Experimental Research On Pyrolysis Process Of Waste Tyres And Characteristics Of Pyrolytic Products

The increasing amounts of waste tyres bring serious pollution to the environment and endanger human health. It is imminent for us to find a reasonable disposal method to sovle these problems. Tyres are mainly composed of organic polymer, and can be converted to some valuable chemical products or fuels, thus they have the potential of resource utilization. Pyrolysis is a resource saving and environment friendly technology, and also meet the requirement of recycling economy. This thesis carried out the experiment in a self-designed fixed bed reactor, investigated how the temperature, residence time and catalyst acting on pyrolytic products, provided a significant basis for the future resource utilization of these products.Based on the tyre composition and material characteristic, the significant factors heating rate and particle size were investigated with the help of thermogravimetric analysis, and the pyrolysis model was established. The experiments were carried out in the self-designed fixed bed reactor, with the liquid yield 55% and the solid yield 33%. With the temperature increasing, the gas yield rised obviously, while the liquid yield reached the highest point at 500⁵50℃; with the residence time extending, the gas yield increaseed, while the liquid yield decreased evidently; adding catalyst(HZSM5 and HY zeolite, NaOH) resulted in the increase of gas yield but derease of liquid yield.With the assistance of GC,FT-IR and H₂S testers, pyrolytic gas was analyzed qualitatively and semi-quantitatively. The gas was mainly composed of CxHy, while oxygen containing gases were low; the gas calorific value was as high as 30MJ/m3; with higher temperature and longer residence time, the second decomposition of larger molecular organics were stonger, leading to higher content of CH4 and H₂; adding catalyst led to higher content of smaller molecular alkenes(ethylene, propylene) and alkanes(ethane, propane); adding NaOH led to higher content of H₂, while adding HZSM5 and HY zeolite led to higher gas yield and calorific value; the element N exsisted in gases mainly as NO, and S exsisted mainly as H₂S.With the assistance of industrial and elemental analyzer, FT-IR and GC-MS, pyrolytic oil was analyzed in detail. The calorific value of tyre pyrolytic oil was very high(>41MJ/kg); the O content was low but C, H, S content was high, where the S content was 31% of raw materials; increasing pyrolytic temperature, prolonging residence time and adding catalyst all led to higher C content and lower H content, and C/H increased evidently; pyrolytic oil contained large amounts of aliphatic hydrocarbons and aromatic hydrocarbons; with higher temperature and longer residence time, the aromaticity of pyrolytic oil was stronger because of polycondensation reaction; the main substance in pyrolytic oil was limonene, benzene, toluene, xylene and some other valuable chemical products; with higher temperature and longer residence time, the limonene content dereased while aromatic compound content increased evidently; adding NaOH led to lower content of limonene, while adding HZSM5 and HY zeolites led to higher content of benzene, toluene and xylene.With the assistance of industrial and elemental analyzer, XRF, XRD and BET instruments, the pyrolytic char was also analyzed in detail. The ash, C, S content was high, while H content was low, and higher temperature led to lower content of S, H; longer residence time led to higher volatile content, and caused more H, S to convert into pyrolytic gas in the form of H₂S; metal elements in pyrolytic char mainly contained Zn, Ca, Ti, Fe, and Zn content was 4⁷% of raw materials; Zn exsisted in pyrolytic char in the form of ZnO and ZnS; besides, the pyrolytic char also contained CaCO₃, Fe₃O₄ and FeS. At 400⁵50℃, the specific surface area of pyrolytic char rised with the increasing temperature and decreasing the residence time; the adsorption loop of pyrolytic char belonged to L1-type, and it generated at P/P0=0.8; the pores in pyrolytic char were mainly composed of mesopore; with the temperature increasing, the specitic surface area increased until 650℃.The pyrolytic oil contains plenty of limonene, benzene, toluene and xylene, so many chemical products can be extracted from it; the pyrolytic oil can also be usd as fuels after proper treatment; the pyrolytic char can be used as carbon black after treatment, and it can also be used to obtain actvated carbon to absorb the pollutants in waste water and exhaust gas.