Yaocihuatl Medina-Gonzalez

Towards green membranes: preparation of cellulose acetate ultrafiltration membranes using methyl lactate as a biosolvent

Ultrafiltration membranes were prepared using cellulose acetate (CA) as a polymer, LiCl and CaCl2 as porogens and methyl-(S)-lactate as a solvent. CA, methyl lactate and the porogens used in this work are obtained from renewable resources; they are biodegradable, non-toxic and non-volatile organic compounds. Flat sheet ultrafiltration membranes were prepared by the phase inversion technique. A molecular weight cut-off between 15 and 35 kDa (polyethylene glycol) and pure water permeability between 13 and 177 litres h− 1m− 2 bar− 1 were obtained. These parameters are in the ideal range for water treatment industry. Improvement of pollutant degree and ecotoxicity of the process was evaluated by ‘green’ metrics by the P (pollutants, persistent and bioaccumulative) and E (ecotoxicity) parameters. Both of these variables were recorded as zero using our method. This study represents a step ahead towards the production of ultrafiltration polymeric membranes by a ‘greener’ process than current methods.

Cellulosic materials as biopolymers and supercritical CO2 as a green process: chemistry and applications

In this review, we describe the use of supercritical CO2 (scCO2) in several cellulose applications. The focus is on different technologies that either exist or are expected to emerge in the near future. The applications are wide from the extraction of hazardous wastes to the cleaning and reuse of paper or production of glucose. To put this topic in context, cellulose chemistry and its interactions with scCO2 are described. The aim of this study was to discuss the new emerging technologies and trends concerning cellulosic materials processed in scCO2 such as cellulose drying to obtain aerogels, foams and other microporous materials, impregnation of cellulose, extraction of highly valuable compounds from plants and metallic residues from treated wood. Especially, in the bio-fuel production field, we address the pre-treatment of cellulose in scCO2 to improve fermentation to ethanol by cellulase enzymes. Other reactions of cellulosic materials such as organic inorganic composites fabrication and de-polymerisation have been considered. Cellulose treatment by scCO2 has been discussed as well. Finally, other applications like deacidification of paper and cellulosic membranes fabrication in scCO2 have been reviewed. Examples of the discussed technologies are included as well.

Improving PVDF Hollow Fiber Membranes for CO2 Gas Capture

Poly(vinylidene fluoride) (PVDF) hollow fiber membranes were obtained by the phase inversion technique. The influence of internal coagulant viscosity (0.001 to 3 Pa s) and air gap (0.6 to 86.4 cm) on the structure and mechanical resistance of the fibers was studied. A “sponge-like” structure free of macrovoids was obtained by using polyvinyl alcohol (PVA) with N-methyl pyrrolidinone and water as internal coagulant (viscosity 3 Pa s). The effect of the air-gap was studied in order to control the structure and obtain mechanically resistant membranes with tensile strength at break between 2.2 and 54.3 N/mm2 and pure water permeability ranging from 4 to 199 Lh−1m−2bar−1. CO2 permeability of these membranes was measured and found to be in the range of 365 to 53200 NLh−1m−2bar−1. The “Dusty Gas” model (DGM) was used to calculate the pore size of the membranes from CO2 permeability experiments, obtaining pore radius values going from 0.6 to 10.8 µm. Results from modeling were compared with pore sizes observed in SEM images showing that this model can accurately predict pore radius of sponge-like structures; however, pore sizes of membranes presenting sponge-like structures together with finger-like pores were inaccurately predicted by the DGM.

CO2-Expanded Alkyl Lactates : A Physicochemical and Molecular Modeling Study

With the perspective of finding alternative benign media for various applications, this paper presents a study of the physicochemical behavior of some members of the alkyl lactate family when expanded by CO2. Experimental and molecular modeling techniques have been used to determine and/or predict relevant physicochemical properties of these systems such as swelling, Kamlet–Taft parameters {polarity/polarizability (π*) and proticity or hydrogen-bond donator ability (α), dielectric constants and solubility parameters}. To complete the study of these properties, sigma profiles of the three lactates molecules have been obtained by performing quantum mechanical and phase equilibria calculations of CO2/alkyl lactate systems by using the Peng–Robinson equation of state.

Chemoenzymatic synthesis of polypeptides in neat 1,1,1,2-tetrafluoroethane solvent

Chemoenzymatic polypeptide synthesis offers several advantages over chemical or other biological routes, however, the use of aqueous-based media suffers from reverse hydrolysis reactions that challenge peptide chain propagation. Herein, the protease from subtilisin Carlsberg biocatalyzed the synthesis of poly-L-PheOEt, poly-L-LeuOEt, and the copolymers poly-L-PheOEt-co-L-LeuOEt from their amino acid ethyl ester substrates in a neat liquid 1,1,1,2-tetrafluoroethane solvent. The products, achieved in acceptable yields (ca. 50%), were fully characterized showing relatively high molar mass (ca. 20 000 Da for poly-L-PheOEt). This non-toxic low-boiling hydrofluorocarbon enhances enzymatic peptide propagation by limiting hydrolysis owing to its hydrophobic and relatively polar characteristics that sustain the protease activity and solubilize substrates and products. Computational molecular dynamic calculations were used to assess the L-PheOEt/L-LeuOEt-solvent and polypeptide-solvent interactions in this system. Additionally, the homopolypeptides displayed higher crystallinity than the copolypeptides with random incorporation of amino acid ethyl esters, notwithstanding the significantly highest specificity for Phe in this system. Interestingly, secondary structure characterization of the products by FTIR and circular dichroism suggests a non-common peptide folding.

Molecular Dynamics Simulations of Gas-Expanded Liquids

Gas-expanded Liquids (GXL’s) are liquids whose volume is expanded by a pressurized gas. The incorporation of the gaseous compound and the expansion of the liquid phase lead to changes in solvation and transport properties of the new expanded phase. This work aims at developing a Molecular Dynamics (MD) computational study for liquid methyl and ethyl acetates when expanded by CO2 at pressures up to 120 bars and at temperatures between 298 and 393 K. Especially, density and viscosity of the liquid expanded phase were calculated by MD simulations. Good agreement with existing literature data has been obtained ascertained the validity of the method