The compositional variation lignocellulosic biomass from CS, CNS, and CPH.
The pyrolysis method has been used in various fields and has attracted the attention of many researchers so that this method can be applied to treat biomass waste. Pyrolysis of biomass occurs through heating a substance with limited oxygen so that the decomposition of complex compounds such as lignocellulose into simpler compounds occurs. The heat energy of the pyrolysis process encourages the oxidation of biomass so that complex carbon molecules break down into carbon and bio-oil. Pyrolysis of biomass for coconut shells, cashew nut shells, and cocoa pod husk was carried out at a temperature of 400–600°C with a flow rate of 6–7°C/min. The content of bio-oil compounds from its biomass based on the analysis of gas chromatography–mass spectroscopy obtained phenolic acid, pyrimidine derivatives, amines, carbamate acids, furans, esters derivatives, pyridine, ketones, furans, and aldehydes that can be used as active compounds for biopesticides.
Global output of biomass production from agricultural and forestry residues is estimated at 146 billion MT per year , most of which are disposed of in landfills or burned to ashes. The burning of these biomass residues can cause soil degradation by affecting soil biota. In addition, large amounts of particulates, volatile organic carbon and semi-volatile organic carbon compounds, ash, sulfate aerosols, and trace gases are also released into the atmosphere . These pollutants contribute to greenhouse gas emissions, which can contribute to many serious environmental problems on a global scale, such as increasing global climate change, extinction of biodiversity, and socioeconomic severe and health problems. Therefore, it is essential to minimize the burning or wasting of plant biomass and instead develop low-cost pollution reduction and sustainable technologies to convert it into valuable bioproducts .
The chemical composition of biomass, both lignocellulosic and herbaceous, can be characterized by five main components: cellulose, hemicellulose, lignin, extractive/volatile, and ash. Cellulose and hemicellulose, combined with the third major component of biomass, lignin, make up more than 90% of lignocellulosic biomass and 80% of herbaceous biomass. Lignin is a complex array of phenolic compounds interwoven with the cellulose and hemicellulose fractions of the biomass structure. This interwoven property of lignin helps impart rigidity to lignocellulosic materials, such as trees . Biomass can be converted into energy through thermal, biological, and physical conversion processes, such as direct combustion, pyrolysis, and gasification .
Pyrolysis of biomass is the decomposition of chemical components of lignocellulosic by heating or incomplete combustion to be broken down into compounds with shorter chains . Pyrolysis is a decomposition process or decomposition of compounds in raw materials in the presence of heat of combustion and limited oxygen so that gas, liquid, and charcoal are obtained, the amount of which is influenced by the type of material, method, and conditions of pyrolysis. Incomplete combustion of pyrolysis causes complex carbon compounds not to be oxidized to carbon dioxide in raw materials containing cellulose, hemicellulose, and lignin . Conversion of agricultural residue biomass by the pyrolysis method into bio-oil is a potentially attractive technology to remove and process waste from agriculture and greenhouses into alternative sources of green energy and value-added chemicals . Researchers at the Institute for Chemicals and Fuels from Alternative Resources (ICFAR) at the University of Western Ontario designed a highly automated rapid pyrolysis to convert biomass to bio-oil, gas, and biochar at the temperature of 250-800°C under nearly atmospheric pressure and in the absence of oxygen . Bio-oil from biomass pyrolysis produces a complex mixture of chemicals including acids, ketones, furans, phenols, hydrosugars, and other oxygenates, which have antibacterial and antifungal properties against several pathogenic and carcinogenic bacteria as well as biopesticides [10, 11, 12].
2. Compositional of lignocellulosic biomass
In particular, lignocellulosic biomass, mainly composed of lignin, cellulose, and hemicellulose, has become an essential topic because lignocellulosic biomass does not compete with food and feed. There are several technologies for the conversion of lignocellulosic biomass into energy and chemicals . As illustrated in Figure 1, the three main components are unevenly distributed in the cell wall as the skeleton, the connecting material, and the hard solid, respectively. Cellulose macromolecules regularly assemble to form tough microfibers that serve as the skeletal material of the cell wall, and the inner space is packed with hemicellulose linking materials and amorphous lignin . Cellulose is linked to hemicellulose and lignin molecules mainly through hydrogen bonds, whereas the relationship between hemicellulose and lignin includes hydrogen and covalent bonds . Carbohydrates and lignin are tightly bound in lignin-carbohydrate complexes, resulting in residual carbohydrates or lignin fragments in the extracted lignin or hemicellulose samples.
Lignocellulosic materials are mainly composed of cellulose (35–50%), hemicellulose (15–35%), and lignin (10–35%) . The concentrations of the components mentioned vary with different plant species (as shown in Table 1). In addition to the three main components, a small fraction of extractives and inorganic ash are also present in the biomass as non-structural components, not cell walls or cell layers. Wood biomass contains significantly higher amounts of the three main components (»90%), while agricultural and herbaceous biomass contains more extractives and ash.
3. Optimization of parameter pyrolysis biomass
Thermal decomposition of organic matter in the absence of oxygen has been widely developed as a promising platform for producing fuels, preservatives, pesticides, and chemicals from various types of biomass. Pyrolysis produces charcoal, liquid, and gas products, which is highly dependent on the reaction conditions. Fast pyrolysis of biomass at a rapid heating rate and a short residence time of hot steam (<1 s) produces bio-oil with a yield of up to 75% of weight [12, 13].
Pyrolysis is a technology that converts lignocellulosic biomass into gaseous, liquid, and solid products by using heat under an inert atmosphere. Depending on the heating rate and residence time of the pyrolysis stream in the reactor, pyrolysis can be broadly classified into slow and fast pyrolysis. Slow pyrolysis involves thermal cracking of lignocellulosic biomass at low heating rates to produce a high-yield solid product known as biochar (or charcoal). In fast pyrolysis, high yields of liquid (bio-oil) products are obtained because the short residence time of the pyrolysis vapor in the reactor suppresses the secondary reaction, promoting the formation of gas and biochar [8, 20]. The reaction temperature for the pyrolysis of lignocellulosic biomass usually ranges from 500 to 800°C . The physical properties characterization of the pyrolysis results of CS, CNS, and CPH biomass at temperatures of 400–600°C can be seen in Table 2.
|Biomass||Temperature (°C)||Density (g/cm3)||pH||Flow rate (°C/min)||Yield (%)|
|CS||400||1.088||5||10 ± 1||39||28||33|
During pyrolysis, biomass undergoes primary and secondary reactions involving heat and mass transfer mechanisms. The immediate response consists of decomposing lignocellulosic biomass, which leads to the formation of introductory and intermediate products. This intermediate species undergoes secondary cracking. The pathways for the first category include dehydration and charring reactions, while the second is decomposition and evaporation of intermediates. The pyrolysis products obtained in these competitive reactions are susceptible to operational variations and types of biomass . Parameters play a significant role to determine the composition and properties of the pyrolysis products. Since biomass consists of cellulose, hemicellulose, and lignin, the degree of thermal fragmentation of these components depends on the operating parameters . Table 2 shows the distribution of products obtained from various biomass and pyrolysis temperatures, indicating considerable flexibility that can change process conditions. During pyrolysis, many factors affect product properties such as type of biomass, residence time, age percentage of moisture in feed biomass, temperature, pressure conditions (atmosphere, vacuum), particle size, and heating rate of biomass so that pyrolysis efficiency also affects product composition. Optimization of reaction conditions can increase the yield of pyrolysis products to any of the three pyrolysis fuels such as pyrolysis oil, gas, or solid charcoal . This parameter has a significant influence on the composition of the pyrolysis product.
4. Chemical compound composition of biomass pyrolysis bio-oil
The chemical composition of bio-oil derived from different biomass feedstocks is different. The difference can also be caused by other reaction conditions for the pyrolysis operation. This regard provides details of experimental results obtained with varying feedstocks of biomass and reaction conditions in pursuit of chemical production through pyrolysis of lignocellulosic biomass. During pyrolysis, the main components of lignocellulosic biomass will be thermally decomposed to produce valuable chemicals. Cellulose is a high-molecular-weight linear polymer consisting of D-glucose monomer units. The basic units are linked to each other by β-1,4-glycosidic bonds. Cellulose provides mechanical strength to plant cells and is generally degraded in the temperature range of 315–400°C . Cellulose is classified as a homopolysaccharide, whereas hemicellulose is a heteropolymer referred to as a heteropolysaccharide. Hemicellulose consists of pentosan or hexosan, forming polymers such as xylan, glucan, xyloglucan, and glucomannan. Hemicellulose is usually degraded at 220–315°C. Lignin has a complex three-dimensional structure. The basic lignin units are three monolignol precursors, namely p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. Lignin degradation occurs over a wide temperature range covering 150–900°C . Figure 2 shows a simple pathway for the formation of chemicals produced during the pyrolysis of biomass.
Based on the results of the GC-MS analysis in Table 3, CS bio-oil contains phenol compounds and their derivatives, amines, amides, ketones, benzene, and furans. In Table 4, CNS bio-oil contains phenolic compounds and its derivatives, pyrimidines, pyridines, amines, amides, ketones, benzene, acids, and furans. In Table 5, CPH bio-oil contains compounds including phenols and its derivatives, amines, amides, ketones, benzene, acids, and furans. The thermal decomposition of cellulose produces carbonyl and furan compounds. Hemicellulose decomposition is similar to cellulose decomposition but produces acids. Meanwhile, the decomposition of lignin produces various types of phenolic compounds. Phenolic compounds contribute to the taste and color of bio-oil and have antibacterial properties. The dominant compounds in CS, SNS, and CPH bio-oils are phenolics and their derivatives. High phenolic content is generally applied in food systems as a browning agent or preservative, while it is applied as a pesticide in the agricultural industry. The use of pyrolysis liquid as a pesticide can be applied to all types of commercial biopesticides .
|Identified compound||Chemical formula||Peak area %|
|Identified compound||Chemical formula||Peak area %|
|Identified compound||Chemical formula||Peak area %|
5. Application and effectiveness of biopesticide
Biopesticides are natural pesticides that can be obtained either from a microorganism or certain plant extracts including biomass waste. Utilization of biopesticides in plantation and agricultural management to inhibit or kill pests that cause disease in plants by using active components is found in microbes or certain plant extracts. The main advantages of biopesticides are specificity to target insects, effectiveness at low doses, biodegradability, and low toxicity compared to conventional chemical pesticides. Furthermore, synthetic pesticides are toxic, can kill various kinds of pests and beneficial insects, and cause environmental pollution.
Lignocellulosic biomass decomposition by pyrolysis method produces bio-oil, which can be applied as a biopesticide. The chemical components of bio-oil resulting from lignocellulosic pyrolysis are ammonia, hexane, alcohol, ketone, carbonyl, acetic, and phenolic acids [26, 27, 28]. One of the groups of compounds that have the most role in inhibiting microbial growth is phenolic compounds. Biomass contains lignin, a source of phenolic compounds either through the pyrolysis method, which functions as an antioxidant and can be used as a functional food ingredient . Epidemiological studies show that phenolic compounds have potential effects to prevent chronic disease and have anticarcinogenic, anti-inflammatory, antimicrobial, antifungal [26, 30], and biopesticides [31, 32]. Bio-oil from the pyrolysis results can be used as a biofungicide because it contains active compounds that are effective as inhibitors for the growth of fungi and bacteria (as shown in Tables 3–5).
Phenol compounds are compounds that contain a hydroxyl group (–OH), which is directly attached to an aromatic hydrocarbon ring group. The activity of phenol compounds comes from the number of hydroxyl groups on the benzene ring. Classification of phenolic compounds contained in plants are simple phenols, benzoquinones, phenolic acids, acetophenone, naphthoquinones, xanthones, coumarin bioflavonoids, stilbenes, tyrosine derivatives, hydroxycinnamic acid, flavonoids, lignans, and tannins. Flavonoids and polyphenols can inhibit the growth of pathogenic bacteria and fungi .
Several researchers have tested the effectiveness of bio-oil from organic waste as a natural pesticide [34, 35]. The bio-oil of the CN exhibited antifungal activity against
The content of phenolic compounds contained in bio-oil can inhibit the growth of the fungus
Biofungicide is a type of natural pesticides that is used to inhibit or kill fungi that cause disease in plants by using active components found in microbes or plants. The use of biofungicides is cheaper and environmental friendly than synthetic fungicides. Bio-oil from the pyrolysis of CN, CNS, and CPH is an alternative that can be used as a raw material for making biopesticides because it contains several active compounds that have the property of inhibiting and killing pathogenic microbes.
The abundance of the variability of biomass resources available today is a significant opportunity for the utilization of biomass. Biomass containing lignocellulose consisting of cellulose, hemicellulose, and lignin with good processing can be converted into useful active compounds. Biomass processing using the pyrolysis method has a positive impact because it produces bio-oil that can be used as a biopesticide, which does not involve chemical solvents in the process. The chemical compound content of bio-oil from CP, CNS, and CPH biomass pyrolysis based on the analysis of gas chromatography-mass spectroscopy (GC-MS) obtained phenolic acid, pyrimidine derivatives, amines, carbamate acids, furans, esters derivatives, pyridine, ketones, furans, and aldehydes that can be used as active compounds for biopesticides. The use of bio-oil as a biopesticide can reduce biomass waste and overcome the negative impacts of using synthetic pesticides so that it can have a positive impact on health and the environment.
This research was supported by the Ministry of Education, Culture, Research, and Technology of the Republic of Indonesia.