CATALYSTS

Figure 2 – Examples of mixer and reactor inlet designs '

‣ the batch reaction ( 9 ) was significantly higher than for the flow system ( 6.5 ). In this case , the differences were attributed to safer and greener solvent use , leading to a less hazardous chemical reaction . This again is reflected in the space-time yields for batch and flow , with 0.44 mol / hr-

1

/ g Pt- ¹ in flow , compared with 0.35 for batch , indicating a more modest increase in process efficiency when compared against MBE .

A mixing problem

In both of these processes and indeed all gas- , liquid- and solid-phase reactions like hydrogenations , the key challenge facing flow chemistry is scaling up . In the range from 1-100 kg / day , scale-up is a particularly acute problem . The issue of scaling up the reactor design can theoretically be solved in several ways . The easiest involves scaling out ( or numbering up ) reactors in order to increase production capacity . In this configuration , flow can be increased without losing control over residence time . In single-phase systems , scaling out is used quite effectively because the flow can be split in a controllable way . In gas-liquid systems , however , flow uniformity is far more difficult to measure and control , making it a major challenge and expense . Stoli has been tackling this issue by developing novel reactors with optimised hydrodynamics . Using gas absorption measures , we have been able to test 3D-printed static mixers based on both commercial and novel designs . 3D printing brings multiple advantages to reactor design and maximising efficiency , as test models for all stages of the reactor can be designed and fabricated without the need for costly large-scale manufacturing equipment . Through our hydrodynamic studies , we have been able to improve gas absorption efficiency threefold compared with a conventional packed bed . When combined with our modular design and reactor cartridges , a wide variety of hydrogenation reactions on a large breadth of scale can be tackled with superior mixing and control over residence time .

Outlook

One of the biggest challenges facing the fine chemical process sector today is the reduction in energy use and simultaneously phasing out fossil fuels and transitioning to cleaner renewable electricity and gas . Continuous manufacturing will clearly have a large role to play in achieving that goal , and , thanks to innovations across the sector , there are many opportunities for moving towards better energy efficiency and decreased waste . We have demonstrated that hydrogenation reactions can be carried out from the lab to pilot scale in continuous flow with improved space-time yields , without the need for potentially hazardous solvent and the extra processing steps . In the case of the MBY hydrogenation , Stoli catalyst-coated reactors allowed enhanced mixing regimes and also increased the turnover number by up to two orders of magnitude from 104 to 106 , representing a 100-fold increase in catalyst utilisation . ⁶ We are seeing increasing interest from customers looking for continuous flow solutions , both to cut process development and manufacturing time and costs and to decrease consumption of materials and energy , combined with lower waster generation . Through this , the synthesis of more sustainable products can be delivered . While the challenges of process scale up and process intensification remain , Stoli aims to remain at the forefront of green , sustainable chemistry . Currently , we are seeking to pilot our 100 kg / day hydrogenation system with a wide variety of feedstocks . •

* DOZN is a Quantitative Green Chemistry Evaluator , a trademark of Merck & Co .

34 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981