12 Aug 2019
To celebrate International Biodiesel Day on 10 August we explore some recent developments in the area, including improved production methods that could help in making the organically-sourced fuel more readily available in the future.
Biodiesel is a clean-burning, alternative renewable fuel. Biodegradable and obtained from animal fat or vegetable oils, it is conventionally produced by the transesterification of triglycerides into esters in the presence of basic homogeneous catalysts.
Biodiesel can be used in most diesel engines and it emits less air pollutants and greenhouse gases than other fuels. Biodiesel use, however, is limited due to it being more expensive than other petroleum-based fuels. A contributor to this elevated cost is because the most common source of oil is the soybean, which is only 20% oil. Other limiting factors is that it takes a vast amount of energy to produce and the reluctance to use farmland to produce fuel instead of food. Finding more efficient ways to produce biodiesel could help to increase uptake of this renewable fuel.
Recent developments in SCI’s Journal of Chemical Technology and Biotechnology on the topic of biodiesel show how the production techniques of biodiesel is advancing.
Oil-bearing seeds as a source
The Jatropha plant offers an interesting promising source of biodiesel. It is highly resistant to drought and can be grown even in abandoned or fallowed agricultural land. The oil content within the seeds is 35–40%, and within the kernel is 50–60%. The downside is that Jatropha oil suffers from high free fatty acid (FFA) content. Oils that contain high FFA content cannot be transesterified directly with an alkaline catalyst as the FFA reacts with the catalyst and produces soap. For feedstock with high FFA, esterification reactions are considered a promising alternative.
A study published in November 2018 explored utilizing Jatropha seeds (as opposed to oil) in situ with ultrasound-assisted esterification. The resultant biodiesel synthesis was successful with considerable yield, proving that this novel technique could be a feasible biodiesel production method for solid oil-bearing seeds in the future.
A promising catalyst
In high FFA-containing feedstock esterification allows for reduced costs, increased sustainability in biodiesel production and it minimizes natural resource consumption.
A recent study set out to investigate the esterification reaction from oleic acid with methyl acetate (MeA) catalyzed by niobium phosphate to produce methyl esters. This catalyst has an amorphous structure and large surface area.
This study showed that Niobium phosphate can be considered as a promising heterogeneous catalyst for biodiesel synthesis.
Conversion of waste cooking oils to biodiesel
The increasing value of pure vegetable oils has made the use of waste cooking oils an attractive alternative feedstock for biodiesel production but the presence of FFAs in the waste significantly reduces efficiency of the conversion.
The authors of a study published in 2017, developed and introduced a novel low-temperature process using a mixed ionic liquid solvent system with dual extraction and catalytic functions for the improved conversion of waste vegetable fats containing high levels of FFAs into biodiesel.
The process achieved the removal of FFAs from waste cooking oils, permitting more efficient conversion of the waste oils to biodiesel but also converted the extracted fatty acids to biodiesel. The results of this study provide a step towards increasing the efficiency of conversion of waste cooking oils to biodiesel.
Heading towards RTFO targets
The Renewable Transport Fuel Obligation (RTFO) in the United Kingdom is one of the Government's main policies for reducing greenhouse gas (GHG) emissions from road transport. Under the RTFO obligation, suppliers of fuel for road and non-road mobile machinery that supply 450,000 litres or more per year must supply 8.5% renewable fuel in 2019, rising to 12.4% in 2032. Recent estimates, published by the Department for Transport (DfT), suggested that 4% of road and non-road fuel used this year has been biofuel in the UK. As we slowly head in the right direction to meet targets, further advances in this area will make switching to biodiesel a more achievable and less expensive option.