Pressure on selectivity

Derivatized amylose is the basis for the Chiralpak AD CSP. This CSP has been utilized for the resolution of ibuprofen and flurbiprofen, as well as other members of the family of nonsteroidal inflammatory drugs (NSAIDs) [39, 61]. Ibuprofen was not resolved on the Chiralpak AD CSP in LC. Pressure-related effects on stereoselectivity were observed by Bargmann-Leyder et al. on a Chiralpak AD CSP [58]. No corresponding effect of pressure on selectivity was observed with a Chiralcel OD CSP. The authors speculated that the helical conformation of the amylose-based CSP is more flexible than that of the cellulose-based CSP. 

Effect of Propylene Pressure on Selectivity - The partial pressure of propylene is also one of key factors for selective formation of 4,4 -DIPB.22"25 The high partial pressure of propylene effectively enhanced the isopropylation, but the selectivity for 4,4 -DIPB decreased at lower partial pressures over HM(220), as shown in Figure 6.24-25 However, the isomerization of 4-IPBP did not occur at any propylene pressures. Because 3,4 -DIPB is a more thermodynamically stable isomer than 4,4 -DIPB,43 this decrease of the selectivity was ascribed to the isomerization of 4,4 -DIPB to 3,4 -DIPB, not to the lower selectivity to 4,4 -DIPB. Figure 7 shows the effect of propylene pressure on the selectivities for 4,4 -DIPB in bulk and encapsulated products. The selectivity of 4,4 -DIPB inside the pores was almost constant at every pressure. These results indicate that the isomerization does not occur inside the pores but at the external acid sites. The effect of the pressure on the isomerization of 4,4 -DIPB was similar to that on the isopropylation of biphenyl. 4,4 -DIPB itself isomerizes significantly to 3,3 - and 3,4 -DIPB over the catalyst in the absence of propylene. However, no significant isomerization of 4,4 -DIPB occurred in the presence of sufficient propylene pressure. On the other hand, the selectivity of 4,4 -DIPB in encapsulated DIPB isomers was almost constant at any pressure. These differences support the hypothesis that the isomerization of 4,4 -DIPB to 3,4 -DIPB occurs on the external surfaces. The isomerization of 4,4 -DIPB under high pressures is considered to be retarded by the preferential adsorption of propylene on acid... 

Further carbonylation can occur, adversely affecting the selectivities obtained. Where it is used, the effect of hydrogen pressure on selectivity is also significant, as not all of the reactions require hydrogen. The production of water and the presence of alcohols lead to esterification-hydrolysis equilibria and water can affect the hydrogen pressure via the reversible water-gas shift reaction (equation 70). 

Table 6. Effect of upstream pressure on selectivity for hydrogen relative to carbon monoxide in assy polyimide film...

Nitrogen Sorption. The outgassed sample was cooled to 77 K by a stirred liquid nitrogen bath maintained at a constant level (6, 7). Nitrogen vapor was introduced and controlled at a constant pressure until the steady state conditions shown in Figure 1 prevailed. Maintaining fixed temperature and pressure on selected intermediate pressures for both adsorption and desorption assured us that there were no slow processes in play detectable in the 2-3-day periods used. The disparity between desorption and adsorption isotherms can be attributed confi-... 

Isothermal temperature control in the fluid-bed reactor was easily maintained under all process conditions investigated. The temperature gradients in the catalyst bed did not exceed 5 C even at mean temperature gradients of 200 to 300 C between the catalyst bed and the heat transfer medium. The plant accumulated 17 months-on-strearn of MTG/MTO operation, including 5 months at MTO conditions. MTO operation started with sensitivity studies to determine the effects of temperature and pressure on selectivity. Deactivation periods to vary catalyst activity and to Drovide a comDarison with the 4 B/D Dilot Diant were Derformed... 

Fig.3. ENMP hydrogenation. Effect of CO2 pressure on selectivity of EAMP formation. Reaction conditions catalyst 4%Pd/C - 0.5 g, water - 20 ml, [ENMP] = 1.0 mol/1,...

Influence of High Pressure on Selectivity 245 Tab. 8.4. Influence of pressure and AAV on selectivity. 

Table 11 Influence of methanol partial pressure on selectivity...

Beaudiy, R. M. (1999). Effect of O2 and CO2 partial pressure on selected phenomena affecting fruit and vegetable quality. Postharvest Biol. Technol, Vol 14, pp. 293-303. 

Figure 21.14 Effect of water content at different transmembrane pressures on selectivity for [BMIMjlPF j-based PES membranes. (Source Camper et al. [74]. Reproduced with permission of American Chemical Society.)...

Nagatomi, J., B. P. Arulanandam et al. 2001. Frequency- and duration-dependent effects of cychc pressure on select bone cell functions. Tissue Eng 7(6) 717-28. 

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