Heterogeneous process methanol yield

A charge transfer complex is involved in the photochemical reaction between 4-cresol and tetranitromethane. Irradiation at 350 nm yields the o-nitrated product 235 ° . Other phenols such as phenol, 2- and 4-chlorophenol and 2- and 4-cresol behave in a similar manner and irradiation yields 2- and 4-nitrated products (236, 237) ° . The quantum yields for product formation are in the range 0.12-0.31. Only the formation of 3-nitrophenol from phenol is inhibited, as might be expected from attack at the 3-position, and shows a low quantum yield. It has been reported that 2-hydroxy- or 4-hydroxybiphenyl and 4,4 -dihydroxybiphenyl are the primary products formed from the photochemical reaction of biphenyl with sodium nitrate in aqueous methanol . Apparently the hydroxybiphenyls are prone to undergo photochemical nitration as a secondary process and yield the biphenyls 238 and 239 as well as 4,4 -dihydroxy-3,3 -dinitrobiphenyl, originally reported by Suzuki and coworkers under heterogeneous conditions. 

On the other hand, studying the influence of the surface material on the DMTM process in one [140] of a series of works, where a very high selectivity of methanol formation (P = 30 atm, T = 350 °C, tj- > 100 s) was observed, revealed no significant differences in the selectivity and yield of methanol in reactors with different surfaces, such as Pyrex, Teflon, stainless steel, silver, and copper. In these experiments, the selectivity of methanol formation on all surfaces reached values close to 90% or more, whereas the methanol yield was as high as 10.7%. However, the authors do not exclude the possibility of influence of the surface material on the temperature and reaction time. In particular, it was found that the maximum selectivity in reactors with metal surfaces was achieved at temperatures higher by nearly 50 °C. This is probably due to the fact that, at lower temperatures in the presence of a metal surface, the oxidation occurs mostly in the heterogeneous mode with the formation of mainly deep-oxidation products. 

A more obvious application of heterogeneous catalysis to the DMTM process is to convert part of the byproducts or highly reactive products into methanol, a more valuable and stable product. An interesting work in this respect is [68], where an increase in the methanol yield from the process promoted by 0.5% NO was achieved by passing the products of the gas-phase reaction with a temperature of 250 °C over a Cu—ZnO/AI2O3 catalyst. In the authors opinion, this occurred due to the catalytic hydrogenation of CH2O ... 

Figure 7.1 also shows the results of calculations by the gas-phase model described in [2] and [89] (Fig. 7.1, curve I). Despite the apparent incomplete accoimting of heterogeneous processes on the surface of the reactor, the resulting dependence satisfactorily describes the experimental pressure dependence of the methanol yield. 

---