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www.chemicalsknowledgehub.com Scavenger


SiliaMetS Thiol SEM26


Trial scale (150mg of compound N-2) [Pd] / ppm Mass recovery / %


24 95 29 98


Table 2 - efficiency of scavenging vs. Scale.


Batch scale (1g of compound N-2) [Pd] / ppm Mass recovery / %


221 89 53 93


Catalysis


Figure 3. Scavenged N-2 and spent E-PAK Cartridge (LHS) & pre vs. post E-PAK scavenging (RHS). Key - 1 – EOR sample; 2 – EOR post work-up; 3 – 0 h; 4 – 1 h; 5 – 2 h; 6 – 3 h; 7 – 4 h.


subjected to an acidic work up, each representing nominally 1 g N-2, were subjected to scavenging at 50°C. SiliaMetS Thiol and SEM26 were used at 0.15 w/w loading under nitrogen over 24 hours (Table 2). The efficiency of scavenging was poorer for SiliaMetS Thiol on this scale than during the previous experiments, whereas SEM26 performed nearly as well at both scales. Unfortunately, the mass recovery for both scavengers was poorer on scale-up owing to decomposition of N-2.


Experimental procedure Screening experiments were conducted using a 5 g (10 vol) reaction in MEK post an acidic work-up under air. According to the scavenging design, EOR samples (1.50 mL) were added to pre-weighed amounts of scavenger in LC vials containing micro-stirrer bars and heated with stirring to 50°C. After the requisite amount of time, samples were centrifuged at 4000 rpm for 5 min and the supernatant was separated and analyzed by UPLC and ICP-MS. An internal


standard was employed in the scale-up study to quantify reaction conversion and the mass recovery of N-2 after scavenging.


Flow scavenging


In order to facilitate tactical delivery of a scavenging protocol that could be used on a process scale, SiliCycle’s E-PAK purification system was trialled with SiliaMetS Thiol. A 10 g (20 vol) reaction post hydrochloric acid work-up was scavenged under air at ambient temperature, using a peristaltic pump with a PTFE head and


tubing. After the first column pass, the system was continuously recirculated at a flowrate of 5 mL min-1 for 4 hours, and samples were taken for analysis (Figure 3, t = 0 h: 1 column pass; t = 4 h: 9 column passes). UPLC data from samples 1-7 demonstrated that near quantitative mass recoveries for N-2 were achieved throughout with very high purity and decomposition was not observed. Recirculating scavenging with the SiliaMetS Thiol E-PAK cartridge allowed for >90% purge of palladium from N-2 in 4 hours at ambient temperature under air (Figure 4). Further reduction of the residual palladium levels could be achieved by increasing the scavenging time and/or temperature (shifting the position of equilibrium towards palladium binding) or by adding another column in series.


In conclusion


Two functionalized silicas, SiliaMetS Thiol and SEM26, were identified as efficient scavengers for the removal of palladium from N-2. Performing scavenging on the neutral compound, post hydrochloric acid work-up, led to high mass recoveries. Loadings of functionalized silica down to 0.15 w/w can be employed with extended reaction times in batch experiments to give <50 ppm levels of residual palladium. The use of SiliaMetS Thiol in an E PAK cartridge system under flow has been demonstrated to lead to a >90% purge of palladium under recirculating conditions in just four hours under ambient conditions.


Further information CatSci Ltd


Capital Business Park Wentloog


Figure 4. Scavenging efficiency with recirculation time. Issue 2 • March/April 2021


Cardiff CF3 2PX United Kingdom Ph: +44 29 2083 7444 E: technical_enquiries@ catsci.com W: www.catsci.com


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