| With the rapid development of transportation industry,the demand for vehicle tires has increased greatly,and the problem of tire consumption as waste tires has become increasingly prominent.Therefore,the environmental risk of waste tire recycling and its resource-based comprehensive utilization have attracted extensive attention.Among various ways of recycling and disposal of waste tires,pyrolysis is recognized as a technology with good prospects for resource utilization.One of the main products of waste tire pyrolysis is pyrolytic carbon black(CBp).Due to the change of its structural composition and the existence of zinc oxide,sulfur and other materials added in the tire production process,it can only be used as additives for low-value rubber products.The ideal way to increase the value of CBp is to reuse it as a composite material for tire manufacturing.Therefore,it is very necessary to explore the mechanism of waste tire pyrolysis process,find suitable process conditions to control the quality of CBp and apply it as reinforcement material of tire rubber.In addition,at present,some studies using dry mixing technology to use CBp as reinforcing agent for tire rubber production show that the quality of the rubber is greatly affected by the addition proportion of CBp,and it is difficult to ensure the quality of tire rubber when replacing more than 10%commercial carbon black(c CB)with CBp.Some studies have reported that the reinforcing agent including white carbon black can be mixed with natural latex in liquid phase system by wet compounding technology.It can also improve the dispersion of the reinforcing agent in the rubber matrix,but there are few reports on the wet compounding of CBp and natural latex to produce tire rubber.Therefore,this study focuses on the research content of pyrolysis resource utilization of waste tires and highvalue utilization of pyrolysis carbon black,develops the complete process of "waste tires-pyrolysis carbon black-wet compounding rubber-new tires",and analyzes the carbon emission of the above process by using two evaluation methods.For recycling of waste tire pyrolysis,the pyrolysis of waste tire particles under atmospheric pressure was carried out in a tubular furnace under laboratory conditions.It is found that the yield of CBp is relatively less affected by temperature and carrier gas flow.Appropriately increasing the carrier gas flow can reduce the proportion of ash in CBp,and appropriately increasing the pyrolysis temperature can increase the specific surface area of CBp,Under appropriate conditions(gas flow≥0.5 L/min,temperature≥500℃),the specific surface area of CBp can meet the requirements of national mandatory standard “carbon black for rubber”(GB 3778-2011).Under the conditions of pilot scale and industrial production,the micro negative pressure pyrolysis experiment of waste tire rubber block is carried out in a rotary kiln(temperature 420±20℃,heating rate 2-8 ℃/min,pressure 95-100 k Pa).The results show that the application of steel wire non-stripping process in raw material pretreatment can help to reduce the frequency of equipment maintenance caused by pipeline blockage.CBp has "core-shell structure".The physical and chemical properties of CBp are similar to those of c CB.However,some performance indexes such as ash content and dibutyl phthalate(DBP)oil absorption value are still different from those of c CB.The recovery path and pyrolysis mechanism of carbon black in the pyrolysis process are preliminarily summarized,through the analysis of the surface morphology,surface element composition and binding state of CBp,combined with the migration and transformation path of sulfur,carbon and nitrogen in the pyrolysis process via material balance.The results show that the continuous pyrolysis reaction of waste tires can be realized by rotary kiln,and the quality of CBp produced is relatively stable.Further realizing the high-value utilization of CBp will greatly improve the environmental and economic benefits of waste tire pyrolysis.For the high-value utilization of CBp,the feasibility of using CBp to partially replace c CB as the reinforcing agent of ordinary rubber products was investigated by using dry mixing technology.It was found that after CBp replaced low and medium proportion of cCB N234(a kind of high structure medium super wear-resistant furnace carbon black),the obtained mixed carbon black had little effect on the wettability of rubber and good crosslinking combination with rubber molecules,which could play a reinforcing role similar to that of c CB(300% constant tensile strength did not decrease).However,overmuch CBp will make the average particle size of the mixed carbon black too large,which will directly lead to a significant decline in the dispersion of the filler,the vulcanization crosslinking efficiency,shore hardness and other rubber properties.Therefore,CBp as a rubber reinforcing agent has a certain application prospect with an appropriate formulation;The wet compounding technology is also adopted in the study,which is used to produce the mixed slurry of CBp in the liquid phase after high-speed dispersion and repeated grinding by ceramic millstone,and then mixed with natural rubber latex to form wet masterbatch.The uniform dispersion of the CBp in rubber matrix is preliminarily realized by compressing the double electric layer,exchange adsorption and breaking the micellar protective layer by potential neutralization.The properties of the vulcanized tire rubber basically meet the needs of commercial application.The granulated CBp is more suitable for the production of composite wet compounding rubber because of its excellent surface characteristics and low aggregation degree.Under the formula of truck tire,granulated CBp can replace 47.9%-50.8% of c CB at most and ensure the physical and mechanical properties of rubber products.Under the specific ratio of passenger tire composites,when granulated CBp replaces 43.75% of Ccb,it can reduce the production cost and ensure the quality of rubber products.Based on the use of silica wet masterbatch process(SiO2-WMB),the technical route,main steps and mixing mechanism of CBp wet masterbatch(CBp-WMB)process were put forward.The results show that the wet compounding of CBp to produce tire rubber is feasible,and it has better effect and broad application prospect as rubber reinforcing agent under wet compounding conditions.For the carbon emission of the whole process,according to the national greenhouse gas inventory guidelines(2006 IPCC)and the CML2001 method provided by the life cycle assessment(LCA)software Gabi,the total carbon emissions of waste tire pyrolysis process are analyzed.The carbon emissions of two common waste tire resource treatment methods,rubber powder production and incineration power generation,are analyzed simultaneously.The life cycle assessment model of radial tire represented by 205/55R16 95 V tire is established,meanwhile,its equivalent carbon dioxide emission and global warming index are calculated and analyzed.It is found that the pyrolysis recycling of waste tire can reduce carbon dioxide emission(up to-496.18 kg CO2/t)compared with other treatment methods,The use of CBp wet compounding technology can reduce the carbon dioxide emission of tire production(-13.02 kg CO2/strip,and the use of reinforcing agent can reduce carbon dioxide by 30.57%).To sum up,the research results of this paper show that the pyrolysis process can become an effective solution to the resource and environmental problems of waste tires.The wet compounding of CBp can prepare high-quality tire rubber and reduce carbon emissions.This study can provide theoretical support for the wet compounding of CBp from waste tires pyrolysis to help carbon emission reduction and carbon neutralization. |
PDF Full Text Request