# Green Pretreatment of Tropical Fruit Peels Using Triethylammonium Hydrogen Sulfate: A Route Toward Sustainable Biomass Valorization

## TL;DR

This paper explores using a low-cost ionic liquid to pretreat tropical fruit peels for bioethanol production, offering a sustainable waste-to-energy solution.

## Contribution

A novel, cost-effective pretreatment method using triethylammonium hydrogen sulfate on tropical fruit peels is proposed for bioethanol production.

## Key findings

- Mango residue showed the highest potential for bioethanol due to high sugar content and favorable cellulosic composition.
- Oven pretreatment was more effective in weakening the lignin-hemicellulose-cellulose complex and removing lignin.
- Triethylammonium hydrogen sulfate is a practical and affordable ionic liquid for biomass pretreatment.

## Abstract

The search for biofuels has recently intensified because
of the
urgent need to replace fossil fuels with renewable alternatives. Investigation
of biomass, especially waste, presents an excellent option for biofuel
production, including second-generation (2G) ethanol, which can be
produced from lignocellulosic waste. 2G Ethanol production requires
pretreatment and hydrolysis of biomass to break down cellulose, generate
higher amounts of sugars, and consequently increase production yields.
Ionic liquids (ILs), composed of organic and inorganic ions, have
low melting points, low vapor pressures, and the ability to solubilize
cellulose, making them effective in breaking down cellulose and thus
emerging as an efficient alternative to acid pretreatment. Therefore,
this study aimed to evaluate the efficiency of triethylammonium hydrogen
sulfate IL in the pretreatment of tropical fruit peel residues such
as bananas, oranges, and mangoes. For this purpose, the biomass was
characterized through sugar quantification and determination of ash,
moisture, extractives, holocellulose, α-cellulose, and hemicellulose
content. Two pretreatment processes were conducted for lignocellulosic
biomass: one in an oil bath and the other in an oven. Additionally,
yield analyses, scanning electron microscopy (SEM), and infrared spectroscopy
(IR) were performed on the products obtained from the pretreatments.
Based on characterization analyses of the raw materials, mango residue
was identified as the biomass with the highest potential for bioethanol
production, followed by orange and banana residues owing to its high
sugar content, low ash and moisture content, and favorable cellulosic
composition. Among the evaluated pretreatments, the oven method showed
the best results in weakening the lignin-hemicellulose-cellulose complex
and lignin precipitation, also indicating mango residues as being
the most promising in terms of cellulose pulp production and lignin
removal. This study adds value by demonstrating a low-cost and practical
approach to pretreating abundant tropical fruit peel residues using
triethylammonium hydrogen sulfate, an accessible and more affordable
ionic liquid. Additionally, it provides significant scientific value
by addressing two major global challenges: the need for renewable
energy alternatives and the growing demand for sustainable waste valorization
methods.