Economic benefits of sustainable practices : Solvent waste recovery case study
Mark Muldowney , head of technology & innovation at Sterling Pharma Solutions , shares a case study of how the company manages THF waste
Figure 1 - Treatment of ECH with Nafion NR50
At its manufacturing site in Cramlington , UK , Sterling Pharma Solutions undertakes a regular manufacturing campaign that results in approximately 3,500 L of waste tetrahydrofuran ( THF )/ batch . On average , this solvent contains up to 2 % epichlorohydrin ( ECH ), with some variation between campaigns . ECH is toxic and carcinogenic , so Sterling has had to pre-treat the waste solvent to neutralise it in a process that involved refluxing the THF with sodium hydroxide .
This treatment process causes a number of operational and economic problems . The method takes longer than the production process that generates the waste , requires high energy input , uses a stream on site that could otherwise be used to make profitable products and results in THF that contains water . This prohibits its reuse at the manufacturing site or recycling as a solvent without further processing , such as distillation .
Historically , Sterling had been able to sell the neutralised solvent into the consumer health industry , but changes in regulations led to THF being restricted in that industry , meaning that the most economically viable option has been to pay for it to be incinerated . However , there is still the need to carry out the same costly neutralisation process prior to incineration , to reduce the ECH content of the waste solvent .
Alternative processing
Sterling has been investigating alternatives to this current treatment process , with a view to reducing energy costs , making the process more sustainable and , importantly , freeing up vessel capacity to increase the efficiency of the manufacturing plant . Any new method to process the solvent would need to be economically favourable , while reducing the use of manufacturing assets .
As a result , a continuous flow approach was investigated to determine whether it could be appropriate . A literature search into applicable industrial solid catalysts to facilitate the breakdown of the ECH identified , Nafion * NR50 as the most suitable . The catalyst was available as 10 mm diameter
spheres , making it ideal for column packing . This , unlike other powdered or granulated options , would avoid problems when implementing within an industrial scale .
Nafion NR50 is a perfluorinated sulfonic acid resin , which is classed as a ‘ super acid ’ and can be used as a catalyst in a wide variety of synthetic applications , including alkylation and acylation reactions . For this reaction , 2-propanol ( IPA ) would be reacted with the ECH-contaminated solvent in the presence of the catalyst , yielding 1-chloro-3-isopropoxy-2- propanol ( Figure 1 ).
The flow conditions were optimised on a small scale with 3 g of catalyst in a 10 ml column . This was then scaled up to investigate the catalyst ’ s lifetime : a flow setup was installed using existing equipment on the site , with a packed bed column reactor that had a heater / chiller unit attached ( pictured ).
The total volume of the column was 250 ml and this was packed with 175 g of Nafion NR50 pellets . These pellets were swelled inside the column by flushing it with THF for four hours before use , and after swelling ,
54 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981