Ultrasound-assisted extraction of chromium from tanned leather shavings: A promising continuous flow technology for the treatment of solid waste.

In this work, a continuous flow extraction system assisted by ultrasound (US) was developed for the extraction of Cr(III) from residual tanned leather shavings. US energy was delivered into the system by a tubular applicator (clamp-on tube US applicator). The effect of the US energy was investigated at 20 kHz of frequency and electrical input power of 75, 150, 300 and 600 W. Residence time and temperature profile were also evaluated. It was observed that the internal temperature profile was affected by the presence of US and inverted in comparison with the conditions without US. In this way, the temperature profile generated by the US was reproduced by using electrical resistances in order to compare the obtained results. The US intensity was measured using a hydrophone connected to a sound pressure meter. The use of the US did not alter the dynamic behavior of the system but increased the extraction efficiency when compared to the silent condition. US power above 75 W did not lead to increased extraction efficiency, when the residence time was 30 min. However, when 60 min of residence time were employed, the optimized US power was 150 W, resulting in an extraction efficiency of 71.7 ± 0.7 %, about 28 % higher when compared to the silent condition in the same temperature and other conditions. The US energy allowed a reduction in processing time and operational temperature when compared to the silent condition with the same temperature profile. The overall energy consumption with US was similar or lower than that observed without US, showing the feasibility of the proposed extraction system.

Development of an eco-friendly sample preparation protocol for metal determination in food samples: an oxygen pressurized single reaction chamber using diluted nitric acid.

Many efforts have been recently made to improve the digestion efficiency by using powerful equipment or by using an auxiliary reagent. In this work, an alternative method is reported, which explores a digestion system based on a single reaction chamber (SRC) technology pressurized with O2 for reducing the amount of acid, without impairing the digestion efficiency. Before digestion, the system was pressurized with compressed air (20 bar, 20% O2) while the temperature was evaluated from 180 up to 270 °C. The procedure was also carried out under O2 pressure (20 bar). For each temperature several acid concentrations were evaluated (0.1 to 3 mol L-1 HNO3), being possible to correlate the effectiveness of each acid concentration with temperature. The proposed method was applied to the simultaneous digestion of several organic matrices with variable content of fat, protein, and carbohydrate (whole milk powder, bovine liver, parsley, and linseed). The residual carbon content was lower than 4% (C lower than 200 mg L-1 in digests), showing the high digestion efficiency of the proposed approach. Up to 250 mg of all food matrices were digested using a sub-stoichiometric amount of HNO3 (1 mol L-1 solution), which was only achieved due to the use of O2 as an auxiliary reagent. Barium, Ca, Cu, Fe, K, Mg, Mn, Na, Sr, and Zn were determined by ICP-OES, and the accuracy was better than 95% for standard reference materials of corn bran, whole milk powder, and bovine liver. It is an important feature, being in agreement with green chemistry recommendations because very low amounts of reagents are required for sample digestion, as well as low amounts of residues are generated.

New possibilities for pharmaceutical excipients analysis: Combustion combined with pyrohydrolysis system for further total chlorine determination by ICP-OES.

An alternative method for the determination of total chlorine content in hydroxypropyl cellulose (HPC) was applied, combining a recently developed system based on a combustion step followed by pyrohydrolysis reaction. Using this approach it the determination of total chlorine by inductively coupled plasma optical emission spectrometry (ICP-OES) without interferences was feasible. It overcame the limitations of European Pharmacopoeia (EP) method for HPC analysis regarding to the inability to determine total chlorine in HPC, once some chlorine compounds (e.g., chloroform) that can not be identified by the official method (EP). The following parameters of combustion and pyrohydrolysis were evaluated: absorbing solution, sample mass, the use of powdered silica as retardant of combustion, oxygen flow rate and reaction time. Reference values for total chlorine were obtained after digestion using microwave-induced combustion and determination by ion chromatography (IC). Microwave-assisted extraction (MAE) was also investigated for Cl extraction. The accuracy of the proposed method was also evaluated by analyte recovery tests (agreement of 95-103%), as well as by the analysis of certified reference materials (CRMs). The agreement with the certified values was higher than 95% and the limit of quantification (LOQ) was 50 µg g-1. Up to 500 mg of sample were efficiently digested by the proposed method in 5 min (dissolved carbon in digests was below 50 mg L-1). Total chlorine content in samples of modified cellulose ranged from 284 to 576 µg g-1. Despite the relatively high chlorine content in all samples, the concentration was lower than the maximum limit allowed by the EP for HPC (0.5%).

Intensification of ultrasonic-assisted crude oil demulsification based on acoustic field distribution data.

Water removal is an essential step during crude oil production due to several problems such as increased transportation costs and high corrosion rate due to dissolved salts. Indirect low frequency ultrasonic energy (US), using baths, has been recently proposed as an effective alternative for crude oil demulsification. However, the reactor position during sonication and its influence on the demulsification efficiency for crude oil has not been evaluated. In this sense, the aim of this study was to develop an automated system based on an open source hardware for mapping the acoustic field distribution in an US bath operating at 35kHz using a hydrophone. Data acquired with this system provided information to evaluate the demulsification efficiency in the different positions of the US bath and correlate it with the acoustic intensity distribution. The automated 3D-mapping system revealed a higher acoustic intensity in the regions immediately above the transducers (ca. 0.6Wcm-2), while the other regions presented a relatively lower intensity (ca. 0.1Wcm-2). Experimental data demonstrated that reactors positioned in the most intense acoustic regions provided a much higher efficiency of demulsification in comparison with the ones positioned in the less intense acoustic field regions. Demulsification efficiency up to 93% was obtained with 15min of sonication (100% amplitude) using few amount of chemical demulsifier. Hence, this work demonstrated that the information acquired with the developed mapping system could be used for inducing a higher efficiency of demulsification only by finding the more suitable position of reactor in the US bath, which certainly will help development of appropriate reactors design when looking for such approach.

Microwave-induced combustion: Thermal and morphological aspects for understanding the mechanism of ignition process for analytical applications.

In the present work, for the first time a systematic study was performed using an infrared camera and scanning electron microscopy (SEM) coupled to energy dispersive X-ray spectrometry (EDS) to evaluate the mechanisms involved in microwave-induced combustion method, which has been extensively used for sample preparation. Cellulose and glass fiber discs, wetted with the igniter solution (6molL-1 NH4NO3), were evaluated under microwave field in a monomode system. The temperature of the discs surface was recorded during microwave irradiation and the effect of NH4NO3 concentration and irradiation time on cellulose oxidation was evaluated. The morphology of the discs surface was characterized by SEM before and after irradiation in an inert atmosphere. According to the results, the surface temperature of the discs increased near to 100°C and remained in this temperature for few seconds while water evaporate. After that, temperature increased over 200°C due to the thermal decomposition of NH4NO3 salt, releasing a large amount of energy that accelerates cellulose oxidation. The higher the igniter concentration, the shorter was the microwave irradiation time for cellulose oxidation. The SEM images revealed that cellulose disc was more porous after microwave irradiation, enhancing oxygen diffusion within the paper and making easier its ignition. The EDS spectrum of cellulose and glass fiber discs showed that signal intensity for nitrogen decreased after microwave irradiation, showing that NH4NO3 was consumed during this process. Therefore, it was demonstrated that the ignition process is the result of synergic interaction of NH4NO3 thermal decomposition and organic matter oxidation (cellulose) releasing heat and feeding the chain reaction.

Determination of elemental impurities in poly(vinyl chloride) by inductively coupled plasma optical emission spectrometry.

In this work, a method for poly(vinyl chloride) (PVC) analysis by inductively coupled plasma optical emission spectrometry (ICP-OES) was developed. Samples were digested by microwave-induced combustion (MIC) and thirteen elements (Ba, Cd, Co, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sr, V and Zn) were determined by ICP-OES. Operational conditions of MIC were investigated allowing quantitative determination of all the analytes and suitable results were achieved using a 3 mol L(-1) HNO3 solution. Microwave-assisted wet digestion (MAWD) using closed quartz vessels and a single reaction chamber microwave digestion system (MAWD-SRC), were also evaluated for PVC digestion for results comparison. All the evaluated sample preparation methods were considered suitable for PVC digestion but MIC was preferable due to the possibility of using diluted HNO3 instead of concentrated reagents and due to the better digestion efficiency. The residual carbon content (RCC) in digests obtained by MIC was significantly lower in comparison with the values obtained after MAWD and by MAWD-SRC. Accuracy for the proposed method was better than 94% for all analytes by comparison of results with those obtained by neutron activation analysis (NAA). Using MIC, it was possible to digest a relatively high sample mass (500 mg) and up to 8 samples in less time (25 min) in comparison with MAWD and MAWD-SRC (about 60 min for both methods). The efficiency of digestion by MIC was higher 99% and lower limits of detection (as low as 0.1 µg g(-1)) were obtained avoiding the use of concentrated acids that is of great concern according to the current green chemistry recommendations.