Semi-continuous flow with Cold Separation

The series of batch reactions for this experiment were carried out over three days; batches 1-4 on the first, 5-8 on the second and the ninth reaction on the third. The rig was assembled as before and the initial reaction was left stirring under 15 bar CO/ H2 and 70 oC for two hours, with the subsequent reactions only reacting for 1 hour.

After the reaction time the heater was removed and the stirring slowed. Once the reactor was observed to be cooling down, the stirring was stopped to allow separation. The reactor was emptied once the temperature was below 35oC, and this was generally about 1 hour after the heater had been removed. The product phase was collected in the separator and removed after every batch reaction to sample vials. The GC-FID analysis of these samples is shown in Figure 3.3.6.7. The results from this experiment appear quite similar to the previous semi-continuous flow experiments.

0 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 Batch No.5 6 7 8 9 10 C o n v e r si o n (% ) 0 1 2 3 4 5 6 L :B

%PFMCH Conversion to Aldehyde %1-Nonanal % 2-Me-Octanal % Isomerised octenes L:B

Figure 3.3.6.7 The GC-FID analysis for the semi-continuous experiment with cold product separation

The results are quite understandable; there is the expected initial high conversion (84 %) for the first reaction, which drops down to around 60 % for the further reactions run on the first day. It is worth noting that this apparent steady state of conversion over these three reactions has a higher conversion to nonanal than is seen in the steady state range of the continuous flow experiments (~30 %). The reactor was then emptied of the organic phase and left to cool at 10 bar CO / H2 overnight. Batch reaction number 5 was run on the following morning, but a fault with the gas pressure controller had to be fixed and involved the reaction being stopped and cooled. The reaction time for this batch was therefore extended by 30 minutes to account for this and may explain the rise in conversion for this batch reaction. The alternative explanation follows the pattern seen in the continuous flow experiments where we observe a steady state of conversion followed by a rise in conversion due to the leaching of phosphine from the catalyst phase and subsequently a drop in conversion as we lose the unliganded Rh to the organic phase as well.

After the final batch reaction, the reactor was opened and emptied and found to contain 37 cm3liquid of which < 4 cm3was the fluorous phase, which had turned a dark orange colour. This indicates that there is still a loss of the fluorous phase through the separation process. The possibility of PFMC dissolving into the organic phase has been disproved by the GC analysis which shows ~1 % of the product phase to be PFMC. It is possible that 30-35 oC was still too hot for separation and that cooling to room temperature or below would be necessary for further experiments.

The Rh leaching data for this experiment, Figure 3.3.6.8, initially looked to be very good with 5 ppm [Rh] observed in the first batch reaction, however this quickly increased and by the seventh reaction was nearly 350 ppm. Again, by simply

observing the colour of the collected product phase, Figure 3.3.6.9, a similar assumption of Rh leaching can be made.

0 50 100 150 200 250 300 350 400 0 2 4 6 8 10 Batch No. [R h ] (p p m )

Figure 3.3.6.8 ICPMS analysis of Rh leaching to the organic phase

1 2 3 4 5 6 7 8 9

Figure 3.3.6.9 Collected product from semi-continuous experiment with cold separation

After the third batch reaction, a much darker colouration of the organic phase is observed with the final batch reactions very dark indeed. In this experiment 315 cm3 of octene was used. In comparison, the continuous flow operation of the reactor could use over a litre of octene in 24 hours.

3.4 Conclusions

This study demonstrates the transference of a simple batch reaction to the continuous flow process and that the specifically designed reactor works effectively for this reaction. However, to optimise the reaction it is evident that maximum mixing of the gas and liquid phases are required to achieve high conversions. Further ligand design may improve the conversions and selectivity, as under these conditions leaching of the catalyst to the organic phase is still a major hindrance to the continued running of the reactor system. The continuous process may be improved further by the addition of a second reactor, so that any unreacted alkene can be converted. However, working two reactors in series, on our small-scale rig was not a viable option.

3.5 Reference List

1. I. T. Horváth and J. Rábai,Science, 1994,266, 72.

2. D. F. Foster, D. Gudmunsen, D. J. Adams, A. M. Stuart, E. G. Hope, D. J. Cole- Hamilton, G. P. Schwarz and P. Pogorzelec, Tetrahedron, 2002, 58, 3901.

3. E. Perperi, Y. Huang, P. ANgeli, G. Manos, C. R. Mathison, D. J. Cole- Hamilton, D. J. Adams and E. G. Hope,Dalton Trans., 2004,14, 2062.

4. P. W. N. M. van Leeuwen, Rhodium Catalyzed Hydroformylation, Kluwer Academic Publishers, The Netherlands, First edn., 2000.

5. Y. Huang, E. Perperi, G. Manos and D. J. Cole-Hamilton, J. Molec. Catal. A: Chem., 2004,210, 17.

Chapter 4