Phase Disengagement Research Articles

Phase Equilibria in High-Pressure Polyethylene Technology

This is a review of the phase equilibria in supercritical monomer solutions of ethylene homopolymers and copolymers, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), poly(ethylene-co-methacrylate) (EMA), poly(ethylene-co-vinyl acetate) (EVA), poly(ethylene-co-methacrylic acid) (EMAA), and poly(ethylene-co-acrylic acid) (EAA). The knowledge of such phase equilibria underlies the high-pressure polyethylene (HPPE) technology. The ability to estimate such phase equilibria allows for smooth and robust process optimization during grade transitions. This is important because the HPPE technology makes it possible to minimize the product cross-contamination and, hence, to make higher-value, fluctuating-demand speciality polymers. Experimental data, phase diagrams, and patterns of phase disengagement presented in this paper are related to the reactor system, the high-pressure separator (HPS), and the high-pressure recycle system. These data and diagrams are used to characterize the monomer-polymer miscibility defined as a cloud point transition. The cloud point pressures in such systems are found to depend on thermodynamic parameters, such as temperature and composition, and on the dissimilarity between the polymer and the monomer. This dissimilarity is characterized in terms of the differences in molecular weight and density (e.g., for LDPE and LLDPE), in polarity (e.g., for EVA and EMA), and in association (e.g., for EAA and EMAA)

Gold recovery with solvent sublation from chloride solutions

Solvent sublation (SS) has been investigated for separating gold from dilute chloride solutions using hexadecyltrimethylammonium bromide (HTMAB) both as collector and surfactant. The composition of organic and aqueous phases, and operating conditions such as gas flowrate and aeration time were studied. As a result, 10% 2-octanol in kerosene with 0.05 M Aliquat 336 was chosen as the organic phase. It is shown that gold can be separated quantitatively from a solution with only 10 ppm Au, with enrichment of 20. Comparisons to ion flotation (IF) and solvent extraction (SX) were also made. SS was found to be more effective than IF. SX is a little more effective than SS, but it takes as long as 24 h for phase disengagement, compared to <3 min for SS.

Interpretation of continuous settling behavior from batch settling data in a Versatic acid 10-water system

Studies on the prediction of phase disengagement in a continuous settler from batch settling data have been carried out. An equation to predict the variation of dispersion band height with dispersion throughput has been derived. The batch decay curve of the present system showed a typical sigmoidal decay mode, at the first stage of which free sedimentation of drops controlled the overall rate, while at the second stage the drop-drop and drop-interface coalescence dominated. It was found that the initial drop size and dispersed phase hold-up had to be taken into account in the interpretation of dispersion behaviour in a continuous settler. It can be concluded that it is possible to express the dispersion band thickness in terms of parameters proposed in this model and that the dispersed liquid drops collapse through an identical coalescence mechanism in both the batch and the continuous settlers.

EXTRACTION OF Pu(IV) AND Th(IV) CHLORIDES WITH n-OCTYL(PHENYL)-N,N-DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE IN TETRACHLOROETHYLENE∗

ABSTRACT The distribution of trace and macro amounts of Pu(IV) and Th(IV) chlorides between solutions of n-octyl(phenyl)-N,N-diiso-butylcarbamoylmethylphosphlne oxide in tetrachloroethylene and aqueous solutions of hydrochloric acid was studied. In extracting macro quantities of Pu(IV), the solvent can be loaded up to a Pu(IV)/extractant ratio of 1:2, but small amounts of a solid are formed which strongly retard phase disengagement. The disengaging problem can be overcome by using a phase modifier such as tributyl phosphate or dibutyl butylphosphonate. Both modifiers only slightly suppress the efficiency of the Pu(IV) extraction. Th(IV) is less extractable than Pu(IV) and a Th(IV) extractant ratio of only 1:3 can be reached even In the presence of excess Th(IV). Both Pu(IV) and Th(IV) form a third phase (second organic phase) at high concentrations of hydrochloric acid or in the presence of chlorides which salt-out hydrochloric acid from the aqueous phase.

Séparation actinides-lanthanides à contre-courant en batterie de mélangeurs-décanteurs

First results dealing with trivalent actinide-lanthanide group separations in mixer-settler using as extractant the mixture tris(2,4,6-(2-pyridyl))-1,3,5,-triazine (TPTZ), dinonylnaphthalene sulphonic acid (HDNNS) are reported. Carbon tetrachloride was used as diluent in order to minimize the phase disengagement difficulties. Aqueous phase was 0.125 N HNO 3 with 0.003 M TPTZ. Group separation at the radioactive traces level was satisfatory, 99.9% of americium(III) being recovered with only 2% of the initial lanthanides. For macroconcentrations 5% of the lanthanides were still present in the organic americium fraction (99.5% of initial americium). These incomplete separations were attributed to temperature fluctuations in the mixer-settler and some incomplete phase disengagement due to the small size of the equipment.

The production of pulsed E.H.T. voltages for electrostatic coalescence

The use of an electric field, applied between immersed electrodes, is known to promote the separation of water-in-oil type dispersions or emulsions. Recent work has established that pulsed unidirectional voltages applied to electrodes insulated from the liquids is an efficient means of promoting phase disengagement particularly for dispersions with a high conducting phase content. The range of applications is thus extended to include chemical engineering operations such as solvent extraction and crude oil dehydration. It has been shown that the rate of coalescence is not only a function of pulse amplitude but also its shape, mark space ratio and frequency; all of these parameters having physical optimum values. There is, at present, no commercially available package capable of generating a pulsed EHT output of any form in the required frequency range (0.1 – 50 Hz). This paper therefore describes an existing arrangement for laboratory use and a more compact solid state version. The implementation of monitoring and external control facilities is also briefly mentioned.

Drop-Interface Coalescence Rate in Tertiary Amine Solvent Extraction

Abstract An important requirement for economical application of solvent extraction technology is rapid and efficient phase disengagement. However, much progress toward a clear fundamental understanding of the factors that affect phase disengagement rate will be needed before a logical approach to the problem will be possible. In this paper, we develop the conceptual framework for the study of drop-interface coalescence in collapsing liquid/liquid dispersions and present the details of the experimental setup employed in our initial work. The method for determining the drop-interface coalescence rate requires measurement of the average volume of drops (vf) adjacent to the interface, their number (n) per unit area of interface, and dispersed-phase throughput (Q) per unit area. We have employed recording videomicrography for measurement of vf and n, while Q is found from the changing position of the major interface as the dispersion band collapses (batch mode).

Hot water process development for Utah tar sands

The hot water process for Utah tar sands differs significantly from that used for Canadian tar sands due to the inherent differences in the respective bitumen viscosities and the nature of sand-bitumen association. Specifically, the high viscosity of Utah bitumen and the direct bonding to sand particles necessitates phase disengagement by hot water digestion in a high shear force field under appropriate conditions of pulp density and solution alkalinity. Interestingly, phase separation is accompanied by a modified froth flotation technique inasmuch as the dispersed bitumen droplets which are collected in the froth phase are not hydrophobic but, nevertheless, entrap air bubbles and are recovered in the bitumen concentrate.

Surface Chemistry Features in the Hot Water Processing of Utah Tar Sand

Abstract The hot water processing of Utah tar sand involves two important steps in the process sequence, phase disengagement (digestion) and phase separation (flotation). Inasmuch as phase separation is accomplished by flotation, the hydrophobic/hydrophilic balance at the surface of the bitumen droplets was studied in conjunction with the system's solution chemistry and the results correlated with the flotation response. Contact angle measurements of solvent extracted bitumen revealed a moderate hydrophobic character; however, air bubble attachment at the surface of bitumen obtained from a hot water concentrate was difficult and required long induction times. These results suggest that the phase separation by flotation is dependent on air bubble entrapment by bitumen droplets rather than attachment due to surface hydrophobicity. In addition, identification of surface functional groups and components solubilized during hot water digestion was attempted using IR and NMR spectra. Strong absorption peaks at 1708 cm−1, 2920 cm−1, and 2855 cm−1 for the solubilized components together with NMR spectra indicate the presence of dissolved paraffinic carboxylates, the amount of which increased as the digestion pH was increased. Potentiometric titration of the water soluble constituents indicated an acid dissociation constant of pKa = 5 which would be expected for such carboxylate species. This phenomenon appears to account, in part, for the polar bitumen surface and the hydrophilic character of the digested bitumen. These and other results indicate that phase disengagement during digestion and bitumen hydrophobicity may be mutually exclusive effects and reinforce the notion that flotation separation is achieved by entrapment of air bubbles in the viscous bitumen droplets. Finally, the surface chemistry associated with phase disengagementhas been considered to alimited extent. It appears from preliminary experiments that phase disengagement by digestion involves the actual chemical attack of the silica surface layers by the hot alkaline solution which allows the release of the quartz particles from the bitumen phase.

Factors Influencing Phase Disengagement Rates in Solvent Extraction Systems Employing Tertiary Amine Extractants

Abstract Phase disengagement rate is a critical property in determining the usefulness of a particular solvent extraction system in hydro-metallurgy. A survey of a number of commercial tertiary amine extractants of the type used in uranium extraction hydrometallurgy has been carried out to suggest whether structural factors influence phase disengagement behavior and to provide a useful comparison of different amines with regard to phase disengagement and uranium extraction. The amines ((CnH2n+1)3N) were chosen to cover a range of alkyl chain lengths including straight-chain and branched-chain compositions, and the chemical makeup of the liquid-liquid systems closely paralleled that of the systems used in the Amex uranium extraction process. Batch phase disengagement tests showed significant trends with respect to amine structure and composition using acid sulfate solutions with or without added colloidal silica and actual ore leach solutions as the aqueous phase. In general, organic continuous (OC) phase ...

Measurement of contact angles in ternary liquid systems

Measurements of equilibrium contact angles in the ternary liquid system water, toluene, acetone are reported on stainless steel, glass and Teflon surfaces. These are shown to vary considerably with acetone concentration. For droplets of aqueous phase on high-energy surfaces the contact angle decreased with increasing acetone concentration until at 60% wt./wt. acetone complete wetting was observed. Similar behaviour was observed for droplets of organic phase on a Teflon surface. The results are of interest in assessing the performance of knitted meshed and packings used in extraction and separation equipment to promote coalescence and phase disengagement.