Abundant waste agricultural residues such as oil palm empty fruit bunch (EFB) can provide alternative sources of biomass for producing furfural. The aims of this study were to propose a method of preparing furfural and dissolving pulp (DP) from EFB using prehydrolysis with nitric acid, and to examine how the prehydrolysate, which contains xylan, can be used for furfural production. The furfural yield in the nitric acid prehydrolysate was increased to 6.2% of the EFB material weight by dehydration with an acid catalyst. Nitric acid prehydrolysis followed by soda cooking under atmospheric pressure was also applied to the preparation of DP. The obtained pulp was then bleached by using peroxymonosulfuric acid (Psa), chlorine dioxide (D0, D1), and hydrogen peroxide (Ep) in the elementary chlorine-free Psa-D0-Ep-D1 sequence. The pulp demonstrated a brightness of 90.4% ISO and a viscosity of 6.5 cP, which met the National Standard of Indonesia, although the xylan content was a little high and the α-cellulose content was 83.0%.

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In this work, pretreatment of wood meals using a recycled ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate ([Emim] Ac), enhanced glucose liberation by enzymatic saccharification, without dissolution of cellulose and lignin. In contrast, previous studies on IL pretreatment have mostly focused on lignocellulosic dissolution to regenerate cellulose and removing lignin. Softwood (Cryptomeria japonica) was pretreated with [Emim]Ac at 60-100 °C for 2-8 h without collecting regenerated cellulose. The pretreatment did not have a strong effect on wood component dissolution (weight of residues: 91.7-98.8%). The residues contained relatively high amounts of lignin (26.6-32.6%) with low adsorption of [Emim]Ac (0.9-2.7%). Meanwhile, the crystallinity index (C r I) of cellulose in the wood was significantly reduced by pretreatment, from 50.9% to 28.4-37.1%. In spite of the high lignin contents in the residues, their glucose liberation values by enzymatic saccharification using a cellulase mixture were 3-16 times greater than that of untreated wood. A good correlation was found between the saccharification effectiveness of pretreated samples and the C r I. Although lignin dissolved in [Emim]Ac continued to accumulate after repeated use of [Emim]Ac, the pretreatment was found to be effective for three consecutive cycles without the need to remove the dissolved materials.

Residual lignin present in alkali pulps prepared from oil palm (Elaeis guineensis) empty fruit bunch was isolated using an enzymatic method and characterized successfully by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). These pulps were prepared by sodaanthraquinone (AQ) and prehydrolysis (PH) soda-AQ cooking methods (pulp yields were 45.3 and 33.9%, respectively). Py-GC/MS of the residual lignin showed that two pyrolysis products which were indole and methylindole originating from the enzyme (contents 12 to 44%), in addition to eight pyrolysis products originating from syringyl (S) and guaiacyl (G) structure of lignin. Furthermore, palmitic acid was also detected in the residual lignin (contents 0.11 to 0.28%). The residual lignin was subjected to further purification by a cellobiose treatment method, and the quantity of enzyme present in the residual lignin was found to decrease after the treatment. Residual lignin in PH-soda-AQ pulp exhibited a higher S/G ratio (0.86 to 0.98) than that in soda-AQ pulp (0.76 to 0.97). This study showed that the contents of lignin (19 to 44%) and enzyme in enzymatically isolated lignin can be estimated by the Py-GC/MS method.