Study On Co-pyrolysis Characteristics Of Discard PVC And Oil-based Drilling Cuttings In Shale Gas Development

Oil-based drilling cuttings?OBDCs?and discarded polyvinyl chloride?PVC?are solid wastes witch are recyclable.In co-pyrolysis,on the one hand,PVC can supply hydrogen to OBDCs';on the other hand,Al₂O₃,Fe₂O₃ and CaO in OBDCs are used as catalysts for thermal dechlorination of PVC.However,the research on the co-pyrolysis of the two is still in the blank.This paper has carried out a preliminary study on the co-pyrolysis of the mixture.The main results are as follows:?1?The pyrolysis characteristics of OBDCs and discarded PVC and the mixture were studied by TG-DTG.The pyrolysis process of OBDCs is roughly divided into three stages.?a?From the room temperature to 300°C,the weight loss was 5.56%,and the precipitation of bound water and small molecular hydrocarbons in oil-based cuttings occurred mainly at this stage.?b?From 300°C to 700°C,the weight loss was 5.91%,and the precipitation of macromolecular hydrocarbons occurred mainly at this stage.?c?From 700°C to 1000°C,the rate of weight loss at this stage became larger because inorganic salts such as calcium carbonate in OBDCs decompose at high temperatures.The pyrolysis process of PVC was roughly divided into three stages too.?a?From the room temperature to 350?,the weight loss was 39.71%,and the weight loss at this stage was due to the dechlorination of PVC to form HCl.?b?From 350°C to 520°C,the weight loss was 16.01%,mainly caused by chain break in PVC and produce some small-molecule hydrocarbons and polycyclic aromatic hydrocarbons.?c?From 520°C to 1000°C,the weight loss was 11.5%,due to the decomposition of fillers such as calcium carbonate in PVC.The integral method called Coats-Redfern and Grobatchev were used to fit the TG,DTG curve of the three kind of samples.It was found that text value A₁ of pre-exponential factor were obviously higher than the theoretical calculated value A2,and test value E1 of activation energy was obviously higher than the theoretical value E₂,in the pyrolysis process.It means that the addition of PVC has a great impact on the co-pyrolysis of mixtrue.?2?The pyrolysis of OBDCs and its co-pyrolysis with PVC were studied in fixed-bed reactor with a quartz tube.In the test,nitrogen was used as carrier gas.The effects of pyrolysis temperature?400⁶00°C?,constant temperature time?20⁷0 min?,heating rate?5²0°C/min?,mixing ratio?5²5%?on distribution of products and oil content of ash were investigated.With the increase of final temperature and the constant temperature time,oil content of residue was reduced first and then almost unchanged,but he temperature had a great influence on the proportion of solid products.With the increase of heating rate,the proportion of solid products did not change a lot,oil content decreased first and then increased;the higher the PVC blending ratio in the mixture,the lower the proportion of solid phase products,oil content decreased first.The optimal pyrolysis conditions for mixed pyrolysis are temperature 550°C,constant temperature time 60 min,heating rate 10°C/min,and PVC blending ratio of 20%.?3?TG-MS,GC-MS,XRD were used to analysis the products.The addition of PVC increased the proportion of hydrocarbons in product,from 16.03%to 49.53%,in which the proportion of alkanes increased from 10.92%to 24.06%.Before and after pyrolysis of oil-based cuttings,the inorganic matter of samples before and after blending PVC The morphology did not change,and the main crystal phase composition was still quartz and a small amount of barite.The total hydrocarbon content in the pyrolysis oil at 400°C,500°C and 600°C were 52.39%,90.64%and 93.50%,respectively,that is,increasing the final temperature of pyrolysis is beneficial to increase the content of hydrocarbons.The pyrolysis of OBDCs and the addition of PVC had no effect on the inorganic form of the sample.The main crystal phase composition were still quartz and a small amount of barite.The content of hydrocarbons in the pyrolysis liquid products obtained at 400°C,500°C and 600°C were 52.39%,90.64%,and 93.50%,respectively.That is,increasing the temperature is beneficial to increase the content of hydrocarbons in pyrolysis process.