CN109776856B - Method for preparing linearized active rubber from waste rubber - Google Patents
Method for preparing linearized active rubber from waste rubber Download PDFInfo
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- CN109776856B CN109776856B CN201711122422.6A CN201711122422A CN109776856B CN 109776856 B CN109776856 B CN 109776856B CN 201711122422 A CN201711122422 A CN 201711122422A CN 109776856 B CN109776856 B CN 109776856B
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/62—Plastics recycling; Rubber recycling
Abstract
The invention provides a method for preparing linear active rubber by using waste rubber. The method comprises the following steps: in supercritical carbon dioxide, the mixture of waste rubber powder and photocatalyst is put under ultraviolet light for photocatalytic desulfurization reaction to obtain the linearized active rubber. The supercritical carbon dioxide can enable part of the photocatalyst to permeate into the waste rubber powder from the surface, and the photocatalyst generates a large amount of active groups under ultraviolet light to catalyze the breakage of S-S bonds and C-S bonds in the waste rubber powder, so that desulfurization and crosslinking decomposition are realized. Moreover, linear molecules formed by the desulfurization and the de-crosslinking on the surface of the waste rubber powder can be quickly stripped and dissolved in the supercritical carbon dioxide. Thus, the waste rubber powder continuously generates the cyclic reciprocation of 'catalyst surface penetration, photocatalytic desulfurization and desulfurization linear molecule stripping dissolution' until the linear active rubber is formed. Meanwhile, the method does not leave any auxiliary agent which causes adverse effect on the application of the linearized active rubber, and can be better applied to the fields of rubber products, asphalt modification and the like.
Description
Technical Field
The invention relates to the technical field of waste rubber recovery, in particular to a method for preparing linear active rubber by using waste rubber.
Background
With the increasing output of rubber products such as tires on the market, more and more waste rubber needs to be recycled. As a precious renewable resource, the problem of recycling of waste rubber is widely regarded internationally. Due to the special three-dimensional cross-linked network structure, the waste rubber needs to be desulfurized and regenerated when being recycled, and the main principle is to reopen the cross-linked network in the waste rubber by using physical, chemical or biological methods and the like.
At present, the most industrially applied methods for desulfurizing and regenerating the waste rubber mainly comprise the following methods:
firstly, chemical desulfurization is carried out by adopting a desulfurizing agent, and the method has higher desulfurization efficiency. However, this method inevitably leaves the desulfurizing agent in the reclaimed rubber after the desulfurization regeneration treatment is completed, which causes disadvantages in secondary utilization of the reclaimed rubber, such as: delayed vulcanization, secondary degradation and the like, and causes the defects of unstable product performance and the like.
And secondly, physical shearing desulfurization, wherein the method mainly depends on mechanical force and other physical shearing modes to destroy the three-dimensional cross-linked network of the waste rubber so as to realize desulfurization regeneration. However, such methods usually require the addition of a large amount of organic softeners during the implementation, which affect the hardness of the reclaimed rubber and the hardness of the rubber product when the reclaimed rubber is used for manufacturing the rubber product; when used for modified asphalt, etc., the modified asphalt product is softened and the use is affected.
And thirdly, photocatalytic degradation, because the rubber can not radiate into the waste rubber due to the shielding effect of the rubber on ultraviolet light, the method can only desulfurize and degrade the surface of the waste rubber, the interior of the waste rubber is still in a crosslinked nuclear structure, and the content of the linearized rubber is low. Such as: chinese patent CN105646932 discloses a method for rapidly depolymerizing waste rubber powder at low temperature by using ultraviolet rays, which comprises spreading the waste rubber powder in an ultraviolet generator, and performing ultraviolet irradiation at an ambient temperature of 50-100 ℃ to depolymerize the waste rubber powder. Although the specification states that the waste rubber powder sol after depolymerization can reach 80%, the test has not yet reached such a degree of depolymerization. For the reasons mentioned above, the degree of depolymerization inside the waste rubber is greatly limited due to the shielding effect of the rubber itself against ultraviolet light.
For the above reasons, it is necessary to provide a process for recovering waste rubber having a high desulfurization degree and free from residual problems of a desulfurizing agent, a softening agent and the like.
Disclosure of Invention
The invention mainly aims to provide a method for preparing linearized active rubber by using waste rubber, which aims to solve the problems of low desulfurization degree and residual desulfurizer and softener in the process of desulfurization and regeneration of the waste rubber in the prior art.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a linearized active rubber from a waste rubber, comprising: in supercritical carbon dioxide, the mixture of waste rubber powder and photocatalyst is put under ultraviolet light for photocatalytic desulfurization reaction to obtain the linearized active rubber.
Further, the photocatalyst is a composite inorganic lightA catalyst; preferably, the photocatalyst is selected from Co-doped TiO2、ZrO2/ZnO composite and ZrO2/TiO2One or more of the complexes.
Further, the preparation method comprises the following steps: mixing waste rubber powder with a photocatalyst to obtain a mixture; under the condition of stirring, putting the mixture into supercritical carbon dioxide for swelling treatment to obtain a swelling mixture; and irradiating ultraviolet light to the swelling mixture in supercritical carbon dioxide to perform photocatalytic desulfurization reaction, thereby obtaining the linearized active rubber.
Further, the swelling treatment step includes: injecting carbon dioxide gas into a system where the mixture is located, and then adjusting the temperature of the system to 80-140 ℃ and the pressure to 10-35 MPa to convert the carbon dioxide gas into a supercritical state so as to form supercritical carbon dioxide; and swelling the mixture for 30-120 min under the stirring condition that the stirring speed is 200-700 rpm, so as to obtain a swelling mixture.
Further, the swelling treatment step includes: injecting carbon dioxide gas into a system where the mixture is located, and then adjusting the temperature of the system to 105-140 ℃ and the pressure to 28-35 MPa to convert the carbon dioxide gas into a supercritical state so as to form supercritical carbon dioxide; and swelling the mixture for 90-120 min under the condition that the stirring speed is 500-700 rpm, so as to obtain a swelling mixture.
Further, in the step of the photocatalytic desulfurization reaction, the reaction temperature is 80-140 ℃, preferably 105-140 ℃, and the reaction pressure is 10-35 MPa, preferably 28-35 MPa.
Further, in the step of photocatalytic desulfurization reaction, the illumination time of the ultraviolet light is 5-30 min, preferably 20-30 min, and the wavelength of the ultraviolet light is 300-420 nm, preferably 350-390 nm.
Further, the step of mixing the waste rubber powder with the photocatalyst comprises: stirring and mixing the waste rubber powder and the photocatalyst for 5-30 min under the condition that the stirring speed is 700-1500 rpm to obtain a mixture; preferably, the waste rubber powder and the photocatalyst are stirred and mixed to a temperature of not higher than 85 ℃ to obtain a mixture.
Further, the amount of the photocatalyst is 0.5-3% by weight of the waste rubber powder, preferably 2-3%.
Further, the particle size of the waste rubber powder is 80-120 meshes; preferably, the waste rubber powder is one or more of waste tire rubber powder, waste mechanical tire rubber powder, waste sole rubber powder and waste conveyor belt rubber powder.
The technical scheme of the invention provides a method for preparing linear active rubber by using waste rubber, which comprises the step of placing a mixture of waste rubber powder and a photocatalyst in supercritical carbon dioxide under ultraviolet light for photocatalytic desulfurization reaction to obtain the linear active rubber.
In the preparation method, the waste rubber powder can be swelled by the supercritical carbon dioxide, so that the aperture of the three-dimensional cross-linked network in the waste rubber powder is increased, and a part of the photocatalyst is permeated into the waste rubber powder from the surface by virtue of the diffusion effect of the supercritical carbon dioxide fluid. Secondly, the photocatalyst generates a large amount of active groups under the irradiation of ultraviolet light to catalyze the breakage of S-S bonds and C-S bonds in the waste rubber powder, thereby realizing the desulfurization and crosslinking of the waste rubber powder. Particularly, since the supercritical carbon dioxide also has an excellent dissolving effect, the linear molecules formed by the desulfurization and de-crosslinking on the surface of the waste rubber powder can be rapidly peeled off from the surface of the waste rubber powder and dissolved in the supercritical carbon dioxide. Along with the continuous reaction, the waste rubber powder can continuously generate the cyclic reciprocating of 'catalyst surface permeation, photocatalytic desulfurization and desulfurization linear molecule stripping dissolution' until the waste rubber powder integrally completes desulfurization and de-crosslinking to form the linear active rubber.
Meanwhile, in the preparation method provided by the invention, reagents such as a desulfurizing agent, an organic softening agent and the like are not required, and an auxiliary agent which causes adverse effect on the application of the linearized active rubber is not remained, so that the preparation method can be better applied to various fields such as rubber products, asphalt modification and the like. Particularly, the photocatalyst can also be used as a filler of linearized active rubber, so that the performance of the rubber and the product thereof is not influenced, the filler consumption of downstream products can be saved, and the two aims can be fulfilled.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail with reference to examples.
The present application is described in further detail below with reference to specific examples, which should not be construed as limiting the scope of the invention as claimed.
As described in the background art, there are problems in the prior art that the desulfurization degree is low and the desulfurizing agent and the softening agent remain when the desulfurization regeneration is performed on the waste rubber.
In order to solve the problems, the invention provides a method for preparing linearized active rubber by using waste rubber, which comprises the step of subjecting a mixture of waste rubber powder and a photocatalyst to a photocatalytic desulfurization reaction in supercritical carbon dioxide under ultraviolet light to obtain the linearized active rubber.
In the preparation method, the waste rubber powder can be swelled by using the supercritical carbon dioxide, so that the aperture of the three-dimensional cross-linked network in the waste rubber powder is increased, and a part of the photocatalyst is permeated into the waste rubber powder from the surface by virtue of the diffusion effect of the supercritical carbon dioxide fluid. Secondly, the photocatalyst generates a large amount of active groups under the irradiation of ultraviolet light to catalyze the breakage of S-S bonds and S-C bonds in the waste rubber powder, thereby realizing the desulfurization and crosslinking of the waste rubber powder. Particularly, since the supercritical carbon dioxide also has an excellent dissolving effect, the linear molecules formed by the desulfurization and de-crosslinking on the surface of the waste rubber powder can be rapidly peeled off from the surface of the waste rubber powder and dissolved in the supercritical carbon dioxide. Along with the continuous reaction, the waste rubber powder can continuously generate the cyclic reciprocating of 'catalyst surface permeation, photocatalytic desulfurization and desulfurization linear molecule stripping dissolution' until the waste rubber powder integrally completes desulfurization and de-crosslinking to form the linear active rubber.
It should be noted that, the primary purpose of desulfurization is to hope that the cross-linking bond S-S/C-S is broken, and the main chain C-C is continuous, so that the molecular weight of the rubber macromolecule can be fully ensured, and in fact, the larger the molecular weight of the macromolecule is, the more obvious the advantage of secondary utilization is, because the larger the molecular weight of the macromolecule is, the more close to the original ecological uncrosslinked rubber molecule can be achieved. However, the traditional mechanical shearing desulfurization has diversified breaking points, which have no obvious selectivity on S-S/C-S bonds and C-C bonds, and C-C is broken while C-S/S-S is broken, so that the average molecular weight of degraded macromolecules is very low, and secondary utilization is not facilitated. Different from the traditional mechanical shearing desulfurization regeneration method, the method has the advantages that the photocatalytic desulfurization is carried out under the swelling action of the supercritical carbon dioxide, the selectivity for the breaking point of a cross-linked network is high, and the breaking point is mostly at the cross-linked part of an S-S bond and an S-C bond. Therefore, based on the preparation method of the invention, the linearization structure of the rubber can be more completely maintained, and the regenerated linearization active rubber has higher molecular weight and correspondingly maintains higher performance, so that the rubber can be more widely applied to various fields.
Meanwhile, in the preparation method provided by the invention, reagents such as a desulfurizing agent, an organic softening agent and the like are not required, and an auxiliary agent which causes adverse effect on the application of the linearized active rubber is not remained, so that the preparation method can be better applied to various fields such as rubber products, asphalt modification and the like. Particularly, the photocatalyst can also be used as a filler of linearized active rubber, so that the performance of the rubber and the product thereof is not influenced, the filler consumption of downstream products can be saved, and the two aims can be fulfilled.
The above-mentioned photocatalyst may be of a type commonly used in the field of photocatalytic technology. In a preferred embodiment, the photocatalyst is a composite inorganic photocatalyst. The composite inorganic photocatalyst has higher catalytic activity and higher selective fracture performance on S-S crosslinking points in the waste rubber powder. More preferably, the photocatalyst is selected from Co-doped TiO2、ZrO2/ZnO composite and ZrO2/TiO2One or more of the complexes. The surface areas of the composite inorganic photocatalysts are greatly increased, so that the probability of exciting the photohole electrons under ultraviolet irradiation is further increased, and the composite inorganic photocatalysts have higher catalytic activity. At the same time, these photocatalysts remain in the linearized active rubber as a filler thereofMore preferably.
In a preferred embodiment, the preparation method comprises the following steps: mixing waste rubber powder with a photocatalyst to obtain a mixture; under the condition of stirring, putting the mixture into supercritical carbon dioxide for swelling treatment to obtain a swelling mixture; and irradiating ultraviolet light to the swelling mixture in supercritical carbon dioxide to perform photocatalytic desulfurization reaction, thereby obtaining the linearized active rubber.
Thus, mixing the waste rubber powder with the photocatalyst in advance enables the photocatalyst to be dispersed in the waste rubber powder in advance. Secondly, the mixture is placed in supercritical carbon dioxide under the condition of stirring for swelling treatment, so that the diffusion effect of supercritical carbon dioxide fluid can be more fully exerted, the waste rubber powder is swelled as soon as possible, and the photocatalyst is enabled to permeate into the surface of the waste rubber powder more quickly. Finally, irradiating ultraviolet light to the system for photocatalytic desulfurization reaction. In the actual operation process, the desulfurization efficiency of the waste rubber powder can be further improved according to the process.
In a preferred embodiment, the swelling treatment step comprises: injecting carbon dioxide gas into a system in which the mixture is located, and then adjusting the temperature of the system to 80-140 ℃ and the pressure to 10-35 MPa to convert the carbon dioxide gas into a supercritical state so as to form supercritical carbon dioxide; and swelling the mixture for 30-120 min under the stirring condition that the stirring speed is 200-700 rpm, so as to obtain a swelling mixture. The swelling treatment is carried out in the technical process, the aperture of the cross-linked network of the waste rubber powder is larger, and the photocatalyst can be more fully permeated and more uniformly dispersed in the rubber network, so that on one hand, the desulfurization efficiency of the waste rubber powder can be further improved, and simultaneously, the fracture number of S-S bonds can be further improved, thereby improving the desulfurization degree of the waste rubber powder and obtaining the desulfurized rubber with higher linearization degree.
More preferably, the swelling treatment step comprises: injecting carbon dioxide gas into a system in which the mixture is located, and then adjusting the temperature of the system to 105-140 ℃ and the pressure to 28-35 MPa to convert the carbon dioxide gas into a supercritical state so as to form supercritical carbon dioxide; and swelling the mixture for 90-120 min under the condition that the stirring speed is 500-700 rpm, so as to obtain a swelling mixture. The desulfurization efficiency and desulfurization degree under the process condition are higher.
In a preferred embodiment, in the step of photocatalytic desulfurization, the reaction temperature is 80-140 ℃ and the reaction pressure is 10-35 MPa. Under the reaction conditions, the S-S bond desulfurization selectivity of the photocatalyst is higher, and the desulfurization degree and the desulfurization linearization degree of the waste rubber powder are higher. More preferably, the reaction temperature in the step of the photocatalytic desulfurization reaction is 105-140 ℃, and the reaction pressure is 28-35 MPa. In the actual production process, after the photocatalytic desulfurization reaction is finished, the method preferably further comprises the following steps: and (3) decompressing the reaction system, recovering carbon dioxide, stopping illumination and cooling to obtain the linearized active rubber.
In a preferred embodiment, in the step of photocatalytic desulfurization, the illumination time of the ultraviolet light is 5 to 30min, preferably 20 to 30min, and the wavelength of the ultraviolet light is 300 to 420nm, preferably 350 to 390 nm. Under the illumination condition, the photocatalyst has higher activity, and the desulfurization effect of the waste rubber powder is better.
In a preferred embodiment, the step of mixing the waste rubber powder with the photocatalyst comprises: and stirring and mixing the waste rubber powder and the photocatalyst for 5-30 min under the condition that the stirring speed is 700-1500 rpm to obtain a mixture. The waste rubber powder and the photocatalyst are mixed according to the process, and the waste rubber powder and the photocatalyst can be mutually dispersed more fully. Preferably, the waste rubber powder and the photocatalyst are stirred and mixed to a temperature of not higher than 85 ℃ to obtain a mixture. Frictional heating can occur in the stirring process, the stirring and mixing temperature is controlled to be not higher than 85 ℃, and performance influence caused by overheating can be prevented on the basis of full dispersion.
As described above, based on the diffusibility and good solubility of supercritical carbon dioxide, the cyclic process of "catalyst surface permeation-photocatalytic desulfurization-desulfurization linear molecule stripping dissolution" is continuously performed in the step of photocatalytic desulfurization reaction of waste rubber powder, which enables the preparation method of the present invention to achieve a higher desulfurization degree by using the cyclic process with less photocatalyst. For the purpose of saving energy and improving the desulfurization efficiency and the desulfurization degree, in a preferred embodiment, the amount of the photocatalyst is 0.5 to 3% by weight, preferably 2 to 3% by weight, based on the waste rubber powder.
In a preferred embodiment, the particle size of the waste rubber powder is 80-120 meshes; preferably, the waste rubber powder is one or more of waste tire rubber powder, waste mechanical tire rubber powder, waste sole rubber powder and waste conveyor belt rubber powder. In addition, the preparation method is suitable for waste rubber powder commonly used in the field, such as one or more of waste nitrile rubber powder, waste natural rubber powder, waste butyl rubber powder, waste ethylene propylene rubber powder and waste styrene butadiene rubber powder.
The beneficial effects of the present invention are further illustrated by the following examples:
examples 1 to 18
In these examples, the following processes were used to conduct the devulcanization regeneration of the waste rubber:
step 1: putting 80-mesh waste tire rubber powder and a photocatalyst into a high-speed stirring and mixing unit, stirring at the stirring speed of 1000rpm for 20min to 70 ℃, stopping stirring, putting the materials into a cooling unit, cooling and discharging to obtain a mixture;
step 2: putting the mixture into a supercritical carbon dioxide reaction kettle, injecting carbon dioxide gas into the reaction kettle by using a high-pressure pump to adjust the pressure in the reaction kettle, and simultaneously heating to convert the carbon dioxide gas into a supercritical state; starting stirring to swell the mixture in supercritical carbon dioxide to obtain a swollen mixture;
and step 3: maintaining the supercritical carbon dioxide environment, starting a built-in ultraviolet light source to perform ultraviolet irradiation on the swelling mixture, and irradiating for a certain time;
and 4, step 4: and (5) releasing pressure and recovering carbon dioxide gas, stopping illumination and cooling, and taking out a target product and testing.
Examples 1 to 18 differ in the following parameters: the type and amount of the photocatalyst (weight percentage of the waste rubber powder), the temperature of the supercritical carbon dioxide system (same swelling temperature and desulfurization reaction temperature), the pressure (same swelling pressure and desulfurization reaction pressure), the swelling time, the ultraviolet light irradiation time and the ultraviolet light wavelength are shown in table 1:
TABLE 1
Example 19
The process flow in this example is the same as in example 9, except that:
step 1: and (3) putting 120-mesh waste tire rubber powder and a photocatalyst into a high-speed stirring and mixing unit, stirring at the stirring speed of 700rpm for 30min to 60 ℃, stopping stirring, putting the materials into a cooling unit, cooling and discharging to obtain a mixture.
Example 20
The process flow in this example is the same as in example 10, except that:
step 1: and (3) putting the 120-mesh waste sole rubber powder and the photocatalyst into a high-speed stirring and mixing unit, stirring at the stirring speed of 1500rpm for 30min to 85 ℃, stopping stirring, putting the materials into a cooling unit, cooling and discharging to obtain a mixture.
Example 21
The process flow in this example is the same as in example 10, except that:
step 1: and (3) putting the 80-mesh waste conveyor belt rubber powder and the photocatalyst into a high-speed stirring and mixing unit, stirring at the stirring speed of 600rpm for 10min to 40 ℃, stopping stirring, putting the materials into a cooling unit, cooling and discharging to obtain a mixture.
Comparative example 1
100 parts of waste tire rubber powder and 10 parts of nano cadmium sulfide are stirred and mixed uniformly by a high-speed plasticizing reaction unit. The rotating speed of the reaction unit is firstly adjusted to 1200rpm, when the temperature reaches 90 ℃, stirring is stopped, the materials are put into a cooling unit, the rotating speed is 50rpm, and when the temperature is about 30 ℃, discharging is carried out. Placing the stirred material into a stirrer, and irradiating the material with ultraviolet lamp for 30 min. The UV lamp used was a 3kw high pressure mercury lamp with UV wavelength of 365 nm.
The main machine rotating speed of the double-screw extruder is adjusted to be 220rpm, the feeding rotating speed is adjusted to be 15rpm, and the temperatures of 7 temperature zones of the double screws are as follows: 54-67-77-76-79-73-42 ℃, the temperature of each area is not higher than 100 ℃, the production state at normal temperature and normal pressure is realized, and the discharge detection is carried out.
Comparative example 2
100 parts of waste tire tread rubber powder with the particle size of 1mm is adopted, 6 parts of pine tar, 4 parts of naphthenic oil, 0.5 part of phenyl mercaptan and 0.5 part of n-butylamine are added as regenerants, and the mixture is mixed and stirred for 10min at the temperature of 100 ℃ in a stirrer and then is placed for 36h at the temperature of 50 ℃. It was then fed into a co-rotating twin-screw extruder (D30 mm, L/D52/1, six heating zones) via a feeding device: screw rotation speed 150rpm, 6 temperature zones: changing the internal thread composition of the screw at 120 ℃, 180 ℃, 230 ℃, 280 ℃, 150 ℃ and 100 ℃, and adding a right-handed thread element to ensure that the maximum pressure reaches 7.5 MPa. And (3) after reacting for 5min, extruding by a screw extruder die to obtain the liquid reclaimed rubber.
Comparative example 3
The process flow in this comparative example is the same as in example 10, except that the system temperature: 30 ℃, pressure 7MPa, critical parameters of CO 2: 31.26 deg.C and 7.29MPa, carbon dioxide is in non-supercritical state.
The devulcanization effect characterization was performed on the devulcanized reclaimed rubbers prepared in examples 1 to 21 and comparative examples 1 to 3(D1 to D3), and the characterization results are shown in table 2, and the characterization methods are as follows:
the following treatments were carried out on each of the above products:
firstly, acetone is used as a solvent, and a Soxhlet extraction method is adopted to continuously extract for 48 hours until small molecules (acetone soluble substances) are completely extracted and separated by the acetone. Subsequently, the soluble fraction was dried in a vacuum drying oven until the mass was unchanged, the insoluble fraction was dried until the mass was unchanged, and secondary extraction was continued using toluene as a solvent to separate a macromolecular soluble substance (toluene soluble substance) and a crosslinked insoluble substance (gel).
The average molecular weights of acetone soluble substances and toluene soluble substances and the polymer polydispersity number PDIThe line tests (GPC test can be characterized simultaneously, molecular weight, polydispersity PDI) were carried out as follows: acetone-soluble and toluene-soluble substances were sufficiently swollen with toluene, and the number average molecular weight (M) of the sample was measured by using a GPC analyzer model 515-n) And calculating the polydispersity index (PDI) by taking tetrahydrofuran as a mobile phase and polystyrene as a standard sample, and measuring the temperature at 35 ℃.
The crosslink density of the gel was measured as follows: the crosslinking density test employs an equilibrium swelling method. The weighed sample was placed in a ground conical flask with a stopper containing 150ml of a good solvent (toluene was used as a good solvent in this experiment), immersed in a constant temperature water bath, kept at 30 ℃ for 72 hours, taken out after equilibration, weighed with an analytical balance, and dried in a vacuum desiccator at 50 ℃ for 4 hours. When the sample swells to equilibrium in a suitable solvent, the solvent molecules enter the crosslinked network at the same rate as they are expelled. And obtaining a crosslinking density formula, namely a Flory-Rehner formula, according to the basis of the rubber elasticity statistical theory.
TABLE 2
The gel content, the sol content, the average molecular weight of the sol, the sol PDI and the gel crosslinking density are the most visual and accurate means for representing the degradation degree of the crosslinked rubber. Higher sol content, lower gel crosslink density, indicate higher rubber degradation. The higher the toluene solubles content and the higher the molecular weight at the same sol content, the higher the content of linearized macromolecules in the reclaimed rubber after decrosslinking.
1. From the comparison of the data in the above examples and comparative example 3, it can be seen that: in the supercritical carbon dioxide fluid state, the same process means is adopted, and the desulfurization and degradation degree of the waste rubber is far higher than that in the non-supercritical state (the carbon dioxide critical point is 38 ℃ and 7.38 MPa). This is due to: in the supercritical state, the carbon dioxide fluid can fully exert the excellent dissolving and extracting performances of the rubber powder, and can fully dissolve linear macromolecules and micromolecules, the macromolecules firstly desulfurized and degraded on the surface of the waste rubber powder are disentangled through the swelling effect of the supercritical carbon dioxide fluid, and are peeled from the crosslinked rubber powder body and dissolved in the fluid. And then, under the action of illumination and a catalyst, the inner layer of the crosslinked rubber powder is continuously desulfurized and degraded and has the same action as the surface layer until the whole crosslinked waste rubber powder is desulfurized and degraded. The linearized active rubber is in a pasty and semi-fluid state at normal temperature. However, in a non-supercritical state, the surface of the waste rubber powder is subjected to desulfurization degradation under the action of illumination and a catalyst, and the surface layer subjected to desulfurization degradation still wraps the surface of the rubber powder due to the absence of the action of an external solvent, so that the rubber of the desulfurized surface layer blocks the penetration of ultraviolet light, namely, the illumination cannot reach the inside of the waste rubber powder, and the inside of the waste rubber powder still is in a three-dimensional cross-linked state. Therefore, even if photocatalytic degradation is carried out in a non-supercritical carbon dioxide state, the degradation efficiency and degree are low, sufficient desulfurization degradation of the crosslinked waste rubber component cannot be realized, and the basically fully uncrosslinked linearized rubber cannot be prepared;
2. as can be seen from the comparison of the data in the above examples and comparative examples 1 and 2, the method of the present invention provides a higher degree of desulfurization of the waste rubber crumb and a higher degree of linearization of the devulcanized rubber. It should be noted that, in comparative example 2, twin-screw mechanical devulcanization was used, which did not perform differential chain scission on the three-dimensional crosslinked network in the waste rubber powder, and thus, the gel content was relatively low, but at the same time, the small molecule content was high, the large molecule content was low, and the molecular weight of the large molecule chain was relatively low. Compared with the comparison document 2, the preparation method adopted by the invention has the advantage of selective chain scission of S-S bonds and S-C bonds in the three-dimensional cross-linked network of the waste rubber powder, so that the desulfurization linearized active rubber prepared by the invention has higher macromolecular content. Meanwhile, the linearized active rubber obtained by the method has no components such as a desulfurizer, an organic softener and the like;
3. more particularly, as can be seen from the comparison of the data in examples 1 to 18, the use of the composite inorganic photocatalyst to optimize the processes in the swelling treatment step and the photocatalytic desulfurization reaction step can significantly improve the desulfurization regeneration degree of the waste rubber powder, resulting in a substantially fully uncrosslinked, linearized rubber. And the process is optimized, and the prepared fully-desulfurized de-crosslinked linearized rubber has high macromolecular polymer (rubber) content, large molecular weight and narrow macromolecular chain distribution coefficient (polydispersity index PDI).
4. The invention has no strict requirement on the wavelength of ultraviolet light and can be realized within the wavelength range of 350-420.
To illustrate the beneficial effects of the linearized active rubber prepared in accordance with the present invention in later applications, a comparison of the properties of the linearized active rubber in accordance with the present invention and conventional reclaimed rubber for asphalt modification is provided below by way of example.
Examples 22 to 25, comparative examples 4 to 7
The specific asphalt modification process comprises the following steps: heating the matrix asphalt (70# asphalt) to 170-190 ℃, starting stirring, and adding the linearized active rubber of the examples 14 and 15 and the reclaimed rubber of the comparative examples 1 and 2 as the rubber asphalt modifier according to different proportions at a stirring speed of 200 rpm. After the addition, the mixture is stirred for 30min under the condition of heat preservation, and the heat preservation temperature is 170-190 ℃. And then starting a colloid mill, grinding the mixture once by the colloid mill, keeping the rotating speed of the colloid mill at 1500-2000 rpm, then keeping the temperature and stirring for different times at 170-190 ℃, and testing the performance indexes of the modified asphalt at a stirring speed of 200rpm after the end.
The types of the rubber asphalt modifiers and the amounts of the raw materials added in examples 22 to 25 and comparative examples 4 to 7 are shown in Table 3, and the holding time after colloid milling and the performance index of each modified asphalt in each example and comparative example are shown in Table 4:
TABLE 3
TABLE 4
Note: the detection method is carried out according to the related detection method in JTG E20-2011 standard.
The penetration degree, softening point and low-temperature ductility of the rubber asphalt are basic indexes for verifying the performance of the rubber asphalt, and generally, the penetration degree is required to be as follows: 40-60 parts; the softening point is more than or equal to 55 ℃, and the ductility is more than or equal to 10cm at the temperature of 5 ℃; the high-temperature Brookfield rotational viscosity of the rubber asphalt is an important index for investigating the construction workability of the rubber asphalt, and generally, the 180 ℃ viscosity design range of the rubber asphalt is as follows: less than 4 Pa.S. Within the range, the rubber asphalt has better storage, transportation, mixing, paving and rolling workability.
In combination with the above basis, from the above experimental results:
(1) under the condition of the same mixing ratio, the ductility of the rubber asphalt prepared by the linearized active rubber product prepared by the invention at 5 ℃ is obviously better than that of a comparative example. The linearization degree of the linearization active rubber prepared by the invention is high, the macromolecular polymer content is high, in an asphalt system, a large number of linearization macromolecules are mutually entangled to form a stable network, and the structure can effectively resist the external stress action and is highlighted on larger deformation (ductility). In comparative examples 4 and 6, however, the core-shell structure, which has a large amount of uncrosslinked core-shell structure and serves as a large stress concentration point in the asphalt system, has a poor resistance to external stress (poor ductility). Compared with cases 5 and 7, although the degree of decrosslinking is also higher, the proportion of small molecules therein is significantly higher than that of the linearized active rubber prepared by the present invention (with the addition of partial softening oil and small molecules generated by degradation), the content of macromolecular rubber is relatively lower, and the small molecules act as a plasticizer in the modified asphalt system, i.e. the cohesion of the network formed by entanglement of macromolecular polymers is weakened, i.e. the capability of the system to resist external force is reduced, and correspondingly, the low temperature ductility is relatively lower. As for the softening point, the rubber asphalt system using the linearized active rubber prepared by the present invention has a high softening point due to less stress concentration points and strong resistance to external force, and accordingly, comparative examples 5 and 7 have lower softening points (high proportion of small molecules, plasticization) and are higher than comparative examples 4 and 6 in the same ratio. For the penetration degree, the penetration degree of the rubber asphalt of the linear active rubber prepared by the invention is moderate, and the penetration degree of the rubber asphalt is lower than that of comparative examples 4 and 6, and because the number of undetached crosslinking components is large, the components can continuously absorb light components in the asphalt, so that the hardness of the whole system is increased; comparative examples 5 and 7 are higher, and the hardness of the system is reduced due to the presence of a large amount of small molecule plasticizer. For a viscosity of 180 ℃ the comparative examples 4 and 6 are the largest, the invention is centered, the comparative examples 5 and 7 are the smallest, again in direct relation to the uncrosslinked fraction content and the small molecule content. By combining four performance indexes, the linear active rubber prepared by the invention is more suitable for preparing rubber asphalt and has better application effect.
(2) Because partial rubber degradation auxiliary agent (thermal degradation type) is remained in the product of the traditional technical scheme, the remained degradation auxiliary agent can further play a role in the longer stirring and storage process of the modified asphalt, so that the rubber is secondarily degraded, namely the rubber is expressed on the performance of the modified asphalt, and the attenuation amplitude is larger. The attenuation amplitude of the modified asphalt prepared by the linear active rubber prepared by the method basically belongs to a controllable range;
(3) compared with the traditional photocatalysis scheme, the technical scheme has higher construction feasibility under the condition of higher rubber mixing ratio. And the traditional photocatalysis scheme causes the viscosity of a modified asphalt system to be increased rapidly due to insufficient degradation, so that the processing feasibility of the modified asphalt is greatly reduced.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A method for preparing linearized active rubber by using waste rubber is characterized by comprising the following steps: mixing waste rubber powder with photocatalyst in supercritical carbon dioxidePlacing the mixture under ultraviolet light for photocatalytic desulfurization reaction to obtain the linearized active rubber; the photocatalyst is selected from Co-doped TiO2、ZrO2/ZnO composite and ZrO2/TiO2One or more of the complexes;
the preparation method comprises the following steps:
mixing the waste rubber powder with the photocatalyst to obtain a mixture; the amount of the photocatalyst is 2-3% of the weight of the waste rubber powder;
under the condition of stirring, putting the mixture into the supercritical carbon dioxide for swelling treatment to obtain a swelling mixture; the swelling treatment step comprises: injecting carbon dioxide gas into a system where the mixture is located, and then adjusting the temperature of the system to 80-140 ℃ and the pressure to 10-35 MPa, so that the carbon dioxide gas is converted into a supercritical state to form supercritical carbon dioxide; swelling the mixture for 30-120 min under the supercritical carbon dioxide under the stirring condition that the stirring speed is 200-700 rpm to obtain a swollen mixture;
irradiating ultraviolet light to the swelling mixture in the supercritical carbon dioxide to perform the photocatalytic desulfurization reaction to obtain the linearized active rubber; in the step of the photocatalytic desulfurization reaction, the reaction temperature is 80-140 ℃, and the reaction pressure is 10-35 MPa.
2. The production method according to claim 1, wherein the swelling treatment step includes:
injecting the carbon dioxide gas into a system in which the mixture is located, and then adjusting the temperature of the system to 105-140 ℃ and the pressure to 28-35 MPa to convert the carbon dioxide gas into a supercritical state so as to form supercritical carbon dioxide;
and swelling the mixture under the supercritical carbon dioxide for 90-120 min under the condition that the stirring speed is 500-700 rpm to obtain the swollen mixture.
3. The preparation method according to claim 1 or 2, wherein in the step of photocatalytic desulfurization, the reaction temperature is 105 to 140 ℃ and the reaction pressure is 28 to 35 MPa.
4. The preparation method according to claim 3, wherein in the step of photocatalytic desulfurization, the illumination time of the ultraviolet light is 5 to 30min, and the wavelength of the ultraviolet light is 300 to 420 nm.
5. The preparation method according to claim 3, wherein in the step of photocatalytic desulfurization, the illumination time of the ultraviolet light is 20 to 30min, and the wavelength of the ultraviolet light is 350 to 390 nm.
6. The production method according to claim 1 or 2, wherein the step of mixing the waste rubber powder with the photocatalyst comprises: and stirring and mixing the waste rubber powder and the photocatalyst for 5-30 min under the condition that the stirring speed is 700-1500 rpm to obtain the mixture.
7. The method according to claim 3, wherein the mixture is obtained by stirring and mixing the waste rubber powder and the photocatalyst to a temperature of not higher than 85 ℃.
8. The method according to claim 1 or 2, wherein the particle size of the waste rubber powder is 80 to 120 mesh.
9. The method according to claim 1 or 2, wherein the waste rubber powder is one or more of waste tire rubber powder, waste shoe sole rubber powder and waste conveyor belt rubber powder.
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| CN112322058A (en) * | 2020-11-24 | 2021-02-05 | 北京路德永泰环保科技有限公司 | Modified plant asphalt and application thereof |
| CN112341831A (en) * | 2020-11-24 | 2021-02-09 | 北京路德永泰环保科技有限公司 | Asphalt regenerant and preparation method thereof |
| CN112457678B (en) * | 2020-11-24 | 2022-08-23 | 北京路德永泰环保科技有限公司 | Warm-mixed rubber asphalt and preparation method thereof |
| CN112724483A (en) * | 2020-12-15 | 2021-04-30 | 嵊州市兴盛胶粉有限公司 | Rubber powder of vulcanized rubber, and manufacturing method and regenerated product based on rubber powder |
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