Biochar as a Catalyst for Biofuel Production
The world has been consuming fossil fuels at an alarming rate since the industrial revolution in the 18th century. The widespread use of fossil fuels has led to two main crises: energy depletion and global warming. As such, developing technologies to harness renewable energy sources and reduce climate change has become a critical priority in the 21st century.
Biofuels, derived from biomass such as plant or algae material or animal waste, serve as an alternative to traditional fossil fuels. Contrary to fossil fuels like petroleum, coal, and natural gas, biofuels are considered a source of renewable energy because the feedstock material can be replenished easily. Considering rising petroleum prices and growing concern over fossil fuels’ role in global warming, advocates frequently promote biofuels as convenient and environmentally friendly substitutes for petroleum and other fossil fuels. Due to the potential removal of large tracts of arable land for food production and the financial and environmental costs associated with the refining process, many critics are concerned about the extent of the expansion of certain biofuels. Furthermore, conventional biofuel production is prohibitively expensive on a large industrial scale.
Biofuels produced using catalysts manufactured from biochar have shown great promise to mitigate high production costs and improve biofuel yield. The following section details some of the recent research into this promising mechanism for the production of biofuels.
Current Research into Biochar as catalysts for Biofuel production
Researchers in the Department of Environment and Energy, Sejong University, Republic of Korea, investigated the effects of a low-cost, efficient, porous catalytic material produced from chicken manure (biochar produced from chicken manure) for converting waste cooking oil into biodiesel via transesterification.Researchers can convert chicken manure at different temperatures (350, 450, 550, and 660°C), and the resulting biochar’s properties depend on the temperature at which they make the biochar.
The biochar in this study contained a large number of inorganic compounds (mostly CaCO3) that expedited catalytic activity during the transesterification of waste cooking oil. Compared to using SiO2, the chicken manure biochar lowered the transesterification reaction temperature at which the maximum biodiesel output of 95% was attained to 350°C. However, despite the advantageous catalytic effect of CaCO3 derived from the chicken manure biochar, undesirable thermal cracking of biodiesel occurred.
Researchers optimized the mass ratio of silica to chicken manure biochar to mitigate this. Researchers at the Universidad Católica de Temuco, Temuco, Chile, found that the optimal mass ratio of silica to chicken manure biochar was less than 0.8. A study was undertaken to produce a biochar-derived catalyst adopting sulfonic group chemicals that could be used to enhance biodiesel production.
Biochar Catalyst for Enhanced Biodiesel Production
Researchers evaluated the transesterification reaction of waste cooking oils using the biochar catalyst in a microwave reactor. The results indicated that an increase in the reaction temperature up to 140°C during biochar sulfonation enhanced the SO3H content on the catalyst surface. Researchers confirmed these results through Fourier Transform Infrared (FTIR) spectrometry and X-Ray Photoelectric Spectroscopy (XPS) analyses. During the sulfonation, researchers observed a reduction in the surface area of the biochar. However, the increase in SO3H groups on the biochar surface led to a biodiesel yield of approximately 90%.
Furthermore, researchers found that the biochar-derived catalyst could be re-used for up to six cycles by washing with hexane. Researchers in the Department of Chemical and Biological Engineering, The University of British Columbia, Canada, have developed a biochar catalyst to produce biodiesel. Researchers created two carbon-based solid acid catalysts by sulfonating biochar using concentrated or fuming sulfuric acids.
Enhanced Biochar Catalysts for Transesterification and Esterification
Researchers then investigated the ability of these prepared catalysts to catalyze the transesterification of vegetable oils and the esterification of free fatty acids for biofuel production. The catalyst exhibited significant conversion in the esterification of free fatty acids while showing little transesterification activity when researchers sulfonated it with concentrated sulfuric acid. Using fuming sulfuric acid, a stronger sulfonating agent, significantly increased the transesterification activity. The impact of sulfonation time (5 and 15 hours) and surface area on the transesterification reaction was the subject of additional research on the latter catalyst. Chemically treating the biochar with potassium hydroxide increased its surface area by creating porosity.
Researchers contrasted the catalytic activity of the four resulting catalysts. The presence of methanol as the reagent showed that the catalyst with the highest surface area and acid density had the highest catalytic activity.
Researchers observed this in the production of biodiesel from canola oil. Additionally, among the catalysts with similar acid densities, the catalyst with the higher surface area indicated higher transesterification activity. Researchers examined the effects of reaction time, catalyst loading, and the alcohol to oil (A:O) molar ratio. These factors influenced the esterification reaction catalyzed by the sulfonated biochar. The researchers found that free fatty acid conversion increased with increasing A:O molar ratio, reaction time, and catalyst loading.
Innovative Biochar Catalysts for Biodiesel and Biofuel Production
Researchers at the Polymer Research Laboratory, Department of Organic and Biochemistry, Faculty of Chemistry, University of Tabriz, Iran, fabricated a new heterogeneous biochar/CaO/K2CO3 catalyst to produce biodiesel from waste edible oil. In this catalyst, researchers produced the biochar from brown algae of Sargassum Oligocystum and CaO from eggshells. The X-Ray Diffraction (XRD) result indicated that the biochar, CaO, and synthesised catalyst exhibited a crystalline structure.
Researchers utilized Response Surface Methodology Central Composite Design (RSM-CCD) and Artificial Neural Network (ANN) techniques to evaluate the impact of parameters and establish ideal circumstances. In addition, the RSM-CCD method predicted the maximum efficiency of biodiesel production (98.83%) at 65°C, 4 wt% catalyst content, 200-minute duration, and an 18:1 methanol to oil ratio. The process of biodiesel production was exothermic. Researchers calculated the activation energy as 45.53 kJ/mol and the frequency factor as 6.03×10^4 min^−1. Researchers used ASTM D6751 and EN14214 international standards to evaluate the properties of the produced biodiesel. The researchers re-used the catalyst 5 times and achieved up to 90% efficiency.
Modified Biochar Catalysts for Enhanced Biofuel Production
A study at the University of Perugia, Italy, investigated the behaviour of two types of modified biochar (functional and iron composite biochars) as catalysts regarding their surface chemistry and morphological properties and their effects on biofuel derived from Cladophora Glomerata macroalgae. Researchers conducted two catalytic experiments in a 25mL slow pyrolysis reactor in the presence of biochar-based catalysts at a temperature of 500°C. Researchers observed no clear effect on biogas production for functional biochar, whereas iron composite biochar increased the hydrogen content by 7.99 ml/g of algae. Iron composite biochar with a 3D network structure demonstrated remarkable catalytic behaviours (especially towards hydrogen production) due to its high surface area, high dispersion of iron particles, and particular structures and compositions. The marine biomass obtained from biochar and the treatment method proposed could offer a potential route for affordable, effective, renewable, and eco-friendly catalysts.
The global biochar market is expected to experience growth from US$164.5 million in 2021 to US$365.0 million by 2028, at a CAGR of 12.1% over the forecast period. Biochar-based catalysts have several advantages for biofuel production. First, researchers have found biochar affordable and practical because it can be made from renewable feedstock and is produced using sophisticated synthesis techniques. Secondly, researchers have created many methods to adjust the physicochemical characteristics of biochar in accordance with its intended use. Finally, some of the biochar’s inherent qualities, like surface functional groups and the presence of inorganic species, may be advantageous for its function as a catalyst or catalyst support. Consequently, biochar-based catalysts can possibly replace existing catalysts that are costly or non-renewable in the future.