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Get Support. Feedback Please let us know what you think of our products and services. Give Feedback. Get Information. Fossil fuels have been a major contributor to greenhouse gases, the amounts of which could be reduced if biofuels such as bioethanol and biodiesel were used for transportation. One of the most promising biofuels is ethyl alcohol. In , the world production of ethanol was The two major bio-source materials used for ethanol production are corn and sugarcane. For 1st generation biofuels, sugarcane and corn feedstocks are not able to fulfill the current demand for alcohol.
Non-edible lignocellulosic biomass is an alternative bio-source for creating 2nd generation biofuels and algae biomass for 3rd and 4th generation biofuels. This review discusses the significance of biomass for the different generations of biofuels, and biochemical and thermochemical processes, and the significance of biorefinery products. Introduction The development of human society and the upsurge in population growth have generated a considerable demand for food and energy. In recent times, the world population has depended heavily on fossil fuels and their derivatives.
The intensive use of fossil fuels and their derivatives has given rise to greenhouse gases GHG , such as methane, carbon dioxide, and nitrous oxide [ 1 , 2 ]. Currently, the primary source of energy for the transport and production of materials in the world is oil.
Approximately 84 million barrels of oil are used per day and this is projected to increase to about million barrels by It is evident that plant-based waste materials lignocellulosic biomass have the potential to be used instead of fossil resources as feedstocks for the production of biofuels and chemicals [ 5 ]. The use of biomass and bioenergy can significantly reduce greenhouse gas emissions. The carbon dioxide given off when is the plants are burned is counterbalanced by the amount absorbed when they were grown [ 6 ]. Thus, bioenergy produced from biomass is an essential substitute for fossil energy and has attracted widespread attention around the world.
Climate change, energy security and food security are the most pressing issues that are driving the search for a substitute feedstock for the production of biofuels, biochemicals, and bioenergy at both regional and national levels. These issues can only be solved by specific governmental policies. However, the challenge of drafting policies is that if they are designed to target one issue, they may be detrimental to another [ 8 ]. Conflicts can be resolved by using solar, wind and hydro power as renewable sources for electricity and heat, and lignocellulosic biomass for transportation fuels and chemicals, since it is the only carbon-rich material source available on the earth other than fossils [ 9 ].
However, the sustainability of the biomass supply is a critical issue, particularly because fertile land needs to be used to cultivate energy crops rather than food. According to the IEA [ 10 ], bioenergy usage can be divided into various categories: 1 traditional use; 2 modern building heat; 3 electricity and co-generation; 4 transport; 5 industry—heat; 6 commercial heat and 7 other uses.
In this regard, liquid biofuel could be used to decarbonize the transport sector, and thus reduce GHG. If a solution is to be found to the over-reliance on oil and climate change mitigated, the transport and chemical sectors need to be completely restructured. It has been acknowledged that there is no single-window solution to these problems and that combined actions aimed at changes in public behavior, the modernization and expansion of public transport, and advances in vehicular technologies are much desired [ 11 ].
This paper first gives an overview of the feedstock used in biofuel production and then goes on to discuss the emerging biorefinery of the two primary biofuels bioethanol and biodiesel with their accompanying biochemicals. For the sustainability of biofuel production, the emerging concept of biorefinery is linked to the idea of a holistic circular economy and discussed in the context of the EU, India and the USA. In this regard, critical analysis and evaluation focuses on: i the supply of lignocellulosic feedstocks and ii the markets for intermediate or end-products.
The progress made in these indicators will assist in transitioning from a petroleum-based economy to a circular—economy. Biomass is composed of cellulose, hemicellulose, lignin and a small fraction of inorganic matter. The relative biochemical composition and the inorganic components vary in each plant. The composition of the pyrolyzed product largely depends on these compositional variations in biomass species. The degree of biomass decomposition and recalcitrance during pyrolysis and hydrolysis, respectively, depends on its composition.
The ease with which the three significant components cellulose, hemicellulose and lignin decompose is attributed to their structural stability [ 12 ]. Pyrolysis of cellulose or hemicellulose produces greater oil yields than lignin.
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Yang et al. Maximum weight loss was observed for cellulose The temperature at which oil yield is maximum clearly depends on the biomass components. Lignin also contributes to the large portion of char residue during the pyrolysis of lignocellulose biomass. Other authors have reported similar observations for the pyrolysis of cellulose, lignin, bark, rice husk, and corn stalk [ 14 ].
The structural differences among significant biomass components cause compositional variability in the pyrolysis products [ 14 ]. The reactivity of biomass species during pyrolysis is also affected by the presence of oxygen contents and heteroatoms. In general, the greater the oxygen and heteroatom content, the better the reactivity of biomass is, although some studies have reported that oxygen content has a relatively small effect on the reactivity of biomass during pyrolysis [ 15 ]. The biochemical composition of biomass feedstock affects the efficiency of biofuel production and energy output.
This is a major challenge for using biorefinery processes [ 16 , 17 ]. According to the International Energy Agency biomass is defined as any organic matter that comes from biogenic sources and is available on a renewable basis.
This includes animals and plants sourced by wood and agricultural crops, and organic waste from municipal and industrial sectors. Biomass resources can be classified according to their origin see Table 1. Various other crops have been scientifically tested and proposed for commercial energy farming. Ideal energy crops should have the following characteristics: i cultivation requires low energy input; ii yields must be high; iii processing requires low energy input; iv cellulose and hemicellulose content is high [ 18 ].
The biochemical content is dependent on local climate and soil conditions. Despite all the excitement associated with biofuel usage, the sustainability of biomass is critical. Issues such as 1 national, regional and local environmental policies; 2 types of bioenergy, feedstocks and processing technologies available in specific areas, and 3 the logistics of biomass transport to the refinery site can hinder the sustainability of biofuel production.
The task of evaluating whether a bioenergy production process or the biomass feedstock used is sustainable is not inconsequential, especially when the above-mentioned concerns about the sustainability of biofuel production are considered. It cannot be claimed that the biomass resources reviewed in this study are sustainable in all aspects, as the final impacts of their use will depend on the local conditions of cultivation, harvest, transport, storage and, eventually, conversion technologies. However, all the assessed biomass resources have a low environmental impact [ 19 ].
In addition, they are residues from agricultural production, and are potentially sustainable when handled efficiently and with respect for nature and the environment.
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First-generation biofuel production is heavily dependent on energy crops such as maize corn and sugarcane. Maize or corn Zea mays is a grain that belongs to the Grimanaceae family [ 22 ]. The corn stover cobs, stalks, and leaves residues obtained from maize cultivation have various advantages over other energy crops [ 23 ]. The corn stover contains cellulose and hemicellulose which can be pretreated with hydrolysis techniques.
Sugarcane Saccharum is a semi-perennial plant C6 group belonging to the Poaceae family grass family , typical of tropical and subtropical countries [ 24 ]. Unlike starchy biomass, the production of bioethanol from sucrose-based feedstocks does not require a saccharification step, as the sugars are readily available, which makes the production process simpler [ 25 ].
Global biofuel production is on the rise.
leondumoulin.nl/language/health/raptured-by-the-tentacle-alien.php Europe is the leader in biodiesel production while the USA is the leading producer of ethanol see Figure 1. Ethanol and biodiesel are the two major fuels with the potential to replace gasoline and diesel, the major contributors to GHGs and particulate matter, respectively. Biohydrogen is also attracting some attention because of its eco-friendly by-product, H 2 O. In , The USA depends heavily on corn for bioethanol production while Brazil tends to use sugar cane. While this seems to be a sign of progress, there are considerable reservations about the source of the starting material used in the production because it can have a negative impact on food security and biodiversity.
The process of ethanol production depends on the raw materials used. Ethanol production can be simplified into three steps: 1 acquire or generate fermentable sugars; 2 convert sugars into ethanol by fermentation and 3 separate and purify, usually by distillation-rectification-dehydration [ 26 ] The simplified process for converting corn and sugarcane to ethanol shown in Figure 3 can be modified for different feedstocks and conversion technologies.
Using a pretreatment, sugars are extracted or made more accessible if corn is the feedstock for further fermentation processes, during which the sugars available depend on the feedstock and pretreatment used. Fermentation can be carried out in any one of three different methods batch, fed-batch or continuous.
In batch fermentation, the hydrolysate liquid fraction containing sugar, yeasts, nutrients and other ingredients is added to the medium at the beginning of the fermentation. In fed-batch fermentation, one or more inputs are added as fermentation progresses. In continuous fermentations, ingredients are constantly injected at a specific flow rate and products are removed from the fermentation reactors.
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The efficiency of the conversion process can be enhanced if the cell density is increased by immobilizing the yeast [ 27 ]. The vinasse obtained from the distillation column can be volatilized to generate co-products see Figure 3. The chemical and physical make up of corn makes ethanol production from corn more complex than from sugarcane sucrose is readily available.
The volume of ethanol produced from corn is five times higher per ton of feedstock while the productivity of ethanol produced from sugar cane is greater per hectare. Biodiesel is produced from raw vegetable oils derived from soybean, canola, palm oil or sunflower, as well as animal fats and used cooking oil, which are also known as 1st generation biodiesel. Biodiesel has become more attractive recently because of its environmental benefits and the fact that it is derived from renewable resources. Burning biodiesel does not increase current net atmospheric levels of CO 2 , a greenhouse gas [ 29 ].
It is safely biodegradable, offers scope for recycling waste oils, and produces less air pollution than fossil diesel [ 30 ]. Biodiesel is simple to manufacture and provides excellent engine performance. It has better lubricating properties than petrodiesel for example, higher density, greater cetane number, low sulfur emission, and low flash point , which makes it the safest fuel to handle [ 31 ]. Renewable biodiesel is produced mainly from vegetable oils and animal fats, which are converted into fatty acid methyl esters.