Natural deep eutectic solvent mediated pretreatment of rice straw: bioanalytical characterization of lignin extract and enzymatic hydrolysis of pretreated biomass residue

Environ Sci Pollut Res (2016) 23:92659275 DOI 10.1007/s11356-015-4780-4

POLLUTION CONTROL TECHNOLOGIES AND ALTERNATE ENERGY OPTIONS

Natural deep eutectic solvent mediated pretreatment of rice straw: bioanalytical characterization of lignin extract and enzymatic hydrolysis of pretreated biomass residue

Adepu K. Kumar1 & Bhumika S. Parikh1 &

Mohanty Pravakar2,3

Received: 17 February 2015 /Accepted: 25 May 2015 /Published online: 3 June 2015 # Springer-Verlag Berlin Heidelberg 2015

Abstract The present investigation demonstrated pretreatment of lignocellulosic biomass rice straw using natural deep eutectic solvents (NADESs), and separation of high-quality lignin and holocellulose in a single step. Qualitative analysis of the NADES extract showed that the extracted lignin was of high purity (>90 %), and quantitative analysis showed that nearly 605 % (w/w) of total lignin was separated from the lignocellulosic biomass. Addition of 5.0 % (v/v) water during pretreatment significantly enhanced the total lignin extraction, and nearly 223 % more lignin was released from the residual biomass into the NADES extract. X-ray diffraction studies of the untreated and pretreated rice straw biomass showed that the crystallinity index ratio was marginally decreased from46.4 to 44.3 %, indicating subtle structural alterations in the crystalline and amorphous regions of the cellulosic fractions. Thermogravimetric analysis of the pretreated biomass residue revealed a slightly higher Tdcp (295 C) compared to the Tdcp

(285 C) of untreated biomass. Among the tested NADES reagents, lactic acid/choline chloride at molar ratio of 5:1 extracted maximum lignin of 684 mg g1 from the rice straw biomass, and subsequent enzymatic hydrolysis of the residual holocellulose enriched biomass showed maximum reducing sugars of 33311 mg g1 with a saccharification efficiency of 36.03.2 % in 24 h at 10 % solids loading.

Keywords Lignocellulosic biomass pretreatment . NADES . Enzymatic saccaharification . Rice straw . Lignin . Holocellulose

AbbreviationsNADESs Natural deep eutectic solvents Tdcp Thermal onset of decomposition

IL Ionic liquidDESs Deep eutectic solventsCMC Carboxymethyl cellulosePNPG p-Nitrophenyl--D-glucopyranoside LA Lactic acidBE BetaineLC Lactic acid/choline chlorideCC Choline chlorideXRD X-ray diffractometerCrI Crystallinity indexIcry Intensity of crystalline region

Iamp Intensity of amorphous regionFTIR Fourier transform infrared spectroscopy KBr Potassium bromideTGA Thermogravimetric analysisNREL National Renewable Energy Laboratory FPU Filter paper unitHPLC High-performance liquid chromatography

Responsible editor: Angeles Blanco

Electronic supplementary material The online version of this article (doi:http://dx.doi.org/10.1007/s11356-015-4780-4

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