Author: Muryanto Muryanto, Yanni Sudiyani, Muhammad Arif Darmawan, Eka Mardika Handayani & Misri Gozan

Photo by Taffpix from Getty Images/Canva

The most considerable solid waste from crude palm oil plants is oil palm empty fruit bunch (OPEFB) which contains cellulose, lignin, and hemicellulose. Hemicellulose can be hydrolyzed to xylose and then converted to furfural via dehydration. Pretreatment is one of the steps in the bioconversion of lignocellulose material to reduce lignin. This study developed a one-pot process to conduct pretreatment and furfural production simultaneously.

This process uses a green solvent called ternary deep eutectic solvent (DES). DES was synthesized by mixing choline chloride, oxalic acid, and ethylene glycol with a molar ratio of 1:1:2 (CHOAEG). Simultaneous delignification and furfural production were carried out in a stainless steel reactor. The temperature was varied at 100, 120, and 150 °C, with the various processing time at 30, 60, and 90 min, respectively. The highest furfural concentration reached 9.68 g/L, and the delignification was achieved up to 55.81% at 150 °C for 90 min. The OPEFB pretreated was hydrolyzed by cellulase and achieved 90.79% glucose yield.

Overall, the simultaneous delignification and furfural production process by ternary DES CHOAEG demonstrated a novel and efficient process by reducing the number of complex processes stages of biorefinery lignocellulose.

Keywords: Deep eutectic solvent, Delignification, Enzymatic hydrolysis, Furfural, Lignocellulose

Lignocellulosic is the most abundant biomass resource. Lignocellulose can be converted into various products, such as chemicals, materials, and energy sourcing. Lignocellulosic biomass has a complex structure consisting of three main polymer components: cellulose, hemicellulose, and lignin [1]. The concept of biorefinery on lignocellulosic aims to produce several products from lignocellulosic. Cellulose can be utilized as raw material for bioethanol, biofuel, pulp mills, lactic acid, nanocellulose, cellulose acetate, and other biochemical materials [2,3,4]. Lignin is a potential biopolymer as a wood adhesive [5, 6]. Hemicellulose can be converted to obtain various products, such as xylose and xylitol, and can be converted into furfural [7].

The bioconversion of cellulose and hemicellulose may be hampered by the lignin present in oil palm empty fruit bunches (OPEFB). By generating a lignin carbohydrate complex (LCC) with hemicellulose upon binding, the lignin complex structure prevents bioconversion. Hence, it is necessary to perform a delignification or pretreatment procedure to decrease the lignin content when utilizing hemicellulose. The pretreatment of lignocellulosic materials involves the utilization of alkaline or acidic solvents. Alkaline solvents are effective in reducing the lignin content by employing intermolecular saponification of hemicellulose, xylan ester cross-links, and other constituents [8]. In pretreatment, acid solvents destroy the lignocellulosic biomass's carbohydrates, turning them into sugar [9, 10]. Due to their toxicity and corrosiveness, these solvents do have some restrictions. The development of green solvents for the pretreatment process has been the subject of current research.

Furfural can be utilized as a raw material for the formation of other compounds, making it a promising building block material [11]. Furfural is commonly used in petroleum processing as a solvent and finds other applications in industries such as agrochemicals and pharmaceuticals [12]. Furfural is obtained from the hydrolysis of hemicellulose to xylose, followed by a dehydration process [7]. The furfural market continues to increase due to the high use of furfural and its derivative compounds. Around 300–700 tonnes/year of furfural is produced worldwide [13]. However, the constraints of the current furfural production process are the low yield and the long process. Therefore, the various efforts to improve the process efficiency of furfural production are interesting to develop.

Obstacles to the creation of commercial furfural production processes from waste biomass include low yield, toxic solvent that used in process, corrosive catalyst caused this process need specialized equipment and materials and industrial furfural production can be energy-intensive, which can increase production costs and limit the scalability of the process [12, 14, 15]. Ensuring sustainable and environmentally friendly production processes is important. Minimizing energy consumption, water usage, and waste generation, as well as addressing any potential environmental concerns, is crucial for commercial furfural production [14, 16, 17]. Furthermore, developing sustainable technologies for the supply of chemicals from renewable raw materials, increasing product yield, and reducing production costs can enhance the efficiency and sustainability of furfural production processes. Addressing these challenges through technological advancements, process optimization, and ongoing research and development efforts can pave the way for the successful commercialization of furfural production processes using waste biomass.

Some research has been performed to increase furfural production. The amount of hemicellulose, the solvent, the catalyst, and the hydrolysis and dehydration procedure were some variables that affected the furfural production from lignocellulose [18,19,20]. Solvent utilization is one of the challenging factors in producing furfural from OPEFB. Sulfuric acid is a common solvent as well as a catalyst for the manufacture of furfural. Several chemicals have also been used to manufacture furfural, including metal chlorides, organic acids, and hydrochloric acids [18, 21, 22]. However, these materials harm the environment and damage equipment, so various studies on solvents to replace sulfuric acid have been conducted.

Recently, deep eutectic solvents (DES) are becoming popular green solvents for converting biomass. While DES functions similarly to ionic liquids, it is simpler to make, generally less expensive, and less harmful [23, 24]. DES, as a new solvent, is created by combining hydrogen-bond donors and acceptors (HBD and HBA) [25, 26]. DES is frequently used for chemical extraction, lignin isolation, biomass processing, and other applications [27,28,29]. Commonly DES used in this process consists of two components. Several recent studies have used the addition of a third material in the DES synthesis, known as "the ternary DES". The addition of this third component can maintain the stability and viscosity of DES. Using ternary DES can improve the reduction of lignin and hemicellulose in lignocellulosic biomass [30, 31]. However, there are fewer publications related to the utilization of ternary DES for delignification and furfural production from OPEFB conducted simultaneously in one-pot production. OPEFB contains high lignin that requires an effective solvent to remove the lignin. In this research, the delignification process and furfural production carried out in a novel one-pot system using ternary DES can reduce the lengthy process stages of furfural production in general. This process is more efficient due to reduced processing time and equipment. This paper discusses the delignification and furfural production by three-constituent DES containing choline chloride/oxalic acid/ethylene glycol in varied temperatures and processing times. Besides that, the characterization of the biomass resulting from DES pretreatment was also investigated, and an enzymatic hydrolysis process was carried out to produce glucose. This study aims to demonstrated an efficient process to produce high yield of furfural from lignocellulose biomaterial and reduce the complexity process stage of biorefinery from lignocellulose.

1. Department of Chemical Engineering, Faculty of Engineering, Universitas Indonesia, Depok, 16424, Indonesia

   Muryanto Muryanto & Misri Gozan

2. Research Center for Chemistry, National Research and Innovation Agency (BRIN), Building No. 452, KST BJ Habibie, Jl. Raya Puspiptek 60, Setu, South Tangerang, 15314, Indonesia

   Muryanto Muryanto & Yanni Sudiyani

3. Research Center for Process and Manufacturing Industry Technology, National Research and Innovation Agency (BRIN), Building No. 452, KST BJ Habibie, Jl. Raya Puspiptek 60, Setu, South Tangerang, 15314, Indonesia

   Muhammad Arif Darmawan

4. Center for Research and Human Resource Development, National Standardization Agency of Indonesia Kawasan, PUSPIPTEK, Serpong, Tangerang, 15314, Indonesia

   Eka Mardika Handayani

To appear in: Arabian Journal for Science and Engineering

DOI: https://doi.org/10.1007/s13369-023-08211-y

Received 12 March 2023, Accepted 10 August 2023, Published 13 September 2023