| Polyvinyl chloride(PVC)is one of the most common types of solid waste and is present in large quantities and difficult to treat in an environmentally sound manner.Pyrolysis technology,which converts conventional solid waste into pyrolysis carbon,pyrolysis tar and pyrolysis gas,is a highly efficient means of harmlessly treating solid waste,and the resulting product can be reused.Considering that PVC pyrolysis gas contains a large amount of harmful gas HCl and the pyrolysis gas must be dechlorinated before it can be used,and the commonly used dechlorination chemicals are expensive,this thesis intends to study the effect of inexpensive CaO additives on the removal of HCl from PVC pyrolysis and pyrolysis gas.The thermogravimetric analysis of the PVC powder raw material was carried out by means of a thermogravimetric analyser to determine its pyrolysis pattern,and an experimental protocol for PVC pyrolysis was developed.The pyrolysis experiments were carried out in a home-made reaction bed to investigate the influencing factors and product characteristics of PVC monolysis;the pyrolysis experiments were repeated under the addition of CaO to study the output of gas,liquid and solid products and the components of solid phase products under different influencing factors,the functional group characteristics of pyrolysis tar,the The experiments were repeated with the addition of CaO to investigate the changes of the composition of pyrolysis gas and the effect of CaO on the removal of HCl from pyrolysis.The details are as follows.(1)In the pyrolysis of PVC alone,the pyrolysis is mainly divided into two stages,with no mass loss at 0～200°C.The first weight loss interval occurs at 255～377°C,which is mainly the stage of C-Cl bond breaking and the generation of HCl gas,and the second weight loss interval occurs at 377～510°C which is the stage of C-C bond breaking and cracking in organic matter to generate small molecule hydrocarbons.The solid phase yield decreased from 54.36% to 9.41% at 300-550 °C;the gas phase yield increased from44.61% to 68.87%,and as the temperature increased,more types of gas phase products were detected by gas chromatography,and HCl gas was the main product in the pyrolysis gas,accounting for 81.92% at 400 °C;the liquid phase yield increased from 1.23% to21.82%.The IR spectra of pyrolysis tar functional groups showed that the phenols and aromatic compounds in the liquid phase products increased with the increase of temperature,and more organic compounds were cracked at high temperature.(2)Two stages of pyrolysis also existed under CaO addition,but the first stage occurred from 265 to 378 °C with reduced mass loss compared to conditions without the presence of CaO;the second stage occurred from 378 to 654 °C;with increased mass loss compared to the presence of CaO.The presence of CaO inhibited the formation of HCl gas and also intensified the thermal cleavage of organic matter.the presence of CaO had a significant effect on HCl removal played a significant role in the test temperature range of350-800°C.In the test temperature range of 2:1 Ca/Cl ratio,for example,the HCl removal efficiency was 73.2% at 350°C,93.4% at 550°C and 75.4% at 800°C,with the highest removal efficiency occurring at 550°C.Meanwhile the CaO dosing ratio obviously affects the HCl removal effect,the more dosing,the better the effect,but after the dosing Ca/Cl ratio exceeds 2:1 ratio,the change is no longer significant,from the economic consideration Ca/Cl ratio 2:1 ratio is more suitable. |
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