Brian J. Brisdon

Performance of PDMS and organofunctionalised PDMS membranes for the pervaporative recovery of organics from aqueous streams

Abstract Modified polysiloxane membranes containing different organofunctional side chains were produced and tested for the recovery of various organic contaminants from aqueous sterams, using the process of pervaporation. Four separate organic components, phenol, chloroform, pyridine and methylisobutylketone (MIBK), each representative of an industrially significant family of chemicals, were chosen for evaluation. In each case significant performance enhancements, over that achieved with an unfunctionalised poly(dimethylsiloxane) membrane, were realise. Phenol transport is significantly facilitated by the incorporation of basic groups into the membrane structure. This is thought to be due to a weak acid-base interaction, increasing phenol sorption into the membrane. For pyridine, chloroform and MIBK separations from water, selectivity towards the organic component is greatly enhanced by the incorporation of long chain alkyl groups. A dual effect of the increased organic content of the membrane leading to increased organic component sorption and reduced water sorption is thought to be responsible. The effect of varying the three process parameters, feed concentration, membrane cross-linking density and membrane functional loading, were investigated. Some flux coupling effects were apparent, particularly affecting the transport of water with changing organic component concentration. Changing the cross-linking density of the membrane was found to have negligible effect across the range studied. An optimal functional loading generally close to 10% exists.

A fundamental study of organofunctionalised PDMS membranes for the pervaporative recovery of phenolic compounds from aqueous streams

Abstract Modified polydimethylsiloxane (PDMS) composite membranes in which a known mol% of the SiMe groups were replaced by a short methylene spacer group terminated by one of the four side-arm functional groups, acetate, CO 2 Me; ethylether, OEt; dimethylamino, NMe 2 ; and pyridyl, py; were fabricated and tested in short term trials for the pervaporative recovery of cresols from aqueous solution. The influences of functional group type, functional group loading, pH, temperature and purity of the feed solution were investigated. Three commercially available hydrophobic membranes were also examined for comparison. It was found that significant performance enhancements, compared with an unfunctionalised PDMS membrane, were realised for all functionalised PDMS membranes, with dimethylamino and ethylether functionalities proving the most effective. A functional group loading level close to 20% was found to be optimal for this application, The influence of feed pH in the range of 5–8.5 was small on total flux but significant on selectivity for amine loaded membranes. By contrast, the effect of feed temperature was significant on total flux but negligible on selectivity. Low levels of phenolic impurities in a p -cresol feed solution were found to have negligible effect on the separation. Compared with commercially available zeolite filled PDMS and PEBA membranes, the functionalised PDMS membranes showed a better overall performance. The PV performance of all new membranes followed the trend: o -cresol> p -cresol>phenol.

Transition metal complexes of N-substituted derivatives of 2-[(N-acetyl) amino]pyridine

Abstract The stereochemistries of complexes formed between the dichlorides of cobalt, nickel, copper and zinc and the tertiary amides 2-[N-acetyl-N-methyl)amino]pyridine (amp) and 2-[(N-acetyl-N-phenyl)amino]pyridine (app) have been investigated by infrared, electronic and nmr spectroscopies. Both ligands chelate via the pyridine-N and amide-O atoms in the pseudotetrahedral M(amp)Cl 2 (M = Co and Zn) and M(app)Cl 2 (M = Co, Ni, Cu and Zn) complexes. The effects of the bulky N-substituents on complex formation and the conformation of the free ligand are discussed in comparison with the parent amide, 2-[(N-acetyl)amino] pyridine (aapH).

Ditertiary phosphine complexes of (ν-allyl)dicarbonylmolybdenum(II) and -tungsten(II)

Abstract Compounds of the type [XM(CO) 2 (ν-allyl)L 2 ] (where X = Cl and Br; M = Mo and W; L 2 = Ph 2 PCH 2 PPh 2 and Ph 2 PCH 2 CH 2 PPh 2 ) have been prepard from the corersponding MeCN complexes. The spectral properties of these compounds and the effects of chelate rign size on 31 P coordination shifts and J ( 183 W— 31 P) have been investigated.

PALLADIUM ASSISTED ORGANIC REACTIONS. II. ORTHO-AMINOMETHYLSTILBENE DERIVATIVES

Di-μ-chlorobis(N,N-dimethyl-3,4-dimethoxybenzylamine-6-C,N)dipalladium (1b) reacts readily with a variety of styrenes to give good yields of the corresponding o-aminomethylstilbene derivatives.

Synthesis and structural characterization of cycloborasiloxanes: The X-ray crystal structures of cyclo-1,3,3,5,5-pentaphenyl-1-bora-3,5-disiloxane and cyclo-1,3,3,5,7,7-hexaphenyl-1,5-dibora-3,7-disiloxane

Cycloborasiloxanes [PhB(OSiPh2)O]2 (1) and RB[(OSiPh2)2] [R= Ph (2); 2,4,6-Me3C6H2 (3)] containing eight- and six-membered rings, respectively, have been synthesized by the reaction of RB(OH)2 with 1,1,3,3-tetraphenyl-1-3-dihydroxy-1,3-disiloxane or diphenylsilanediol. The structures of 1 and 2 have been determined, and both contain essentially planar SiOB rings, although the SiO and BO bonds are shorter in the larger ring. The factors affecting the structural parameters of related heterocyclic ring systems are reviewed.

Reactions of (η-allyl)dicarbonylmolybdenum(II) complexes with phosphorus and arsenic donor ligands

Reaction of [MoX(CO)2(η-C3H5)(MeCN)2] with the arsines Ph2AsCH2CH2AsPh2 (dae) and Ph2AsCH2AsPh2 (dam) yields complexes of stoichiometry [MoX(CO)2(η-C3H5)dae] (where X = Cl, Br or I) and [MoX(CO)2(η-C3H5)]2dam (where X = Cl or Br). The former are isomorphous with the known Ph2PCH2CH2PPH2 complexes, whereas the latter probably contain halogen and dam bridges. Under forcing conditions the corresponding ditertiary phosphines form the molybdenum(0) derivatives cis-Mo(CO)2(Ph2P(CH2)nPPh2]2 (where n = 1 or 2).

THE PERMSELECTIVITY OF POLYORGANOSILOXANES CONTAINING ESTER FUNCTIONALITIES

Abstract The permeabilities of carbon dioxide, methane, oxygen and nitrogen in a range of polyorganosiloxane membranes containing a side-chain ester functionality of 0-21.4 mol% of Si atoms, have been determined by a continuous flow method over the temperature range 35-100°C. The ratio of the CO 2 and CH 4 permeabilities, or permselectivity, increases with increase in ester functionality. As measurement of the diffusivities at 35°C shows that there is little change in the relative diffusivity of CO 2 to CH 4 with increase in ester functionality, the greater permselectivity results from an increase in the relative solubility of CO 2 to CH 4 . This is confirmed by measurements of the relative solubility using a vacuum microbalance. Moreover, since the activation energy for CO 2 permeation is much lower than that for CH 4 , the permselectivity becomes greater as the temperature is lowered. In contrast, the ratio of the oxygen/nitrogen permeabilities decreases slightly with increase in ester functionality as a result of a decreasing relative solubility, the relative diffusivity again remaining virtually unchanged.

Anionic tricarbonyl derivatives of molybdenum and tungsten and their reactions with allyl halides

A series of carbonylmetallate anions fac-[MX(CO)3L2]−, where M = Mo or W, X = Cl, Br or I and L2 = 1,10-phenanthroline(phen) or 2,2′-bipyridine(bipy) have been prepared from the corresponding cis-M(CO)4L2 complexes. No evidence of fac-to mer-isomerisation was evident on dissolution, although in MeCN solvolysis occurred with the formation of fac-M(CO)3L2(MeCN). Reaction of the anions with various allyl halides resulted in high yields of η3-allyl complexes [MX(CO)2(η3-RC3H4)L2]. The significance of these observations for the mechanism of the allyl oxidative-addition reaction are discussed.

The structure of hexa(cyclohexylsesquisiloxane), (C6H11)6Si6O9

The structure of hexa(cyclohexylsesquisiloxane), Cy6Si6O9, has been determined and shown to be based on a cage arrangement in which two non-planar six-membered Si3O3 rings are joined co-facially by SiOSi bridges, so generating three further Si4O4 rings. The structural variations in six- and eight-membered (SiO)n rings in this and other known cage sesquisiloxanes are analysed and compared with those of analogous rings in two-dimensional diorganosiloxane heterocycles.