有机酸处理条件对玉米秸秆热解特性的影响

Effects of acid treatment conditions on pyrolysis characteristics of corn stovers

酸洗预处理能有效改善K^+对生物质热解的影响,该文利用热重分析仪和裂解-气相色谱质谱联用仪进行了玉米秸秆的热解试验,研究了不同有机酸酸洗浓度(3%、5%和7%)、酸洗温度(25、50和75℃)和酸洗时间(1、2和3 h)对玉米秸秆热解特性的影响。结果表明:酸洗能显著降低玉米秸秆内在K^+的含量;经过不同条件的有机酸洗预处理后,玉米秸秆的TG/DTG(thermogravimetry/differential thermogravimetry)曲线均向高温段移动,最大热解速率随着酸洗浓度和酸洗温度的增加逐渐增大,随着酸洗时间的增加先增大后降低,在酸洗温度为75℃时,最大热解速率达到最大值15.49%/min;与此同时,玉米秸秆热解主要产物为酚类、酮类和呋喃类化合物,酸洗后,其酚类物质产率明显增加,在酸洗浓度为7%时达到最大值16.75%,而酮类和呋喃类化合物产率减少,分别在酸洗时间为1 h和酸洗浓度为7%时达到最小值0.10%和7.13%。酸洗后,焦炭产率减少,在酸洗浓度为3%时达到最小值18.79%。通过研究不同处理条件下有机酸对玉米秸秆热解特性的影响,为生物质预处理中酸溶液的选择提供了参考。

Biomass pyrolysis is an important way for converting biomass to high-value products. It is significant to improve the quality of biomass pyrolysis products through pretreatment. Acid washing is one of the key technologies to effectively remove alkali metals and alkaline earth metals(AAEMs) from biomass. In this paper, acetic acid was used as the washing solution, K^+ was used as research objects, and pyrolysis experiments of corn straw were carried out by thermogravimetric and pyrolysis-gas chromatography/mass spectrometry analyses. The study of the effects of different acid washing concentration(3%, 5%, 7%), acid washing temperature(25, 50, 75 ℃)and acid washing time(1, 2, 3 h) on the pyrolysis characteristics of corn straw were conducted. The results showed that the K^+ can be effectively removed by acid washing, and as the acid washing concentration, acid washing temperature and acid washing time increase, the removal efficiency is higher, at the acid washing time is three hours, the K^+ content reaches a minimum of 39.49 mg/kg. The TG and DTG curves of pretreated corn straw moved to a high temperature range, and the peaks caused by the degradation of hemicellulose in the DTG curve of pretreated corn straw reduced. Meanwhile, the maximum pyrolysis weight loss rate increases in parallel with the increase of washing concentration and washing temperature, but the trend of increase goes first and then it decreases with the growing of washing time, finally it reaches a maximum value of 15.49 %/min when the acid washing temperature was 75 ℃. At the same times, the pyrolysis kinetics results show that, after acid washing under different conditions, the pyrolysis activation energy and frequency factor of the samples were increased compared with the original sample. With the increase of acid washing concentration and temperature, the sample pyrolysis activation energy and frequency factor gradually increased, but too long acid washing time had a negative effect on the sample activation energy and frequency factor. What is more, the main products of pyrolysis of corn straw were phenols, ketones and furan compounds. After corn straw was pretreated by acid washing, the yield of phenol substances increased significantly and gradually increased with the increase of acid washing concentration. When acid washing concentration was 7%, the maximum yield reached 16.75%. However, the yields of ketones and furan compounds decreases, and gradually decreased with the increase of acid washing concentration, reaching the minimum values of 0.10% and 7.13% at an acid washing time of one hour and an acid washing concentration of 7%, respectively. For the carbon yield, when the temperature is lower than 361 ℃,the yield of acid-washed carbon is higher than the original samples. When the temperature is higher than 361 ℃,the yield of the acid-washed carbon is decreased, and reached the minimum value when the acid washing time is two hours, but increasing the acid washing time had little effect on the yield of carbon. To study the effects of different treatment conditions of organic acid on the pyrolysis characteristics of corn straw is useful to find a good way for the selection of acid solution in biomass pretreatment.