Abstract
Abstract 
 In this study, modified organic solvent (organosolv) method was applied to remove high lignin content in the date palm fronds (type Al-Zahdi) which was taken from the Iraqi gardens. In modified organosolv, lignocellulosic material is fractionated into its constituents (lignin, cellulose and hemicellulose). In this process, solvent (organic)-water is brought into contact with the lignocellulosic biomass at high temperature, using stainless steel reactor (digester). Therefor; most of hemicellulose will remove from the biomass, while the solid residue (mainly cellulose) can be used in various industrial fields. Three variables were studied in this process: temperature, ratio of ethanol to water and digestion time. Statistical experimental design type Central Composite Design (CCD) has been used to find a mathematical relationship between the variables and the remaining lignin percent as dependent variable. The results obtained in this study were represented by a polynomial mathematical equation of the second degree. The results showed that the best digestion time was (80 minutes), which gave the best percent remaining concentration of lignin (3%) at temperature of 185oC and ratio of ethanol: water equal to 50: 50 wt/wt. In order to reduce digesting time, the effect of using different catalysts have been studied such as (NaOH, H2SO4, Ca (OH) 2) at low concentration (0.025, 0.025, 0.05M) respectively. It was found that the best catalyst is sodium hydroxide at concentration (0.025) mol/L which gave the same percent of lignin 3% but with low digestion time about 30 min.
 Keywords: Biomass pre-treatment, delignification, lignin, organosolv, date palm fronds.
Highlights
Delignification is removal of lignin from woody tissue as by natural enzymatic or industrial chemical processes so that it can be used for applications like making Rayon or making paper [1]
The wood chips are digesting at high pressure and elevated temperature in the existence of whit liquor. This process is carried out either batch or continuous in a bioreactor that called digester [4]. Another method is oxygen delignification, which is a process between cooking and bleaching sequences, where part of the residual lignin left in pulp after cooking is removed using oxygen and alkali[5]
The targeted reactions are the oxidation of lignin and breaking it down parts which dissolve in alkali, as well as destroying the colored groups in lignin and removal of impurities, such as resin
Summary
Delignification is removal of lignin from woody tissue as by natural enzymatic or industrial chemical processes so that it can be used for applications like making Rayon or making paper [1]. Lignin is an organic substance binding the cells, fibers and vessels which constitute wood and the lignified elements of plants, as in straw. Kraft process is one of these methods [3], which is capable to remove about 95% of lignin from woody biomass In this method, the wood chips are digesting at high pressure and elevated temperature in the existence of whit liquor (solution of sodium hydroxide and sodium sulfide). The wood chips are digesting at high pressure and elevated temperature in the existence of whit liquor (solution of sodium hydroxide and sodium sulfide) This process is carried out either batch or continuous in a bioreactor that called digester [4].
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