# Efficient 2G Ethanol Production via Optimized Dilute Acid Pretreatment, High-Solids Enzymatic Hydrolysis, and High-Temperature Fermentation

## TL;DR

This paper presents an efficient process for producing second-generation ethanol using optimized pretreatment, high-solids hydrolysis, and high-temperature fermentation.

## Contribution

The study introduces an optimized dilute acid pretreatment and high-solids enzymatic hydrolysis process for rice straw, leading to high ethanol yields.

## Key findings

- Optimized dilute acid pretreatment produced a cellulose-rich solid with 58.2% w/w cellulose.
- High-solids enzymatic hydrolysis achieved a 78.6% cellulose conversion yield and 129 g/L fermentable sugars.
- Fermentation with Kluyveromyces marxianus at 43°C achieved a high ethanol titer of 37 g/L.

## Abstract

The growing demand for 2G ethanol emphasizes the need
to improve
its economic sustainability through different approaches, including
optimized pretreatments, high-solids enzymatic hydrolysis, and high-temperature
fermentation. This study evaluated the dilute acid pretreatment of
deacetylated rice straw using the response surface methodology. Under
optimal conditions (85 mg of H2SO4/g biomass,
for 10 min at a constant temperature of 150 °C), the process
was scaled up to an 80 L reactor, obtaining a cellulose-rich (58.2%
w/w) pretreated solid. Then, high-solids enzymatic hydrolysis at 24%
w/v solids loading was performed in a vertical ball mill (VBM) reactor
in fed-batch mode, resulting in a hydrolysate of 129 g/L of fermentable
sugars, which corresponded to a cellulose conversion yield (CCY) of
78.6%. Finally, the effect of nutritional supplementation of the obtained
slurry and hydrolysate on the fermentability of Kluyveromyces
marxianus at 43 °C was studied in conical flasks
under orbital shaking. The higher
YP/S
(0.46 g/g), Q
P (1.74 g/L/h), and η (90%) were achieved in the hydrolysate
+ nutrients medium. Additionally, the effect of the VBM reactor on
ethanol production was evaluated, further increasing Q
P (3.04 g/L/h) with an ethanol titer of 37 g/L. Therefore,
the processing sequential steps and conditions efficiently produced
a glucose-rich hydrolysate, which was successfully fermented into
ethanol at high temperatures and could support the process feasibility
at a large scale.