OBTAINING CELLULOSE FROM PLANT STEMS BY THE ORGANOSOLVENT METHOD

ABSTRACT

In this study, a technology for extracting technical cellulose from the biomass of annual lignocellulosic plants - rice stalks, wheat straw, and miscanthus (Miscanthus sinensis) - using the organosolvent method was developed. The aim of the research is to optimize the oxidative-organosolvent cooking process, which is environmentally safe, energy-efficient, and economically viable. Peracetic acid (CH₃CO₃H) and hydrogen peroxide (H₂O₂) are used as the main delignifying reagents in the process. Peracetic acid effectively breaks down the aromatic structure of lignin, while hydrogen peroxide acts as a component maintaining balance in the system. Under optimal conditions (peracetic acid consumption 0.3-0.4 g/g, in the presence of 0.01% organophosphonate stabilizer), the yield of technical cellulose reached 57-60%, and the degree of bleaching up to 90%. The use of organophosphonate increased the stability of the peroxide system and enhanced the selectivity of the delignification process. As a result, the obtained cellulose is of high purity, bleached, and mechanically strong, and can be used as a promising raw material in the production of paper biocomposites, biosorbents, nanocellulose, and biofuel. Thus, the oxidative-organosolvent technology is recommended as a sustainable and environmentally safe method for obtaining technical cellulose from annual plants.

АННОТАЦИЯ

В данной работе разработана технология получения технической целлюлозы из биомассы однолетних лигноцеллюлозных растений – стеблей риса, соломы пшеницы и мискантуса (Miscanthus sinensis) – органосольвентным методом. Целью исследования является оптимизация процесса окислительно-органосольвентной варки, который является экологически безопасным, энергоэффективным и экономически выгодным. В качестве основных делигнифицирующих реагентов в процессе используются надуксусная кислота (CH₃CO₃H) и пероксид водорода (H₂O₂). Перуксусная кислота эффективно разрушает ароматическую структуру лигнина, а пероксид водорода выступает в качестве компонента, поддерживающего равновесие в системе. В оптимальных условиях (расход надуксусной кислоты 0,3-0,4 г/г, в присутствии 0,01% органофосфонатного стабилизатора) выход технической целлюлозы достигает 57-60%, а степень отбелки – до 90%. Использование органофосфоната повышает устойчивость пероксидной системы и повышает селективность процесса делигнификации. В результате полученная целлюлоза отличается высокой чистотой, отбеленностью, механической прочностью и может быть использована в качестве перспективного сырья для производства бумажных биокомпозитов, биосорбентов, наноцеллюлозы и биотоплива. Таким образом, окислительно-органосольвентная технология рекомендуется как экологически безопасный и экологичный способ получения технической целлюлозы из однолетних растений.

Keywords: miscanthus stalk, rice stalk, wheat straw, corn stalk, cellulose, polymers, organosolvent, peracetic acid.

Ключевые слова: стебель мискантуса, стебель риса, пшеничная солома, стебель кукурузы, целлюлоза, полимеры, органорастворитель, надуксусная кислота.

Introduction. In recent years, due to technological advancements, there has been a growing interest in developing new types of materials from environmentally friendly, renewable, and sustainable raw materials. Considerable research has focused on obtaining high value-added products from natural polymers such as cellulose, hemicellulose, and lignin, which are abundant in plant biomass [1,2]. These studies contribute to environmental protection, waste reduction, and carbon-neutral technologies [3].

Traditionally, cellulose has been extracted from wood and cotton fibers, but these resources have long growth cycles and their excessive exploitation results in resource depletion [4]. Therefore, current studies are expanding toward annual lignocellulosic plants such as rice stalks, wheat straw, corn stalks, miscanthus, hemp, and flax, which are readily available and renewable [5–7]. This approach not only ensures secondary utilization of agricultural waste but also facilitates the production of new bio-based materials [8].

Various technological methods are used to extract cellulose from plant stems, including hydrothermal, chemical (alkaline, sulfate, sulfite), organosolvent, and biological methods [9,10]. Among them, the organosolvent method stands out due to its advantages - high extraction efficiency, low-temperature processing, the possibility of lignin processing, and environmental safety [11,12]. In this method, ethanol, acetone, methanol, organic acids, or their mixtures are typically used as solvents. This approach allows for the extraction of cellulose with minimal impurities by softening the chemical bonds between lignin, hemicellulose, and cellulose [13,14].

Cellulose obtained through the organosolvent method from annual plants is a promising raw material for the production of paper, biocomposites, biofuels, biosorbents, biopolymers, and nanocellulose [15]. Furthermore, this technology enables economically efficient processing of industrial waste and agricultural residues.

Therefore, the main goal of this study is to develop a technology for extracting high-purity cellulose from annual plant stems using the organosolvent method and to analyze its physicochemical properties. This aims to create an environmentally sustainable, energy-efficient, and economically viable technological solution.

Materials and methods of research. Local agricultural waste - rice stalks, wheat straw, and miscanthus (Miscanthus sinensis) stalks were selected as the research objects [10,13]. Preliminary mechanical cleaning was carried out on these biomass samples: soil, dust, and foreign particles were removed. Subsequently, they were washed several times with clean water and dried at a temperature of 60°C for 24 hours. The dried samples were ground to a particle size of 0.5-1 mm using a grinder [12].

In the study, the organosolvent cooking process was used. In oxidizing-organosolvent cooking processes, peroxide compounds - peracetic acid (CH₃CO₃H) and hydrogen peroxide are used as the main active cooking reagents. Due to its strong oxidizing properties, peracetic acid breaks down the aromatic structure of lignin. It is based on the following reaction:

Lignin+CH₃CO₃H→decomposition products+H₂O+CH₃COOH

As a result, cellulose fibers are easily released, meaning the cellulose separation process becomes easier. These compounds are sensitive to heavy and transition metal ions, which act as catalysts for their decomposition. To increase the targeted use of peroxide compounds, stabilizers belonging to the organophosphonate group are added to the cooking composition [9,12].

During the cooking process, the temperature and pressure were maintained constant. After the reaction, the mixture was cooled and separated by vacuum filtration. The residue (cellulose) was washed several times with hot water, then with 70% ethanol. It was then treated with a 0.1 M NaOH solution for 30 minutes to remove the remaining traces of lignin. The purified cellulose was washed with distilled water to a neutral pH and dried at 60°C.

Figure 1. Quantity of main components during the step-by-step processing of miscanthus

Research results and discussion. Analysis of the obtained experimental data confirms that the preliminary extraction of components from miscanthus leads to an enrichment of the raw material with cellulose by reducing the content of lignin and ash. This, in turn, is a favorable factor for obtaining technical cellulose using the oxidative-organosolvent method. To assess the influence of the cooking composition components on the delignification process, the dependence of the consumption of cooking components over time was studied (Figure 2).

Figure 2. Dependence of cooking component consumption on process duration

As shown in Figure 2, the concentration of hydrogen peroxide remains virtually unchanged during the first 60 minutes, which indirectly indicates that the main delignifying agent is peracetic acid (PAA). Consequently, PAA performs the functions of delignification and partial bleaching, while hydrogen peroxide in this case serves to maintain the equilibrium concentration of PAA.

Therefore, the kinetic parameters of all subsequent delignification processes were studied specifically for PAA. As can be seen from Figure 2, during the period of temperature increase, the concentration of PAA decreases by 20% however, no lignin release is observed during this time. Presumably, during this period, the acid is adsorbed onto the surface of the natural polymer. Thermal decomposition of peroxide compounds was also taken into account in the experiment.

To achieve the desired degree of delignification and obtain high-quality technical cellulose, the influence of PAA consumption on the delignification process was studied. The data are presented in Table 1.

Table 1.

Dependence of product yield on cooking conditions when obtaining technical cellulose from miscanthus

Analysis of the data in Table 1 shows that the best results are observed at a sodium acetate (SA) consumption of 0.3-0.4 g/g. In this case, as a result of using organophosphonate, the selectivity of the boiling composition increases significantly.

Without preliminary stages of component separation, technical cellulose with uneven boiling and a low degree of bleaching (less than 60%) is obtained under boiling conditions with practically the same degree of yield.

The kinetics of the delignification process was studied at the selected consumption of sodium acetate (SA) (0.3-0.4 g/g). The kinetics of the boiling process was investigated in isothermal mode. It was established that with an initial raw material content of approximately 63% holocellulose and a technical cellulose yield of 62.8%, the oxidizing-organosolvent method allows for the preservation of 94.5% of the holocellulose complex.

Conclusion. The results of the conducted research show that the extraction of cellulose from annual plant stalks - rice stalks, wheat straw, and miscanthus biomass - using the organosolvent method is an environmentally safe, energy-efficient, and highly effective technological solution. In oxidizing-organosolvent cooking, peracetic acid (CH₃CO₃H) serves as the main delignifying reagent, effectively breaking down the aromatic structure of lignin, while hydrogen peroxide acts as an auxiliary component, maintaining the equilibrium concentration of Sodium acetate (SA). According to the research results, the most optimal outcomes were observed at a Sodium acetate (SA) consumption of 0.3-0.4 g/g - the yield of technical cellulose was about 57-60%, and the degree of bleaching reached up to 90%. The use of organophosphonate stabilizers increased the stability of the peroxide system and enhanced the selectivity of the delignification process. Analysis of the process kinetics shows that in the initial stages, Sodium acetate (SA) decomposes lignin as the main active reagent, and subsequently, the balanced decomposition of peroxide compounds ensures high purity of cellulose. In this case, a decrease in the content of lignin and ash leads to an enrichment of the biomass with cellulose. As a result, the cellulose obtained by the oxidizing-organosolvent method is of high purity, bleached, and mechanically stable, and can be used as a promising raw material in the production of paper, biocomposites, biosorbents, nanocellulose, and biofuel. Thus, organosolvent technology is recommended as a sustainable, environmentally safe, and economically viable method for obtaining technical cellulose from annual lignocellulosic plants.

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