Separation of lignosulfonate from its aqueous solution using supported liquid membrane

This paper presents an experimental and theoretical study on facilitated transport of lignosulfonate (LS) through a flat sheet supported liquid membrane using trioctylamine (TOA) as carrier and dichloroethane as diluent. The studies were carried out with various support materials and operating conditions (viz. carrier concentration, strip phase concentration, salt concentration, etc.) and their effects on the transport of LS. The results were analyzed to identify a suitable combination of support and operating condition that would yield best performance of the supported liquid membrane (SLM) in terms of fast and efficient transport of LS. The stability of the SLM was assessed in terms of loss of liquid from the pores of membrane support. The SLM is found to be stable till 10 h. Co-transport mechanism has been adopted in this work by using NaOH as the strip phase. It was observed that extraction of LS is increased with increase in concentration of NaOH up to a limiting value of 0.5 M NaOH. Difference of salt concentration between feed and strip phase considerably affect the separation process. The diffusional resistances of organic membrane (Δorg) and aqueous solution (Δaq) calculated from the permeation model, which is again a combination of three unique mechanisms viz., diffusion through a feed aqueous layer, a fast interfacial chemical reaction, and diffusion of carrier–complex through the organic membrane, are found to be 609.9 and 176.6 s cm⁻¹, respectively. The values of the diffusion coefficient in the membrane (D_org) and in the bulk organic phase (D_complex) are 1.67×10⁻⁹ and 6.68 × 10⁻⁸ m²s⁻¹, respectively. The extraction of LS is about 90%. Nearly 43% of LS can be recovered at optimum condition.     

Simultaneous separation of mercury and lignosulfonate from aqueous solution using supported liquid membrane

This paper presents an experimental investigation on facilitated and simultaneous transport of mercury and lignosulfonate (LS) through a flat sheet supported liquid membrane (SLM) having Nylon 6,6 as support, trioctylamine (TOA) as carrier and dichloroethane as solvent. The experiments were performed at various operating conditions such as strip phase concentration, feed pH, carrier concentration and feed concentration to find the best set of parameters that would yield the maximum separation of pure mercury as well as its mixture with LS. The experiments were performed in co-transport mode using NaOH as the strip phase. It was observed that extraction of mercury as well as its mixture increases with increase in concentration of NaOH up to a certain limit 0.1 M NaOH in case of pure solution and 0.2 M NaOH in case of mixture). Feed phase pH significantly affects the mercury separation process. However, initial feed concentration does not affect the extraction process appreciably. Separation of mixture of mercury and LS behaves in a similar way as their pure solution; however the extraction is low in comparison to pure solution. The extraction of mercury from its pure solution is about 81% in 1 h. The extraction of mercury and LS from their mixture is about 52.6% and 50.2%, respectively at optimum condition and in a period of 2 h.     

Extraction and recovery of lignosulfonate from its aqueous solution using bulk liquid membrane

The paper presents an experimental study on the coupled transport of lignosulfonate (LS) through bulk liquid membrane (BLM) and thereby to identify the best set of solvent, operating conditions and mode of transport that would yield optimum performance of the BLM. Trioctylamine (TOA) is used as carrier. Among various solvents, tested for the above purpose, dichloroethane is found to be the best. The effects of operating condition, viz. pH, temperature, and carrier concentration, on the equilibrium distribution of LS are investigated. The effects of temperature, stirring of aqueous and organic phases, stirring speed, carrier concentration, initial feed and strip phase concentration on the separation of LS using BLM are also studied. It is observed that transport of LS can be enhanced by increasing the temperature and stirring speed of feed phase. Stirring of strip phase has no appreciable effects on the transport of LS. With increase in initial feed concentration the initial rate of the transport of LS is higher but continues for a longer time. Recovery of LS is much higher in co-transport mode in comparison to counter transport mode. Application of 1.25 M NaOH as stripping solution gives high recovery (70%) and high strip flux (70% of feed flux).     

Electrochemical Reduction of 4,4′‐(2,2,2‐Trichloroethane‐1,1‐diyl)‐ bis(chlorobenzene) (DDT) and 4,4′‐(2,2‐Dichloroethane‐1,1‐diyl)‐ bis(chlorobenzene) (DDD) at Carbon Cathodes in Dimethylformamide

In dimethylformamide containing tetramethylammonium tetrafluoroborate, cyclic voltammograms for reduction of 4,4′‐(2,2,2‐trichloroethane‐1,1‐diyl)bis(chlorobenzene) (DDT) at a glassy carbon cathode exhibit five waves, whereas three waves are observed for the reduction of 4,4′‐(2,2‐dichloroethane‐1,1‐diyl)bis(chlorobenzene) (DDD). Bulk electrolyses of DDT and DDD afford 4,4′‐(ethene‐1,1‐diyl)bis(chlorobenzene) (DDNU) as principal product (67–94%), together with 4,4′‐(2‐chloroethene‐1,1‐diyl)bis(chlorobenzene) (DDMU), 1‐chloro‐4‐styrylbenzene, and traces of both 1,1‐diphenylethane and 4,4′‐(ethane‐1,1‐diyl)bis(chlorobenzene) (DDO). For electrolyses of DDT and DDD, the coulometric n values are essentially 4 and 2, respectively. When DDT is reduced in the presence of a large excess of D₂O, the resulting DDNU and DDMU are almost fully deuterated, indicating that reductive cleavage of the carbon–chlorine bonds of DDT is a two‐electron process that involves carbanion intermediates. A mechanistic scheme is proposed to account for the formation of the various products.     

Thermal Behavior of Syndiotactic Polystyrene/1,2‐Dichloroethane Gels and Stoichiometry of Polymer‐Solvent Compounds

Abstract

The phase behavior of syndiotactic polystyrene (sPS)/1,2‐dichloroethane (DCE) gels has been investigated by differential scanning calorimetry (DSC) and wide angle x‐ray diffraction (WAXD) for different gel formation conditions. DSC data show that the gel melting temperatures are independent of the cooling conditions leading to gel formation, whereas the melting enthalpies of the gels depend on the cooling history. WAXD measurements show that for low concentration gels the sPS/DCE clathrate structure is obtained, whereas for high concentration gels both the clathrate structure and the solvent‐free β phase can be obtained. Furthermore, the onset of formation of the β phase is dependent on the cooling rate. In light of combined DSC and WAXD data, the reliability of the DSC in evaluating the absolute stoichiometry of polymer‐solvent compounds formed in sPS/DCE gels is discussed.