The design of a high pressure solvent extraction process using liquid ammonia as solvent

The literature on the potential use of liquid ammonia as a solvent for the extraction of aromatic hydrocarbons from mixtures with paraffins, and the application of reflux, has been reviewed. Reference is made to extractors suited to this application. A pilot scale extraction plant was designed comprising a Scm. diameter by 12Scm. high, 50 stage Rotating Disc Contactor with 2 external settlers. Provision was made for operation with, or without, reflux at a pressure of 10 bar and ambient temperature. The solvent recovery unit consisted of an evaporator, compressor and condenser in a refrigeration cycle. Two systems were selected for study, Cumene-n-Heptane-Ammonia and Toluene-Methylcyclohexane-Ammonia. Equlibrium data for the first system was determined experimentally in a specially-designed, equilibrium bomb. A technique was developed to withdraw samples under pressure for analysis by chromatography and titration. The extraction plant was commissioned with a kerosine-water system; detailed operating procedures were developed based on a Hazard and Operability Study. Experimental runs were carried out with both ternary ammonia systems. With the system Toluene-Methylcyclohexane-Ammonia the extraction plant and the solvent recovery facility, operated satisfactorily, and safely,in accordance with the operating procedures. Experimental data gave reasonable agreement with theory. Recommendations are made for further work with plant.

High-pressure XPS of crotyl alcohol selective oxidation over metallic and oxidized Pd(111)

Here, we report on the first application of high-pressure XPS (HP-XPS) to the surface catalyzed selective oxidation of a hydrocarbon over palladium, wherein the reactivity of metal and oxide surfaces in directing the oxidative dehydrogenation of crotyl alcohol (CrOH) to crotonaldehyde (CrHCO) is evaluated. Crotonaldehyde formation is disfavored over Pd(111) under all reaction conditions, with only crotyl alcohol decomposition observed. In contrast, 2D Pd5O4 and 3D PdO overlayers are able to selectively oxidize crotyl alcohol (1 mTorr) to crotonaldehyde in the presence of co-fed oxygen (140 mTorr) at temperatures as low as 40 °C. However, 2D Pd5O4 ultrathin films are unstable toward reduction by the alcohol at ambient temperature, whereas the 3D PdO oxide is able to sustain catalytic crotonaldehyde production even up to 150 °C. Co-fed oxygen is essential to stabilize palladium surface oxides toward in situ reduction by crotyl alcohol, with stability increasing with oxide film dimensionality.

Investigation of the effects of low energy high dose ion bombardment in metals and compound semiconductors

The effect of low energy nitrogen molecular ion beam bombardment on metals and compound semiconductors has been studied, with the aim to investigate at the effects of ion and target properties. For this purpose, nitrogen ion implantation in aluminium, iron, copper, gold, GaAs and AIGaAs is studied using XPS and Angle Resolve XPS. A series of experimental studies on N+2 bombardment induced compositional changes, especially the amount of nitrogen retained in the target, were accomplished. Both monoenergetic implantation and non-monoenergetic ion implantation were investigated, using the VG Scientific ESCALAB 200D system and a d. c. plasma cell, respectively. When the samples, with the exception of gold, are exposed to air, native oxide layers are formed on the surfaces. In the case of monoenergetic implantation, the surfaces were cleaned using Ar+ beam bombardment prior to implantation. The materials were then bombarded with N2+ beam and eight sets of successful experiments were performed on each sample, using a rastered N2+ ion beam of energy of 2, 3, 4 and 5 keV with current densities of 1 μA/cm2 and 5 μA/cm22 for each energy. The bombarded samples were examined by ARXPS. After each complete implantation, XPS depth profiles were created using Ar+ beam at energy 2 ke V and current density 2 μA/cm2 . As the current density was chosen as one of the parameters, accurate determination of current density was very important. In the case of glow discharge, two sets of successful experiments were performed in each case, by exposing the samples to nitrogen plasma for the two conditions: at low pressure and high voltage and high pressure and low voltage. These samples were then examined by ARXPS. On the theoretical side, the major problem was prediction of the number of ions of an element that can be implanted in a given matrix. Although the programme is essentially on experimental study, but an attempt is being made to understand the current theoretical models, such as SATVAL, SUSPRE and TRIM. The experimental results were compared with theoretical predictions, in order to gain a better understanding of the mechanisms responsible. From the experimental results, considering possible experimental uncertainties, there is no evidence of significant variation in nitrogen saturation concentration with ion energy or ion current density in the range of 2-5 ke V, however, the retention characteristics of implantant seem to strongly depend on the chemical reactivity between ion species and target material. The experimental data suggests the presence of at least one thermal process. The discrepancy between the theoretical and experimental results could be the inability of the codes to account for molecular ion impact and thermal processes.

Base modified peptidic nucleic acids: synthesis and crystallographic analysis of intermediates

Peptidic Nucleic Acids (PNAs) are achiral, uncharged nucleic add mimetics, with a novel backbone composed of N-(2-aminoethyl)glycine units attached to the DNA bases through carboxymethylene linkers. With the aim of extending and improving upon the molecular recognition properties of PNAs, the aim of this work was to synthesjse PNA building block intermediates containing a series of substituted purine bases for subsequent use in automated PNA synthesis. Four purine bases: 2,6~diaminopurine (D), isoGuanine (isoG), xanthine (X) and hypoxanthine (H) were identified for incorporation into PNAs targeted to DNA, with the promise of increased hybrid stability over extended pH ranges together with improvements over the use of adenine (A) in duplex formation, and cytosine (C) in triplex formation. A reliable, high-yielding synthesis of the PNA backbone component N -('2- butyloxycarbonyl-aminoethyl)glycinate ethyl ester was establishecl. The precursor N~(2-butyloxycarbonyl)amino acetonitrile was crystallised and analysed by X-ray crystallography for the first time. An excellent refinement (R = 0.0276) was attained for this structure, allowing comparisons with known analogues. Although chemical synthesis of pure, fully-characterised PNA monomers was not achieved, chemical synthesis of PNA building blocks composed of diaminopurine, xanthine and hypoxanthine was completely successful. In parallel, a second objective of this work was to characterise and evaluate novel crystalline intermediates, which formed a new series of substituted purine bases, generated by attaching alkyl substituents at the N9 or N7 sites of purine bases. Crystallographic analysis was undertaken to probe the regiochemistry of isomers, and to reveal interesting structural features of the new series of similarly-substituted purine bases. The attainment of the versatile synthetic intermediate 2,6-dichloro~9- (carboxymethyl)purine ethyl ester, and its homologous regioisomers 6-chloro~9- (carboxymethyl)purine ethyl ester and 6-chloro-7-(carboxymethyl)purine ethyl ester, necessitated the use of X-ray crystallographic analysis for unambiguous structural assignment. Successful refinement of the disordered 2,6-diamino-9-(carboxymethyl) purine ethyl ester allowed comparison with the reported structure of the adenine analogue, ethyl adenin-9-yl acetate. Replacement of the chloro moieties with amino, azido and methoxy groups expanded the internal angles at their point of attachment to the purine ring. Crystallographic analysis played a pivotal role towards confirming the identity of the peralkylated hypoxanthine derivative diethyl 6-oxo-6,7-dihydro-3H-purlne~3,7~djacetate, where two ethyl side chains were found to attach at N3 and N7,