Ethylene Oxide (EO) and Propylene Oxide (PO) are utilized as sterilants for medical products and food products as well as in the manufacture of chemical products such as surfactants. Although both compounds are readily soluble in water and, in fact, hydrolyze to form ethylene and propylene glycol the removal of these compounds is not a simple matter.
Both EO and PO are characterized by relatively high vapor pressures in aqueous solution. Consequently, unless the EO and PO are transformed into other substances in solution, the scrubbing liquid stream cannot practically be recirculated within the scrubbing system and still result in effective removal. The alternative, using once-through water for scrubbing, is not generally practical due to the cost of the water and its treatment. However EO and PO can be transformed to their respective glycols when hydrolyzed but the hydrolysis reaction is very slow. The Clean Air Group, LLC approach is to make use of the catalyzing effect of acid to increase the rate of hydrolysis and make a liquid recirculating system workable. The acid of choice is sulfuric acid in strengths of 5 – 7% by weight.
As shown in the diagram below, a counter current packed tower is used to absorb the EO or PO in aqueous solution. The liquid exiting the packed tower drains to the “Reactor Tank” which is designed with sufficient residence time and with certain proprietary internals such that the liquid discharging from the top of the “Reactor Tank” contains only minute amounts of EO or PO since conversion to the glycols has taken place.
The liquid stream then flows over to the “Solution Feed Tank” where the flexibility of operating with varying liquid levels allows for the “swell” of volume as glycol is generated, the discharging of “spent solution” when the tank’s capacity has been reached, and the addition of fresh sulfuric acid and water to replace that lost when the “spent solution” is discharged. As a result this system can operate continuously, if necessary, as discharging of “spent solution” and make-up of fresh solution is accomplished automatically.
The scrubbing liquid stream leaving the “Solution Feed Tank” is recirculated by a centrifugal pump, through a heat exchanger for cooling, and back to the packed tower for continual scrubbing.
The Clean Air Group, LLC EO and PO scrubbing systems have been designed to provide efficiencies of removal of in excess of 99.9% when needed. These systems can be supplied in the form of the major components only all the way to a completely skid mounted, instrumented, and automatically controlled package.