In the quest for finding the appropriate biofuel for the future – which is both sustainable and cheap – it appears that researchers have found a new technology to turn cellulose into bioethanol. The resource for cellulose also raises questions, however, Arundo with its highest bioethanol yield provides all the answers needed.
Belgian researchers with the collaboration of the Hungarian Academy of Sciences (MTA) Energy Research Center (EC) have developed an innovative biofuel production technology based on cellulose from corn and vegetable oils, which can be fully integrated into existing oil refining processes.
Cellulose and hemicelluloses, main substrates for second generation bioethanol making are the most abundant carbohydrates in nature and their transformation to ethanol could have several benefits, including reductions in greenhouse gas emissions and fossil fuels dependence.
What is bioethanol?
Bioethanol is a completely renewable source of energy, meaning it provides an infinite supply of fuel. It does not damage the ozone layer as much as conventional petrol, since the exhaust gas is generally cleaner due to the higher percentage of combustion and the emission is less reactive with sunlight. If bioethanol is blended with petrol, it secures fuel supply by extending lifespan of diminishing oil sources. Events of oil spills have had devastating effects on wildlife and the general environment. However, bioethanol is biodegradable and non-toxic, unlike crude oil based fuels.
How could bioethanol replace gasoline?
Bioethanol is a first-generation biofuel produced by fermentation which is subsequently blended with fossil-based gasoline. Researchers produced 10 percent bio-gasoline from cellulose in a two-phase (aqueous-organic) catalytic process, using crude petroleum gas as an organic phase. All in all, 11-18% of carbonaceous carbon deposits have been detected, corresponding to the 10% biofuel content requirement. It has been revealed, that the octane number of the new biofuel is still unsatisfactory as of now, so in an additional isomerization step, the octane number will be increased to 80, so the biofuel will be at the value of full-fledged gasoline. Due to the full integration of the refinery process, the method can be seamlessly integrated into existing infrastructures. In addition, it is competitive with other “primarily-lignin” technologies that use raw lignocellulos as the starting material, so not only can they convert cellulose into biofuel, but also the other two components of lignocellulose: hemicellulose and lignin.
Arundo donax: the feedstock for bioethanol
Several studies have been carried out to assess the feasibility of using giant reed (Arundo donax) for bioethanol production via pre-treatment, enzymatic hydrolysis, and fermentation.
Arundo donax versus woody feedstock
In Bura’s (2012) research, sugar and ethanol yields from giant reed were compared with those from hybrid poplar, a well-known woody biomass feedstock.
Arundo donax and hybrid poplar are characterized by different types of hemicellulose and different amount of ethanol yield. It has been suggested that arabinoxylan is the major hemicellulose found in giant reed, while the most abundant hemicellulose constituent of hybrid poplar is glucuronoxylan.
The results of the study [Figure 1] showed that hybrid poplar provided 0.205 L ethanol/kg raw material. The lower overall ethanol yields for giant reed were due to the low glucan recovery after pre-treatment and also to lower hexose content in Arundo donax compared to hybrid poplar, because the final ethanol yields were based on the conversion of only six carbon sugars (glucose, mannose, and galactose) to ethanol.
However, giant reed is still a superior feedstock, regardless of its slightly lower ethanol yield. The higher biomass yields per hectare per year for giant reed (from 29 to 46 t/ha/year) compared with hybrid poplar (from 8 to 22 t/ha/year) will result in approximately twice the ethanol produced per area of land under cultivation. Excellent ethanol yields and high biomass productivity, along with low cultivation (nutrient) demands during growth and minimum biomass loss during storage, make giant reed an outstanding feedstock for the future bio refinery.
Arundo donax: the best candidate for bioethanol production?
Clearly, fuel grade bioethanol can be manufactured from a number of lignocellulosic biomass sources, such as corn, sugarcane or switchgrass. Still, the comparative bioethanol yield (L/ha) of various biomasses that may vary according to the cultivation and processing technologies – and even various climates may have an impact. A Norwegian study revealed that Arundo donax produced 299 litres of ethanol per tonne of dry matter biomass, in a process time of less than 24 hours.
This equates to 11,000 litres/hectare of bioethanol from Arundo from 40 tonnes/hectare/year.
Yields from other species were:
- 4,400 L/ha from corn kernels (Zea mays)
- 4,600 L/ha from switch grass (Panicum virgatum)
- 8,800 L/ha from sugarcane (Saccharum officinarum)
High yielding, non-food crop and relatively high carbohydrate composition makes giant reed a promising feedstock for an ethanol bio refinery concept. Dilute oxalic acid pre-treatment can remove, at high combined severities, hemicelluloses and prepare the solid residue for enzymatic hydrolysis and simultaneous saccharification and fermentation. Xylose and arabinose, released from hemicellulose hydrolysis, were found as monomers in almost all conditions.
High yields of bioethanol are further backed and thus simplified into a formula seen below:
4 tons of Arundo = 1 ton of cellulose ethanol
1 tonne of Arundo = 330 liters of cellulose ethanol.
Overall, Arundo has prevailed as one of the most competitive resource for bioethanol, not only because of its high cellulose content but also for its high biomass yielding per hectare (which can be achieved with low cost and low input production). Regardless of comparisons with woody or herbaceous plants, giant reed will almost always compensate for any cellulose deficit with its bioethanol output per hectare. This advantage can be further assessed and elevated by calculating the cultivation costs of various plants per plantation – a cost efficient attribute Arundo excels in.
To find out more about Arundo as a supply for bioethanol, visit our website or email us at info@arundobioenergy.com.
