Carbon footprint of the hot-dip galvanisation process using a life cycle assessment approach

This work presents the carbon footprint (CF) of two hot-dip galvanisation (HDG) installations located in Spain with differences in the galvanising capacity and in the manufacturing process. The study determines the influence of the direct emissions (scope 1), emissions from electricity production (scope 2), and indirect emissions from upstream and downstream processes (scope 3). The results showed that steel and primary zinc production were the principal contributors to the CF. So, efforts should be focused on reducing the impact of the raw material production included in scope 3. Furthermore, two sensitivity analyses are presented: i) the production of one kg of two types of zinc products, special high-grade and redistilled zinc; ii) the use of two coatings: zinc for galvanisation and paint for pre-printed steel. The environmental impacts in SHG zinc were higher than in redistilled zinc, for all the impact categories due to the great influence of heavy metals emission. The results for zinc and paint protections showed that under the same level of corrosion, a greater thickness of paint is needed to protect steel pieces, compared to zinc coating. This sustainability assessment of the HDG industry recommends the sought of technology alternatives aimed at resource efficiency, such as zinc recovery from spent pickling baths, that could provide the desirable reduction of the environmental impacts associated to primary resource usage and waste treatment.Project LIFE-2-ACID Towards a sustainable use of metal resources in the galvanic industry 3 (LIFE 16 ENV/ES/000242) is co-financed by the European LIFE programm

Comprehensive kinetics of electrochemically assisted ammonia removal in marine aquaculture recirculating systems

This work reports a comprehensive kinetic analysis and modelling of the electrochemically assisted ammonia removal from marine aquaculture waters (RAS). The proposed model combines the kinetics of chlorine electro generation, experimentally determined, with the mechanism and kinetic parameters, taken from literature, of break point chlorination reactions involving aqueous chlorine (HClO and ClO-), total ammonia nitrogen (TAN as NH3 and NH4 +), and the chlorinated derivatives of ammonia (monochloramine (NH2C1), dichloramine (NHC12), and nitrogen trichloride (NC13)). The model has been validated with laboratory experiments, obtained in an electrochemical cell provided with Ti/RuO2 anode and Ti cathode, and working with model sea water in the range of operating variables [TAN]0 = 10-60 mg L-1 and j = 5 - 20 A m-2 ; good agreement between simulated and experimental data for the progress of ammonia and combined chlorine concentrations assesses the validity and robustness of the kinetic model. Thus, this study provides the tools to analyse, predict and explain ammonia removal performance in the electrochemical treatment of marine RAS water.Funding of project CTM2016-75509-R (MEIC, Spain/FEDER 2014- 2020) is gratefully acknowledged. The invitation by the E3TECH Spanish Network of Excellence (CTQ2017-90659-REDT (MEIC/AEI)) is kindly acknowledged

Hydrolytic degradation and mechanical stability of poly(Ɛ-caprolactone)/reduced graphene oxide membranes as scaffolds for in vitro neural tissue regeneration

The present work studies the functional behavior of novel poly(Ɛ-caprolactone) (PCL) membranes functionalized with reduced graphene oxide (rGO) nanoplatelets under simulated in vitro culture conditions (phosphate buffer solution (PBS) at 37 º C) during 1 year, in order to elucidate their applicability as scaffolds for in vitro neural regeneration. The morphological, chemical, and DSC results demonstrated that high internal porosity of the membranes facilitated water permeation and procured an accelerated hydrolytic degradation throughout the bulk pathway. Therefore, similar molecular weight reduction, from 80 kDa to 33 kDa for the control PCL, and to 27 kDa for PCL/rGO membranes, at the end of the study, was observed. After 1 year of hydrolytic degradation, though monomers coming from the hydrolytic cleavage of PCL diffused towards the PBS medium, the pH was barely affected, and the rGO nanoplatelets mainly remained in the membranes which envisaged low cytotoxic effect. On the other hand, the presence of rGO nanomaterials accelerated the loss of mechanical stability of the membranes. However, it is envisioned that the gradual degradation of the PCL/rGO membranes could facilitate cells infiltration, interconnectivity, and tissue formation.Financial support of the Cantabria Explora call through project JP03.640.69 is gratefully acknowledged. The support of project CTM2016-75509-R (MINECO and FEDER-Spain) is granted. We also thank Marta Romay at University of Cantabria who performed part of the experiments

Recovery of carbon monoxide from flue gases by reactive absorption in ionic liquid imidazolium chlorocuprate(I): mass transfer coefficients

Recovery of carbon monoxide from flue gases by selective absorption of carbon monoxide in an imidazolium chlorocuprate(I) ionic liquid is considered in this work as an alternative to the use of molecular volatile solvents such as aromatic hydrocarbons. The present work evaluates the CO mass transfer rates from the gas phase to the ionic liquid solutions in the absence of chemical reaction. To that end, carbon dioxide was employed as an inert model gas and absorption experiments were performed to assess the influence of different process variables in a batch reactor with flat gas–liquid interface. The experimental mass transfer coefficients showed significant variation with temperature, (3.4–10.9) × 10- 7 m·s- 1 between 293 and 313 K; stirring speed, (10.2–33.1) × 10- 7 m·s- 1 between 100 and 300 r·min- 1; and concentration of copper(I), (6.6–10.2) × 10- 7 m·s- 1 between 0.25 and 2 mol·L- 1. In addition, the mass transfer coefficients were eventually found to follow a potential proportionality of the type kL ? µ- 0.5 and the dimensionless correlation that makes the estimation of the mass transfer coefficients possible in the studied range of process variables was obtained: Sh = 10- 2.64 · Re1.07 · Sc0.75. These results constitute the first step in the kinetic analysis of the reaction between CO and imidazolium chlorocuprate(I) ionic liquid that determines the design of the separation units.Supported by the projects ENE2010-15585 and CTQ2012-31639, and the FPI post-graduate research grant (BES-2011-046279

Novel solvents based on thiocyanate ionic liquids doped with copper(I) with enhanced equilibrium selectivity for carbon monoxide separation from light gases

This work focuses on the research of novel carbon monoxide (CO) capture solvents to be applied to the separation of CO from other light components contained in gas streams of the process industry, e.g., nitrogen and hydrogen. More specifically, we examine the use of CO-selective capture solutions composed of the ionic liquid 1-ethyl-3-methylimidazolium thiocyanate ([C2mim][SCN]) and the transition metal salt copper(I) thiocyanate (CuSCN) as greener alternatives to the tetrachloroaluminate(III)-aromatic hydrocarbon solutions currently employed for CO separation from gas mixtures. In order to gain insight into the behavior of the selected ionic liquid solutions as chemical solvents for CO, their density and viscosity are characterized with respect to temperature and composition in a wide range of temperatures (273.15-303.15 K), pressures (up to 24 bar) and copper(I) concentrations (0-30 mol%). Moreover, the CO absorption has been assessed and gas-liquid equilibria are successfully described with a thermodynamic model as a function of those variables. The [C2mim]x[Cu]1-x[SCN] solutions exhibit favorable properties in terms of competitive CO sorption capacity and high selectivity towards slightly soluble gases, e.g., 996.1 mmol L-1 and CO/N2 selectivity of ~25 at 283.15 K and 23.3 bar, combined with low heat of absorption (-29.5 kJ mol-1) as well as easiness of regeneration and reuse. Consequently, these copper(I)-containing ionic liquids are promising for the development of novel and greener CO/N2 separation processes alternative to the use of flammable and toxic solvents or energy-intensive cryogenic distillations.Financial support from the Spanish Ministry of Economy and Competitiveness (CTQ2015-66078) and Fundación Iberdrola España is gratefully acknowledged. The authors would also like to thank Prof. A. Soto, Dr. E. Rodil and Dr. H. Rodriguez from Universidad de Santiago de Compostela for their valuable help with the characterization of the thermophysical properties of the IL solutions

Comparison of microcrystalline and ultrananocrystalline boron doped diamond anodes: Influence on perfluorooctanoic acid electrolysis

This work aims to study the effect of the distinctive chemical and structural surface features of boron doped diamond (BDD) anodes on their electrochemical performance for perfluorooctanoic acid (PFOA) degradation. Commercial BDD anodes were compared: (i) a microcrystalline (MCD) coating on silicon; and (ii) an ultrananocrystalline (UNCD) coating on niobium. MCD gave rise to the complete PFOA (0.24 mmol L−1) degradation in 4 h, at any applied current density in the range 1–5 mA cm−2. On the contrary, only 21% PFOA removal was achieved when using UNCD at 5 mA cm−2 under comparable experimental conditions. Similarly, the total organic carbon (TOC) was reduced by 89% using MCD, whereas only 13% TOC decrease was obtained by UNCD. In order to explain the dissimilar electrochemical activities, the morphological and chemical characterization of the electrode materials was developed by means of FESEM microscopy, XPS and Raman spectroscopy. The UNCD anode surface showed characteristic ultrananocrystalline grain size (2–25 nm), higher boron doping and greater content of H-terminated carbon, whereas the MCD anode was less conductive but contained higher sp3 carbon on the anode surface. Overall, the MCD electrode features allowed more efficient PFOA electrolysis than the UNCD anode. As a result of their distinctive performance, the energy needed for the maximum PFOA degradation (after 4 h) using MCD anode was only 1.4 kWh m−3, while the estimated energy consumption for the UNCD anode would be 37-fold higher. It is concluded that the use of the MCD anode involves considerable energy costs savings.Financial support from the projects CTM2013-44081-R, CTM2016-75509-R and to the Spanish Excellence Network E3TECH (CTQ2015-71650-RDT) (MINECO, SPAIN-FEDER 2014–2020) is gratefully acknowledged. B. Gomez also thanks the FPI research scholarship (BES-2014-071045). Dr. J. Carrillo-Abad is gratefully acknowledged for performing the cyclic voltammograms included in supplementary data

Separation of refrigerant gas mixtures containing R32, R134a and R1234yf through poly(ether-block-amide) membranes

Hydrofluorocarbons (HFCs) are powerful greenhouse gases whose production and consumption must be phased down in order to reach the reduction goals established by the Kigali Amendment to the Montreal Protocol. However, the share of recycled refrigerant gases remains very low owing to the extremely inefficient separation of refrigerant mixtures by cryogenic distillation. In this sense, the HFCs, difluoromethane (R32, GWP = 675) and 1,1,1,2-tetrafluoroethane (R134a, GWP = 1430), together with the hydrofluoroolefin (HFO) 2,3,3,3-tetrafluoropropene (R1234yf, GWP = 4), are among the most common constituents of HFC/HFO refrigerant mixtures currently employed in the refrigeration and air-conditioning sector. Therefore, the feasibility of using membrane technology for the selective separation of these compounds is assessed in this work for the first time. A comprehensive study of their gas permeation through several poly(ether-block-amide) (PEBA) membranes that differ on the content and type of backbone segments is performed. Results show that PEBA membranes exhibit superior permeability of R32 (up to 305 barrer) and R134a (up to 230 barrer) coupled with reasonably high selectivity for the gas pairs R32/R1234yf (up to 10) and R134a/R1234yf (up to 8). Moreover, for the blends R32/R1234yf and R32/R134a, the membrane separation performance is not significantly affected under the mixed gas conditions tested. Thus, results evidence that consideration should be given to membrane technology for the cost-efficient separation of HFC/HFO mixtures in order to boost the recycling of these compounds.This research is supported by Project KET4F-Gas-SOE2/ P1/P0823, which is co-inanced by the European Regional Development Fund within the framework of Interreg Sudoe Programme. The authors acknowledge the collaboration of Dr. Mar Lopez-Gonza ́ lez and Dr. Rosario Benavente (Institute of Polymer Science and Technology-CSIC) to perform the sorption and DSC experiments. F.P. acknowledges the postdoctoral fellowship (FJCI-2017-32884, ‘Juan de la Cierva Formacioń ’) from the Spanish Ministry of Science, Innovation and Universities

BDD anodic treatment of 6:2 fluorotelomer sulfonate (6:2 FTSA). Evaluation of operating variables and by-product formation

The concerns about the undesired impacts on human health and the environment of long chain perfluorinated alkyl substances (PFASs) have driven industrial initiatives to replace PFASs by shorter chain fluorinated homologues. 6:2 fluorotelomer sulfonic acid (6:2 FTSA) is applied as alternative to PFOS in metal plating and fluoropolymer manufacture. This study reports the electrochemical treatment of aqueous 6:2 FTSA solutions on microcrystalline BDD anodes. Bench scale batch experiments were performed, focused on assessing the effect of the electrolyte and the applied current density (5-600 A m-2) on the removal of 6:2 FTSA, the reduction of total organic carbon (TOC) and the fluoride release. Results showed that at the low range of applied current density (J=50 A m-2), using NaCl, Na2SO4 and NaClO4, the electrolyte exerted a minimal effect on removal rates. The formation of toxic inorganic chlorine species such as ClO4- was not observed. When using Na2SO4 electrolyte, increasing the applied current density to 350-600 A m-2 promoted a notable enhancement of the 6:2 FTSA removal and defluorination rates, pointing to the positive contribution of electrogenerated secondary oxidants to the overall removal rate. 6:2 FTSA was transformed into shorter-chain PFCAs, and eventually into CO2 and fluoride, as TOC reduction was >90%. Finally, it was demonstrated that diffusion in the liquid phase was controlling the overall kinetic rate, although with moderate improvements due to secondary oxidants at very high current densities.Support from MINECO and SPAIN-FEDER 2014–2020 to project CTM2016-75509-R and to the Spanish Excellence Network E3TECH (CTQ2015-71650-RDT) is acknowledged. J. Carrillo-Abad thanks the Generalitat Valenciana for granting a post doctoral fellowship (APOSTD/2015/019). The authors are thankful to Dr. R. Buck (Chemours Co.) for kindly providing samples of Capstone FS10

Enhanced treatment of perfluoroalkyl acids in groundwater by membrane separation and electrochemical oxidation

This work explores the treatment of poly- and perfluoroalkyl acids (PFAAs) in groundwater by coupling membrane separation and electrochemical oxidation (ELOX). A process system engineering approach based on modelling and empirical data was followed. Two nanofiltration (NF90) and reverse osmosis (BW30) membranes were characterized for treating an electrolyte (NaCl and CaSO4) mixture of perfluorocarboxylic acids (PFCAs) containing PFOA, PFHpA, PFHxA, PFPeA and PFBA with initial concentrations of 10 µg L−1 each. Membrane surface charge shielding and concentration polarization negatively influenced NF90 performance, and the BW30 membrane was selected. Electrochemical oxidation with boron doped diamond anodes treated the PFCAs mixture amended with PFOS and 6:2 FTSA, emulating previously pre-concentrated feed and non-preconcentrated feed conditions. Working at different current densities (J) between 20 and 350 A m−2, the removal of PFOA, PFOS and 6:2 FTSA followed first order apparent kinetics, although shorter chain PFCAs initially showed increasing trends because of their simultaneous electrogeneration and degradation. Overall, ΣPFAA electrolysis followed first order kinetics linearly correlated to J in the full range of testing. Unexpectedly, PFAAs electrolysis was faster for the low conductive non-preconcentrated feed, a result that was ascribed to the enhanced direct electron transfer mechanism resulting from the higher cell voltage. For 99.9% PFAAs removal, the total specific cost of treatment was minimized using a cascade of four RO stages and ELOX treatment of the concentrate, to reach ΣPFAA below the Health Advisory Levels recommended by the USEPA in drinking water (<70 ng L−1 sum of PFOA and PFOS).Financial support by the Spanish Ministry of Economy and Compet- itiveness through projects CTM2016-75509-R (MINECO, SPAIN-FEDER 2014-2020) and PID2019-105827RB-I00 (AEI, Spain) is gratefully acknowledged

Efficient treatment of perfluorohexanoic acid by nanofiltration followed by electrochemical degradation of the NF concentrate

The present study was aimed at the development of a strategy for removing and degrading perfluorohexanoic acid (PFHxA) from industrial process waters at concentrations in the range 60–200 mg L-1. The treatment train consisted of nanofiltration (NF) separation followed by electrochemical degradation of the NF concentrate. Using a laboratory-scale system and working in the total recirculation mode, the DowFilm NF270 membrane provided PFHxA rejections that varied in the range 96.6–99.4% as the operating pressure was increased from 2.5 to 20 bar. The NF operation in concentration mode enabled a volume reduction factor of 5 and increased the PFHxA concentration in the retentate to 870 mg L-1. Results showed that the increase in PFHxA concentration and the presence of calcium sulfate salts did not induce irreversible membrane fouling. The NF retentate was treated in a commercial undivided electrochemical cell provided with two parallel flow-by compartments separated by bipolar boron doped diamond (BDD) electrode, BDD counter anode, and counter cathode. Current densities ranging from 20 to 100 A m-2 were examined. The electrochemical degradation rate of PFHxA reached 98% and was accompanied by its efficient mineralization, as the reduction of total organic carbon was higher than 95%. Energy consumption, which was 15.2 kWh m-3 of treated NF concentrate, was minimized by selecting operation at 50 A m-2. While most of the previous research on the treatment of perfluoroalkyl substances (PFASs) focused on the removal of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), these compounds have been phased out by chemical manufacturers. Our findings are relevant for the treatment of PFHxA, which appears to be one of the present alternatives to long-chain PFASs thanks to its lower bioaccumulative potential than PFOA and PFOS. However, PFHxA also behaves as a persistent pollutant. Moreover, our results highlight the potential of combining membrane separation and electrochemical oxidation for the efficient treatment of PFAS-impacted waters.Financial support from projects CTM2013-44081-R and CTM2016-75509-R (MINECO, SPAIN-FEDER 2014e2020) is gratefully acknowledged