Method for carbonizing-solidifying natural latex by using carbon dioxide under normal pressure

Abstract

The invention discloses a method for carbonizing-solidifying natural latex by adopting CO2 microbubbles under normal pressure. The method comprises the following steps: 1) introducing carbon dioxide into a microbubble generating device from a gas inlet; 2) adding natural latex into a microbubble generating device from a material inlet; 3) contacting the carbon dioxide with the natural latex in a microbubble form under a normal pressure condition; and 4) collecting the natural latex at a material outlet, and standing and solidifying to obtain the natural rubber clot. According to the invention, CO2 microbubbles are adopted to solidify natural latex, and the microbubbles provide larger specific surface area and longer retention time to significantly accelerate the dissolution process of gas in liquid. The method is mild in process condition, and can be carried out under normal pressure and realize continuous operation; latex solidification speed is fast, and time is less than or equal to 1h; the finally prepared natural rubber product is good in quality, the initial plasticity value is larger than or equal to 40, the plasticity retention rate is larger than or equal to 92, and the tensile strength after vulcanization is larger than or equal to 24 MPa.

Description

Technical Field

[0001] The invention belongs to the technical field of natural latex coagulation, and in particular relates to a method of coagulating natural latex by using CO 2 Microbubble carbonization - a method of coagulating natural rubber latex. Background Art

[0002] Natural latex is a milky liquid derived from rubber trees, the main component of which is polyisoprene. In the industrial field, natural latex is coagulated, dried, processed and other steps to produce various rubber products, such as gloves, condoms, balloons and medical supplies. The coagulation methods of natural latex can be roughly divided into physical, biological and chemical methods.

[0003] The physical method is to use heat source, cold source or mechanical force to make the emulsion system unstable and solidify. This method has been studied relatively little, and there are problems such as extremely long solidification time, high energy consumption, and difficult process control, making it difficult to achieve industrialization.

[0004] The biological method refers to the method of using the original or added bacteria in natural latex to coagulate the latex. This method has a low production cost, but there are phenomena such as odor and swelling of the clots, and it is difficult to control the product quality.

[0005] Chemical method refers to the method of coagulating natural latex by adding acid, inorganic salt, chemical coagulant, etc. Acid coagulation is the most widely used method at present, but this method has the problems of high coagulation cost, strong corrosiveness and generation of a large amount of acid-containing wastewater, and the addition of chemical substances can have a serious impact on the performance of natural rubber. Many studies have attempted to replace acid with various chemical reagents in the coagulation process to improve the problem, such as the disclosed technologies of Chinese patent applications CN111909290A, CN113265015A, etc. These technologies use different additives to shorten the coagulation time and reduce wastewater discharge, but there are still problems in industrial production. Therefore, it is of great significance to develop a new method for coagulating natural latex.

[0006] The principle of carbon dioxide coagulation is based on the solubility of carbon dioxide in water and the regulation of the pH value of latex by the carbonic acid formed. When carbon dioxide is dissolved in latex, some carbon dioxide molecules react with water molecules to form carbonic acid, which reduces the pH value of latex and promotes the aggregation and coagulation of natural latex. Chinese patent application CN111718432A provides a method for coagulating natural latex with high-pressure carbon dioxide. Carbon dioxide, as a chemically inert gas, can protect the components in natural latex from being damaged and is an excellent acid substitute. The final rubber product has better quality, but the operating pressure is 10 to 30 MPa, which has high requirements on equipment and reduces the safety of the production process. Summary of the invention

[0007] The present invention aims to provide a method for producing a 2 A method for carbonizing and solidifying natural latex with microbubbles; microbubbles significantly accelerate the dissolution process of gas in liquid by providing a larger specific surface area and a longer residence time. The method has mild process conditions and can be carried out under normal pressure and realize continuous operation; the latex solidifies quickly, and the time is ≤1h; the natural rubber product finally prepared has good quality, with an initial plasticity value of ≥40, a plasticity retention rate of ≥92, and a tensile strength of ≥24MPa after vulcanization.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method using CO at normal pressure 2 The method for microbubble carbonization-coagulation of natural rubber latex comprises the following steps:

[0010] 1) Passing carbon dioxide into the microbubble generating device from the gas inlet;

[0011] 2) adding natural rubber latex from the material inlet into the microbubble generating device;

[0012] 3) Carbon dioxide contacts natural rubber latex in the form of microbubbles under normal pressure;

[0013] 4) Collecting the natural rubber latex at the discharge port and coagulating it to obtain natural rubber clots.

[0014] Preferably, in step 1) or step 2), the microbubble generating device is at least one of a stirred tank, a bubbling tower, a rotating 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.

[0016] Preferably, in step 2), the natural latex is fresh latex without any additive treatment.

[0017] Preferably, in step 3), the CO 2 The size of microbubbles ranges from 1nm to 100μm.

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

[0019] Preferably, in step 4), the solidification is carried out at room temperature of 10 to 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 clot, the rubber clot is successively thinned, creped and dried to obtain a natural rubber product.

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

[0023] Any range described in the present invention includes the end value and any numerical value between the end values ​​and any sub-range formed by the end value or any numerical value between the end values.

[0024] Unless otherwise specified, all raw materials in the present invention can be purchased from the market, and the equipment used in the present invention can adopt conventional equipment in the relevant field or refer to the existing technology in the relevant field.

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

[0026] 1. The present invention provides a method of using CO at normal pressure 2 A new method for microbubble carbonization-coagulation of natural latex. The method of the present invention promotes the efficient dispersion of carbon dioxide microbubbles in natural latex with the help of a microbubble generating device. Microbubbles have a larger specific surface area and a longer residence time than ordinary bubbles, which further promotes the diffusion and dissolution of carbon dioxide in latex. Finally, the natural latex is collected at the discharge port and coagulated to obtain natural rubber. The present invention uses carbon dioxide microbubbles to coagulate natural latex. The form of microbubbles improves the solubility of carbon dioxide in latex, breaks through the limitation of high-pressure operating conditions, and realizes efficient and high-quality natural latex coagulation under normal pressure. The invented method has mild process conditions, fast latex coagulation speed, and the prepared natural rubber product is of good quality.

[0027] 2. In the method of the present invention, no coagulant needs to be added during the coagulation process, and the generated wastewater can be directly put into the wastewater treatment link without neutralization. Compared with the existing acid coagulation method, the method of the present invention can not only shorten the coagulation time and improve production efficiency, but also achieve zero emission of tail gas, thereby reducing pollution to the environment, reducing production costs, and realizing the recycling of resources.

[0028] 3. The natural rubber product obtained by the method of the present invention has good quality, with an initial plasticity value of ≥40, a plasticity retention rate of >92, and a tensile strength after vulcanization of >24MPa. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 1 It shows that the present invention uses CO at normal pressure 2 Process flow chart of microbubble carbonization-coagulation of natural rubber latex. DETAILED DESCRIPTION

[0031] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0032] As one aspect of the present invention, the present invention uses CO at normal pressure 2 The method for microbubble carbonization-coagulation of natural rubber latex comprises the following steps:

[0033] 1) Passing carbon dioxide into the microbubble generating device from the gas inlet;

[0034] 2) adding natural rubber latex from the material inlet into the microbubble generating device;

[0035] 3) carbon dioxide and natural rubber latex are contacted in a nano-micro bubble generating device under normal pressure;

[0036] 4) Collecting natural rubber latex at the material outlet and coagulating it to obtain natural rubber clots.

[0037] According to some embodiments of the present invention, in step 1) or step 2), the microbubble generating device is at least one of a stirred tank, a bubbling tower, 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.

[0039] According to some 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 CO 2 The microbubble range is 1nm~100μm.

[0041] According to some embodiments of the present invention, in step 3), the gas-liquid volume ratio of the carbon dioxide to natural rubber 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 being denatured due to overheating.

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

[0044] According to some embodiments of the present invention, in step 4), after obtaining the natural rubber curd, the rubber curd is sequentially thinned, creped and dried to obtain a natural rubber product. The present invention has no particular limitation on the dehydration process, and any process known in the art can be used to obtain a natural rubber product.

[0045] According to some embodiments of the present invention, the drying temperature is 40-120° C., more preferably 60-80° C.; the present invention has no particular limitation on the drying time, and a natural rubber product can be obtained according to a process well known in the art.

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

[0047] Example 1

[0048] A method using CO at normal pressure 2 The method for microbubble carbonization-coagulation of natural rubber latex comprises the following steps:

[0049] Take 2kg of fresh natural latex, carbon dioxide is industrial waste gas, after treatment, its purity is 98%;

[0050] The selected microbubble generating device is a microchannel reactor;

[0051] First, carbon dioxide is introduced into the microchannel reactor from the air 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, it is allowed to stand for 20 minutes to allow a large amount of latex to solidify.

[0052] Example 2

[0053] A method using CO at normal pressure 2 The method for microbubble carbonization-coagulation of natural rubber latex comprises the following steps:

[0054] Take 2kg of fresh natural latex, carbon dioxide is industrial waste gas, after treatment, its purity is 98%;

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

[0056] First, carbon dioxide is introduced into the equipment from the air inlet, and natural latex is fed by a pump with a gas-liquid ratio of 5:1. The rotating packed bed speed is 1200rpm. Under normal pressure and 25°C, it is allowed to stand for 10 minutes to solidify a large amount of latex.

[0057] Example 3

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

[0059] Take 2kg of fresh natural latex, carbon dioxide is industrial waste gas, after treatment, its purity is 98%;

[0060] The selected microbubble generating device is a stirred tank;

[0061] Carbon dioxide is introduced into the stirring tank from the microbubble generator, and natural latex is continuously fed with a peristaltic pump. The gas-liquid ratio is 1:1, the speed of the stirring tank is 1000rpm, and the residence time is 10min. Under normal pressure and 25°C, it is allowed to stand for 30 minutes to solidify a large amount of latex.

[0062] Example 4

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

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

[0065] The microbubble generating device selected is a bubbling tower;

[0066] The carbon dioxide is introduced into the bubbling tower from the air inlet, and mixed with the natural latex through the disperser, with a gas-liquid ratio of 1:1 and a residence time of 10 minutes. Under normal pressure and 25°C, a large amount of latex is solidified after standing for 15 minutes.

[0067] Comparative Example 1

[0068] As in Example 1, natural latex of the same condition was left to stand under natural conditions to achieve coagulation according to its own conditions. After standing for 2 hours, only a small amount of latex was coagulated.

[0069] It can be seen from this that the natural solidification effect is poor and takes a long time.

[0070] Performance Testing

[0071] The rubber curds prepared in the above examples and comparative examples were pressed and creped in turn, and then placed in a hot air drying oven to dry at 80°C to obtain natural rubber products. The performance of the natural rubber products prepared in Examples 1 to 5 and Comparative Example 1 was tested using conventional methods, and the results are shown in the following table:

[0072] Case <![CDATA[Plastic initial value P 0 > 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] It can be seen from the data in the table that the indicators of the natural rubber products prepared from the rubber clots of Examples 1 to 5 are significantly better than those of the sample of Comparative Example 1.

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

[0075] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all implementation methods here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for carbonizing and coagulating natural rubber latex using CO2 microbubbles under normal pressure, characterized in that: The following steps are involved: 1) Passing carbon dioxide into the microbubble generating device from the gas inlet; 2) adding natural rubber latex from the material inlet into the microbubble generating device; 3) Carbon dioxide contacts natural rubber latex in the form of microbubbles under normal pressure; 4) Collecting natural rubber latex at the material outlet and coagulating it to obtain natural rubber clots.

2. The method for carbonizing and coagulating natural rubber 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 bubbling tower, a rotating packed bed, a membrane bubble generator, and a microchannel device.

3. The method for carbonizing and coagulating natural rubber 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.

4. The method for carbonizing and coagulating natural rubber latex using CO2 microbubbles under normal pressure according to claim 1, characterized in that: In step 2), the natural latex is fresh latex without any additive treatment.

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

1.

7. The method for carbonizing and coagulating natural rubber 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 rubber 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 the natural rubber clot, the rubber clot is successively thinned, creped and dried to obtain a natural rubber product.

10. The method for carbonizing and coagulating natural rubber 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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