Optimal Design of Liquid-Liquid Extraction for Wastewater Streams and Potential Application to Remove Emerging Contaminants

As water resources become scarce and the industry continues to move toward decarbonization, the chemical processing industry is challenged to find new and innovative ways to recycle its wastewater and further reduce energy consumption. This challenge is further complicated by increased regulatory compliance to both remove regulated contaminants to increasingly lower concentration levels as well as address emerging contaminants such as Per- and Polyfluoroalkyl Substances (PFAS). Given that emerging contaminants such as PFAS break down very slowly over time, making the removal of PFAS from our environment extremely difficult and energy intensive.

When assessing which technology is optimal to remove contaminants and recycle wastewater streams, available options for consideration are determined by whether streams contain organic chemicals that are either lower or higher boiling than water. Distillation or stripping is usually used to remove the lower boiling components, whereas liquid-liquid extraction is often used when the chemicals are either higher boiling than water or are non-volatile.

When it comes to addressing wastewater streams containing high boilers, a process widely used in the organic chemistry field is an extraction step allowing for counter-current contact with an immiscible solvent that is lower boiling than water followed by a distillation column to recover the solvent as an overhead stream for recycling back to the extraction column and a stripping column to strip and recovery the solvent from the aqueous raffinate stream.

However, for years a different technology has been employed by the mining and metals industry for the recovery and purification of non-volatile metals from aqueous streams. This technology has the potential for application in the chemical processing industry as a more energy-efficient process to treat wastewater streams containing high boilers. For example, extraction for the recovery of metals from dilute aqueous streams typically involves several extraction columns operating in series without the need for any distillation step, and as such these processes can often have lower operating costs than their counterparts in the organic chemical field. A high boiling Extractant is dissolved into a diluent, which is also higher boiling than water. Following the extraction step, the extracted metals are then re-extracted (or stripped) out of the “loaded solvent” using a second extraction step. The solvent used in this column is called a stripping solution which is often pH-adjusted water.

In order to provide a more efficient and economical solution to the decarbonization of the chemical processing industry while both addressing increasing water scarcity and future energy-intensive remediation challenges, such as mitigating emerging contaminants, the organic chemicals industry should learn from the metal extraction industry and consider applying multiple extraction columns in series without a distillation step as an alternative process improvement solution to address wastewater streams containing high boilers.

This paper will be presented using both types of processes; extraction followed by a distillation step and extraction using a high boiling solvent in multiple extraction columns. The selection of which one is best for a particular wastewater process requires an economic study for both methods.

By: Donald J. Glatz and Brendan Cross, Koch Modular Process Systems LLC, Paramus, New Jersey, USA

Author Bio

Don Glatz is the Manager of Extraction Technology at Koch Modular. Don’s activities include the evaluation and optimization of extraction processes plus the scale-up and design of extraction systems. He has been working in this field for the past 30 years and has published a number of papers and articles covering this subject. Don holds a BS in chemical engineering from Rensselaer Polytechnic Institute and an MBA from Fairleigh Dickinson University.

Brendan Cross is a Principal Extraction Engineer at Koch Modular that works in the Extraction Technology Group. Brendan is responsible for liquid-liquid extraction application evaluation, extraction process development, and pilot test design, extraction column design, and commissioning & process startup. He has been with Koch Modular for 15 years and also has substantial experience in distillation and process design. Brendan holds a BS in chemical engineering from Columbia University.