Algae, biodiesel and challenges

7/29/2019 Algae, biodiesel and challenges

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Algae

fastest-growing plants

competitive as a source for biofuel

can be grown almost anywhere, even on sewage or salt water, and

does not requirefertile land or food crops, and processing requires

less energy than the algae provides

about 50% of their weight is oil-algae contain anywhere between 2%and 40% of lipids/oils by weight

trend is towards using alternate energy sources-Reducing the use of fossilfuels, reduce the amount of carbon dioxide and other pollutantsproduced

clean and environmentally safe

extensiveuse of vegetable oils may cause other significant problemssuch as starvation indeveloping countries.

algae are among the most photosyntheticallyefficient plants on earth-very efficient solarenergy converters

They are categorized intofour main classes: diatoms, green algae, blue-green algae andgoldenalgae. There are two main populations of algae: filamentous andphytoplankton algae.These two species, in particular phytoplankton,increase in numbers rapidly to form algaeblooms.

Industrial reactors-openponds, photobioreactors and closed systems.Photobioreactors aredifferent types of tanks or closed systems in which algae are cultivated.Open pond systems are shallow ponds in which algae are cultivated.

closed systems, - capital intensive-only when a fine chemical is to be produced-because ofthe infrastructure costs

yield of oilfrom algae is over 200 times the yield from the best-performingplant/vegetableoils.potential to yield19,00057,000 l of microalgal oil per acre per year

production of microalgal biodiesel requires large quantitiesof algal biomass.

none of the projected algae and oilyields has been achieved

require largequantities of nitrogen fertilizer and water, plus significant fossilenergy inputs forthe functioning system

Harvesting the algaefrom tanks and separating the oil from the algae are difficult andenergy

intensive processes


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Algae generallyproduce a lot of polyunsaturates, which may present a stabilityproblem sincehigher levels of polyunsaturated fatty acids tendto decrease the stability of biodiesel.However polyunsaturates alsohave much lower melting points than monounsaturates orsaturates;thus algal biodiesel should have much better cold weatherproperties than manyother bio-oils

higher heating value of petroleum diesel is 42.7 MJ/kg

biodiesel derived from seed oils, such as rapeseed or soybeanproduces, 39.5 MJ/kg, whilebiomass derived from algaeyields 41 MJ/kg

Soybean can only produce about 450 l of oil perhectare. Canola can produce 1200 l perhectare, and palm can produce6000 l. Now, compare that to algae which can yield 90,000 lper hectare

Microalgalbiomass production step that requires light, carbon dioxide,water and inorganicnutrients. The latter are mainly nitrates, phosphates,iron and some trace elements.Optimaltemperature- between 293 and 303 K

three well-known methods to extract the oil from algae:(1) Expeller/Press,(2) solvent extraction with hexane(3)supercritical fluid extraction.

A simple process is to use a press toextract a large percentage (7075%) of the oils out ofalgae. Algaloil can be extracted using chemicals- most popular chemical -hexane, which is

relatively inexpensive.Supercritical fluid extraction is far more efficient than traditionalsolventseparation methods. Supercritical fluids are selective, thusproviding the high purity andproduct concentrations This canextract almost 100% of the oils all by itself. In thesupercritical fluidcarbon dioxide (CO2) extraction, CO2 is liquefied under pressureand heatedto the point that it has the properties of both a liquidand gas.

After oil extraction from algae, the remaining biomass fractioncan be used as a high proteinfeed for livestock. This givesfurther value to the process and reduces waste.


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conventional solvent extraction technology, the recovery of green crude from microalgaewhich generally requires multiple solidliquid separation steps is still a challenging phase ofthe algal green crude production process. The processes involved include drying, celldisruption, solvent extraction and evaporation; which are highly energy intensive andenvironmental damaging

Challengesbroad commercialization of biofuel production from microalgae has been hampered due to

the high costs involved .The production of biodiesel from microalgae worldwide is still at thepilot-scale.Several crucial research gaps remain that must be overcome in order to achieve a full-scaleoperation including the following: (1) a robust selection method and evaluation system foridentifying algal strains that are suited to a large-scale culture system; (2) investigations intothe mechanism and regulation ofCO2 fixation, lipid synthesis, and lipid accumulation inmicroalgae;(3) optimization and scale-up methods for the development of photobioreactors that arehighly efficient and cost-effective;(4) process optimization and scale-up technology for culturing microalgae at a large-scale;(5) economical technologies for cell harvesting, oil extraction, and biofuel production;(6) exploitation of the components after oil extraction;(7) an economical and environmental evaluation for the process of biofuel production frommicroalgae; and(8) a technical route and research platform for a highly efficient and cost-effectivecommercialization of microalgal biofuel production


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Algae, biodiesel and challenges