Ruben Vasquez-Medrano

Organic electrosynthesis: a promising green methodology in organic chemistry

Over the last decade, organic electrosynthesis has become recognized as one of the methodologies that can fulfill several important criteria that are needed if society is to develop environmentally compatible processes. It can be used to replace toxic or dangerous oxidizing or reducing reagents, reduce energy consumption, and can be used for the in situ production of unstable and hazardous reagents. These are just a few of the most important attributes that render electrochemistry environmentally useful. In this review the main characteristics of electrochemistry as a promising green methodology for organic synthesis are described and exemplified. Herein we provide basic information concerning the nature of electrosynthetic processes, paired electrochemical reactions, electrocatalytic reactions, reactions carried out in ionic liquids, electrogeneration of reactants, electrochemical reactions that use renewable starting materials (biomass), green organic electrosynthesis in micro- and nano-emulsions, the synthesis of complex molecules using an electrosynthetic key step, and conclude with some insights concerning the future. Throughout the review the “green aspects” of these topics are highlighted and their relationship with the twelve green chemistry principles is described.

Characterization and detoxification of a mature landfill leachate using a combined coagulation-flocculation/photo Fenton treatment.

The aim of the present work was to characterize and treat a mature landfill leachate using a coagulation/flocculation process followed by a photo-Fenton oxidation treatment. The leachate was obtained from a landfill in Tetlama, Morelos (Mexico) during the drought season and was characterized in terms of its major pollutants. Considerable levels of chemical oxygen demand (COD), total carbon (TC) and NH4+ were identified, as well as high concentrations of Hg, Pb, and As. Other heavy metals such as Ni, Co, Zn, Cd, and Mn were detected at trace levels. The lethal concentration (LC50) of the leachate, evaluated on Artemia salina, was 12,161±11 mg/L of COD, demonstrating an antagonistic interaction among the leachates components. The treatment of this effluent consisted of a coagulation-flocculation process using an optimal dose of FeCl3 · 6H2O of 300 mg/L. The supernatant was treated using a photo-Fenton process mediated with FeCl2 · 4H2O and H2O2 in a compound parabolic concentrator (CPC) photo-reactor operating in batch mode using an R ratio (R=[H2O2]/[Fe2+]) of 114. The global removal efficiencies after treatment were 56% for the COD, 95% for TC, and 64% for NH4+. The removal efficiencies for As, Hg, and Pb were 46%, 9%, and 85%, respectively.

A ferrous oxalate mediated photo-Fenton system: Toward an increased biodegradability of indigo dyed wastewaters

This study assessed the applicability of a ferrous oxalate mediated photo-Fenton pretreatment for indigo-dyed wastewaters as to produce a biodegradable enough effluent, likely of being derived to conventional biological processes. The photochemical treatment was performed with ferrous oxalate and hydrogen peroxide in a Compound Parabolic Concentrator (CPC) under batch operation conditions. The reaction was studied at natural pH conditions (5-6) with indigo concentrations in the range of 6.67-33.33 mg L(-1), using a fixed oxalate-to-iron mass ratio (C(2)O(4)(2-)/Fe(2+)=35) and assessing the systems biodegradability at low (257 mg L(-1)) and high (1280 mg L(-1)) H(2)O(2) concentrations. In order to seek the optimal conditions for the treatment of indigo dyed wastewaters, an experimental design consisting in a statistical surface response approach was carried out. This analysis revealed that the best removal efficiencies for Total Organic Carbon (TOC) were obtained for low peroxide doses. In general it was observed that after 20 kJ L(-1), almost every treated effluent increased its biodegradability from a BOD(5)/COD value of 0.4. This increase in the biodegradability was confirmed by the presence of short chain carboxylic acids as intermediate products and by the mineralization of organic nitrogen into nitrate. Finally, an overall decrease in the LC(50) for Artemia salina indicated a successful detoxification of the effluent.

Modeling and simulation of lithium-ion batteries

Abstract In this work the dynamic one-dimensional modeling and simulation of Li ion batteries with chemistry Li x C 6 −− Li y Mn 2 O 4 is presented. The model used is robust in terms of electrochemical variables prediction rather than only the electrical ones. This enables us to analyze the internal behavior of the battery under different discharge rates. The method of lines (MOL) was used for predicting the behavior from the model without any loss of exactitude for regular geometries. The boundary conditions were modified to achieve a better convergence of the solver. The simulation results were compared to experimental data from the research literature. Some examples of application are also presented that include the simulation for the optimization of design parameters, the evaluation of the behavior of the battery under dynamic discharge rates simulating real simplified conditions of operation and the simulation of the parallel discharge of different capacity pairs of batteries.

Cathodic Production of ClO2 from NaClO3

A study is presented on the cathodic reduction in ClO ― 3 ions in acidic and circumneutral solutions. The systems thermodynamics (i.e., the corresponding Pourbaix diagram) is an aid in predicting the appropriate conditions for the different processes to occur and in interpreting the results. Linear sweep and cyclic voltammetries on a Pt electrode, together with a spectroelectrochemical arrangement that allows for real-time monitoring of these processes by means of both a UV/visible spectrophotometer and a potentiostat, yield evidence of the ClO ― 3 to ClO ― 2 reduction in circumneutral media and of a multiplicative effect in the production of ClO 2 in highly acidic sulfate media due to a chemical/electrochemical/chemical pathway.

Ferrioxalate-Mediated Processes

Abstract Advanced oxidation processes have been successfully applied for wastewater treatment at a laboratory pilot and semi-industrial scale. Sustainable alternatives such as photo-Fenton processes have been scarcely applied due to technical, environmental, and economic barriers. Photo-Fenton intensification with organic complexes appears to be an important alternative to overcome two important disadvantages of Fenton processes, i.e., catalyst regeneration and operation at acidic pH. The addition of organic ligands is critical in improving process performance because it makes operation at circumneutral conditions possible, increases •OH radicals production rate, the regeneration of the iron catalyst, and allows the formation of additional radicals. Although Fenton intensification with organic ligands requires the addition of more reagents, technical and economic advantages such as near neutrality operation, reduction of chemical auxiliaries consumption (acid and base), and reaction time can enhance the environmental performance of Fenton and photo-Fenton processes.