Extraction of Lignin from Wheat Straw in 1, 4-Butanediol Medium Catalyzed by NaOH

Abstract

Wheat straw lignin was extracted in 1, 4-butanediol medium catalyzed by NaOH for the first time. Reaction time, temperature, dosage of NaOH and 1, 4-butanediol, as well as volume percentage of 1,4butanediol medium were optimized to improve lignin recovery in the experiment. As a result, lignin yield was up to 74% when the reaction condition was: 10% (w/w) of NaOH, volume of 60% BDO medium is six times of the quality of WS, reaction time for 3 h at 120 °C. KEYWORD: 1, 4-butanediol; wheat straw; lignin; base catalyzed International Conference on Industrial Technology and Management Science (ITMS 2015) © 2015. The authors Published by Atlantis Press 1098 1: 2) in a Soxhlet extractor for 8 h to remove resin, wax, and fat. Secondly, the solid was air dried in a fume hood. Next, the dried solid was suspended in 15 mL 72% H2SO4 in a 100 ml beaker under magnetic stirring. After 4 h stirring at room temperature, the mixture was diluted with 560 ml deionized water, boiled and refluxed for 4 h, and cooled to room temperature. The solution was left undisturbed overnight and then filtered. The filtered residue was washed with deionized water (DIW) until the pH was 7. The lignin residual was freezedried and weighed. Klason lignin measurements were performed in triplicate. The lignin content of wheat straw was determined as 19 ± 0.1% (eq. (1)). X=( / ) 100% A W  (1) Y=( / ) 100% A W  ’ ’ (2) (1) Where X = Lignin content in WS, A = weight of lignin output, and W = oven-dry weight of WS. The theoretical yield of lignin output was 19%; (2) where Y = Lignin yield, A’ = weight of lignin recovered, and W’ = weight of lignin theoretical output. 3.2 Lignin separation from WS by NaOH 25 g of wheat straw was added to a 1 L autoclave reactor and mixed with 150 to 375 ml of BDO (from 0% to 100%, v/v) medium and 0.5 to 3.75 g of NaOH, reaction time for 1 to 4 h, temperature range from 120 to 200 °C. The flow chart of the extraction process is shown in Figure 1. Adding hydrochloric acid to regulate pH to 2. The lignin residual was freeze-dried with the vacuity less than 20 Pa. Figure 1. Extraction of lignin from WS catalyzed by NaOH (WS: wheat straw; DIW: deionized water; BDO: 1, 4butandiol; “+” denotes mixing) 4 RESULTS AND DICUSSION Figure 2 showed the effect of reaction temperature (a) and liquid / WS ratio (b) on lignin yield. The trend of the two curves are similar. Exactly, Lignin recovery decreased as the temperature escalated as well as liquid / WS ratio increased. This may be because when temperature was up beyond 120 °C, lignin was decomposed by NaOH in BDO medium. And when liquid / WS ratio was far beyond 6, lignin dissolved in BDO medium, resulted in a lower lignin recovery. When liquid/WS ratio was 6, the reactants was dense enough to be fetched out of the autoclave. So the optimum reaction temperature was 120°C, and the optimum liquid/WS ratio was 6, with the highest yield 74%. Figure 2. a. The effect of reaction temperature on lignin yield. Conditions: 25 g of WS, 2.5 g of NaOH, 300 ml 80% (v/v) BDO, reaction time for 3 h; b. The effect of liquid / WS ratio on lignin yield. Conditions: 25 g of WS, 2.5 g of NaOH, 150 to 375 ml 60% (v/v) BDO, 120 °C, reaction time for 3 h. As shown in Figure 3a, the curve displays the highest value at 20% (v/v) BDO medium. However, it took very long time to finish reduced pressure filtration. And when the volume percentage of BDO medium was increased to 60%, filtration was easy to carry out. This manifested that the existence of BDO medium contribute to filtration speed. The optimum volume percentage of BDO medium was 60%, with lignin yield up to 72.4%. The curves depicted in Figure 3b and Figure 3c showed very similar trend that ordinate values increased first and then decreased as abscissa value extending. As shown in Figure 3b, when the dosage of NaOH was 10%