Micro-electrolysis System Research Articles

Identification of degradation products of ionic liquids in an ultrasound assisted zero-valent iron activated carbon micro-electrolysis system and their degradation mechanism

Ionic liquids (ILs) have potential applications in many areas of chemical industry because of their unique properties. However, it has been shown that the ILs commonly used to date are toxic and not biodegradable in nature, thus development of efficient chemical methods for the degradation of ILs is imperative. In this work, degradation of imidazolium, piperidinium, pyrrolidinium and morpholinium based ILs in an ultrasound and zero-valent iron activated carbon (ZVI/AC) micro-electrolysis system was investigated, and some intermediates generated during the degradation were identified. It was found that more than 90% of 1-alkyl-3-methylimidazolium bromide ([Cnmim]Br, n = 2, 4, 6, 8, 10) could be degraded within 110 min, and three intermediates 1-alkyl-3-methyl-2,4,5-trioxoimidazolidine, 1-alkyl-3-methylurea and N-alkylformamide were detected. On the other hand, 1-butyl-1-methylpiperidinium bromide ([C4mpip]Br), 1-butyl-1-methylpyrrolidinium bromide ([C4mpyr]Br) and N-butyl-N-methylmorpholinium bromide ([C4mmor]Br) were also effectively degraded through the sequential oxidization into hydroxyl, carbonyl and carboxyl groups in different positions of the butyl side chain, and then the N-butyl side chain was broken to form the final products of N-methylpiperidinium, N-methylpyrrolidinium and N-methylmorpholinium, respectively. Based on these intermediate products, degradation pathways of these ILs were suggested. These findings may provide fundamental information on the assessment of the factors related to the environmental fate and environmental behavior of these commonly used ILs.

Degradation of 1-butyl-3-methylimidazolium chloride ionic liquid by ultrasound and zero-valent iron/activated carbon

It has been reported that ionic liquids (ILs) are commonly toxic in nature, and thus the removal of ILs in various environmental systems would be of great significance. In this work, an ultrasonic irradiation and zero-valent iron activated carbon (ZVI/AC) micro-electrolysis system was applied to degradation of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) residues in water. The experimental conditions were optimized, and the degradation processes were investigated by using UV, HPLC and GC–MS techniques. It was found that more than 95% of [C4mim]Cl could be degraded in aqueous solution and 81% of [C4mim]Cl could be mineralized within 110min, and the degradation could be described by a pseudo-first-order kinetics. The presence of hydroxyl radical scavenger can greatly reduce the reaction rate but could not prevent degradation of [C4mim]Cl. GC–MS analyses demonstrated that this degradation led to the formation of 1-butyl-3-methyl-2,4,5-trioxoimidazolidine, 1-butyl-3-methylurea and N-butylformamide. On the basis of these intermediates, degradation pathway was also suggested. These results indicate that ZVI/AC micro-electrolysis with ultrasonic irradiation degradation could serve as an efficient treatment technology for removing [C4mim]Cl from wastewater.

Degradation of 3,3′-iminobis-propanenitrile in aqueous solution by Fe0/GAC micro-electrolysis system

The degradation of 3,3′-iminobis-propanenitrile was investigated using the Fe0/GAC micro-electrolysis system. Effects of influent pH value, Fe0/GAC ratio and granular activated carbon (GAC) adsorption on the removal efficiency of the pollutant were studied in the Fe0/GAC micro-electrolysis system. The degradation of 3,3′-iminobis-propanenitrile was affected by influent pH, and a decrease of the influent pH values from 8.0 to 4.0 led to the increase of degradation efficiency. Granular activated carbon was added as cathode to form macroscopic galvanic cells between Fe0 and GAC and enhance the current efficiency of the Fe0/GAC micro-electrolysis system. The GAC could only adsorb the pollutant and provide buffer capacity for the Fe0/GAC micro-electrolysis system, and the macroscopic galvanic cells of the Fe0/GAC micro-electrolysis system played a leading role in degradation of 3,3′-iminobis-propanenitrile. With the analysis of the degradation products with GC–MS, possible reaction pathway for the degradation of 3,3′-iminobis-propanenitrile by the Fe0/GAC micro-electrolysis system was suggested.

Oxidation of Phenol by Microbubble‐Assisted Microelectrolysis

AbstractThe degradation of phenol under microelectrolysis was enhanced by O2‐microbubbles. Phenol solution was circled in a microbubble‐assisted microelectrolysis reactor under acid conditions. The degradation rate of phenol reached 65 % within 2 h with O2‐microbubbles, compared to 9.5 % and 4 % with air‐ and N2‐microbubbles due to better dissolution of oxygen with finer microbubbles and at higher dissolution pressure. Higher efficiencies of phenol degradation at lower temperature further confirm the role of dissolved oxygen. In the microbubble‐assisted microelectrolysis system dissolved oxygen, carbon steel pellets, and sulfuric acid are necessary conditions for the oxidation of phenol. The conversion of phenol increases with an increasing amount of carbon steel pellets and/or sulfuric acid. Catechol, hydroquinone, and low‐molecular‐weight carboxylic acids are the major products.

Pretreatment of wastewater from acrylonitrile–butadiene–styrene (ABS) resin manufacturing by microelectrolysis

Pretreatment of acrylonitrile–butadiene–styrene (ABS) resin wastewater by microelectrolysis system was investigated to improve the biodegradability of the toxic aromatic compounds and organic nitriles. Two experiment systems, (a) control experiment of Fe and carbon and (b) microelectrolysis reactor, were set up to confirm the importance of macroscopic galvanic cells. In addition, the effect of the influent pH and Fe/C ratio on the efficiency of the microelectrolysis reactor was studied. The experimental results showed that the maximum COD removal efficiency was in the range of 50–55%, and the BOD 5/COD ratio was enhanced from 0.32 to 0.71 under the best condition of the influent pH 4 and Fe/C ration of 1:1 ( v/ v). The microelectrolysis reactor could not remove the nitrogen in ABS resin wastewater, but it could transform the organic nitriles into NH 3-N, amine and acylamide, and the NH 3-N transformation efficiency reached 50% when the influent pH was 4. The decomposition and transformation of the aromatic compounds and organic nitriles in ABS resin wastewater was monitored by UV–vis, fourier transform infrared spectroscopy (FTIR) and gas chromatography mass spectrometry (GC–MS). This study showed that an almost total decomposition or transformation of the toxic organic pollutants and an increasing biodegradability of the pretreated ABS resin wastewater could be achieved by microelectrolysis reactor.

Development of a new microelectrolysis system for in-situ electrodeposition of ultra-traces of gold prior to measurement by ETAAS.

Electrodeposition is known to be suitable for separation and preconcentration of extremely low concentrations of analyte from bulk samples and is instrumentally is very simple. In this approach a new combined system was designed for in-situ electrodeposition of ultratrace levels of gold from micro samples on to a graphite furnace prior to determination by electrothermal atomic absorption spectrometry (ETAAS). Sediment samples were digested and traces of the gold content were extracted with boiling aqua regia. To prevent the highly corrosive effect of aqua regia media, the graphite tube surface was pre-coated by electrodeposition of ppm amounts of Pd prior to sample introduction. Separation of the analyte from the matrix was achieved by electrodeposition of the analyte in situ on the Pd/C surface of the furnace tube. Vanadium was also used as a modifier to stabilize the analyte from decomposition at charring temperatures. By using the proposed microelectrolysis preconcentration technique a considerable improvement in sensitivity and detection limit was achieved compared with conventional ETAAS. Characteristic masses for ED-ETAAS techniques in both nitric acid and aqua regia were reported to be m(o)=4.1 pg, with %RSD=2.9; the calculated LOD was 0.105 ppb, and typical calibration graphs for this element in nitric acid and aqua regia for both techniques were linear up to 70 microg L(-1) with about 99% recovery. Six reference sediments samples were tested by the proposed technique and by the Conv-ETAAS method. The results were in agreement with recommended values (reported by a reference laboratory using UV-visible spectrometry), demonstrating the efficiency of extraction and preconcentration of ultratrace levels of gold.