The Next Semi-continuous experiment

In order to monitor the recycling of the catalyst solution, it was only necessary to remove the product phase after every batch reaction, but to do this the dip-tube had to be shortened so that it only removed the organic phase from the reactor and left the fluorous phase. By doing this, the catalyst would effectively be preformed for all subsequent reactions after the initial two-hour reaction and so batch reactions 2-9 were reacted for just one hour each.

The separation was carried out without cooling, but with the heater turned off during removal of the organic phase to prevent overheating of the catalyst solution.

The GC-FID analysis of the product phases is shown in Figure 3.3.6.4 and the Rh leaching data of selected samples are shown in Figure 3.3.6.5. The initial conversion is lower than the previous experiment. Nevertheless, the differences between conversions in the first five reactions are much less and appear to have reached a steady level of conversion of around 40 % nonanal, and although this is nowhere near the anticipated >90 % conversions we would expect for individual batch reactions. The GC analysis of the final 4 batch reactions shows a steady drop in conversion which, as before, is attributed to the loss of rhodium to the organic phase, and assuming the leaching of phosphine over the initial reactions.

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

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

Figure 3.3.6.4 GC data for Semi-Continuous reaction with hot removal of organic phase

0 20 40 60 80 100 120 0 2 4 6 8 10 Batch No. [R h ] (p p m )

Figure 3.3.6.5 Rh leaching during semi-continuous reaction with hot separation of organic phase

Encouragingly, the leaching levels were much lower in this second experiment, but corresponded to lower conversions which were in disagreement with the previously reported work by Huang et al5 which stated that higher conversion to nonanal decreased the rhodium leaching levels in the organic phase. A similarity in pattern of leaching was observed between this semi-continuous experiment and the

previous one, an initial low loss of rhodium, which rose to a peak after five reactions and then dropped away after that.

This pattern of leaching is much easier to explain in the second experiment due to there being only one addition of catalyst phase to the reactor and no topping-up occurred throughout the reaction. An initially low [Rh] in the organic phase was expected from the previous batch reactions carried out in the kinetic experiments. There was an obvious loss of phosphine in the third and fourth batch reactions, which was determined by the strong yellow colour of the collected product see Figure 3.3.6.6.

We eventually reached a peak (batch 5) of [Rh] in the product phase that reduced after this because of the overall drop in [Rh] in the reactor. There was simply not enough Rh left in the reactor to maintain these high concentrations.

1 2 3 4 5 6 7 8 9

Figure 3.3.6.6 Product phase collected after each batch reaction

From this photograph of the product phases collected, the extent of Rh leaching is obvious. Samples 2 and 5 also show a small amount of the fluorous phase that had been removed from the reactor during separation. It is interesting to note the change in colour of these two samples.

The small amount of fluorous phase collected in 2 was a bright orange colour as expected when emptying the kinetic rig or HPIR equipment after heating the catalyst solution under CO / H2. By the fifth run, however, the catalyst phase had turned very dark brown, almost black. This had also been observed before when the HPIR cell was overheated and the catalyst destroyed.

The Rh leaching was obvious from the colour of these samples. The large loss of Rh in the sixth reaction can perhaps be explained by both the large loss of Rh measured in the fifth reaction and the dark colour of the catalyst phase, which is suggestive of free Rh metal, which would occur upon large losses of phosphine leaching (likely to have occurred prior to the Rh leaching).

When the ninth reaction had been run and the analysis showed less than 20 % conversion the experiment was stopped and the reactor opened. It was obvious that there was very little fluorous phase in the reactor. The contents of the reactor were almost entirely pale yellow organic phase. This loss of fluorinated phase throughout the experiment does not concur with the small amounts of fluorous phase collected with the product phase. It is likely that this loss of the fluorinated solvent occurs during the emptying of the organic phase to the separator. When the reactor was first opened to the separator along with the liquid a cloud of vapour was observed and it is likely that this was partly PFMC. This might have been proved by condensing the vapour from the vent, but was not carried out, because the problem was not realised until the reactor was opened.

To try to prevent the loss of PFMC during the experiment, it was considered worthwhile to cool the reaction mixtures before separation of the organic phase and this was done in the final semi-continuous flow experiment that was carried out.