Methanol selectivity

Sodium borohydride in methanol selectively reduces the double bond of nitrocompounds (20) while leaving the... 

The Holy Grail of catalysis has been to identify what Taylor described as the active site that is, that ensemble of atoms which is responsible for the surface reactions involved in catalytic turnover. With the advent of atomically resolving techniques such as scanning tunnelling microscopy it is now possible to identify reaction centres on planar surfaces. This gives a greater insight also into reaction kinetics and mechanisms in catalysis. In this paper two examples of such work are described, namely CO oxidation on a Rh(llO) crystal and methanol selective oxidation to formaldehyde on Cu(llO). 

GL 1] [R 4][P 2] For the dual-channel micro reactor, the highest yield of 14% was found using acetonitrile (58% conversion 24% selectivity) [13]. Slightly lower yields were obtained for methanol. The selectivities were as high as for acetonitrile, the conversion being lower. Still lower yields (7%) were achieved in octafluorotoluene for the same reason as for methanol, selectivity decreasing considerably. 

The obtained results show that the prepared membranes are methanol selective, but the performance of these membranes (separation factor=30, for PVA/Pacr.Ac.=80/20, 5 wt% methanol in the feed, 25 °C) is lower than those reported by J.W. Rhim and Y.K. Kim [75] (separation factor 1250 for PVA/Pacr.Ac.=75/25, 20 wt% methanol in the feed, 30 °C). 

It is of interest to assess the process potential of methanol production by a direct partial oxidation of methane. This way the steam reformer and the shift reactor can be saved, and the catalytic methanol reactor can be replaced by a noncatalytic partial oxidation reactor. It is estimated that direct partial oxidation is competitive if a conversion of methane of at least 5.5% can be obtained with a methanol selectivity of at least 80%. 

Compare modeling predictions with the experimental data shown in Fig. 14.11, assuming plug flow. Evaluate how well the the model describes methane oxidation under these conditions. Using the model, assess whether addition of hydrogen may enhance methanol selectivity. 

Ng, H.-J., C.-J. Chen, and D.B. Robinson. 1985. Hydrate formation and equilibrium phase compositions in the presence of methanol Selected systems containing hydrogen sulfide, carbon dioxide, ethane, or methane. GPA Research Report RR-87, Tulsa, OK. 

The concept of electroauxiiiaiy is quite powerful to solve these problems. The pre-introduction of a siiyi group as an electroauxiliary decreases the oxidation potential of dialkyl ethers by virtue of the orbital interaction. As a matter of fact, we demonstrated that the anodic oxidation of a-silyl ether took place smoothly in methanol. " Selective dissociation of the C-Si bond occured and the methoxy group was introduced on the carbon to which the silyl group was attached. Therefore, a-silyl ethers seemed to serve as suitable precursors for alkoxycarbenium ions in the cation pool method. 

Flow oattem Conversion of methanol Selectivity to formaldehyde... 

The composite membrane gave 4—5 times larger flux than commercial membrane without appreciable loss in selectivity. Downstream pressure of -6.67 KPa had little effect on the total flux Methanol selectivity PVA > CA > CTA > B1 > B2. The influence of the membrane material with varying solubility parameter is investigated... 

Ray SK, Sawant SB, Joshi JB, and Pangarkar VG. Development of methanol selective membranes for separation of methanol-MTBE mixtures by pervaporation. J. App. Poly. Sci. 1999 74(ll) 2645-2559. 

The challenge of this reaction is to reduce the Weinreb amide to the aldehyde while simultaneously reducing the methyl ester to the primary allylic alcohol. Different reagents were tested, but only an excess of sodium aluminum hydride delivered the desired product 13. The substrate was either inert or degraded if LiAlH4 or DIBAL were used. NaBH4 in methanol selectively reduced only the amide, but to form the primary alcohol. Because of its instability, hydroxyaldehyde 13 was not purified but directly subjected to the next reaction. 

At 300°C, both methanol yield and methanol selectivities are decreasing during a 70 h. run. Figure 4 shows that no essential difference appears during this aging process if the Cu-pyrochlore (Zr/La ratio = 1) prepared via the oxalate or the carbonate intermediates are compared. Thus the catalysts obtained from the carbonate precipitation show a 39% loss of the MeOH yield and a 45% loss of selectivity. In the same conditions the decreases are respectively of 25% and 34% with the system originating from oxalates. 

In the presence of CO2+H2 the observed conversion and methanol yields can be roughly related to the copper surface areas measured for the different catalyst samples. Thus the CuZn-i-LaZr [ex carbonate] catalyst with 31 m2/g copper surface area shows the best catalytic activity. For the same catalyst, the methanol selectivities illustrated in figure 4 are generally lower than those of the other samples. This phenomenon can be related to the presence of La2Zr07 which is not in interaction with copper and which induces mainly the reverse water gas shift reaction. 

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