Harnessing flow chemistry to optimise THF waste treatment

Tetrahydrofuran (THF) is a commonly used solvent in pharmaceutical development. A certain process on the Sterling site produces a THF waste stream containing epichlorohydrin, which must be be neutralised prior to recovery or disposal.

In order to enhance efficiency, improve safety, and produce less hazardous waste streams, Sterling is exploring the possibility of harnessing flow chemistry to streamline waste treatment, bring waste back to its virgin specification, and create opportunities for reuse on site. This approach has the potential to free up batch reactors and minimise energy usage, enabling more optimised waste treatment and stronger environmental sustainability. However, orchestrating this approach requires a combination of expertise in flow chemistry, hazardous materials management, environmental sustainability and scalable process design.

Because of the presence of epichlorohydrin in THF waste, the possibilities for recovery and reuse are limited. Given that epichlorohydrin is corrosive, toxic and hazardous to human health1, incineration is not an environmentally optimal means of disposal, and waste companies may not have the facilities to support it. Therefore, the waste cannot be sent off for treatment until traces of epichlorohydrin are removed.

Current approaches to making THF waste streams suitable for purification are time consuming and inefficient, often taking longer than the process that generates the waste. Denaturing the waste to make it suitable for incineration involves refluxing it in a batch vessel with sodium hydroxide for at least three days. This process requires a great deal of energy and operator involvement, and it makes a vessel unavailable for other processes for a significant amount of time.

After neutralisation of the waste stream, the process results in THF with water, which cannot be easily recovered to its virgin specification. As a result, the waste is not a viable candidate for reuse and instead must be incinerated. Given the high costs and environmental impact of incineration, the Sterling team has worked to identify a more efficient and effective outcome.

At Sterling, we are committed to maximising efficiency for our customers and minimising environmental impact in every project and across every process. To support these goals with processes involving THF, we are working to develop a continuous flow process to enable safe treatment, disposal and reuse.

Identifying a suitable catalyst was the first step in designing a flow approach that would reduce energy costs while enhancing efficiency and sustainability. After a thorough literature review, the Sterling team identified Nafion™ NR50 as the most suitable catalyst. Its small and spherical particle shape made it optimal for column packing, as opposed to alternative powder catalysts that could cause issues during scale-up.

In developing a flow process, the Sterling team aimed to completely remove epichlorohydrin from the waste stream, which existed in concentrations up to two percent. Converting the epichlorohydrin to a diol or alcohol would make the waste streams much less hazardous, more suitable for treatment and potentially reusable.

To carry out the process in flow, the Sterling team successfully trialled the process in a 10 mL column. Then, the team scaled the process using a purpose-built 250 mL column, successfully running it for 730 hours to treat 250 L of waste. Over this period, the solvent had a residence time of 20 minutes in the column with no significant decrease in catalytic activity and waste that fell within specification for recovery. For every gram of catalyst, the team was able to treat 1.42 litres of waste. Initial carbon footprint calculations from the envrionment, health and safety (EHS) team also showed a significant drop in the process’ environmental impact compared to the batch process. According to a mass balance and Tradebe (2019), the team could expect a reduction of 1805 kg CO2 over the process lifecycle based on 270 L of THF.

Now that the process has demonstrated its success in the lab, the team will conduct a longer trial run to confirm results and assess the catalyst’s lifespan. Then, the team will design a pilot scale process using an 80L flow column to support a larger volume of waste in a short period of time. This will translate to reduced costs, greater efficiency and improved sustainability.

In the near term, once the process has successfully scaled, the Sterling team will have the ability to more efficiently generate safer waste that can be readily recovered and reused on site.