, and the energy consumption of the liquefaction device is 0.5 kWh / kg CO2. Through the heat recovery system, the energy consumption can be reduced to 0.4 kWh / kg CO2.

[0097] In step S4, the liquid carbon dioxide is input into a dry ice maker and converted into solid dry ice through rapid expansion under low-temperature conditions, so as to make the particle uniformity and sublimation stability of the dry ice. The liquid carbon dioxide output by the low-temperature liquefaction device enters the dry ice maker through a heat-insulating pipeline (temperature -25°C, pressure 2.5 MPa);

[0098] Among them, the manufacturing conditions of the dry ice maker are:

[0099] Temperature is -78.5°C;

[0100] The expansion pressure is 0.1 MPa to 0.5 MPa.

[0101] Preferably, the model of the dry ice maker is DI-4000 (under the conditions of -78.5°C and 0.3 MPa, the dry ice density is 1.52 g / cm 3) The particle size range of the dry ice particles is from 1 mm to 5 mm, and 90% of the particle sizes are between 2 mm and 4 mm.

[0102] The manufacturing conditions are as follows:

[0103] Temperature: -78.5 °C.

[0104] Expansion pressure: 0.3 MPa.

[0105] Flow rate of liquid carbon dioxide: 10 L / min.

[0106] The operation process of step S4 is as follows:

[0107] Step S401, input high-purity liquid carbon dioxide into the dry ice manufacturing machine.

[0108] Step S402, under low-temperature conditions, the liquid carbon dioxide is converted into solid dry ice through rapid expansion.

[0109] Step S403, output dry ice with uniform particles and stable sublimation, and the dry ice density ≥ 1.5 g / cm 3 .

[0110] In this embodiment, the manufacturing conditions of -78.5 °C and 0.3 MPa can quickly convert liquid carbon dioxide into solid dry ice; the optimized condition of 10 L / min ensures the particle uniformity and sublimation stability of the dry ice.

[0111] In step S4, the storage conditions of the dry ice are as follows:

[0112] Storage temperature: -78.5 °C.

[0113] Storage humidity: ≤ 10% RH.

[0114] Under the above conditions, the sublimation rate of the dry ice is 2 kg / m 2 ·h.

[0115] Step S5, conduct quality inspection on the manufactured dry ice, including carbon dioxide purity, evaporation residue and microbial indicators, and perform heat-insulating packaging after passing the inspection;

[0116] Among them, the quality inspection includes the following indicators:

[0117] Carbon dioxide purity, detected by gas chromatography, with the purity ≥ 99.9%;

[0118] Evaporation residue, detected by gravimetry, with the residue content ≤ 0.01%;

[0119] Microbial indicators, detected by microbial culture method.

[0120] The heat-insulating packaging adopts multi-layer composite heat-insulating materials, including:

[0121] The outer layer is made of high-strength polyethylene with a thickness of 0.5 mm and a tensile strength of ≥20 MPa;

[0122] The middle layer is a vacuum heat-insulating panel with a thermal conductivity of ≤0.005 W / m·K;

[0123] The inner layer is an aluminum foil composite material with a thickness of 0.1 mm and a reflectivity of ≥95%.

[0124] Preferably, the model of the gas chromatograph is GC-5000, the model of the gravimetric detector is WM-6000, and the model of the microbial incubator is MB-7000.

[0125] The detection indexes are as follows:

[0126] Carbon dioxide purity: Using gas chromatography, the detection time is 10 minutes and the sample volume is 1 mL.

[0127] Evaporation residue: Using gravimetry, the dry ice sample is dried at 105°C for 2 hours and the residue mass is weighed.

[0128] Microbial index: Using microbial culture method, it is cultured at 37°C for 48 hours to detect the total number of colonies.

[0129] The operation process of step S5 is as follows:

[0130] Step S501, conduct quality inspection on the manufactured dry ice to ensure compliance with food-grade standards.

[0131] Step S502, after passing the inspection, pack the dry ice into the heat-insulating packaging to prevent the dry ice from sublimating during transportation and storage.

[0132] In this embodiment, the detection of carbon dioxide purity, evaporation residue and microbial index ensures the food safety of dry ice; the multi-layer composite heat-insulating material can effectively prevent the dry ice from sublimating during transportation and storage.

[0133] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0134] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for producing dry ice using carbon dioxide, characterized in that: The following steps are involved: Step S1, passing the carbon dioxide waste gas produced as a byproduct of mining processing into a plasma catalytic reactor to remove impurities under plasma catalytic conditions, wherein the impurities include sulfides, nitrogen oxides and organic pollutants; Step S2, passing the high-purity carbon dioxide gas after plasma catalysis into a supercritical fluid extraction device, further purifying the carbon dioxide under supercritical conditions to remove trace impurities, so that the purity of the carbon dioxide reaches food grade standards; Step S3, passing the carbon dioxide gas extracted by the supercritical fluid through a cryogenic liquefaction device to convert the carbon dioxide gas into liquid under low temperature conditions, thereby providing high-purity liquid carbon dioxide for subsequent dry ice production; Step S4, inputting liquid carbon dioxide into a dry ice making machine, and converting it into solid dry ice by rapid expansion under low temperature conditions, so that the particles of dry ice are uniform and sublimation stable; Step S5, the manufactured dry ice is subjected to quality inspection, including carbon dioxide purity, evaporation residue and microbial index, and is thermally packaged after passing the inspection.

2. The method for producing dry ice using carbon dioxide according to claim 1, characterized in that: The plasma conditions of the plasma catalytic reactor are: The frequency is 13.56MHz; Power ranges from 500W to 1000W; The catalyst is nano-sized titanium dioxide with a specific surface area of ​​≥200m 2 / g, and the pore diameter is 2nm to 50nm.

3. The method for producing dry ice using carbon dioxide according to claim 1, characterized in that: The supercritical conditions of the supercritical fluid extraction device are: The temperature is 31.1°C; The pressure is 7.39MPa; The extractant is supercritical carbon dioxide.

4. The method for producing dry ice using carbon dioxide according to claim 1, characterized in that: The liquefaction conditions of the low-temperature liquefaction device are: Temperature is -20℃ to -30℃; The pressure is 2.0MPa to 3.0MPa.

5. The method for producing dry ice using carbon dioxide according to claim 1, characterized in that: The manufacturing conditions of the dry ice making machine are: The temperature is -78.5°C; The expansion pressure is 0.1MPa to 0.5MPa.

6. The method for producing dry ice using carbon dioxide according to claim 1, characterized in that: The quality inspection includes the following indicators: The purity of carbon dioxide is tested by gas chromatography to ensure that the purity is ≥ 99.9%; The evaporation residue is tested by weight method to make the residue content ≤ 0.01%; Microbiological indicators are detected by microbial culture method.

7. The method for producing dry ice using carbon dioxide according to claim 1, characterized in that: The thermal insulation packaging adopts a multi-layer composite thermal insulation material, including: The outer layer is high-strength polyethylene; The middle layer is a vacuum insulation panel; The inner layer is aluminum foil composite material.

8. The method for producing dry ice using carbon dioxide according to claim 1, characterized in that: The gas flow rate of the plasma catalytic reactor is 10 L / min to 50 L / min, so that the residence time of the carbon dioxide waste gas in the reactor is 0.5 s to 2.0 s.

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