IntroductionBiofuels are one of the main substitutes for fossil fuel with benefitssuch as sustainability, eco-friendly and decent compliance.
In the last tenyears, biofuels development has been led by the government guidelines andregulations. Laws and policies have been conducted by many countries across theworld to ensure biofuels are being sustainably developed. Many biofuel relatedprojects commercialized with the support of governments. Furthermore, thisreport aims to classify the most sustainable options for producing biofuels.
Italso shows a comparison of several options based on energy return on energyinvested (EROEI), water and land required for the production as well as their effectson universal climate change.Biofuels are currently a provieder of over 1.5% of the overall transportationfuels around the world.
Also, under 2% is the percentage taken by corps grownfor biomass feedstock of the arable land world widely. The United states hascurrently overcome Brazil by becoming the largest producer and consumer ofbiofuels. Europe is remaining above China as the third largest producer,although consumption has dramatically decreased recently due to change ofpolicies in number of European countries. The following figure shows the globaltrends in biofuels production by region. 1st and 2ndgen pdf Anoverview of biofuels policies and industrialization in the major biofuelproducing countriesReview ArticleRenewable and Sustainable Energy Reviews, Volume 50, October2015, Pages 991-1003Yujie Su, Peidong Zhang, Yuqing Su (http://www.sciencedirect.
com/science/article/pii/S1877705813004414) Generations of Biofuels1st generationLiquid biofuels are becoming competitivewith petroleum fuels in terms of costs. That is due to the increase in oil costs,this has also led to a sudden interest inresearch and production of biofuels across the globe. Biodiesel,Bioethanol and Biogas are the most commonly used types of the 1stgeneration which are obtained largely from oils, seeds and lignocellulosesproduced by vegetables. Biodiesel can be used as an alternative of diesel while bioethanol is used in terms ofpetrol.
The main biodiesel feedstock are plant oils such as rapeseed, soybean,sunflower, palm and some other inedible oils like Mahua, Neem, Karanja,Jatropha, animal fats such as beef tallow. Consumed cooking oil is also being reproducedas biodiesel by undergoing refining processes. Biodiesel contains no petroleum,however, it can be combined at the desired ratio with Number two diesel fuelfor the purpose of being consumed bydiesel engines with slight or no adaptation. The transesterification process isused to produced Fuel grade biodiesels. On the other hand, bioethanol isproduced commonly from the fermentation of many feedstock, for instance,sugarcane, corn, maize, wheat as well as potatoes. Moreover, biogas is producedby cleaning and purifying the raw gases produced by organic wastes of animalsin order to produce a reliable methane-rich fuel. 1st generation ethanol technologiesAs mentioned, the main feedstock used to produce ethanol aresucrose as well as starch. For ethanol production using sucrose, a mechanicalequipment is used to press the juices from the cooked sugarcane or sugar beetcorps followed by fractionation.
The next step is that yeast cells are used toabsorb the sucrose and ferment the hexoses. The final step is that the ethanolis recovered by distillation. For starch, the starch crops are hydrolysed intoglucose prior to the conversion of the carbohydrates by yeast cells intoethanol. The next step includes milling the grains of wheat, corn or barley beforeundergoing liquefaction as well as fractionation processes. Also, acidic orenzymatic hydrolysis occurs prior to fermentation of the resulting hexoses.This route ensures high efficiency of the production, however, it uses moreenergy which results of more CO2 emissions into the air which varies dependingon the energy sources used.
On the other hand, the route that uses sucroseconsumes less energy which means less CO2 emissions.1st and 2nd biofuel gen 1stgeneration biodiesel technologiesBiodiesel is produced using thetransesterification method. The process aims to extract oil from oleaginousplants and convert vegetable oil into fuel which can be consumed by the enginesdirectly. The direct vegetable oils could be used just as a fuel in themodified engines. The transesterification uses enzymatic catalyzers or acids,alkaline and ethanol or methanol and produces glycerin and fatty acids as aresidue. The process is summarised in the followingsteps: 1.
To mixthe alcohol with the catalyst, usually a strong base, for instance, NaOH or KOHand wait for the reaction. 2. The transesterificationbegins after The combined alcohol and catalyst are reacted with the fatty acid.3.
The Glycerolis then formed and should be separated from the biodiesel.4. Alcoholshould be detached and recycled from the glycerol and biodiesel.
5. Water isadded to both the biodiesel and glycerol in order to separate them. 6.
The wateris evaporated out of the biodiesel and acid is added to the glycerol in orderto deliver neutralized glycerol.Renewable and Sustainable Energy Reviews 73 (2017) 205–2141stgeneration biogas technologiesIt is claimed that biogas production process has higher efficiencyin terms of energy gain amongst the technologies of converting biomass tofuels, the reason is that an aerobicdigestion can utilise carbohydrate, protein and fat in the feedstock to producebiogas .Furthermore, the energy invested for an aerobic digestion technologywas found significantly high compared to other thermo-chemical and biological conversionprocedures, this includes the production of ethanol from cellulose.
An aerobicdigestion is a process that includes the degradation of biomass by bacteria aswell as methanogenic organisms in the absence of oxygen. The process alsoinvolves aerobic digesters to transform some of the resulted products by the degradationinto carbon dioxide and methane. Anaerobic digestion consists of four groups ofchemical reactions. The reactions are as follows: hydrolysis, acidogenesis,acetogenesis and methanogenesis. However, since amino and fatty acids areproduced by hydrolysis, it is believed that acidogenesis occurs as a part ofthe hydrolysis group.
Hydrolysis occurs where proteins, fats and carbohydratesare separated into smaller molecules, for instance: amino acids, fatty acidsand simple sugars. On the other hand, methanogens use some of the hydrolysisproducts in the anaerobic digestion process. These products are thentransformed in acetogenesis before they are made available as nutrients for themethanogenic organisms. Energy is generated byThe organisms using theirnutrients while converting them to methane. Also, while organisms are absorbingthe nutrients in the biomass, the formation of the acetate ion occurs. Theacetogens are fermentative bacteria which produce an acidic atmosphere, ammoniumsalts, carbon dioxide as well as hydrogen in the digestive environment.Methanogenesis is the final reaction of anaerobic digestion which produces methane from the final product with thesupport of some products from hydrolysis. Technologies and developments of third generation biofuelproduction 2nd Generation of biofuelsUnlike first generation,second generation is more sustainable in terms of biomass used, which meansless CO2 emissions are formed during the production process.
This generation isfully dependent on affordable and abundant inedible resources produced by vegetation.However, although the second generation production is more sustainable and hasless effects on environment it still lacks cost efficiency, that’s due someissues surrounding the production process. Plant biomass are abundant andunderutilised biological resources which can be used efficiently in the fuelproductions.
As it is most basic, electricity and heat can be generated by theburning process of plant biomass. However, plant biomass can also be aneffective source for many types of biofuel productions. moreover, efforts toproduce biofuels using wood shaving and straw as a sugar feed stock are beingattempted . However, biofuel produced based on agricultural feedstock couldonly fulfill a proportion of the growing demand for liquid fuels.
2nd generation technologiesThe second generation biofuel production processes are relied oncellulose hydrolysis followed by sugar fermentation. The biological matters canbe very useful for production of syngas (synthesis gas) by gasificationprocess. This syngas can be converted into liquid biofuels with the help ofseveral catalytic processes. In addition, the anaerobic digestion process isused to produce methane and natural gas. The process includes digestion ofagriculture waste or crops.Compared to the first generation,the second generation feedstock are treated differently, for instance,lignocellulose feedstock, which requires a number of processing steps beforebeing fermented into ethanol as in first generation. The technologies used inthe processing of biofuels second generation are as following: ThermochemicalConversionThe first technology is gasification,This method has been used broadly in fossil fuels processing. Second generationgasification tools have been considerably improved to suit the variances inbiomass stock.
Wood, black and brown liquor as well as other feedstock are usedin this process. Throughout the gasification process, carbon-based resourcesare transformed to carbon monoxide, hydrogen, in addition to carbon dioxide.This process is unlike combustion in that oxygen is limited. The resulted gasis known as synthesis gas or syngas which is used to generate heat as well asenergy.
Pyrolysis (bio-oil)Similarly to gasification, fossilfuels have been produced using this process for years. Moreover, wood, a numberof energy crops as well as an inert gas such as halogen are used throughout theprocess with no oxygen involved. The fuel is usually transformed into twoproducts which are tars and char.torrefactionThe third reaction is known as torrefaction,which is comparable to pyrolysis, however, no high temperatures are required inthis reaction. The procedure tends to produce improved fuels for additional usein gasification or combustion. Torrefaction is often used to convert biomassfeedstock into an easy to transport and store form.Biochemical Conversionunique or genetically modifiedbacteria is used in the fermentation process to deal with second generation’sfeedstock such as landfill gas and municipal waste.
3rd generation of biofuelsThe current production process from algaeis classified as third generation of biofuels. Algae can produce oil which canbe further refined to diesel and some products of gasoline easily. The maindisadvantage of this process is that the biofuel produced by the thirdgeneration have less stability than the previous two processes. 3rdgeneration technologiesMicroalgal biodieselOne of the most efficient methods toproduce microalgal biofuel isthrough transesterification of the algaloils to produce biodiesel. Biodiesel production includes mixing triglycerides,methanol, and catalyst (may be alkali such as potassium hydroxide or acid) in acontrolled reaction chamber in order to stimulate transesterification. Theprimary product is positioned in an extractor to remove the glycerine from theproduct.
While the extra methanol is recovered from the methyl esters throughevaporation. The final biodiesel is washed with water, pH neutralised, and thendried. The remaining biomass from the productionprocesses, lipidextractedmicroalgal biomass residues (LMBRs), hashigh concentrations of carbohydratesand proteins. Therefore, LMBRs are potentialsubstrates for darkfermentation to produce hydrogen, that servesan important role in the sustainable growth of microalgal biodiesel production.
Alternatively, the production of methane usingthe anaerobic digestionof microalgal biomass remains of thebiodiesel production processcan meet some energy necessities of the processof converting primary biomass to fuel. Otherwise, the remaining biomass wouldbe considered as waste with its disposal cost increasing the total costs forbiodiesel production from microalgae. Thus, the energy extraction from theresidual biomass can be used as a method to maximise the microalgal energyproduction, and reduce the total process expenses as well as wastes. It hasalso been suggested that thenon-lipid portion of the algal biomass maybe an alternative for electricity generation.Renewable and Sustainable Energy Reviews Microalgal bioethanolFermentation is theprocess of obtaining gases and ethanol from sugar along with yeast catalyst.
Thefermentation process is widely used bioethanol production by sugar as well asstarch crops as in the first and the second generations. Fermentation method isalso applicable by third generation’s microalgae. Microalgae contain largeamounts of starch, that can be transformed into sugar. The production processescan be presented as follows: 1. starch is extracted from the microalgae cellswith the support of an enzyme or mechanical machine.
2. when the microalgae cells start degrading,saccharomycess cerevisiae is added into the microalgae feedstock forfermentation which leads to the production of ethanol and carbon dioxide. https://www.diva-portal.org/smash/get/diva2:665095/FULLTEXT01.pdf EIOER enegy investment over energy returnThe energy investedover the energy returned for biofuels from larger to lower is as follows:Sugar Cane Ethanolhas the largest EROEI which is from 8.3:1 to 10.2:1Switch GrassCellulosic Ethanol with EROEI of 4:1Corn Biodiesel whichhas EROEI of 3:1Corn Ethanol with EROEIof 1.
2:1Compared to othersources of energy, biofuels have larger EIOER than some of them such ashydrogen that has an EROEI of 0.5:1. However, other sources have a slightlylarger EIOER, for instance: Coal and natural gas with EROEI of up to 10:1each,and Oil Conventional EROEI that is currently estimated average 25:1, however itis declining.
Land requirementsOne of the mainissues surrounding the production of biofuels is their requirement for greatquantities of land. In fact, biofuels require more land than petroleum fuels.According to McDonald, biofuels willrequire approximately 100 to 200 times more land per unit of area than fossilfuels by 2030. This means energy demands and food resources cannot be met atthe same time.
This issue can be solved by growing inedible plants to be usedas feedstock such as in the second generation of biofuels. Moreover, producingenergy dense feedstock as in the biofuels third generation can help reduce thequantity of land required by biofuel productions, that is due to not competing forland or clean water with agriculture or forestry. In fact, non-arable land andwater are suitable for third generation feedstock, for instance, they can belocated in the desert where large quantities of carbon dioxide are produced.Water requirementsBoth, first andsecond generation feedstock growing as well as their production require water.This means large amounts of water are required to produce fuel from biologicalfeedstock.
Therefore, biofuel productions need to decrease the water usage inorder to remain sustainable. The limits in pure water supplies and thepopulation growth which leads to higher energy demands are the main challengesfacing the sustainability of biofuel production. On the other hand, some secondgeneration biofuels such as, cellulose feedstock which use small amounts ofwater, however, they can only be obtained on small scale which is not enoughfor meeting the current fuel demands. Third generationbiofuels are no better, the level of water used in the feedstock growing andthe production of Algae biofuels is not sustainable, for instance, around 123billion liters of water are required to produce 5% of transportation fuel inthe United states. Biofuel impacts onclimate changeHundreds of analysishave been performed over the last 20 years regarding the CO2 emissions from thelife cycle of biofuels. The analysis state that first generation biofuels requirefertilizer which produces more N2O, while less fertilizer is used by secondgeneration, which means less N2O is produced. Also, the second generationproduction use non fossil materials hence they do not emit fossil CO2, thismeans that their CO2 emissions are lower than first generation as well aspetroleum fuels. The main two impacts of biofuel production on climate changeare the biogeophysical impacts and the nitrogen cycle impacts.
biogeophysicalimpactsthe change in landuse can lead to changes in the physical parameters of the vegetation as well asevapotranspiration rates. These changes can cause direct effects on theenergy’s absorption and disposition at the surface of the earth, which affectsthe regional as well as the local temperatures. Furthermore, the changes affectthe hydrologic cycle as well as climate change in many ways, for instance, viacloud formation and the forcing of water evaporation using direct radiationswhich affect the carbon sequestration and the growth of the vegetation.
The nitrogen cycleThe nitrogenproduced by fuels fertilizer or the combustion, can affect sides of the universalnitrogen cycle, that has a wide variety of environmental impacts, including coastaland lakes eutrophication, fertilisation of global ecosystems, water and landacidification, biodiversity changes, respiratory disease in humans, crops canbe damaged by the ozone, and it can also cause changes to global climate. ConclusionIn conclusion,productions of the first generation are slightly larger than the secondgeneration although the second generation uses inedible and less expensivefeedstock. however, more industrial developments are being built around thesecond generation. Moreover, the third generation is the least developedamongst the three generations due to being in the early stages of scale up andcommercialization, though, it offers the same advantages as the first and thesecond generations. Furthermore, the third generation can produce larger yields/ acre than other biofuels. In general, biofuels require larger quantities ofland as well as huge amounts of water to remain operative. In fact, they usemore land and water than other fuels which technically makes them not sustainable.
Overall, biofuels must do more efforts in terms of their sustainability basedon feedstock options, water, land use as well as their effects on climatechange in order to be able to compete with other energy sources.