Method for preparing liquid reclaimed rubber through co-pyrolysis of lignin and waste rubber

Abstract

The invention provides a method for preparing liquid reclaimed rubber through co-pyrolysis of lignin and waste rubber, and belongs to the field of rubber production and manufacturing. The industrial lignin, the waste rubber powder and the softening agent are uniformly mixed and then put into a screw extruder, moderate thermal cracking of the lignin and decrosslinking of the waste rubber powder are realized, and the prepared liquid regenerated rubber is added into a rubber composition and can replace tackifying resin, the softening agent and a plasticizer, so that the viscosity of a rubber semi-finished product is improved, the processability of a rubber material is improved, and the service life of the rubber material is prolonged. Meanwhile, the dispersion of the filler is facilitated. Meanwhile, the application range and the exerting effect of the lignin in the rubber material are also expanded, and the high-valued utilization rate of the lignin is improved.

Description

Technical Field

[0001] The invention relates to a regenerated rubber manufacturing technology, in particular to a method for preparing liquid regenerated rubber by co-pyrolysis of lignin and waste rubber, belonging to the technical field of liquid regenerated rubber manufacturing. Background Art

[0002] As fossil energy reserves continue to decrease, human society needs to develop and utilize green, renewable new energy sources. Lignin, one of the three main components of woody biomass, is composed of randomly bonded styrene structural units. It has outstanding characteristics such as wide sources, huge reserves, and recyclable renewable, and has great application potential. However, in actual production, lignin is mainly discharged as waste or directly burned as fuel, resulting in serious waste of resources. Therefore, finding ways to utilize lignin at a high value has become the focus of many research studies.

[0003] Applying lignin to rubber materials can prepare environmentally friendly and degradable composite materials, which not only protects the environment, but also is conducive to the development of a green circular economy. Lignin can be used as a reinforcing agent in rubber and also has an anti-aging effect. However, lignin is an aromatic polymer, and its molecules contain a large number of active groups such as hydroxyl and carboxyl groups, which leads to a large intermolecular force and is easy to agglomerate in rubber. Therefore, applying lignin to rubber requires certain modification treatment, and the process is relatively complicated.

[0004] For example, the modified lignin mentioned in the patent (202010484885.2 A modified lignin reinforced rubber and its preparation method) is prepared by composite modification of lignin with compounds containing carbon-carbon double bonds, compounds containing sulfur elements, and compounds that can block hydroxyl groups.

[0005] The patent (202011583948.6 A modified lignin and its preparation method and application in rubber composite materials) mentions that lignin is reacted with an acetylenic compound in an organic solvent to obtain modified lignin.

[0006] These methods in the prior art all require modification of lignin, which limits the scope of use of lignin to a certain extent and is not conducive to its large-scale use in industrial production. Summary of the invention

[0007] The present invention provides a novel method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber. The method moderately cracks lignin at high temperature so that its product can promote the de-crosslinking of waste rubber, thereby solving the technical problem in the prior art that lignin cannot be used industrially in rubber production.

[0008] The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber according to an embodiment of the present invention comprises the following steps:

[0009] The first step is to classify, sort, clean and dry the recycled waste rubber, and put it into a crushing device to obtain 20-50 mesh waste rubber powder;

[0010] The second step is to dry, grind and crush the recovered industrial lignin to obtain 5-20 mesh lignin powder;

[0011] The third step is to put the waste rubber powder obtained in the first step, the lignin obtained in the second step, and the softener into a stirring and mixing device, stir for 2-5 minutes, and discharge the material when the material temperature reaches 120-150°C;

[0012] The fourth step is to feed the material obtained in the third step into the first twin-screw extruder in a closed and oxygen-proof state, control the temperature of the first twin-screw extruder to be 250-380° C., and react for 4-8 minutes to achieve de-crosslinking of the waste rubber powder and moderate thermal cracking of the lignin;

[0013] The fifth step is to feed the material obtained in the fourth step into a second closed twin-screw extruder through a continuous closed conveying device, and pass a cooling medium through the outer side of the barrel for cooling;

[0014] In the sixth step, the material obtained in the fifth step is sent into the closed third screw extruder through a continuous closed conveying device, and an inert gas is passed into the barrel. The barrel above the extruder outlet is connected to an exhaust gas treatment device. The material is extruded from the extruder to obtain a liquid regenerated rubber with a sol content greater than 80%, a number average molecular weight Mn of 7000 to 25000, and a molecular weight distribution of 6 to 12.

[0015] The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber as described above, wherein the water content of the waste rubber powder in the first step is less than 1%, and the waste rubber is any one or more of waste tires, tread rubber, waste rubber shoes, waste EPDM rubber and waste butyl rubber.

[0016] In the method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber as described above, the water content of the lignin powder in the second step is less than 1%, so the industrial lignin is a combination of any one or more of sulfate lignin, lignin sulfonate, alkali lignin and organic solvent lignin.

[0017] The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber as described above, wherein in the third step, the ratio of waste rubber powder, lignin and softener is 100:15-30:2-5, and the softener is any one or more of soybean oil, castor oil, rapeseed oil, palm oil, rapeseed oil foot, soybean oil foot and palm oil foot.

[0018] The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber as described above, wherein the temperature of the mixing and heating section of the first twin-screw extruder in the fourth step is 260-280°C, the temperature of the reaction section is 340-380°C, the temperature of the cooling section is 250-270°C, and the aspect ratio of the screw is 32-44:1.

[0019] In the method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber as described above, the aspect ratio of the screw of the second twin-screw extruder in the fifth step is 32 to 40:1, and the cooling medium is water or oil.

[0020] In the method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber as described above, the third screw extruder in the sixth step is a single-screw or twin-screw extruder, and the screw aspect ratio is 24 to 32:1.

[0021] The invention uses renewable lignin as a raw material to assist in preparing liquid regenerated rubber, which can effectively reduce the use of regeneration activators and softeners and promote the use of renewable energy. Combining the thermal cracking of lignin with the preparation process of liquid regenerated rubber not only saves the use of energy, but also the prepared liquid regenerated rubber, when added to the rubber composition, can replace tackifying resin, softener, plasticizer, increase the viscosity of the semi-finished rubber product, improve the processing performance of the rubber compound, and help the dispersion of the filler. DETAILED DESCRIPTION

[0022] The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber described in the present invention can be made of the following materials and components, but is not limited to the following materials and components, for example: waste rubber, lignin, softener, etc.

[0023] The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber according to an embodiment of the present invention comprises the following steps:

[0024] In the first step, the recycled waste rubber is classified, sorted, cleaned, dried, and put into a crushing device to obtain 20-50 mesh waste rubber powder; the water content of the waste rubber powder in the first step is less than 1%, and the waste rubber is any one or more combinations of waste tires, tread rubber, waste rubber shoes, waste EPDM rubber and waste butyl rubber.

[0025] In the second step, the recovered industrial lignin is dried, ground and pulverized to obtain lignin powder of 5-20 mesh; the water content of the lignin powder in the second step is less than 1%, so the industrial lignin is any one or more combinations of sulfate lignin, lignin sulfonate, alkali lignin and organic solvent lignin.

[0026] The third step is to put the waste rubber powder obtained in the first step, the lignin obtained in the second step, and the softener into a stirring and mixing device, stir for 2-5 minutes, and discharge the material when the material temperature reaches 120-150°C;

[0027] In the third step, the ratio of waste rubber powder, lignin and softener is 100:15-30:2-5, and the softener is any one or more combinations of soybean oil, castor oil, rapeseed oil, palm oil, rapeseed oil foot, soybean oil foot and palm oil foot.

[0028] The fourth step is to feed the material obtained in the third step into the first twin-screw extruder in a closed and oxygen-proof state, control the temperature of the first twin-screw extruder to be 250-380° C., and react for 4-8 minutes to achieve de-crosslinking of the waste rubber powder and moderate thermal cracking of the lignin;

[0029] The mixing and heating section temperature of the first twin-screw extruder in the fourth step is 260-280°C, the reaction section temperature is 340-380°C, the cooling section temperature is 250-270°C, and the aspect ratio of the screw is 32-44:1.

[0030] The fifth step is to feed the material obtained in the fourth step into a second closed twin-screw extruder through a continuous closed conveying device, and pass a cooling medium through the outer side of the barrel for cooling;

[0031] The screw length-to-diameter ratio of the second twin-screw extruder in the fifth step is 32-40:1, and the cooling medium is water or oil.

[0032] In the sixth step, the material obtained in the fifth step is sent into the closed third screw extruder through a continuous closed conveying device, and an inert gas is passed into the barrel. The barrel above the extruder outlet is connected to an exhaust gas treatment device. The material is extruded from the extruder to obtain a liquid regenerated rubber with a sol content greater than 80%, a number average molecular weight Mn of 7000 to 25000, and a molecular weight distribution of 6 to 12.

[0033] The third screw extruder in the sixth step is a single-screw or twin-screw extruder, and the screw aspect ratio is 24-32:1.

[0034] The present invention has at least the following beneficial effects:

[0035] A small amount of plant softener added to the formula, due to the chemical structure of the plant oil itself, has a long and flexible high-grade fatty acid chain, which can easily penetrate into the interior of the rubber powder, so that the temperature of the rubber powder and lignin can be quickly raised during the mixing process. When the material enters the first twin-screw extruder, as the temperature rises, under oxygen-isolated conditions, the lignin first undergoes moderate thermal cracking to produce active free radicals. Existing studies have shown that the thermal degradation of high molecular polymers is mainly a free radical-dominated mechanism. Therefore, the active free radicals released by the thermal cracking of lignin will effectively promote the de-crosslinking reaction of the waste rubber powder. The effective hydrogen-carbon ratio of the waste rubber powder is relatively high, and the hydrogen free radicals are released into the "free radical pool". Through the hydrogen transfer reaction, the bio-oil produced by the pyrolysis of lignin is promoted from oxygen-containing compounds to hydrocarbons, thereby improving the stability of the bio-oil and its compatibility with the waste rubber powder. When the decomposed material enters the second twin-screw extruder, the material is initially cooled under the condition of passing the cooling medium, and the condensable gas generated by the thermal decomposition of lignin is condensed. When entering the third screw extruder, the inert gas introduced not only cools the material further, but also takes away the non-condensable gas generated by the thermal decomposition of lignin. The biochar generated by the thermal decomposition of lignin can be used as a filler to reduce costs, improve the processing performance of liquid recycled rubber, and improve the quality of liquid recycled rubber.

[0036] Using renewable lignin as raw material to assist in the preparation of liquid regenerated rubber can effectively reduce the use of regeneration activators and softeners and promote the use of renewable energy. Combining the thermal cracking of lignin with the preparation process of liquid regenerated rubber not only saves energy, but also the prepared liquid regenerated rubber, when added to the rubber composition, can replace tackifying resins, softeners, and plasticizers, increase the viscosity of semi-finished rubber products, improve the processing performance of rubber compounds, and help disperse fillers.

[0037] Example 1

[0038] S1: The recycled waste rubber is classified, sorted, cleaned, dried, and put into a crushing device to obtain 30% waste rubber powder, the water content of which is less than 1%;

[0039] S2: drying, grinding and crushing the recovered industrial lignin to obtain 12 mesh lignin powder with a water content of less than 1%;

[0040] S3: Put the waste rubber powder obtained in S1, the lignin obtained in S2, and rapeseed oil into a stirring and mixing device in a mass ratio of 100:18:3, stir for 3 minutes, and discharge the material when the material temperature reaches 129°C;

[0041] S4: The material obtained in S3 is fed into the first closed twin-screw co-rotating extruder, and the temperature of the mixing and heating section of the extruder is controlled to be 265°C, the temperature of the reaction section is 352°C, the temperature of the cooling section is 253°C, the aspect ratio of the screw is 40:1, and the reaction is performed for 6 minutes to achieve de-crosslinking of the waste rubber powder and moderate thermal cracking of the lignin;

[0042] S5: The material obtained in S4 is fed into a second closed twin-screw extruder through a continuous closed conveying device, the aspect ratio of the screw is 32:1, and a cooling medium is passed through the outer side of the barrel for cooling;

[0043] S6: The material obtained in S5 is sent into the third single-screw extruder through a continuous closed conveying device. The aspect ratio of the screw is 28:1. Inert gas is passed into the barrel. The material is extruded from the extruder to obtain liquid regenerated rubber with a sol content greater than 80%, a number average molecular weight Mn of 12826, and a molecular weight distribution of 8.6.

[0044] Example 2

[0045] S1: The recycled waste rubber is classified, sorted, cleaned, dried, and put into a crushing device to obtain 40-mesh waste rubber powder with a water content of less than 1%;

[0046] S2: drying, grinding and crushing the recovered industrial lignin to obtain 16 mesh lignin powder with a water content of less than 1%;

[0047] S3: Put the waste rubber powder obtained in S1, the lignin obtained in S2, and the soybean oil into a stirring and mixing device in a mass ratio of 100:15:3, stir for 4 minutes, and discharge the material when the material temperature reaches 137°C;

[0048] S4: feeding the material obtained in S3 into the first closed twin-screw co-rotating extruder, controlling the temperature of the mixing and heating section of the extruder to 271°C, the temperature of the reaction section to 360°C, the temperature of the cooling section to 255°C, the aspect ratio of the screw to 44:1, and reacting for 5 minutes to achieve de-crosslinking of the waste rubber powder and moderate thermal cracking of the lignin;

[0049] S5: The material obtained in S4 is fed into a second closed twin-screw extruder through a continuous closed conveying device, the aspect ratio of the screw is 32:1, and a cooling medium is passed through the outer side of the barrel for cooling;

[0050] S6: The material obtained in S5 is sent into the third single-screw extruder through a continuous closed conveying device. The aspect ratio of the screw is 24:1. Inert gas is passed into the barrel. The material is extruded from the extruder to obtain liquid regenerated rubber. The sol content is greater than 80%, the number average molecular weight Mn is 15842, and the molecular weight distribution is 9.3.

[0051] Example 3

[0052] S1: The recycled waste rubber is classified, sorted, cleaned, dried, and put into a crushing device to obtain 50-mesh waste rubber powder with a water content of less than 1%;

[0053] S2: drying, grinding and crushing the recovered industrial lignin to obtain 20-mesh lignin powder with a water content of less than 1%;

[0054] S3: Put the waste rubber powder obtained in S1, the lignin obtained in S2, and the palm oil into a stirring and mixing device in a mass ratio of 100:19:4, stir for 5 minutes, and discharge the material when the material temperature reaches 142°C;

[0055] S4: The material obtained in S3 is fed into the first closed twin-screw co-rotating extruder, and the temperature of the mixing and heating section of the extruder is controlled to be 267°C, the temperature of the reaction section is 370°C, the temperature of the cooling section is 250°C, the aspect ratio of the screw is 44:1, and the reaction is carried out for 5 minutes to achieve de-crosslinking of the waste rubber powder and moderate thermal cracking of the lignin;

[0056] S5: The material obtained in S4 is fed into a second closed twin-screw extruder through a continuous closed conveying device, the aspect ratio of the screw is 36:1, and a cooling medium is passed through the outer side of the barrel for cooling;

[0057] S6: The material obtained in S5 is sent into the third single-screw extruder through a continuous closed conveying device. The aspect ratio of the screw is 28:1. Inert gas is passed into the barrel. The material is extruded from the extruder to obtain liquid regenerated rubber. The sol content is greater than 80%, the number average molecular weight Mn is 18285, and the molecular weight distribution is 10.1.

[0058] The serial numbers of the above embodiments of the present invention are for description only and do not represent the advantages and disadvantages of the embodiments. Through the description of the above implementation methods, those skilled in the art can clearly understand that the above embodiment methods can be implemented by means of some deformations plus the necessary general technology superposition; of course, they can also be implemented by simplifying some important technical features. Based on this understanding, the technical solution of the present invention is essentially or contributes to the prior art in the following aspects: the overall structure and connection method, and the structure described in each embodiment of the present invention.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber, characterized in that: The following steps are involved: The first step is to classify, sort, clean and dry the recycled waste rubber, and put it into a crushing device to obtain 20-50 mesh waste rubber powder; The second step is to dry, grind and crush the recovered industrial lignin to obtain 5-20 mesh lignin powder; The third step is to put the waste rubber powder obtained in the first step, the lignin obtained in the second step, and the softener into a stirring and mixing device, stir for 2-5 minutes, and discharge the material when the material temperature reaches 120-150°C; The fourth step is to feed the material obtained in the third step into the first twin-screw extruder in a closed and oxygen-proof state, control the temperature of the first twin-screw extruder to be 250-380° C., and react for 4-8 minutes to achieve de-crosslinking of the waste rubber powder and moderate thermal cracking of the lignin; Step 5: The material obtained in step 4 is fed into a second closed twin-screw extruder through a continuous closed conveying device, and a cooling medium is passed through the outer side of the barrel for cooling; In the sixth step, the material obtained in the fifth step is sent into the closed third screw extruder through a continuous closed conveying device, and an inert gas is passed into the barrel. The barrel above the extruder outlet is connected to an exhaust gas treatment device. The material is extruded from the extruder to obtain a liquid regenerated rubber with a sol content greater than 80%, a number average molecular weight Mn of 7000 to 25000, and a molecular weight distribution of 6 to 12.

2. The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber according to claim 1, characterized in that: The water content of the waste rubber powder in the first step is less than 1%, and the waste rubber is any one or more combinations of waste tires, tread rubber, waste rubber shoes, waste EPDM rubber and waste butyl rubber.

3. The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber according to claim 1, characterized in that: The water content of the lignin powder in the second step is less than 1%, so the industrial lignin is any one or more combinations of kraft lignin, lignin sulfonate, alkali lignin and organic solvent lignin.

4. The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber according to claim 1, characterized in that: In the third step, the ratio of waste rubber powder, lignin and softener is 100:15-30:2-5, and the softener is any one or more combinations of soybean oil, castor oil, rapeseed oil, palm oil, rapeseed oil foot, soybean oil foot and palm oil foot.

5. The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber according to claim 1, characterized in that: The mixing and heating section temperature of the first twin-screw extruder in the fourth step is 260-280°C, the reaction section temperature is 340-380°C, the cooling section temperature is 250-270°C, and the aspect ratio of the screw is 32-44:

1.

6. The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber according to claim 1, characterized in that: The screw length-to-diameter ratio of the second twin-screw extruder in the fifth step is 32-40:1, and the cooling medium is water or oil.

7. The method for preparing liquid reclaimed rubber by co-pyrolysis of lignin and waste rubber according to claim 1, characterized in that: The third screw extruder in the sixth step is a single-screw or twin-screw extruder, and the screw aspect ratio is 24-32:1.