Comparative experimental investigations of alkaline reagents on the delignification efficiency and cellulose recovery from Ethiopian coffee pulp waste

The selection of suitable reagents for cellulose recovery and delignification of lignocellulosic biomass (LCB) is considered the primary factor affecting the structure of extracted cellulose and ultimately determines its applications. In this study, to explore the influence of different alkaline reagents for the underutilized Ethiopian arabica coffee pulp, reagents with distinct cations (NaOH, KOH, and NH 4 OH) at varying dosages (2–8% w/v or v/v), and constant pretreatment severity were chosen. The biomass composition analysis of pretreated residues reveals that each alkaline reagent causes heterogeneous disruption. For each alkali treatment, optimal samples were identified and bleached using hydrogen peroxide in an alkaline medium. Results showed coffee pulp bleached with 4% (w/v) KOH and H 2 O 2 achieved the highest cellulose recovery (94.98 ± 0.83%), with a delignification efficiency of 70.06 ± 0.17%. Under the same conditions, bleaching with 4% (w/v) NaOH and H 2 O 2 revealed high-crystalline cellulose (CrI=65.93%) and removed 73.29 ± 0.55% of lignin. NH 4 OH pretreatment exhibited low results for both cellulose recovery (91.81 ± 0.76) and delignification efficiency (62.9 ± 0.85) compared to NaOH and KOH treatments. XRD, FTIR, TGA, and SEM analyses were conducted for further characterization of the optimal results. The findings demonstrate that each alkaline reagent produces distinct biomass properties, suggesting that reagent selection should be tailored to the intended use of the recovered cellulose. • The effectiveness of alkaline reagents was evaluated for delignification and cellulose recovery. • Alkaline peroxide bleaching in NaOH and KOH solutions produces high-crystalline cellulose. • Each alkaline reagent produces distinct structural & physicochemical characteristics of cellulose. • KOH emerges as the most effective reagent for producing high-yield bleached cellulose. • NH 4 OH + H 2 O 2 - bleached coffee pulp exhibits a distinct altered microstructure morphology.