Molecular carbide

Data from Union Carbide Molecular Sieves, UOP, Tarrytown, N.Y. 

The business that grew out of the Linde Laboratories was the Union Carbide Molecular Sieve business which, since 1988, has been integral to UOP s Catalysts Adsorbents and Specialties business segment. 

Union Carbide Molecular Sieves for Selective Adsorption, 2nd edn, British Drug Houses, Poole,... 

The first synthetic zeolites were known as Linde Molecular Sieves but are now marketed as Union Carbide Molecular Sieves they are available from Union Carbide International Company, USA. or Union Carbide (UK) Ltd directly, or through the usual chemical suppliers, t Booklets giving detailed information on the structure, action and applications of molecular sieves are available from most suppliers of laboratory chemicals. 

Bulletin Union Carbide Molecular Sieves for Selective Absorption, The British Drug Houses Ltd. D. W. Breck, Crystalline Molecular Sieves," X Chem. Ld., 41,678 (1964)... 

AES Amount of coke (approximately) Fraction of amorphous/graphitic Vs carbidic/molecular. 92,93... 

Moles of calcium carbide = mass of calcium carbide/molecular weight of calcium carbide = 1,000 [g]/64 [g/mol] = 15.625 [mol].Given that, accordingto (8.11), to produce 1 [mol] acetylene... 

Fig. 37C.4. Intensity pattern of carbide molecular ions from a Y20t-graphite pellet spectra (from Cook, 1966).

Flowing liquid carbon dioxide (CO2) in the supercritical state (70 atm and 40°C) is used to dissolve and separate the organometaUic analyte compounds in a capillary column fitted with a gas restrictor at its exit. As the compounds sequentially leave the separation column, they are transported in the vapor state, along with the now gaseous carbon dioxide, to the plasma in the heated argon carrier gas stream. The introduction of the CO2 into the plasma creates potential interferences fiom the formation of carbide molecular compounds. Species such as C 0, and Ar C ... 

The formal relationship between interstitial carbide molecular clusters and M-C binary phases with respect to coordination of the carbide atom and M-C bonding interactions has already been discussed in several reviews [10,11,71,72]. We confine ourselves to the latest results obtained in this field. The best example of bulk metal carbide structural behaviour in a large metal cluster is probably represented by the recently characterized [HNi3g(00) 2 51 penta-anion, which has been obtained by reaction of [Ni5(CO)i2j with hexachloropropene [73]. The Ni32Cb inner core of this cluster is closely related to a fragment of the Cr23C binary phase [74]. 

Material Molecular Weight (g/ mol) Molar Volume (cmVmol) Metal Carbide Molecular Weight (g/ mol) Molar Volume (cmVmol) % Expansion MtoMC... 

An example of a commercial semibatch polymerization process is the early Union Carbide process for Dynel, one of the first flame-retardant modacryhc fibers (23,24). Dynel, a staple fiber that was wet spun from acetone, was introduced in 1951. The polymer is made up of 40% acrylonitrile and 60% vinyl chloride. The reactivity ratios for this monomer pair are 3.7 and 0.074 for acrylonitrile and vinyl chloride in solution at 60°C. Thus acrylonitrile is much more reactive than vinyl chloride in this copolymerization. In addition, vinyl chloride is a strong chain-transfer agent. To make the Dynel composition of 60% vinyl chloride, the monomer composition must be maintained at 82% vinyl chloride. Since acrylonitrile is consumed much more rapidly than vinyl chloride, if no control is exercised over the monomer composition, the acrylonitrile content of the monomer decreases to approximately 1% after only 25% conversion. The low acrylonitrile content of the monomer required for this process introduces yet another problem. That is, with an acrylonitrile weight fraction of only 0.18 in the unreacted monomer mixture, the low concentration of acrylonitrile becomes a rate-limiting reaction step. Therefore, the overall rate of chain growth is low and under normal conditions, with chain transfer and radical recombination, the molecular weight of the polymer is very low. 

Of the three worldwide manufacturers of poly(ethylene oxide) resins. Union Carbide Corp. offers the broadest range of products. The primary quaUty control measure for these resins is the concentrated aqueous solution viscosity, which is related to molecular weight. Specifications for Polyox are summarized in Table 4. Additional product specifications frequendy include moisture content, particle size distribution, and residual catalyst by-product level. 

In the physical separation process, a molecular sieve adsorbent is used as in the Union Carbide Olefins Siv process (88—90). Linear butenes are selectively adsorbed, and the isobutylene effluent is distilled to obtain a polymer-grade product. The adsorbent is a synthetic 2eohte, Type 5A in the calcium cation exchanged form (91). UOP also offers an adsorption process, the Sorbutene process (92). The UOP process utilizes ahquid B—B stream, and uses a proprietary rotary valve containing multiple ports, which direct the flow of Hquid to various sections of the adsorber (93,94). The cis- and trans-isomers are alkylated and used in the gasoline blending pool. 

To imrove mechanical properties, increased axial molecular orientation was required. Union Carbide workers under government contract worked on... 

In 1958 the Union Carbide Corporation introduced high molecular weight, highly crystalline ethylene oxide polymers under the trade name Polyox. Although similar in appearance to polyethylene they are miscible with water in all proportions at room temperature. 

This polymer first appeared commercially in 1965 (Parylene N Union Carbide). It is prepared by a sequence of reactions initiated by the pyrolysis of p-xylene at 950°C in the presence of steam to give the cyclic dimer. This, when pyrolysed at 550°C, yields monomeric p-xylylene. When the vapour of the monomer condenses on a cool surface it polymerises and the polymer may be stripped off as a free film. This is claimed to have a service life of 10 years at 220°C, and the main interest in it is as a dielectric film. A monochloro-substituted polymer (Parylene C) is also available. With both Parylene materials the polymers have molecular weights of the order of 500 000. 

Attempts to classify carbides according to structure or bond type meet the same difficulties as were encountered with hydrides (p. 64) and borides (p. 145) and for the same reasons. The general trends in properties of the three groups of compounds are, however, broadly similar, being most polar (ionic) for the electropositive metals, most covalent (molecular) for the electronegative non-metals and somewhat complex (interstitial) for the elements in the centre of the d block. There are also several elements with poorly characterized, unstable, or non-existent carbides, namely the later transition elements (Groups 11 and 12), the platinum metals, and the post transition-metal elements in Group 13. 

Such binary borides (p. 145), carbides (p. 297) and nitrides (p. 417) as are formed have been referred to already. The ability of the metals to absorb molecular hydrogen has also been alluded to above. While the existence of definite hydrides of nickel and platinum is in doubt the... 

---