Continuous biomass fractionation process for producing ethanol and low‐molecular‐weight lignin

Abstract

A continuous biomass fractionation process for producing ethanol and low-molecular-weight lignin was developed, and its economic feasibility was evaluated. The two-stage process fractionates biomass into three streams: a solid cellulose stream and two liquid streams containing mostly hemicellulosic sugars and lignin, respectively. Process optimization was conducted using corn stover as feedstock in a continuous pilot-scale unit, with the goals of efficient hemicellulose and lignin hydrolysis for the countercurrent first and cocurrent second stage, respectively. Countercurrent prehydrolysis in an extruder is a novel feature of the process. Autohydrolysis at 2108C followed by NaOH (0.06 g/g biomass) catalyzed delignification at 2208C was determined to be optimal. Economic feasibility of the process for ethanol production was compared to that of the National Renewable Energy Laboratory (NREL; Golden, CO) process. Major differences between the two scenarios are that the PureVision process generates lignin as a sellable output but needs to replace the lost fuel value of the lignin with additional stover. The minimum ethanol selling price, calculated following the NREL protocol, is projected to be lower for the PureVision process ($0.94/gal) than that for the NREL process ($1.07/gal)-the differential depending on lignin selling price-indicating a process with commercial potential.

Characterisation of Sequential Solvent Fractionation and Base-catalysed Depolymerisation of Treated Alkali Lignin

“…The severity factor, log R0, is calculated using Eqs. 1 and 2, (1) (2) where Texp is the experimental temperature in °C, Tb is the boiling temperature of water (100 °C), and t is the reaction time in minutes (Kadam et al 2009). …”

The Third Generation Technology of Biorefining: Dawn

“…There exist more than ten percent of other organic chemicals in lignocelluloses besides lignin, cellulose, and hemicellulose. They are proteins, fats and oils; wax, acids, and alcohols; and polyphenols such as tannins, flavonoids, and quinines; starch, pectic materials, and acid soluble lignin (13,14,15). These organic materials went to the waste stream in biochemical refining technologies.…”

The effect of direct and counter‐current flow‐through delignification on enzymatic hydrolysis of wheat straw, and flow limits due to compressibility

“…Flow-through processes have been shown to improve the efficiency of different alkaline and organosolv delignification methods (Kadam et al, 2009;Park and Kim, 2012;Tae and Lee, 2005;Tirtowidjojo et al, 1988). Flow-through treatment is typically performed by percolation through material packed in a column.…”

“…Nevertheless, only a few reports exist on countercurrent pretreatment of lignocellulose, since establishing a moving bed of solids against liquid flow is difficult. These include a continuous hydrothermal process in pilot scale (Petersen et al, 2009) and a smaller scale extruder setup with a combination of hydrothermal and NaOH-pretreatments (Kadam et al, 2009), but the counter-current processes were not compared to regular percolation. Progressing batch percolation is a semi-continuous solution for establishing counter-current treatment of solids without the need to actually move the solid material (Lee et al, 1999).…”