Method for low-temperature devulcanization of waste rubber and raw material recovery

Abstract

The application provides a low-temperature devulcanization and raw material recycling method of waste rubber, and belongs to the technical field of rubber devulcanization. The method uses chloramine and organic amine to perform low-temperature devulcanization on the waste rubber, and devulcanized rubber and carbon black are obtained through separation; the organic amine is selected from alcohol amine or tetraethylenepentamine. Through the compounding effect of chloramine and organic amine, the cross-linking bond is broken under the premise of ensuring that the polymer C-C chain is not damaged, the polymer is effectively separated and the carbon black is released, the regeneration of the rubber and the recycling and reuse of the carbon black are realized, the performance of the recycled rubber is not affected, and compared with the traditional thermal decomposition or chemical devulcanization method, the devulcanization efficiency is significantly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of rubber desulfurization, and particularly relates to a method for low-temperature desulfurization of waste rubber and recovery of raw materials. Background Art

[0002] Waste rubber products such as tires, rubber hoses, and rubber shoes are difficult to degrade in the natural environment due to their durable physical and chemical properties. Long-term accumulation not only occupies a large amount of land but also may pollute soil and water bodies. Therefore, converting these waste rubber products into reusable resources has become an important research direction in the environmental protection field and the rubber industry.

[0003] Traditional rubber recycling methods rely primarily on physical or chemical methods, such as mechanical crushing, pyrolysis, and chemical dissolution. However, these methods often suffer from high energy consumption, reduced recycled rubber performance, and environmental pollution. In recent years, with the continuous development of new materials and environmental protection technologies, rubber recycling technology has also continued to develop.

[0004] Chinese invention patent publication number CN102775633A mentions a low-temperature desulfurization production method for recycling and reusing waste rubber. The selected waste rubber is crushed using a two-roll rubber crusher, and the crushed waste rubber is ground into fine powder using a grinder. The expansion and crushing agent and the fine powder are put into a two-roll rubber mixing mill and stirred. Under a certain temperature, pressure and time, the rubber can be completely desulfurized.

[0005] Chinese invention patent publication number CN117164953A mentions a low-temperature desulfurized oil-free high-molecular-weight reclaimed rubber, its preparation method, and its application in tire carcasses. The high-molecular-weight reclaimed rubber is pretreated by mixing waste rubber powder, an activator, and a modifier in a certain proportion, and then spirally extruded for desulfurization reaction. The oil-free high-molecular-weight reclaimed rubber is obtained by temperature-controlled extrusion.

[0006] Chinese invention patent publication number CN117487263A mentions a recycled rubber prepared from waste tires and its preparation method. The waste tires are crushed into tiny particles of 40-60 mesh and activated and desulfurized with an activator (to improve the cross-linking activity and cross-linking performance of the rubber powder, and to increase the strength after re-vulcanization). Modified silica is also prepared, its surface is oxidized, and anti-aging amino groups are introduced into the surface. The migration resistance of silica is utilized to maintain anti-aging properties for a long time; silica is treated with 2,4-pentadienoic acid to achieve the purpose of improving the strength of the rubber.

[0007] While these rubber recycling technologies have achieved some success, some challenges and problems remain. For example, how to further improve the performance of recycled rubber to approach or even reach the level of virgin rubber; how to reduce energy consumption and emissions during the recycling process to achieve truly green production; and how to establish an effective waste rubber recovery and recycling system to promote the industrial application of rubber recycling technologies. Summary of the Invention

[0008] The present invention addresses the problems of the prior art and provides a low-temperature desulfurization and raw material recovery method for waste rubber. The waste rubber is desulfurized at low temperatures using a combination of chloramine and an organic amine. Unreacted waste rubber, desulfurized rubber, and carbon black are separated and recovered. This method achieves both rubber regeneration and carbon black recovery and reuse, while retaining the original properties of the recovered rubber and significantly improving desulfurization efficiency.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] The invention provides a low-temperature desulfurization and raw material recovery method for waste rubber. The method uses a combination of chloramine and an organic amine to perform low-temperature desulfurization on the waste rubber, and obtains unreacted waste rubber powder, desulfurized rubber and carbon black through separation; the organic amine is selected from alcoholamine or tetraethylenepentamine (TEPA).

[0011] Preferably, the organic amine is an alcoholamine.

[0012] Furthermore, the molar ratio of the organic amine to the chloramine is 0.3-0.6:1.

[0013] Furthermore, the chloramine is selected from one or more of monochloramine, dichloramine, trichloramine and hypochlorite.

[0014] Furthermore, the alcoholamine is selected from one or more of ethanolamine (ETA), diethanolamine (DEA) and hydroxyethylethylenediamine (AEEA).

[0015] The principle of the desulfurization process of the present invention is as follows:

[0016] The amine group in the organic amine used promotes the breaking of cross-linking bonds. The vulcanized rubber molecule contains four chemical bonds: C=C, CC, CS, and SS (the bond energy decreases in sequence). Due to the difference in bond energy, mechanical shearing will first destroy the SS bond (two types of dissociation: ① homogeneous dissociation, producing two sulfur-free free radicals; ② heterogeneous dissociation, producing positively charged -S + and negatively charged -S - ), the amine group can capture the positively charged -S + and release H + , free H + Further with -S -Combined to form -SH terminal groups, the dissociation of the cross-linking bond is completed, the molecular chain is combined with the amine chain, blocking the activity of sulfur and the re-cross-linking process. TEPA contains multiple amine groups, and one molecular chain can be connected to multiple rubber molecular chains. Similarly, the amine groups of AEEA, ETA, and DEA can be combined with -S + and -S - The reaction blocks its activity, reducing the SS bond content and introducing hydroxyl groups into the rubber molecular chain. Alkanolamines effectively promote the breaking of crosslinks during the desulfurization process. Simultaneously, the targeted sulfur crosslinking reaction of chloramines decomposes the waste rubber powder, effectively separating the polymers without destroying the CC polymer chains, releasing carbon black, and maintaining the rubber's inherent properties. When using an alkanolamine compound, its structure also contains a hydroxyl group, which reduces Mooney viscosity, increases plasticity, and improves desulfurization efficiency.

[0017] Furthermore, the method further comprises: using a dehydrating agent and the compound chemical reagent simultaneously to perform low-temperature oxidative desulfurization treatment on the waste rubber.

[0018] Furthermore, the dehydrating agent is selected from one or more of calcium oxide, silica gel and organic solvent.

[0019] Furthermore, the organic solvent is selected from one or more of ethanol, n-butanol, acetone and dioxane.

[0020] Furthermore, the waste rubber is selected from one or more of full tire rubber, tread rubber, inner tube rubber and shoe material rubber.

[0021] Furthermore, the main components of the waste rubber include one or more of butadiene rubber, styrene-butadiene rubber, butyl rubber, chlorinated butyl rubber, brominated butyl rubber and nitrile rubber.

[0022] Furthermore, the low-temperature desulfurization and raw material recovery method specifically includes the following steps:

[0023] (1) collecting waste rubber, grinding and sieving it, and removing iron powder to obtain waste rubber powder;

[0024] (2) dissolving an organic amine and a chloramine in water respectively to obtain an organic amine aqueous solution and a chloramine aqueous solution, and mixing them to obtain a composite chemical reagent;

[0025] (3) adding a compound chemical reagent to the waste rubber powder, or adding a compound chemical reagent and a dehydrating agent to the waste rubber powder at the same time to carry out a desulfurization reaction;

[0026] (4) After the reaction is completed, the reaction mixture is separated and treated to recover unreacted waste rubber, devulcanized rubber and carbon black.

[0027] Furthermore, the concentration of the organic amine aqueous solution is 0.6-15 mol / L; the concentration of the chloramine aqueous solution is 3.0-30 mol / L.

[0028] Furthermore, the mass ratio of the waste rubber powder, the compound chemical reagent and the dehydrating agent is 100:0.7-4.5:0.5-4; preferably 100:0.7-2.5:0.5-0.7.

[0029] When the dehydrating agent is not used, the mass volume ratio of the waste rubber powder to the compound chemical reagent is 100:0.7-4.5, preferably 100:0.7-2.5.

[0030] Furthermore, the desulfurization reaction temperature is 50-200°C.

[0031] Furthermore, the desulfurization reaction pressure is 70-100 kPa.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention uses a combination of organic amine and chloramine to desulfurize waste rubber. The synergistic effect of the two is significant. Under the premise of ensuring that the CC bond of the rubber main chain remains intact, the SS bond and CS bond can be selectively broken, which can effectively separate the polymer, release carbon black and maintain the performance of the rubber itself.

[0034] (2) Compared with traditional thermal decomposition or chemical desulfurization, the mixed reagent of alcohol amine and chloramine used in the present invention not only effectively promotes the breaking of cross-linking bonds, but also helps to reduce Mooney viscosity, improve plasticity, and effectively improve the efficiency of oxidative desulfurization;

[0035] (3) The present invention is simple in post-processing the reaction mixture, and can adopt a variety of separation means or a combination thereof to effectively separate the unreacted waste rubber powder, desulfurized rubber and carbon black, and the unreacted waste rubber powder is returned to the previous step to continue the reaction. DETAILED DESCRIPTION

[0036] The embodiments of the present invention will be described in detail below with reference to the examples, but those skilled in the art will appreciate that the following examples are intended only to illustrate the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, conventional conditions were used. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0037] Example 1

[0038] (1) Take waste tires (mainly composed of 61.67% polyisoprene rubber, 26.5% carbon black, steel wire and a small amount of additives), grind them to a particle size of less than 1 mm, and use a magnetic method to remove iron powder to obtain waste rubber powder;

[0039] (2) dissolving monochloramine and hydroxyethylethylenediamine (AEEA) in water respectively to prepare a monochloramine aqueous solution with a concentration of 19.4 mol / L and a hydroxyethylethylenediamine aqueous solution with a concentration of 5.83 mol / L, and compounding them in a molar ratio of monochloramine to hydroxyethylethylenediamine (AEEA) of 10:3 to obtain a compound chemical reagent;

[0040] (3) Mix the waste rubber powder, compound chemical reagent and dehydrating agent (calcium oxide) in a mass ratio of 100:2.5:0.6 and add them into the reactor, and carry out oxidative desulfurization reaction at 200°C and 85kPa for 0.5h;

[0041] (4) After the reaction is completed, the reaction liquid is firstly separated by filtering and centrifuging system. The carbon black aggregates into a paste and sinks, while the desulfurized rubber and unreacted waste rubber powder remain in the upper liquid. The separated paste is transferred to a batch reactor and heated to 100-200℃ for 30 minutes. It is then sent to the ultrafiltration system for two-stage filtration:

[0042] ① Use a 20nm ultrafiltration membrane to filter (to intercept larger particles and impurities, including some unreacted waste rubber powder) to obtain filter residue 1 and filtrate 1;

[0043] ② The filtrate 1 is further filtered using a 3 nm ultrafiltration membrane (to retain smaller particles, dissolved matter and carbon black) to obtain a residue 2 and a filtrate 2; the residue 2 is concentrated for subsequent reuse; the filtrate 2 is mixed with the above-mentioned upper liquid and returned to step (1) for further processing.

[0044] Example 2

[0045] (1) Waste tires (mainly composed of 61.67% polyisoprene rubber, 26.5% carbon black, steel wire, and a small amount of additives) were ground to a particle size of less than 750 μm, and iron powder was removed by magnetic attraction to obtain waste rubber powder;

[0046] (2) dissolving dichloramine and diethanolamine (DEA) in water respectively to prepare a dichloramine aqueous solution with a concentration of 11.64 mol / L and a diethanolamine aqueous solution with a concentration of 5.24 mol / L, and compounding them at a molar ratio of dichloramine to diethanolamine (DEA) of 20:9 to obtain a compounded chemical reagent;

[0047] (3) Adding waste rubber powder and compound chemical reagents in a mass ratio of 100:2.5 into the reactor, and carrying out oxidative desulfurization reaction at 50°C and 100 kPa for 2 hours;

[0048] (4) The reaction solution was post-processed and separated according to the method of Example 1.

[0049] Example 3

[0050] (1) Take waste tires (main components are 61.67% of polyisoprene rubber, 26.5% of carbon black, steel wire and a small amount of additives), grind to a particle size of less than 550μm, remove iron powder using magnetic attraction method, and obtain waste rubber powder;

[0051] (2) Dissolve trichloroamine and ethanolamine (ETA) in water respectively to prepare trichloroamine aqueous solution with a concentration of 8.30mol / L and ethanolamine aqueous solution with a concentration of 4.98mol / L, and compound the chemical reagent according to a molar ratio of trichloroamine to ethanolamine (ETA) of 5:3;

[0052] (3) Add the waste rubber powder and the compounded chemical reagent to the reactor according to a mass ratio of 100:4.5, and perform oxidative desulfurization reaction under the conditions of 50℃ and 70kPa for 12h;

[0053] (4) Post-treat and separate the reaction liquid according to the method of Example 1.

[0054] Example 4

[0055] (1) Take waste tires (main components are 61.67% of polyisoprene rubber, 26.5% of carbon black, steel wire and a small amount of additives), grind to a particle size of less than 1mm, remove iron powder using magnetic attraction method, and obtain waste rubber powder;

[0056] (2) Dissolve monochloroamine and tetraethylenepentamine (TEPA) in water respectively to prepare monochloroamine aqueous solution with a concentration of 9.71mol / L and tetraethylenepentamine aqueous solution with a concentration of 2.91mol / L, and compound the chemical reagent according to a molar ratio of monochloroamine to tetraethylenepentamine (TEPA) of 3:10;

[0057] (3) Add the waste rubber powder, the compounded chemical reagent and a dehydrating agent (calcium oxide) to the reactor according to a mass ratio of 100:4.5:0.6, and perform oxidative desulfurization reaction under the conditions of 200℃ and 85kPa for 0.5h;

[0058] (4) Post-treat and separate the reaction liquid according to the method of Example 1.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that the compounded chemical reagent is replaced by monochloroamine aqueous solution with a concentration of 29.1mol / L, and the mass ratio of the waste rubber powder, the monochloroamine aqueous solution and calcium oxide is 100:2.5:0.6.

[0061] Comparative Example 2

[0062] The only difference from Example 1 is that the compound chemical reagent is replaced by an aqueous solution of hydroxyethylethylenediamine with a concentration of 8.65 mol / L, and the mass ratio of waste rubber powder, aqueous solution of hydroxyethylethylenediamine and calcium peroxide is 100:2.5:0.6.

[0063] The results of the desulfurization treatment of waste tires in the embodiments and comparative examples are shown in Table 1.

[0064] (1) Determination of sol content: Using the Soxhlet extraction method, a certain mass of sample was weighed and wrapped with filter paper. The sample was extracted with acetone in a Soxhlet extractor for 12 h, then taken out of the vacuum drying oven and dried at 60°C to constant weight. The mass m0 was measured. The sample was then covered with toluene and extracted for 14 h. The sample was taken out of the vacuum drying oven and dried at 60°C to constant weight, which was measured as m1. Sol content: Sol content = [(m0-m1) / m1] × 100%.

[0065] (2) Desulfurization rate: Determined using infrared spectroscopy, desulfurization rate = [(sulfur content before desulfurization - sulfur content after desulfurization) / sulfur content before desulfurization] × 100%. The higher the desulfurization rate, the more thoroughly the sulfur in the rubber has been removed.

[0066] Table 1 Results of desulfurization treatment of waste rubber

[0067]

[0068]

[0069] As can be seen from the above table: compared with Example 1, the desulfurized rubber sol content obtained by using a single chemical reagent of alcoholamine or chloramine in Comparative Examples 1 and 2 is lower than that obtained by using a compound chemical reagent. It can be seen that the compound chemical reagent used in the present invention has a significant effect on breaking the cross-linked bonds in the waste rubber material; at the same time, the combined use of the two also improves the desulfurization rate, and the synergistic effect is significant; in addition, compared with chloramine, the desulfurization effect of alcoholamine is more significant, which further verifies the role of hydroxyl groups in reducing Mooney viscosity, improving plasticity, and improving desulfurization efficiency.

[0070] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for low-temperature desulfurization and raw material recovery of waste rubber, characterized in that: The waste rubber is subjected to low-temperature desulfurization by using a combination of chloramine and organic amine, and unreacted waste rubber powder, desulfurized rubber and carbon black are obtained through separation; the organic amine is selected from alcoholamine or tetraethylenepentamine; and the chloramine is selected from one or more of monochloramine, dichloramine and trichloramine.

2. The low-temperature desulfurization and raw material recovery method according to claim 1, characterized in that: The molar ratio of the organic amine to the chloramine is 0.3-0.6:

1.

3. The low-temperature desulfurization and raw material recovery method according to claim 1, characterized in that: The alcoholamine is selected from one or more of ethanolamine, diethanolamine and hydroxyethylethylenediamine.

4. The low-temperature desulfurization and raw material recovery method according to claim 1, characterized in that: The method further comprises: using a dehydrating agent, chloramine and organic amine simultaneously to perform low-temperature oxidative desulfurization treatment on the waste rubber.

5. The low-temperature desulfurization and raw material recovery method according to claim 4, characterized in that: The dehydrating agent is selected from one or both of calcium oxide and silica gel.

6. The low-temperature desulfurization and raw material recovery method according to claim 1, characterized in that: The waste rubber is selected from one or more of full tire rubber, tread rubber, inner tube rubber and shoe material rubber; the main components of the waste rubber include one or more of butadiene rubber, styrene butadiene rubber, butyl rubber, chlorinated butyl rubber, brominated butyl rubber and nitrile rubber.

7. The low-temperature desulfurization and raw material recovery method according to any one of claims 1 to 6, characterized in that: The specific steps include: (1) Collecting waste rubber, grinding and screening, and removing iron powder to obtain waste rubber powder; (2) dissolving an organic amine and a chloramine in water respectively to obtain an organic amine aqueous solution and a chloramine aqueous solution, and mixing them to obtain a compound chemical reagent; (3) Adding compound chemical reagents to waste rubber powder, or adding compound chemical reagents and dehydrating agents to waste rubber powder at the same time to carry out desulfurization reaction; (4) After the reaction is completed, the reaction mixture is separated and treated to recover unreacted waste rubber, devulcanized rubber and carbon black.

8. The low-temperature desulfurization and raw material recovery method according to claim 7, characterized in that: The concentration of the organic amine aqueous solution is 0.6-15.0 mol / L; the concentration of the chloramine aqueous solution is 3.0-30 mol / L.

9. The low-temperature desulfurization and raw material recovery method according to claim 7, characterized in that: The mass ratio of the waste rubber powder, the compound chemical reagent and the dehydrating agent is 100:0.7-4.5:0.5-4.

10. The low-temperature desulfurization and raw material recovery method according to claim 7, characterized in that: The desulfurization reaction temperature is 50-200° C.; the desulfurization reaction pressure is 70-100 kPa.

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