Bleaching of lignocellulosic material with in-situ-generated dioxirane

A chemical pulp which contains reactants capable of generating dioxirane within the pulp is produced in a process which comprises mixing a pulp with reactants comprising a carbonyl compound, preferably acetone, and an oxygen donor, preferably monoperoxysulfate, in proportions which produce a water-soluble dioxirane having a molecular diameter of less than 140 angstrom units. Such a pulp bleaching process which employs dioxirane as a bleaching agent is rendered environmentally and economically acceptable by recycling the reactants employed to produce the dioxirane. For the most up-to-date information about these patents, including the availability of Certificates of Correction, be sure to check the United States Patent and Trademark Office\u27s free, publicly accessible database: Patent Public Search https://ppubs.uspto.gov/pubwebapp/static/pages/landing.htmlhttps://irl.umsl.edu/patents/1005/thumbnail.jp

Environmental and economic assessment of the formic acid electrochemical manufacture using carbon dioxide: Influence of the electrode lifetime

This paper focuses on the study of the environmental and economic feasibility of the formic acid (FA) synthesis by means of electrochemical reduction (ER) of carbon dioxide (CO2) with special emphasis on the cathode lifetime. The study has used a Life Cycle Assessment (LCA) approach in order to obtain the environmental indicators as Global Warming Potential (GWP) and Abiotic Depletion (ADP) (both elements and fossil resources ADPs). The values of the indicators obtained in the assessment were representative of the Carbon Footprint (CF) and resource savings of this fabrication process. The commercial/conventional process for FA production was used as benchmark. The novelty of the study is the incorporation into the Life Cycle Inventory (LCI) of those materials and chemicals that are used in the fabrication of an ER cell, and in particular in the cathode. Hence, the lifetime of the cathode was used as a main parameter. The results obtained for a baseline case demonstrated that cathode lifetimes over 210 h would be enough to neglect the influence of the cathode fabrication from an environmental perspective. A first approach to the utility costs of CO2 ER process was also proposed in the study. Cost of utilities ranged between 0.16 € kg and 1.40 € kg-1 of FA in an ER process compared with 0.21 € kg-1 and 0.43 € kg-1 of FA in the conventional process depending on the market prices. This study demonstrated that the ER-based process could be competitive under future conditions if a reasonable electrocatalytic performance (in terms of cell voltage, current density, and faradaic efficiency) is achieved within a reasonable medium or long-term horizon. The results obtained aim to provide useful insights for decision-makers on the future developments within a decarbonized chemical industry.Authors thank to Spanish Ministry of Economy and Competitiveness (MINECO) for the financial support through the project CTQ2016-76231-C2-1-R. We would like also to thank MINECO for providing Marta Rumayor with a Juan de la Cierva postdoctoral contract (FJCI-2015-23658)

Sn nanoparticles on gas diffusion electrodes: Synthesis, characterization and use for continuous CO2 electroreduction to formate

Electrochemical reduction of CO2 has been pointed out as an interesting strategy to convert CO2 into useful chemicals. In addition, coupling CO2 electroreduction with renewable energies would allow storing electricity from intermittent renewable sources such as wind or solar power. In this work, an easy and fast method is adapted for the synthesis of pure and carbon supported Sn nanoparticles. The resulting nanoparticles have been characterized by transmission electron microscopy and their electrocatalytic properties towards CO2 reduction evaluated by cyclic voltammetry. Carbon supported Sn nanoparticles have been subsequently used to prepare Gas Diffusion Electrodes (Sn/C-GDEs). The electrodes have been characterized by scanning electron microscopy and also by cyclic voltammetry. Finally, the electrodes were tested on a continuous and single pass CO2 electroreduction filter-press type cell system in aqueous solution, to obtain formate at ambient pressure and temperature. These Sn/C-GDEs allow working at high current densities with low catholyte flow. Thus, for instance, at 150 mA cm−2, a 70% Faradaic Efficiency (FE) was obtained with a formate concentration of 2.5 g L−1. Interestingly, by increasing the current density to 200 mA cm−2 and decreasing the flow rate, a concentration over 16 g L−1 was reached. Despite the high concentrations obtained, further research is still required to keep high FE operating at high current densities.This work was conducted under the framework of the Spanish Ministry of Economy and Competitiveness projects CTQ2013-48280-C3-1-R and CTQ2013-48280-C3-3-R. Andrés Del Castillo also acknowledges the research grant from University of Cantabria, co-financed by the Regional Government of Cantabria

Continuous electrochemical reduction of carbon dioxide into formate using a tin cathode: comparison with lead cathode

Electrochemical reduction has been pointed out as a promising method for CO2valorisation into useful chemicals. This paper studies the influence of key variables on the performance of an experimental system for continuous electro-reduction of CO2 to formate, when a tin plate is used as working electrode. Particular emphasis is placed on comparing the performance of Sn and Pb as cathodes. As was previously found with Pb, the influence of current density (“j”) using Sn was particularly noteworthy, and when j was raised up to a limit value of 8.5 mA cm−2, important increases of the rate of formate production were observed at the expense of lowering the Faradaic efficiency. However, unlike what was found with Pb, the performance using Sn improved when the electrolyte flow rate/electrode area ratio was increased within the range studied (0.57–2.3 mL min−1 cm−2). In this way, the use of Sn as cathode allowed achieving rates of formate production that were 25% higher than the maximum rates obtained with Pb, together with Faradaic efficiencies close to 70%, which were 15 points higher than those with Pb. These results reinforce the interest in Sn as electrode material in the electro-reduction of CO2 to formate.This work was conducted under the framework of the Spanish Ministry of Science and Innovation Project ENE2010-14828

The carbon footprint of power-to-synthetic natural gas by photovoltaic solar powered electrochemical reduction of CO2

The search for more sustainable production and consumption patterns entails the integration of emerging edge-cutting technologies. Holistic studies are needed in order to accurately evaluate properly the environmental competitiveness of the suggested solutions. Among those alternatives, it has been suggested the utilisation of CO2 for the production of synthetic natural gas, the so-called Power-to-Gas (PtG) technology. In this work, we use the PtG technology to analyse the environmental rationality in terms of the carbon footprint (CF) of a Photovoltaic (PV) solar powered Electrochemical Reduction (ER) process for the utilisation of CO2 as carbon source for the production of CH4. This synthetic natural gas is ready to be injected into the transmission and distribution network. The raw materials for the process are a source of CO2 (mixed with different ratios of N2), H2O and electricity from PV solar. The separated products are CH4, C2H4, H2/CO, O2 and HCOOH. The reaction, separation/purification and compression stages needed to deliver commercially distributable products are included. Mass and energy balances were used to create a black-box model. The input to the model is the faradaic efficiency and cathodic potential of the best cathodesperforming at lab-scale (over 60% faradaic efficiency towards CH4). It was assumed that cathodes were long-lasting. The output of the model is the distribution of products (related to 1 kg of pure CH4) and the energy consumption at each of the aforementioned stages. The overall CF is then calculated as a function of the CF PV solar reference and the total energy consumption. The effect on the distribution of each stage to the total energy consumption of both the purity of the CO2 stream and the conversion of CO2 in the reactor was analysed. The results show that the principal contributor to the total energy consumption is the ER of CH4 across all CO2concentrations and conversions. When a CO2 conversion of 50% is chosen together with an inlet stream with a N2:CO2 ratio of 24, the electricity consumption of the process is between 2.6 and 6.2 times the minimum obtained for a reference ER reactor including the separation and compression of gaseous products (18.5 kWh kg−1 of CH4). The use of PV solar energywith low CF (14⋅10−3 kg kWh−1) allows the current lab-scale performers to even the CF associated with the average world production of natural gas when the valorisation of C2H4 is included (∼1.0 kg kg−1 of CH4).Authors gratefully acknowledge the funding provided by the State Research Agency, Ministry of Science, Innovation, and Universities (Spain) through the project CTQ2016-76231-C2-1-R

Ionic liquids in the electrochemical valorisation of CO2

The development of electrochemical processes for using captured CO2 in the production of valuable compounds appears as an attractive alternative to recycle CO2 and, at the same time, to store electricity from intermittent renewable sources. Among the different innovative attempts that are being investigated to improve these processes, the application of ionic liquids (ILs) has received growing attention in recent years. This paper presents a unified discussion of the significant work that involves the utilisation of ILs for the valorisation of CO2 by means of electrochemical routes. We discuss studies in which CO2 is used as one of the reactants to electrosynthesise value-added products, among which dimethyl carbonate has been the focus of particular attention in the literature. Approaches based on the electrochemical reduction of CO2 to convert it into products without the use of other carbon-based reactants are also reviewed, highlighting the remarkable improvements that the use of ILs has allowed in the CO2 electroreduction to CO. The review emphasises on different aspects related to process design, including the nature of IL anions and cations that have been used, the working conditions, the electrocatalytic materials, the electrode configurations, or the design of electrochemical cells, as well as discussing the most relevant observations, results and figures of merit that the participation of ILs has allowed to achieve in these processes. Several conclusions are finally proposed to highlight crucial challenges and recommendations for future research in this area.The financial support from the Spanish Ministry of Economy and Competitiveness Project CTQ2013-48280-C3-1-R is gratefully acknowledged. J. Albo particularly thanks Juan de la Cierva program (JCI-2012-12073)

Electroreduction of oxygen to hydrogen peroxide of particulate electrodes

The generation of hydrogen peroxide in dilute sodium hydroxide solutions was investigated by the electro-reduction of oxygen on beds of graphite particles. Two continuous electrochemical reactors were used to study the process at 16 to 20°C with oxygen pressures up to 12 atmospheres. The study embraced operation of the graphite cathode as both a fixed and a fluidised bed, though only the fixed bed was used at superatmospheric pressure. In each case both a two-phase system (cathode/oxygenated catholyte) and a three-phase system (cathode/catholyte/oxygen gas) were employed. The effects of the catholyte flow rate, catholyte pH, graphite particle size, bed depth, bed expansion, oxygen pressure, oxygen flow rate and the applied current on the process efficiency were measured. Depending on the conditions, the current efficiency for the conversion of oxygen to peroxide was between 20% and 100%, the yield of peroxide from oxygen was up to about 85% and the product peroxide concentration ranged from 0 to 0.15 molar. The results are interpreted in terms of the hydrodynamics and electrochemical kinetics in the cathode bed.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat