Date of Award

Spring 5-5-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

William J. DeSisto

Second Committee Member

Sampath Gunukula

Third Committee Member

Thomas J. Schwartz

Abstract

Because of the Covid-19 pandemic along with the delay in the worldwide supply chain, there were disinfectant shortages that lasted for weeks around the world. Therefore, on-site production is a promising solution to satisfy the increasing demand. As more and more people are shifting toward safer and more environmentally friendly products, we are interested in investigating the electrolysis of sodium chloride (NaCl) solution to produce hypochlorous acid (HOCl). Electrolysis is inexpensive as it requires only sodium chloride and electricity, and it does not have any negative impact on the environment. Moreover, electrolysis can be coupled with renewable energy to utilize the excess energy that is hard to store. Meanwhile, hypochlorous acid was proven to be 80-100 times more effective than sodium hypochlorite, commonly known as bleach. Hypochlorous acid was also shown to be a non-toxic, anti-inflammatory, and non-corrosive disinfectant. Since electrolysis is an energy-intensive process, this project will study if using a pulsed direct current to perform electrolysis can improve the current efficiency or electricity requirements of the process. There was evidence showing that pulsed electrolysis was able to improve the electrolysis efficiency because of the reduction of bubbles coverage, perturbation of the electrical double layer, and enhancement of mass transportation. A flow-through reactor was made with a cathode made from titanium and an anode made from titanium coated with mixed metal oxide (a mixture of Iridium oxide and Tantalum oxide). The squared-shaped pulsed current was generated by utilizing MOSFET. The results showed that pulsed electrolysis increased the number of electrons converted into final products up to 10% more. Pulsed electrolysis also reduced the electricity requirement by 10%-15%. However, it significantly increased the need for sodium chloride because there was no reaction during the off-time. There are several proposed methods to minimize this disadvantage, but more experiments need to be done to assess them. Nevertheless, in the current density range from 2000 to 4500 A/m2, for the same amount of supplied power, pulsed electrolysis with a duty cycle of 80% required less sodium chloride to produce 1 kg of Cl2 than conventional constant electrolysis. Although frequency only affected the electrolysis efficiency slightly, operating at the optimized frequency extended the improvement of the pulsed electrolysis compared to the constant electrolysis. Utilizing pulsed electrolysis with the optimized settings can effectively decrease the operating cost of producing disinfectant (hypochlorous acid).

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