In recent years, use of fossil fuel as the primary source of energy has caused many problems such as the energy crisis, environmental pollution, and climate change. Such environmental issues are receiving a great deal of attention across the globe. Current environmental issues and resource sustainability are driving the global development of renewable energy.
Biodiesel is used worldwide and has become increasingly popular as less pollution and more sustainable solution. The annual consumption of biodiesel was 33.5 billion liters in 2016. The trend shows a 14% increase in demand by 2020. Unfortunately, high cost is still a main barrier hindering biodiesel production at commercial scale.
Biodiesel as a replacement of petroleum-based diesel can have much lower emissions. A sketch figure gives 86% reduction in greenhouse gases, 47% less in particulate matter, and 67% cut in hydrocarbon emission. Biodiesel is biodegradable and provides excellent lubricity. Moreover, it is derived from remarkable plant oils, animal fats, and used cooking oils.
The diagram below shows the conversion of plant oil or animal fat into biodiesel of fatty acid esters. Converting oil or fat into biodiesel involves two processes, regardless of the type of catalyst used: transesterification and esterification. When the feedstock is triglyceride/oil/fat, the process is call a transesterification reaction. When the feedstock is fatty acid, the process is called an esterification reaction. Biodiesel is also commonly referred to as fatty acid methyl ester (FAME) since the most common alcohol reactant is methanol.
Currently, there are two established methods for biodiesel production: chemical and enzymatic approaches. Problems persist for both the chemical and conventional enzymatic approaches.
Challenges in Chemical Approach
Challenges in Conventional Enzymatic Biodiesel Process
Compared to chemical approach, enzymatic reaction is more advantageous because of no saponification, easier purification, no wastewater generation, mild reaction condition, and higher product quality. However, current enzymatic biodiesel can not overcome lipase poison problem and result in some inefficiency.
High Operating Cost
High operating cost is related to high lipase consumption. This process needs high consumption of lipase due to lipase deactivation by glycerol droplet that shorten its lifespan. Furthermore, the residual fatty acids, mono-, and diglycerides need to be treated in another way.
Lengthy Reaction Time
The use of conventional enzymatic process will lead to a long reaction time. Typical reaction time for enzyme transesterification is 12 - 24 hours or even longer.
The cost of feedstocks represents 70- 85 % of production cost of biodiesel. Nowadays the use of feedstock from nonedible and waste are the cheapest alternative. However, the utilization chemical approach won't be efficient due to the high FFA in such kind of feedstock. On the other hand, the utilization of conventional enzymatic will incur high lipase cost or just be a pretreatment for alkaline process.
A new enzymatic transesterification process (ET Process®, patented), has been developed to address prevailing concerns about biodiesel production technology. This technology would allow flexible feedstock, lower lipase consumption, shorter reaction time, high value-added byproducts, no wastewater, and no hazardous waste.