Green and more efficient production of specialty chemicals

February 10, 2022

Roel Kleijwegt defended his PhD at the department of Chemical Engineering and Chemistry on a more durable production of a specific type of surfactant.

The industry of surfactants is currently worth billions of euros and is continuously expanding. These specialty chemicals allow for substances to better mix or dissolve, and they are used in a lot of household products and in various industrial sectors, with applications ranging from fuel additives to detergents – with the COVID-19 pandemic causing even more demand for detergents. The efficient production of these complex chemicals is vital for the sustainability of our everyday life and of our planet. In his PhD research, Roel Kleijwegt demonstrated how the production process of a specific type of surfactant, Quaternary Ammonium Salts (QAS) can be made more efficient and greener.

Currently, these QASs are primarily made in deprecated and cumbrous batch reactors. Harmful alkyl halides are conventionally used, and the process is hampered by undesired side reactions, as well as decomposition of the product if it is overexposed to high temperatures.

In a continuous reactor, the control of reaction time and temperature is generally better. By investigating the rates of the different reactions, optimum conditions can be predicted for such reactors. Moreover, Kleijwegt elucidated the use of a more benign reactant, dimethyl carbonate (DMC), which has an additional benefit that it provides a more versatile product.

Lab-scale flow reactor

First, he tested different solvents in small batch reactors to find the most suitable one. Methanol proved to be the best, as it offered high product stability and reactivity. Then, to gain accurate insight into the rates of the reactions, Kleijwegt built a lab-scale flow reactor.

In this reactor, the reaction time and temperature could be precisely monitored and regulated. He developed a new method where the time that the reactants spent in the reactor was gradually changed while constantly measuring the resulting exit concentrations.

The analysis was performed by Nuclear Magnetic Resonance (NMR), one that fits on top of the bench and where the reaction mixture directly flows through. This allowed Kleijwegt and his colleagues to efficiently gather a lot of accurate and valuable data in a very efficient manner.

The reaction kinetics (speeds) were determined for both reactant types, and DMC showed more potential for acceleration, as it was slower. The data was combined with other experiments which determined the stability of the pure QAS, and QASs in different solvents. He discovered that water and methanol greatly improve the thermal stability of the products.

Increased productivity

All the data was then used in a computational model (in MATLAB) for different flow reactors, to optimize the conditions that were not feasible in the lab. Also, the reactors were up scaled to an industrial size.

Kleijwegt demonstrated that by using a flow reactor, the right solvent, and much higher temperatures the productivity could be greatly increased (by orders of magnitude). The required reactor could therefore be made much smaller, increasing its safety while substantially lowering its costs.

For the conventional alkyl halides, a relatively novel Spinning Disc Reactor was proposed. The new and green DMC could be better produced with a Plug Flow Reactor. Overall, this green and more efficient production of surfactants can contribute to a more sustainable chemical industry.

Roel Kleijwegt defended his PhD at the department of Chemical Engineering & Chemistry on February 4th titled ‘Intensification of Continuous Tertiary Amine Alkylation with Renewable Dimethyl Carbonate’. He was supervised by John van der Schaaf. Other main parties involved: Nouryon (formerly AkzoNobel).