Development of a Water Activity Control and Reaction Monitoring System for Acidolysis and Transesterification Reactions using Immobilized Lipases in a Rotating Bed Reactor
Abstract: Controlled water activity in an enzymatic reaction can influence enzyme activity and productivity. A small layer of water around an enzyme gives it a required flexibility to catalyze reactions at a higher rate in contrast with the one that is dry (Adlercreutz, Dicko, Larsson, & Månsson, 2017). The hypothesis of this research project is that the product yield and productivity of acidolysis and transesterification reactions will be increased with the controlled water activity. The acidolysis reaction is performed in two steps, where the first one is hydrolysis of the ester followed by reversed hydrolysis creating the new ester with the desired acid. Higher water activity promotes hydrolysis and vice versa for the reversed hydrolysis. In this degree project a modified SpinChem rotating bed reactor was developed for the acidolysis and transesterification reactions. The reactor was equipped with an automatic water activity control system which was designed in the laboratory. The automatic water activity control system was made from two sub-systems. A nitrogen sparging and a relative humidity sensing system. The latter was kept in the headspace of the reactor while the nitrogen sparger was installed in the bottom of the reactor and was connected to dry and wet nitrogen. An Arduino UNO R3 micro-controller was used for communication between mentioned systems. The automatic water activity control system was designed in a way where a 3-way valve was switched between the dry and wet nitrogen source based on the setpoint of the humidity ant the actual value in the reactor, and where the flow of nitrogen gas was regulated by the Aalborg thermal mass flow controller based on the difference between the setpoint and the actual relative humidity. A software for the communication between the sub-systems was written using C++ programming language using Notepad++ free source code editor. The code was later imported in the Arduino integrated development environment (IDE) and transferred to the micro-controller. The code was written in the way were the micro-controller was able change the parameters of the gas flow and switch the 3-way valve between the dry or wet nitrogen based on the data received from the relative humidity sensor. The automatically controlled relative humidity system was able to maintain water activity in the reactor with the standard deviation ranging from 0.015 to 0.058 aw units when going from 0.1 to 1.00 aw respectively. Automatically controlled water activity system was later used in a transesterification and acidolysis reactions. Different water activities were maintained in the reactor while the conversion of a substrates was tracked with the gas chromatography. Results suggested that the water activity has a significant influence on the enzyme activity during transesterification reaction. In some cases, the activity of an enzyme in the reactor was increased several times by increasing the water activity. During acidolysis reaction the water activity had of a great importance on final substrate conversion and reaction rate. At the water activity of 0.9, 2.5 times more product was converted after 5 hours, compared to the water activity of 0.25. This shows that there is a great importance of controlling the water activity of enzymatic processes.
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