Process parameters aldehydes concentration

As mentioned earlier, in the Ruhrchemie-Rhone Poulenc process for propene hydroformylation the pH of the aqueous phase is kept between 5 and 6. This seems to be an optimum in order to avoid acid- and base-catalyzed side reactions of aldehydes and degradation of TPPTS. Nevertheless, it has been observed in this [93] and in many other cases [38,94-96,104,128,131] that the [RhH(CO)(P)3] (P = water-soluble phosphine) catalysts work more actively at higher pH. This is unusual for a reaction in which (seemingly) no charged species are involved. For example, in 1-octene hydroformylation with [ RhCl(COD) 2] + TPPTS catalyst in a biphasic medium the rates increased by two- to five-fold when the pH was changed from 7 to 10 [93,96]. In the same detailed kinetic studies [93,96] it was also established that the rate of 1-octene hydroformylation was a significantly different function of reaction parameters such as catalyst concentration, CO and hydrogen pressure at pH 7 than at pH 10. 

To gain a better understanding of the observed parameters listed in Table 7, additional experiments were performed. The formation of these internal olefins in the case of the aluminum-containing catalyst 36 was low and remained more or less constant over time. In the case of 37, the isomerization selectivity increased with time up to 2 h, indicating the importance of the isomerization. However, the ability of the gallium-containing catalyst 37 to catalyze hydroformylation of the internal olefins decreased the concentration of internal olefins present in the solution. In the case of the indium-containing catalyst 38, the rates of formation of both aldehydes and internal olefins increased as a function of time, and the process was not complete even after 5 h. 

For example, in the case of pyrene (the most widely used fluorescent dye) the measured parameter is /1//3, the ratio of intensity of the first (372 nm) and third (385 nm) fluorescence peaks for pyrene aldehyde it is the wavelength of maximum absorption (36,37). In the presence of interacting polymer the plot is displaced to lower surfactant concentration this implies that a surfactant aggregation process, formally akin to micelli-... 

The water-based process is normally operated at a pH-value between 5 and 6 to provide reaction conditions, which depress unwanted side reactions of the formed aldehydes. It turned out that a careful pH-control is beneficial for various operation parameters of the protic reaction media catalyst reactivity and selectivity are directly influenced by and thus dependent on the H3O+ concentration present in the aqueous phase. 

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