Study On Upgrading Pyrolytic Residue From Waste Tires To Commercial Carbon Black

Waste tires as a kind of solid waste,is more difficult to deal with in the field of modern transportation.It is a threat to the natural environment and could bring about the potential harm to human life and health.It could also restrict the progress of human civilization and the development of social economy.With the acceleration of urbanization and the rapid development of transportation industry,the problems caused by waste tires in developing countries are more outstanding.There are a large number of useful chemical composition(benzene and its homologue,limonene,etc.)in the liquid produced in waste tires pyrolyzing,and its calorific value is similar to diesel.So it can be used as both the material for recycling chemicals and fuel.Therefore,pyrolysis is considered as an effective way to dispose of waste tires.However,the large amount of solid residue(mainly carbon)produced in pyrolysis is usually burned out directly and does not play its due value.In the view of this,that upgrading pyrolytic residues into commercial carbon black is studied to find an effective way to utilize them has application value and scientific significance to make full use of pyrolytic products and enhance their added values.In this paper,waste tires as raw material were pyrolyzed to preparepyrolytic residue.And then the pyrolytic residue were upgraded to prepare the substitute of tire-use commercial carbon black,through combined pickling with hydrochloric and hydrofluoric acids and alternate washing with hydrochloric acid and sodium hydroxide,respectively.The reaction conditions were optimized through the single factor and orthogonal test with the ash content of pyrolytic residue as measure.The properties of commercial carbon black and pyrolytic carbon black were compared through the characterization methods of elements analysis,XRF,TG,FTIR,XRD and Raman spectroscopy,nitrogen adsorption and SEM analysis.The economic rationality analysis of the two upgrading schemes of waste tire pyrolytic residue were carried out.The main conclusions are as follows:1.In this study,the influence of pyrolysis terminal temperatures on the properties of pyrolytic residues were examined.It could be concluded that the properties of pyrolytic residues obtained at 650~700 ? terminal temperatures were very close.It means that the effect of final pyrolysis temperatures on the properties of pyrolysis residue was very small,almost negligible.In addition,the three kinds of rubber commonly used in tire were pyrolyzed alone and the yields of their pyrolytic residue were very little,only less than 0.1 wt.%.This indicated that the carbon black in pyrolytic residue from waste tire was mainly derived from commercial carbon black added in tire during manufacture,rather than produced by other organic matter pyrolyzing.The results of XRF analysis shows that the ash contents in waste tire pyrolytic residues were composed of metaloxide,sulfide and silica.2.The reaction conditions of upgrading pyrolytic residue of waste tires were systematically studied by using the method of hydrochloric acid-hydrofluoric acid combined pickling with ultrasonic.The sulfur content of pyrolytic residue was reduced from 1.81 wt% to 0.54 wt%(removal rate of70 %),ash content was reduced from 13.98 wt.% to 0.24 wt.%(removal rate reached more than 98 %).And the both of ash and sulfur contents were accordance with the standard of tire-use commercial carbon black.On the basis of single factor and orthogonal analysis,as pyrolytic residue:HCl=1 g: 10 ml,the optimal reaction conditions were hydrochloric acid concentration 4 mol/L,reaction temperature 60 ?,reaction time 18 h(6 h/time,repeated three times).On the optimal conditions,the ash content of pyrolytic residue was to a minimum of 1.26 wt.%.The reaction conditions of hydrofluoric acid pickling were pyrolytic residue:HF=1 g: 2 ml,reaction temperature 25 ?,reaction time5 h.3.Comparing the properties of pyrolytic carbon blacks and commercial carbon blacks(N326 and N339),it was found that the pyrolytic carbon black obtained from waste tire pyrolysis at 650 ? was very similar to commercial carbon black N326 in the aspects of element composition,the absorption values of iodine and DBP.Through TG,FTIR,XRD,Raman and SEM analysis,the conclusion of the similarity between pyrolytic carbon black and commercial carbon black N326 was further proved.Therefore,the pyrolytic carbon black isexpected to be used as a high reinforcing carbon black for tire production.4.Because hydrofluoric acid is harmful to human health and more expensive,sodium hydroxide solutions were chosen to replace hydrofluoric acid to remove the silicon dioxide in pyrolytic residue.On the basis of single factor and orthogonal analysis,the reaction conditions of deashing pyrolytic residue using sodium hydroxide solution were optimized,and as pyrolytic residue:NaOH=1 g: 10 ml,the optimum reaction conditions were sodium hydroxide concentration 3 mol/L,reaction temperature 80 ?,reaction time 30 h(10 h/time,repeated three times).On the optimal conditions,the ash content of pyrolysis residue was reduced from 1.26 wt.% to 0.91 wt.%.It can be seen from the experimental results that sodium hydroxide solution can remove some of the silicon dioxide in pyrolytic residue and fail to achieve the effect of hydrofluoric acid deashing.However,since this alternative route can realize zero pollutant discharge,it is also a strong contender for upgrading waste tire pyrolysis residue to tire-use carbon black.5.In the end,the economic rationality of the two methods to upgrade pyrolytic residue were analyzed.It could be found that the profit margin(37~43 %)of combined pickling was higher than alternate washing with hydrochloric acid and sodium hydroxide whose profit margin was 27~36 %.However both of them were higher than the profit margin(12 %)of traditional carbon black production enterprise.So the two methods to upgrading pyrolytic carbon black to tire-use carbon black both have good economic benefit.Andcompared to the traditional method of producing carbon black,the two ways have the characteristics of lower energy consumption,lower pollution and higher benefit.When the requirement to carbon black ash content is not very strict,the method that using alternate washing with hydrochloric acid and sodium hydroxide upgrade pyrolyic residue was more competitive.