Palladium integration

Survey of the patent Hterature reveals companies with processes for 1,4-butanediol from maleic anhydride include BASF (94), British Petroleum (95,96), Davy McKee (93,97), Hoechst (98), Huels (99), and Tonen (100,101). Processes for the production of y-butyrolactone have been described for operation in both the gas (102—104) and Hquid (105—108) phases. In the gas phase, direct hydrogenation of maleic anhydride in hydrogen at 245°C and 1.03 MPa gives an 88% yield of y-butyrolactone (104). Du Pont has developed a process for the production of tetrahydrofuran back-integrated to a butane feedstock (109). Slurry reactor catalysts containing palladium and rhenium are used to hydrogenate aqueous maleic acid to tetrahydrofuran (110,111). 

Electronic Applications. The PGMs have a number of important and diverse appHcations in the electronics industry (30). The most widely used are palladium and mthenium. Palladium or palladium—silver thick-film pastes are used in multilayer ceramic capacitors and conductor inks for hybrid integrated circuits (qv). In multilayer ceramic capacitors, the termination electrodes are silver or a silver-rich Pd—Ag alloy. The internal electrodes use a palladium-rich Pd—Ag alloy. Palladium salts are increasingly used to plate edge connectors and lead frames of semiconductors (qv), as a cost-effective alternative to gold. In 1994, 45% of total mthenium demand was for use in mthenium oxide resistor pastes (see Electrical connectors). 

The design of the Pd-membrane reactor was based on the chip design of reactor [R 10]. The membrane is a composite of three layers, silicon nitride, silicon oxide and palladium. The first two layers are perforated and function as structural support for the latter. They serve also for electrical insulation of the Pd film from the integrated temperature-sensing and heater element. The latter is needed to set the temperature as one parameter that determines the hydrogen flow. 

Some companies are successfully integrating chemo- and biocatalytic transformations in multi-step syntheses. An elegant example is the Lonza nicotinamide process mentioned earlier (.see Fig. 2.34). The raw material, 2-methylpentane-1,5-diamine, is produced by hydrogenation of 2-methylglutaronitrile, a byproduct of the manufacture of nylon-6,6 intermediates by hydrocyanation of butadiene. The process involves a zeolite-catalysed cyciization in the vapour phase, followed by palladium-catalysed dehydrogenation, vapour-pha.se ammoxidation with NH3/O2 over an oxide catalyst, and, finally, enzymatic hydrolysis of a nitrile to an amide. 

An integrated proof-of-concept (POC) size fluidized-bed methane reformer with embedded palladium membrane modules for simultaneous hydrogen separation is being developed for demonstration (Tamhankar et al., 2007). The membrane modules will use two 6 in. X 11 in. Pd-alloy membrane foils, 25-pm thick, supported on a porous support. The developmental fluidized-bed reactor will house a total of five (5) membrane modules with a total membrane area of about 0.43 m2 and is scheduled for demonstration by September 2007. 

Integrated guides can also be used as a chemical sensor. Fig. 19 shows a Mach-Zehnder interferometer where one of the two branches has been covered by palladium, a catalytic metal for H2 [4]. The output phase change measurement determination of parts per million of H2 has proven to be possible. 

The cells shown in Figs. 28 and 29 all operate according to the same principles, which have been developed by Arup. The interior of the cell acts as the anode chamber, and a metal oxide cathode placed inside the cell in an alkaline electrolyte acts as the counter electrode. The hydrogen flux across the integrated membrane (coated with palladium on the internal surface) can be measured as the potential drop across a resistor placed between the membrane and the counter electrode. 

The hydrogen contact cell (HCC-11 in Fig. 29) does not have an integrated membrane, but merely a palladium window, and is intended for clamp-on purposes. It can be used on any smooth or flat surface and measures the effluent hydrogen permeation through vessels, pipelines, etc., for example, during full-scale testing as demonstrated by Christensen etal ... 

The next step in the processor development will be to integrate the palladium alloy membrane with the methanol steam reformer reactor. The researchers anticipate that the addition of the palladium membrane will improve the reactor performance due to in-situ hydrogen removal. 

The integration of a catalyzed kinetic enantiomer resolution and concurrent racemization is known as a dynamic kinetic resolution (DKR). This asymmetric transformation can provide a theoretical 100% yield without any requirement for enantiomer separation. Enzymes have been used most commonly as the resolving catalysts and precious metals as the racemizing catalysts. Most examples involve racemic secondary alcohols, but an increasing number of chiral amine enzyme DKRs are being reported. Reetz, in 1996, first reported the DKR of rac-2-methylbenzylamine using Candida antarctica lipase B and vinyl acetate with palladium on carbon as the racemization catalyst [20]. The reaction was carried out at 50°C over 8 days to give the (S)-amide in 99% ee and 64% yield. Rather surpris-... 

Judging from experimental data for palladium-hydrogen (11,52) the relations in 22 hold very well. The integral in Equation 21 now may be rewritten, using the relations in 22, as ... 

It has been shown that the two-phase pressure variation for palladium-hydrogen yields values of ASa— and AHa—/ , and that these values are closely temperature independent. The temperature independence results because the value of the integral in Equation 21 can be approximated closely by the corresponding relative partial value at the critical composition. Variations of ASg o and AHh—o with temperature (see Figure 6) are apparently too small to be detected in the plot of In /22(two-phase) against T ly but can be detected by the more sensitive plot of RT In P /2 against T or possibly could be detected by calorimetric determinations of AHa—over a wide temperature range. 

M. L. Kovarik, M.W. Li and R.S. Martin, Integration of a carbon microelectrode with a microfabricated palladium decoupler for use in microchip capillary electrophoresis/ electrochemistry, Electrophoresis, 26 (2005) 202-210. 

Franz et al. [93] developed a palladium membrane micro reactor for hydrogen separation based on MEMS technology, which incorporated integrated devices for heating and temperature measurement. The reactor consisted of two channels separated by the membrane, which was composed of three layers. Two of them, which were made of silicon nitride introduced by low-pressure chemical vapor deposition (0.3 pm thick) and silicon oxide by temperature treatment (0.2 pm thick), served as perforated supports for the palladium membrane. Both layers were deposited on a silicon wafer and subsequently removed from one side completely... 

The location of the metal in a particle can also be determined by running a line scan to detect the X rays characteristic of palladium. As the electron beam moves across the particle, the detector signal is integrated and displayed on a cathode ray tube as intensity versus electron beam position. The resulting signal is shown in Fig. 11C. 

The potential cycling illustrated by Figure 5.20 is a commonly used pre-treatment procedure for attainment of a reproducible active surface. Less widely known is the fact that in aqueous solution this cycling procedure causes the dissolution of appreciable quantities of metal. The discrepancy between the integrated anodic and cathodic oxygen adsorption-desorption peaks has been shown to be due to dissolution of the metal. Typical values are given in Ref. 68 and indicate that platinum and gold dissolve to a much lesser extent than do palladium and rhodium. 

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