Optical tweezing for bio refining applications

Every year only about 4% of approximately 130 billion metric tons of carbohydrates found in biomass are currently utilised. Triglycerides in biomass can be reacted with methanol to form biodiesel, a bio-renewable source of energy that has the potential to be a promising candidate for the replacement of traditional fossil fuels and reduce CO2 emissions. In the synthesis of biodiesel, glycerol is produced as a by-product and is being produced in significant amounts due to the rapid increase in biodiesel production over recent years. It is therefore useful to develop efficient ways to react glycerol further to make more valuable by-products and these reactions require a catalyst.

This research focuses on the efficient conversion of biomass to biodiesel by developing an effective solid catalyst for use in the reaction. The use of a solid catalyst in this reaction is advantageous as it can be easily separated from the reaction mixture upon completion. The solid catalyst can then be washed and reused in further production, making the process more efficient. This will reduce both production costs and the waste produced by the reaction. Furthermore, typical biodiesel production and the reaction to valorise glycerol are carried out on large scales, which is advantageous in scaling up reactions, products and by-products. However, when reactants are used in large volumes the kinetics and dynamics of the reaction are more challenging to examine in detail due to averaging effects. In comparison by using optical tweezing of fL - pL volume droplets the reaction can be studied on a molecular level and the chemistry kinetics of transformation revealed.

Optical tweezing utilises highly focussed laser light to hold droplets in a controlled environment away from surfaces that could impact behaviour and reaction dynamics. Droplets of reactants held in the optical tweezers can then be coalesced and the kinetics of the reaction studied in real time as the reaction proceeds. Optical tweezers are combined with Raman spectroscopy to quantify the properties of droplets and identify bands as they are broken and formed throughout the reaction. 3D printing will be used to design an optical tweezing chamber for controlling and quantifying droplet chemical reactions in a controlled environment. Chamber parts with specific features and inlets will be optimised for an efficient analysis of particles in different phases undergoing reactions. This research will focus on the synthesis of biodiesel as well as two reactions to valorise glycerol, these reactions all involve two separate liquid phases (an oil, biomass or glycerol and the liquid reactant used) as well as a solid phase (the catalyst). This complex analysis means the tweezing chamber needs to be optimised to overcome the inherent issues of analysing three interacting phases and to avoid inhalation of any of the reactants being used.

The motivation for this research comes from the desire to understand the fundamental chemistry and kinetics of the synthesis reaction of biodiesel and the reactions to valorise glycerol. By studying the dynamics of these reactions on a molecular level insight will be gained into how efficient each respective catalyst is. New catalysts can be developed and functionalised to optimise the reaction. Biodiesel synthesis is a promising area of research to address current climate concerns relating to the use of fossil fuels. Developing efficient, cost effective catalysts for these reactions is essential to make biodiesel synthesis viable and sustainable. By studying reactions to valorise the by-product of the biodiesel synthesis (glycerol) and optimising the catalysts used in these reactions the biodiesel synthesis will be made more efficient. The compounds derived from the reactions by-product will be far more useful and valuable than glycerol.