Technology Research and Development Prospects of Biofuels

: The energy consumption that results from economic growth and the pollution it releases into the environment has been the subject of widespread concern in academics and society in recent years, and they have grown in importance as the times progress. There is a growing need for renewable and alternative energy sources due to the possible depletion of non-renewable fossil energy sources like coal and oil as well as the acceleration of global climate change. One of the hottest areas of study right now is the hunt for clean, renewable, and alternative energy sources. A thorough analysis of the biofuels industry's present level of growth indicates a dynamic environment fueled by the rising demand for sustainable energy throughout the world. This review aims to analyze in detail the research background, significance, and rationale for selecting biofuels. It will start with first-generation biofuels and focus on the current third-generation biofuels. Biofuels derived from renewable bioresources have emerged as a promising alternative because of the need to address environmental issues associated with traditional fossil fuels. The dual impact of biofuels on reducing greenhouse gas emissions and enhancing energy security is explored. The choice to focus on third-generation biofuels emphasizes the commitment to innovation and is in line with the United Nations sustainable development goals, in particular those related to clean energy, climate action, and environmental protection.


Introduction
Energy consumption has increased significantly as a result of the economic development.Between 2005 and 2030, energy consumption is expected to increase by 2.6 times, and by 2040, energy demand is expected to increase by about twothirds, making for one-tenth of the growth in worldwide demand [1].Approximately 80% of the world's energy demand is currently met by fossil fuels [2], and in 2020, greenhouse gases (GHG) from fossil fuel consumption will make up 89% of all GHG emissions [3].Due to the effects of climate change, countries around the world need to start developing renewable energy supplies at a rapid pace.
With 10.4% of the world's main energy supply and 77.4% of the world's renewable energy supply, biomass energy is by far the most abundant renewable energy source [4].
Biomass, as the largest renewable energy source, is characterized by its variety and quantity.It is the most promising resource to replace non-renewable fossil energy sources due to its rich sources, diversity, and large reserves.Biofuels can be produced from plants or agricultural, domestic, or industrial biowastes [5].However, human exploitation of biomass energy is far from being sufficient to replace conventional fossil energy sources.
Biofuel technology involves the production and utilization of renewable fuels derived from biological sources such as plants, algae, and organic waste.These fuels are considered alternatives to traditional fossil fuels because they are more sustainable and have the potential to reduce greenhouse gas emissions.Biofuels can currently be categorized into three main generations based on the feedstock used, as well as a fourth generation that is beginning to utilize biogenetic engineering.

Research Background
The background of biofuel research can be traced to the growing global demand for energy and the urgent need to mitigate climate change.As conventional fossil fuels are seriously contributing to environmental degradation, there is a growing demand for sustainable alternatives.Biofuels derived from renewable bioresources emerge as a promising solution with the potential to reduce greenhouse gas emissions and enhance energy security.The significance of this research lies in its ability to address energy and environmental challenges and align with the broader goals of sustainable development.By choosing this theme, I aim to contribute to the advancement of clean energy technologies, with a special focus on third-generation biofuels, and to seek innovative ways to achieve the United Nations Sustainable Development Goals (SDGs), especially those related to affordable and clean energy, climate action, and life underwater and on land [6].This review article endeavors to provide a comprehensive overview of the current state of biofuel development and bridge the gap between research and practical applications in pursuit of a sustainable energy future.
How to identify and implement more sustainable alternatives to biofuel production and how to overcome the economic challenges of implementation is a contentious issue.The environmental impacts of biofuel production alternatives, with a focus on biodiversity and ecosystem services, are contrasted with the development of a set of criteria to guide the identification of sustainable biofuel production alternatives (i.e., those that maximize socio-economic and environmental benefits), as well as strategies for reducing economic barriers to the implementation of more sustainable biofuel production systems [7].Recent advances related to extraction processes for biofuel production are discussed by Li et al.An in-depth evaluation of classified extraction methods for third-generation algal biofuel production was presented.Although stress conditions increased the yield of biofuel compounds, the growth of microalgae was severely affected [8].Nagappan et al. evaluated various two-stage microalgal biofuel production employed in microalgae biofuel production by comparing the strategies Lipid, carbohydrate and hydrogen production rates were the same as single-stage cultures [9].Algal biomass contains a variety of biochemical components such as carbohydrates, lipids and proteins, which makes them viable feedstocks for biofuel production.Khoo et al. aimed to explore the recent developments in the conventional technologies for algal biofuel production, such as biochemical and chemical conversion pathways and extraction of algal biofuels.Various bioproducts from algal biomass for various potential applications [10].

Four Generations of Biofuels
Biofuels are an alternative to fossil fuels, which are derived from organic matter and therefore renewable and are renewable energy sources.Biofuels emit fewer greenhouse gases and are generally more environmentally friendly (nontoxic, non-sulfur, and biodegradable) than their fossil fuel predecessors [11].Typically, the four main types of biofuels that one can obtain using fermentation are biogas, bioethanol, biobutanol and biodiesel.
Biogas formation is a fairly simple process, and humans have been utilizing biogas for decades.It consists of four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis.During biogas production, microorganisms hydrolyze waste products into sugars, peptides and amino acids, fatty acids, and partially into acetic acid and hydrogen.Acid-producing bacteria then convert these intermediates into organic acids, the main components of which are acetic acid, carbon dioxide, and hydrogen.In the third step, acetic acid is produced, which is formed from the hydrogen and carbon dioxide produced in the previous stage.Finally, methane is produced from the products of the first three stages [12].
Liquid fuels have a higher energy density and are more advantageous for transportation and storage than gaseous fuels such as biogas.Bioethanol, with its low boiling point and high octane number, can be blended with gasoline to reduce CO2 emissions.Meanwhile, biodiesel has a similar chemical structure to regular diesel and can be blended with fossil diesel.Biobutanol is highly promising as it shows superior properties to bioethanol such as higher energy density and generally lower water content due to increased hydrophobicity [13] [14] [15] Biobutanol is less volatile and less corrosive, making it easier and safer to use and store.It can even completely replace gasoline, while ethanol can only be used as an additive.

First-generation Biofuels
First-generation biofuels are mainly bioethanol and biodiesel.Bioethanol is produced primarily by fermenting sugar from crops such as sugar cane, corn and wheat.The production process involves converting sugar to ethanol through yeast fermentation.Bioethanol is commonly used as a gasoline additive to reduce greenhouse gas emissions and increase octane rating.blends such as E10 (10% ethanol, 90% gasoline) and E85 (85% ethanol, 15% gasoline) are widely used.The most common feedstocks used to produce bioethanol are wheat, sugarcane and corn.Strains used for fermentation include Saccharomyces cerevisiae, S. stipites, and S. pombe.
Biodiesel, on the other hand, is not produced exclusively by biosynthesis, and its production step encompasses the reaction of vegetable oils or animal fats via a transesterification process (usually methanol or ethanol) and a catalyst [16][17].Common feedstocks for biodiesel production include soybean oil, canola oil, palm oil and waste cooking oil.Animal fats can also be used.Biodiesel can be blended with conventional diesel or used as a stand-alone fuel for diesel engines.Biodiesel blends such as B20 (20% biodiesel, 80% diesel) are commonly used.
Since first-generation biofuels can be used in conventional engines and fuel systems, they can be easily integrated into existing transportation and energy distribution infrastructures.The production technologies for first-generation biofuels have matured, making them commercially viable and widely adopted.Feedstocks for first-generation biofuels are also typically crops used for food and feed production.While these biofuels played an important role in the early development of the bioenergy industry, the use of food crops for biofuel production has triggered debates about ethical issues, especially the potential impact on global food prices and food security [18].Expansion of biofuel crop production may lead to land use changes that result in deforestation and habitat loss [19].

Second-generation Biofuels
Compared to first-generation biofuels, second-generation biofuels represent an advancement in biofuel technology that addresses some of the limitations of using food crops for fuel production.These biofuels are produced from non-food feedstocks, including lignocellulosic biomass, agricultural residues and other non-food plant materials.For example, bioethanol produced from lignocellulosic biomass includes materials such as wood chips, agricultural residues (corn stover, wheat straw), and specialty energy crops as feedstocks.
Unlike first-generation bioethanol, which uses sugars directly from crops, second-generation bioethanol production employs methods such as enzymatic hydrolysis or thermochemistry to break down the complex lignocellulosic structure into sugars, which are then fermented into ethanol for higher yields.Second-generation bioethanol has the potential to utilize a wider range of feedstocks [20] and reduce the impact on food production.
Biomass to Liquefaction (BTL): Biomass to Liquefaction (BTL) fuels produce syngas by gasification or pyrolysis of biomass feedstocks such as wood, agricultural residues or energy crops.The syngas is then converted to liquid fuel through processes such as Fischer-Tropsch synthesis.Syngas is a mixture of mainly CO, CO 2 and H 2 .The advantages of syngas fermentation over other second-generation methods are high feedstock flexibility as well as high energy and carbon capture rates [21].
Second-generation biofuels can be produced from a wide range of non-food feedstocks, reducing competition with food production and potentially utilizing marginal or uncultivated land [22].The use of lignocellulosic biomass allows for the extraction of more energy per unit compared to firstgeneration biofuels and contributes to overall efficiency.Second-generation biofuels have the potential to reduce lifecycle greenhouse gas (GHG) emissions compared to conventional fossil fuels and first-generation biofuels, thus contributing to environmental sustainability.
Compared to first-generation biofuels, second-generation biofuels can be more complex and technologically challenging to produce, which may affect cost competitiveness [23] [24].Despite progress, secondgeneration biofuels may still face economic challenges in terms of production costs and market competitiveness, especially when compared to low-cost fossil fuels.
Second-generation biofuels play a crucial role in the development of the bioenergy sector by providing a more sustainable alternative to traditional fossil fuels while addressing some of the limitations associated with firstgeneration biofuels.Ongoing research and innovation in this area are aimed at further improving the viability and environmental benefits of second-generation biofuels.

Third-generation Biofuels
Third-generation biofuels aim to overcome some of the challenges associated with first-and second-generation biofuels.These biofuels are typically derived from non-food sources, such as microorganisms like algae and certain nonphotosynthetic bacteria.The focus of third-generation biofuels is to maximize efficiency, reduce environmental impact and minimize competition with food production.
Third-generation biofuels are mainly derived from microalgae and cyanobacterial biomass, which can be used to naturally produce alcohols and lipids that can be converted into biodiesel or any other high-energy fuel product.More than half of the stored carbon is bound in marine biomass, especially macroalgae and seagrass.It is estimated that up to 40 million tons of dried seagrass biomass is available for biofuel production [25].Algal biofuels are produced from microalgae, which are tiny photosynthetic organisms that can be grown in a variety of water sources, including ponds, bioreactors, or photobioreactors, and algae are cultivated without the need for arable or fresh water.Algae accumulate lipids (oils) through photosynthesis, and lipids are extracted from algae and converted to biofuels through processes such as transesterification for biodiesel production or hydrotreating for renewable diesel production.Efficient algal cultivation requires a direct supply of CO 2 , which can come from industrial emission sources or atmospheric carbon capture [26].Therefore, algal biofuels may have a negative carbon footprint because they directly bind greenhouse gases in their biomass [27].
One of the most economical and versatile operations in the production of algal biofuels is algal culture, independent of location and climate.For inexpensive, high-yield products, algae are usually cultured in open ponds.Open pond reactors are much cheaper to build and operate but have some drawbacks such as high water losses due to evaporation and lack of temperature control, which reduces biomass productivity [28] [29].Algae may have higher oil yields than plants because lipids are mainly accumulated in specific parts of the plant (e.g., rapeseed), whereas in algae, each cell can contain a large amount of lipids, making the process qualitatively more efficient [30].
Lin Xihuang et al. analyzed the composition and content of 35 fatty acids in each microalgae extract by supercritical CO 2 extraction of seven oil-rich microalgae combined with boron trifluoride-methanol derivatization and GC-MS.The results showed that the oil yield of each alga increased from 54.60% to 82.16% to 75.61% to 104.46% with the addition of ethanol trainer.A total of 18 fatty acids were detected in the microalgae, and the contents of fatty acids of the C16-C18 series were above 55.97%, which are ideal substitutes for biodiesel [31].
Zhang Ze et al. developed a nickel-based metal-organic skeleton catalyst and investigated its performance in catalyzing the deoxygenation and bond-breaking of microalgae biomass and its hydrothermally extracted lipids to produce jet fuel.When the metal-organic skeleton was loaded with nickel, the conversion and selectivity of microalgae subcritical hydrothermal extracted oil to jet fuel reached 90.51% and 37.83%, respectively, which were significantly higher than that of the direct catalytic conversion of microalgae biomass [32].Certain non-photosynthetic microorganisms (e.g., bacteria and fungi) can also produce biofuels.These microorganisms can be engineered to convert various feedstocks into fuel molecules.Through metabolic engineering, these microbes can produce specific biofuel molecules, such as alcohols or hydrocarbons, from sugars or other organic compounds.This approach can utilize a variety of feedstocks and offers the potential for more efficient and scalable biofuel production.
Microorganisms such as algae grow rapidly and can produce large quantities of biomass or oil per unit of land, making them a more efficient biofuel feedstock than some first-and second-generation microorganisms.Thirdgeneration biofuels, especially those from non-food sources such as algae, do not compete directly with food crops for arable land.This reduces the potential negative impact on global food production and prices.Algae and nonphotosynthetic microorganisms can be cultivated in a variety of environments, including non-arable land and wastewater, providing flexibility in feedstock sources and reducing competition for resources.Third-generation biofuels have the potential to contribute to climate change mitigation by reducing life-cycle greenhouse gas emissions compared to traditional fossil fuels.Algal cultures for biofuel production can be combined with wastewater treatment processes to realize the dual benefits of biofuel production and wastewater purification.
Integrating third-generation biofuels into existing energy and transportation infrastructure may require modifications and investments to accommodate new production and distribution methods.Continued research is essential to optimize production processes, reduce costs and enhance the scalability of third-generation biofuel technologies.Although algal cultures can be practiced on non-arable land and in wastewater, concerns about their environmental impacts remain, including potential competition for water and land requirements.Scaling up production from laboratory or pilot scale to commercial scale may pose significant challenges, and the feasibility of large-scale third-generation biofuels remains to be fully demonstrated.
In summary, third-generation biofuels hold great promise for addressing some of the limitations of previous generations of biofuels while mitigating some of the challenges associated with previous generations of biofuels, but they also face challenges that require continued research and development.Balancing economic viability, environmental sustainability and societal concerns will be critical for the successful integration of third-generation biofuels into the broader energy landscape.

Fourth-generation Biofuels
The latest generation of biofuels, known as fourthgeneration biofuels, involves the use of genetic engineering to increase the desired traits of the organisms used in biofuel production.This applies to traits ranging from the utilization of multiple types of sugars (e.g.pentoses and hexoses) to higher lipid synthesis or increased photosynthesis and carbon fixation.Transgenic algae can provide higher product yields and a variety of other improvements compared to wild-type algae.To increase photosynthetic efficiency, the tentacle system of the algae, which is capable of absorbing a wider spectral range, can be transferred to a more suitable production organism [33].Production of ethanol as well as other fuel products such as butanol and isobutanol has been successfully achieved in a fourth-generation biofuel process focused on genetically optimized cyanobacteria [34] [35].
Using genetic engineering tools, the quantity and quality of biofuels can be controlled and enhanced, but political acceptance and support are needed for widespread adoption [36].Controversy exists regarding genetic engineering in agriculture and medicine, so similar concerns can be expected surrounding the use of biofuel production.

Conclusion
While significant progress has been made in current biofuel research, it is important to recognize certain shortcomings that deserve attention.A notable challenge lies in competition for land and resources.The cultivation of biofuel feedstocks, such as crops or algae, may compete with food production or natural ecosystems, which may lead to deforestation or higher food prices.In addition, the efficiency of the biofuel production process remains an issue.Converting biomass to biofuels usually involves energy-intensive processes that may offset the environmental benefits of using biofuels.
Another limitation is the reliance on first-generation feedstocks such as corn and sugarcane, which can present ethical and environmental dilemmas.The use of food crops for biofuel production raises questions about food security, equitable resource allocation and potential social impacts.To overcome these issues, there is a need to focus on the development of second-and third-generation biofuels that utilize non-food feedstocks and employ more sustainable production methods.
In addition, the current state of biofuels research faces technical challenges in achieving cost competitiveness with conventional fuels.The economic viability of large-scale biofuel production remains a barrier to widespread adoption.Continued research efforts should address these economic barriers and work to make biofuels more economically competitive in the energy market.
Finally, the environmental impacts of biofuel production need to be carefully considered.While biofuels are intended to reduce overall greenhouse gas emissions, certain production processes and land use changes may lead to unintended environmental consequences.Balancing the environmental benefits and drawbacks of biofuels is essential to ensure their long-term sustainability.
Addressing these drawbacks through continued research and technological innovation is critical to realizing the full potential of biofuels as a sustainable energy solution.
The government should also play an active role in promoting the application of biofuels, such as providing policy and economic support, and introducing relevant legislation to promote biofuels to gradually replace fossil fuels.
I think the main direction of biofuel technology should focus on how to use catalysts and greener means of synthesis (e.g., using supercritical CO 2 ) to reduce the cost of the production process.As well as improving catalysts to make them cheaper and more readily available.By lowering the reaction conditions to bridge the gap between reaction and actual production.