Effects of biochar on sunflower straw pyrolysis characteristics and gas products

Abstract: The development of slow pyrolysis technology has great significances for using crop residue resources and relieving energy and environment crisis. In China, sunflower is an important oil crop, which is widely planted. The yield of sunflower straw is about 120 million tons. In this study, Sunflower straw was used as the raw material, the biochars derived from sunflower straw was used as additives, and TG-FTIR was used to analyze the pyrolysis process, and to study the effects of different preparation temperatures (500, 700, 900 ℃) and proportions (10%, 20%,30%,40%) of biochar on the pyrolysis characteristics of sunflower straw and gas products，which mainly include furans, acids, carbonyl compounds, aromatic aldehydes, CO, CH4, etc. The results showed that the activation energy of sunflower straw pyrolysis decreased from 60.21 kJ/mol to 38.07-50.35 kJ/mol at different proportions of biochar. With increasing proportion of biochar, the activation energy for the pyrolysis of mixed samples decreased, With the increase of biochar prepared at 500 ℃, the pyrolysis final temperature of sunflower straw increases from 367 to 380 ℃, the maximum weight loss rate of sunflower straw decreased from 15.68%/min to 9.83% /min, and the maximum weight loss temperature increased from 328 to 334 ℃. When biochar prepared at 500 ℃ with 10% addition, aromatic aldehydes showed the maximum release, and the release amounts of aromatic aldehydes and carbonyl compounds in the pyrolysis gas products decreased, while those of CO and CH4 decreased，furans and acids have no obvious change. With the addition of biochar at different preparation temperatures, the main pyrolysis range of sunflower straw was extended and shifted to different degrees, which migrated to high temperature zone when adding biochar prepared at 500 ℃, and migrated to low temperature zone when adding biochar prepared at 700 and 900 ℃. Maximum weightlessness temperature of sunflower straw pyrolysis rise from 319 to 334 ℃, then decreased to 309 ℃, and maximum weight loss rate has decreased, which indicates that biochar prepared at 500 ℃ shows strongest inhibitory effect of sunflower straw pyrolysis; The pyrolysis of biochar prepared at 700 ℃ and 900 ℃ promoted at the initial stage and inhibited at the whole process of pyrolysis. As the preparation temperature of added biochar increased, the pyrolysis activation energy of sunflower straw decreased from 60.21 kJ/mol to 45.05-50.35 kJ/mol. The release of furan, acid and carbonyl compounds from sunflower straw pyrolysis added with biochar prepared at three different temperatures was reduced. Upon the addition of biochar prepared at 500 and 700 ℃, the aromatic aldehydes in sunflower pyrolysis gas products were increased; upon the addition of biochar prepared at 900 ℃, the CO production in sunflower pyrolysis gas products increased. Compared with biochar prepared at the medium-and low-temperature，biochar prepared at 900 ℃, the furan, carbonyl compounds and CH4 in the pyrolysis products of sunflower straw decreased more obviously and the CO increased more obviously, which was related to the loose structure of biochar prepared at 900 ℃，which fully contact with sunflower straw. It is concluded that when the proportion of biochar prepared by 500 ℃ is 40%, the furans, acids and carbonyl compounds in the gas products are all decreased the effect of reduction is the best. And when the addition ratio is 10%, the low-temperature preparation of biochar (500 ℃) is conducive to the production of combustible gas, while the high-temperature preparation of biochar (900 ℃) is conducive to reducing the emissions of furans, acids and carbonyl compounds in the gas products.