A method for carbonation and coagulation of natural latex at atmospheric pressure with carbon dioxide

Abstract

The application discloses a method for carbonizing and coagulating natural latex by using CO2 micro-bubbles under normal pressure, which comprises the following steps: 1) introducing carbon dioxide from a gas inlet into a micro-bubble generating device; 2) adding natural latex from a material inlet into the micro-bubble generating device; 3) contacting carbon dioxide in the form of micro-bubbles with the natural latex under normal pressure; and 4) collecting the natural latex at a material outlet and coagulating and solidifying the natural latex to obtain a natural rubber coagulum. The application coagulates the natural latex by using CO2 micro-bubbles, and the micro-bubbles can significantly accelerate the dissolution process of the gas in the liquid by providing a larger specific surface area and a longer residence time. The method has mild process conditions, can be continuously operated under normal pressure, and has a fast latex coagulation speed (less than or equal to 1 h). The finally prepared natural rubber product has good quality, and has a plasticity initial value of more than or equal to 40, a plasticity retention rate of more than or equal to 92 and a tensile strength of more than or equal to 24 MPa after vulcanization.

Description

Technical Field

[0001] This invention belongs to the field of natural latex coagulation technology, and in particular relates to a method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure. Background Technology

[0002] Natural latex is a milky liquid derived from rubber trees, with polyisoprene as its main component. In industry, natural latex is used to produce various rubber products, such as gloves, condoms, balloons, and medical supplies, through coagulation, drying, and processing. Natural latex coagulation methods can be broadly categorized into physical, biological, and chemical methods.

[0003] Physical methods utilize heat sources, cold sources, or mechanical forces to destabilize the emulsion system, causing it to solidify. However, this method has been relatively limited in research and suffers from problems such as extremely long solidification times, high energy consumption, and difficulties in process control, making industrialization challenging.

[0004] The biological method refers to the use of bacteria naturally present in or added to natural latex to coagulate the emulsion. This method has lower production costs, but it can result in issues such as foul odor, clumping and swelling, and difficulty in controlling product quality.

[0005] Chemical coagulation refers to the process of coagulating natural rubber latex by adding acids, inorganic salts, or chemical coagulants. Acid coagulation is currently the most widely used method, but it suffers from problems such as high coagulation costs, strong corrosiveness, and the generation of large amounts of acidic wastewater. Furthermore, the addition of chemical substances can severely impact the properties of natural rubber. Many studies have attempted to replace acids with various chemical reagents during the coagulation process to improve these issues, as illustrated by technologies disclosed in Chinese patent applications CN111909290A and CN113265015A. These technologies, utilizing different additives, have played a role to varying degrees in shortening coagulation time and reducing wastewater discharge, but problems remain in industrial production. Therefore, developing a new method for coagulating natural rubber latex is of great significance.

[0006] The principle of carbon dioxide coagulation is based on the solubility of carbon dioxide in water and the effect of the resulting carbonic acid on the pH value of latex. When carbon dioxide dissolves in latex, some carbon dioxide molecules react with water molecules to form carbonic acid. This carbonic acid lowers the pH value of the latex, promoting the aggregation and coagulation of natural latex. Chinese patent application CN111718432A provides a method for coagulating natural latex using high-pressure carbon dioxide. Carbon dioxide, as a chemically inert gas, can protect the components in natural latex from damage and is an excellent acid substitute, resulting in a high-quality final rubber product. However, the operating pressure is 10–30 MPa, which places high demands on equipment and reduces the safety of the production process. Summary of the Invention

[0007] The purpose of this invention is to provide a method for carbonizing and coagulating natural rubber latex using CO2 microbubbles under normal pressure. Microbubbles significantly accelerate the dissolution process of gas in liquid by providing a larger specific surface area and a longer residence time. The method features mild process conditions, can be carried out under normal pressure, and can achieve continuous operation; the latex coagulation speed is fast, with a time ≤1 hour; the final natural rubber product has high quality, with an initial plasticity value ≥40, a plasticity retention rate ≥92%, and a tensile strength ≥24 MPa after vulcanization.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure includes the following steps:

[0010] 1) Introduce carbon dioxide into the microbubble generator through the gas inlet;

[0011] 2) Add natural latex into the microbubble generator through the material inlet;

[0012] 3) Carbon dioxide comes into contact with natural latex in the form of microbubbles under normal pressure;

[0013] 4) Collect natural latex at the discharge port and coagulate it to obtain natural rubber clumps.

[0014] Preferably, in step 1) or step 2), the microbubble generating device is at least one of a stirred tank, a bubble column, a rotary packed bed, a membrane bubble generator, and a microchannel device.

[0015] Preferably, in step 1), the purity of the carbon dioxide is 80% to 99.99% by volume percentage.

[0016] Preferably, in step 2), the natural latex is fresh latex that has not undergone any additive treatment.

[0017] Preferably, in step 3), the CO2 microbubbles range from 1 nm to 100 μm.

[0018] Preferably, in step 3), the gas-liquid volume ratio of carbon dioxide and natural latex is 0.5:1 to 8:1.

[0019] Preferably, in step 4), the solidification is carried out at room temperature of 10–45°C.

[0020] Preferably, in step 4), the solidification is carried out under static conditions; the static time is 10 to 60 minutes.

[0021] Preferably, after step 4), after obtaining the natural rubber block, the rubber block is successively pressed thin, creased and dried to obtain the natural rubber product.

[0022] Preferably, the drying temperature is 40–120°C.

[0023] Any range described in this invention includes the endpoint, any value between the endpoints, and any subrange consisting of the endpoint or any value between the endpoints.

[0024] Unless otherwise specified, all raw materials used in this invention can be obtained commercially, and the equipment used in this invention can be conventional equipment in the relevant field or refer to existing technology in the relevant field.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. This invention provides a novel method for carbonizing and coagulating natural rubber latex using CO2 microbubbles at atmospheric pressure. The method utilizes a microbubble generator to promote the efficient dispersion of carbon dioxide microbubbles in the natural rubber latex. Microbubbles have a larger specific surface area and longer residence time than ordinary bubbles, further promoting the diffusion and dissolution of carbon dioxide in the latex. Finally, the natural rubber latex is collected at the outlet and coagulated to obtain natural rubber. This invention uses carbon dioxide microbubbles to coagulate natural rubber latex. The microbubble form enhances the solubility of carbon dioxide in the latex, overcoming the limitations of high-pressure operation conditions and achieving efficient and high-quality natural rubber latex coagulation under atmospheric pressure. The invented method features mild process conditions, rapid latex coagulation, and produces high-quality natural rubber products.

[0027] 2. In the method described in this invention, no coagulant needs to be added during the coagulation process, and the generated wastewater can be directly introduced into the wastewater treatment stage without neutralization. Compared with the existing acid coagulation method, the method described in this invention can not only shorten the coagulation time and improve production efficiency, but also achieve zero emissions of exhaust gas, thereby reducing environmental pollution, lowering production costs, and realizing the recycling of resources.

[0028] 3. The natural rubber products obtained by the method of the present invention are of good quality, with an initial plasticity value ≥40, a plasticity retention rate >92%, and a tensile strength >24MPa after vulcanization. Attached Figure Description

[0029] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0030] Figure 1 The process flow diagram of the present invention, which uses CO2 microbubble carbonization-coagulation of natural latex under normal pressure, is shown. Detailed Implementation

[0031] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0032] As one aspect of the present invention, a method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure includes the following steps:

[0033] 1) Introduce carbon dioxide into the microbubble generator through the gas inlet;

[0034] 2) Add natural latex into the microbubble generator through the material inlet;

[0035] 3) Carbon dioxide and natural latex are contacted in a nano-micro bubble generator under normal pressure;

[0036] 4) Collect natural latex at the material outlet and coagulate it to obtain natural rubber clumps.

[0037] According to certain embodiments of the present invention, in step 1) or step 2), the microbubble generating device is at least one of a stirred tank, a bubble column, a rotating packed bed, a membrane bubble generator, and a microchannel device.

[0038] According to certain embodiments of the present invention, in step 1), the purity of the carbon dioxide is 80% to 99.99% by volume percentage.

[0039] According to certain embodiments of the present invention, in step 2), the natural latex is fresh latex without any additive treatment.

[0040] According to certain embodiments of the present invention, in step 3), the CO2 microbubbles range from 1 nm to 100 μm.

[0041] According to certain embodiments of the present invention, in step 3), the gas-liquid volume ratio of the carbon dioxide and natural latex is 0.5:1 to 8:1.

[0042] According to certain embodiments of the present invention, in step 4), the coagulation is carried out at room temperature of 10–45°C; the present invention controls the coagulation temperature within the above range to prevent the natural latex from deteriorating due to overheating.

[0043] According to certain embodiments of the present invention, in step 4), the solidification is carried out under static conditions; the static time is 10 to 60 minutes.

[0044] According to certain embodiments of the present invention, in step 4), after obtaining the natural rubber clot, the rubber clot is sequentially pressed, crepedized, and dried to obtain the natural rubber product. The present invention does not specifically limit the dehydration process; any process well-known in the art that can obtain the natural rubber product can be selected.

[0045] According to some embodiments of the present invention, the drying temperature is 40–120°C; more preferably 60–80°C; the present invention does not have a special limitation on the drying time, as long as a natural rubber product can be obtained by following a process well known in the art.

[0046] The microbubble generating device used in this invention is a prior art, such as the stirred tank disclosed in CN116726822A; the rotating packed bed disclosed in CN117619303A; the bubble column disclosed in CN118477616A; the membrane bubble generator disclosed in CN103361747A; and the microchannel reactor disclosed in CN116173855A.

[0047] Example 1

[0048] A method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure includes the following steps:

[0049] Take 2 kg of fresh natural latex. Carbon dioxide is industrial waste gas. After treatment, its purity is 98%.

[0050] The selected microbubble generator is a microchannel reactor;

[0051] Carbon dioxide is first introduced into the microchannel reactor through the inlet, and natural latex is fed by a pump with a gas-liquid ratio of 1:1 and a residence time of 3 minutes. Under normal pressure and 25°C conditions, after standing for 20 minutes, a large amount of latex is coagulated.

[0052] Example 2

[0053] A method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure includes the following steps:

[0054] Take 2 kg of fresh natural latex. Carbon dioxide is industrial waste gas. After treatment, its purity is 98%.

[0055] The selected microbubble generator is a rotating packed bed;

[0056] First, carbon dioxide is introduced into the equipment through the air inlet. Natural latex is fed by a pump with a gas-liquid ratio of 5:1. The rotating packed bed speed is 1200 rpm. Under normal pressure and 25°C conditions, after standing for 10 minutes, a large amount of latex is solidified.

[0057] Example 3

[0058] A method for carbonizing and coagulating natural latex using carbon dioxide under normal pressure includes the following steps:

[0059] Take 2 kg of fresh natural latex. Carbon dioxide is industrial waste gas. After treatment, its purity is 98%.

[0060] The selected microbubble generator is a stirred tank.

[0061] Carbon dioxide was introduced into the stirred tank from the microbubble generator, and natural latex was continuously fed by a peristaltic pump at a gas-liquid ratio of 1:1. The stirring tank was rotated at 1000 rpm and the residence time was 10 minutes. Under normal pressure and 25°C, after standing for 30 minutes, a large amount of latex solidified.

[0062] Example 4

[0063] A method for carbonizing and coagulating natural latex using carbon dioxide under normal pressure includes the following steps:

[0064] Take 2 kg of fresh natural latex. The carbon dioxide is industrial waste gas. After treatment, its purity is 98%.

[0065] The selected microbubble generator is a bubble column;

[0066] Carbon dioxide is introduced into the bubble column through the inlet and mixed with natural latex through a disperser at a gas-liquid ratio of 1:1 for a residence time of 10 minutes. Under normal pressure and 25°C conditions, after standing for 15 minutes, a large amount of latex solidifies.

[0067] Comparative Example 1

[0068] Similar to Example 1, natural latex under the same conditions was left to stand under natural conditions and solidified according to its own characteristics. After standing for 2 hours, only a small amount of latex solidified.

[0069] This shows that natural solidification has a poor effect and takes a long time.

[0070] Performance testing

[0071] The rubber clumps prepared in the above examples and comparative examples were sequentially thinned and creped, then dried in a hot air drying oven at 80°C to obtain natural rubber products. The performance of the natural rubber products prepared in Examples 1-5 and Comparative Example 1 was tested using conventional methods, and the results are shown in the table below:

[0072] Case <![CDATA[Initial plastic value P0]]> Plasticity retention rate PRI Tensile strength / MPa Elongation at break / % Example 1 47.6 97 25.62 746.2 Example 2 49.3 99 25.64 758.4 Example 3 42.0 92 24.04 714.1 Example 4 44.1 92 25.30 743.9 Comparative Example 1 38.4 89 24.90 742.7

[0073] The data in the table show that the natural rubber products prepared from the rubber blocks in Examples 1-5 are significantly better than those in Comparative Example 1.

[0074] In summary, compared with the method disclosed in Chinese patent application CN111718432A, the method of the present invention does not require high pressure and can be carried out under normal pressure; the performance of the obtained product is similar to that of the product in Chinese patent application CN111718432A.

[0075] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure, characterized in that, Includes the following steps: 1) Introduce carbon dioxide into the microbubble generator through the gas inlet; 2) Add natural latex into the microbubble generator through the material inlet; 3) Carbon dioxide comes into contact with natural latex in the form of microbubbles under normal pressure; 4) Collect natural latex at the material outlet and coagulate it to obtain natural rubber clumps.

2. The method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure according to claim 1, characterized in that: In step 1) or step 2), the microbubble generating device is at least one of a stirred tank, a bubble column, a rotary packed bed, a membrane bubble generator, and a microchannel device.

3. The method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure according to claim 1, characterized in that: In step 1), the purity of the carbon dioxide is 80% to 99.99% by volume percentage.

4. The method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure according to claim 1, characterized in that: In step 2), the natural latex is fresh latex that has not undergone any additive treatment.

5. The method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure according to claim 1, characterized in that: In step 3), the CO2 microbubbles range from 1 nm to 100 μm.

6. The method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure according to claim 1, characterized in that: In step 3), the gas-liquid volume ratio of carbon dioxide and natural latex is 0.5:1 to 8:

1.

7. The method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure according to claim 1, characterized in that: In step 4), the solidification is carried out at room temperature of 10–45°C.

8. The method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure according to claim 1, characterized in that: In step 4), the solidification is carried out under static conditions; the static time is 10 to 60 minutes.

9. The method according to any one of claims 1 to 8, characterized in that: After obtaining natural rubber clumps, the rubber clumps are successively pressed thin, creped, and dried to obtain natural rubber products.

10. The method for carbonizing and coagulating natural latex using CO2 microbubbles under normal pressure according to claim 9, characterized in that: The drying temperature is 40–120°C.

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