Extraction Of Lignin From Wheat Straw And Application Research Of Lignin As An Adsorbent

Straw is one of the most abundant sources of renewable energy, whose annual output is about 700 million ton. At present, most of the straws have been abandoned or burned, which can cause severe environmental pollution and the waste of resources. Straw contains abundant lignin, which can be modified to produce a variety of high-added-value products. Hence, separating, modifying and utilizing lignin of straw play an important role in environmental protection and resources utilization.Using wheat straw for raw material, a pretreatment method based on oxalic acid prehydrolysis followed by organic solvents/1-ethyl-3- methylimadazolium acetate([EMIM]Ac) is reported for the extraction of lignin. Influences of different factors on lignin yield of wheat straw was analyzed. Then, a novel magnetic lignin composite was prepared and modified with diethylenetriamine(M-lignin-ECH-DETA). The adsorption of aniline blue and chromium(VI) from aqueous solutions using this magnetic lignin composite was investigated. The main research results was as follows:(1) It has a positive effect on extracting lignin(PHL) from wheat straw which prehydrolyzed by oxalic acid. Compared to extraction from untreated wheat straw, it has the advantage of higher extraction rate. We investigated the ratio of extraction from the following aspects: organic solvent, the ratio of [EMIM]Ac and organic solvent type, temperature and time. Results showed that 62.3% lignin extraction to the total lignin in wheat straw can be obtained under the optimized condition. The products, PHL and L, were characterized by FTIR, TG, GPC and antioxidant activity measurement, respectively.(2) Magnetic lignin composite was prepared and then chemically modified with diethylenetriamine(M-lignin-ECH-DETA). The properties of the M-lignin-ECH-DETA adsorbent were characterized by SEM, FTIR, XRD, TG and VSM. Results indicated that Fe3O4 nanoparticles was packed in the M-lignin-ECH-DETA, and the mass of Fe3O4 nanoparticles was estimated to be about 14 wt%. The saturation magnetization of M-ligninECH-DETA was about 10.6 emu/g, which indicated M-lignin-ECH-DETA can be easily separated with the help of the external magnetic ?eld.(3) The adsorption behaviour for the aniline blue and chromium(VI) were studied, the experimental factors which contain p H, M-lignin-ECH-DETA dosage, temperature and time had also been explored and optimized. The removal of aniline blue and chromium(VI) was p H dependent and the optimum adsorption was observed at p H 2.0. The adsorption of aniline blue was more effective at higher temperature. However, the adsorption of chromium(VI) was more effective at lower temperature. The pseudo-second-order model and the Langmuir adsorption isotherm model were applied to describe the adsorption kinetics and adsorption isotherm, for the aniline blue and chromium(VI) adsorption, respectively. The maximum adsorption amount of aniline blue and chromium(VI) in Langmuir isotherm was aniline blue 634.4 mg/g and chromium(VI) 122.7 mg/g. M-lignin-ECH-DETA showed good reusability remaining 84.0% for aniline blue and 87.8% for chromium(VI) of its capacity after 5 cycles. All these results demonstrated that the material is promising as sorbent in reducing water pollution of aniline blue and Cr(VI).