Isolation and characterization of lignin from black liquor of arecanut leaf sheath (Areca catechu L.) with hydrochloric acid and phosphoric acid

Most of the Arecanut Leaf Sheath (ALS) was burned and disposed of as waste, in which lignin, including a major cell wall component of ALS, has potency as a green chemical. Up to now, there is a limited report on lignin extraction and isolation from ALS. Hence, this research used kraft pulping with different percentages of active alkaline (17 and 19%) and sulfidity (20%) as a delignification method for lignin extraction from ALS. And this study aimed to describe the effect of the variation of inorganic acids (HCl and H3PO4) in the lignin isolation process on lignin characterization. Furthermore, the characterization of isolated lignin entails moisture content, yield, purity, ash content, thermogravimetry analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and PyGCMS. Interestingly, acid precipitation had a critical effect on lignin yield, where HCl obtained a higher yield (38-40%) than H3PO4 (14-15%). The result showed that less active alkali resulted in higher lignin purity by both acid precipitation, AIL of 19.11 and 15.69 % for each 17 and 19% active alkali (AA) by HCl precipitation and 40.74 and 30.62 % by H3PO4. Less AA also obtained less residue by TGA analysis and a lower s/g ratio by Py-GCMS. Nevertheless, the difference of acids (HCl or H3PO4) does not show any difference in terms of s/g ratio, but they impact the purity and thermal properties of produced lignin. FTIR spectrum showed that all isolated lignin has a similar functional group to commercial lignin. Therefore, the lignin produced can be influenced by the use of various active alkalis in the pulping process and various acids in the lignin isolation process.