Roberto Castro-Muñoz

Mixed Matrix Membranes Based on PIMs for Gas Permeation: Principles, Synthesis, and Current Status

Over the last decades, different polymers have been employed as a material for fabrication of selective membranes for gas separation. Today, some of these membrane materials have been commercially consolidated as polymer-matrix; however, the need to improve the performance of polymeric gas separation membranes above Robeson’s upper bound has conducted the development of mixed matrix membranes (MMMs). One of the most recent approaches is the use of polymers of intrinsic microporosity (PIM), which seem to provide high permeability using different composites as fillers dispersed into the polymer matrix. The aim of this work is to provide a brief overview of the current studies on developments of new MMMs by using PIMs. These recent studies are also summarized and discussed according to the main applied filler, techniques used for characterizing the membranes, and the highlighted remarks in the studies. Finally, it denotes the prospects and future trends of membrane applications in this field.

Nanofiltration and Tight Ultrafiltration Membranes for the Recovery of Polyphenols from Agro-Food By-Products

Pressure-driven membrane-based technologies represent a valid approach to reduce the environmental pollution of several agro-food by-products. Recently, in relation to the major interest for natural compounds with biological activities, their use has been also addressed to the recovery, separation and fractionation of phenolic compounds from such by-products. In particular, tight ultrafiltration (UF) and nanolfiltration (NF) membranes have been recognized for their capability to recover phenolic compounds from several types of agro-food by-products. The separation capability of these membranes, as well as their productivity, depends on multiple factors such as membrane material, molecular weight cut-off (MWCO) and operating conditions (e.g., pressure, temperature, feed flow rate, volume reduction factor, etc.). This paper aims at providing a critical overview of the influence of these parameters on the recovery of phenolic compounds from agro-food by-products by using tight UF and NF membranes. The literature data are analyzed and discussed in relation to separation processes, molecule properties, membrane characteristics and other phenomena occurring in the process. Current extraction methodologies of phenolic compounds from raw materials are also introduced in order to drive the implementation of integrated systems for the production of actractive phenolic formulations of potential interest as food antioxidants.

Matrimid® 5218 in preparation of membranes for gas separation: Current state-of-the-art

ABSTRACT Over the last decades, different polymers have been used as continuous phase for preparing selective membranes for gas separation. Today, some of these materials have been consolidated commercially; however, the necessity to improve the performance (in terms of permeability/selectivity) of polymeric membranes above Robeson’s upper bound has been conducted by blending polymers, use of additives, implementation new methods, development of new materials, coating films, development of mixed matrix membranes, and so on. One of the most recent approaches is the use of polymers such as polyimides, i.e., Matrimid® 5218, which has demonstrated, to provide remarkable gas separation performance using the attempts aforementioned. The aim of this work is to present the current state-of-the-art of the use of Matrimid® 5218 in preparation of membrane for gas separation. The progress in this field is summarized and discussed chronologically in two periods, decade (from 1998 to 2008) and current (from 2009 up to now) frameworks. This contribution leads to take a complete and compelling overview of the state-of-the-art based on Matrimid. Furthermore, the main approaches, aim of study, gas separation evaluated, main techniques used for membrane characterization, main supplier of the polymer, main secondary materials for blending, fillers incorporated into the matrix, and remark of the study are summarized in detail. Finally, it denotes the prospects and future trends on use of Matrimid® 5218 for membrane applications.

Progress of Nanocomposite Membranes for Water Treatment

The use of membrane-based technologies has been applied for water treatment applications; however, the limitations of conventional polymeric membranes have led to the addition of inorganic fillers to enhance their performance. In recent years, nanocomposite membranes have greatly attracted the attention of scientists for water treatment applications such as wastewater treatment, water purification, removal of microorganisms, chemical compounds, heavy metals, etc. The incorporation of different nanofillers, such as carbon nanotubes, zinc oxide, graphene oxide, silver and copper nanoparticles, titanium dioxide, 2D materials, and some other novel nano-scale materials into polymeric membranes have provided great advances, e.g., enhancing on hydrophilicity, suppressing the accumulation of pollutants and foulants, enhancing rejection efficiencies and improving mechanical properties and thermal stabilities. Thereby, the aim of this work is to provide up-to-date information related to those novel nanocomposite membranes and their contribution for water treatment applications.

Progress on Incorporating Zeolites in Matrimid®5218 Mixed Matrix Membranes towards Gas Separation

Membranes, as perm-selective barriers, have been widely applied for gas separation applications. Since some time ago, pure polymers have been used mainly for the preparation of membranes, considering different kinds of polymers for such preparation. At this point, polyimides (e.g., Matrimid®5218) are probably one of the most considered polymers for this purpose. However, the limitation on the performance relationship of polymeric membranes has promoted their enhancement through the incorporation of different inorganic materials (e.g., zeolites) into their matrix. Therefore, the aim of this work is to provide an overview about the progress of zeolite embedding in Matrimid®5218, aiming at the preparation of mixed matrix membranes for gas separation. Particular attention is paid to the relevant experimental results and current findings. Finally, we describe the prospects and future trends in the field.

Economic Framework of Membrane Technologies for Natural Gas Applications

Natural gas is one of the most highly used resources, not only as a fuel but also as a raw material for many industrial processes. In addition, it is an environmental friendly fuel due to its lower greenhouse gas emission than that of coal or oil. However, it is a nonrenewable energy source and the quality of the available resources is expected to deplete continuously. In this scenario, membrane technologies can play an important role in the purification of the reduced and contaminated resources, competing with the current technologies owing to their simpler adaptability to different feed compositions, lower energy consumption and investment costs. In this review, the current state of the natural gas sources, including nonconventional resources (tight/shale gas and biogas), is explored, along with the current market status of the conventional natural gas. A comparison between the conventional purification technologies and membrane processes is provided, together with the currently available commercial membranes as well as new materials. Furthermore, the latest materials in research stage are reviewed, pointing out their limitations to the current membranes technologies. Finally, future research trends to overcome the current membrane technology limitations are proposed, and the conclusions are addressed.

Chemical Crosslinking of 6FDA-ODA and 6FDA-ODA:DABA for Improved CO2/CH4 Separation

Chemical grafting or crosslinking of polyimide chains are known to be feasible approaches to increase polymer gas-pair selectivity and specific gas permeance. Different co-polyimides; 6FDA-ODA and 6FDA-ODA:DABA were synthesized using a two-step condensation method. Six different cross-linkers were used: (i) m-xylylene diamine; (ii) n-ethylamine; and (iii) n-butylamine, by reacting with 6FDA-ODA’s imide groups in a solid state crosslinking; while (iv) ethylene glycol monosalicylate (EGmSal); (v) ethylene glycol anhydrous (EGAn); and (vi) thermally labile iron (III) acetylacetonate (FeAc), by reacting with DABA carboxyl groups in 6FDA-ODA:DABA. The gas separation performances were evaluated by feeding an equimolar CO2 and CH4 binary mixture, at a constant feed pressure of 5 bar, at 25 °C. Fractional free volume (FFV) was calculated using Bondi’s contribution method by considering the membrane solid density property, measured by pycnometer. Other characterization techniques: thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) were performed accordingly. Depending on the type of amine, the CO2/CH4 selectivity of 6FDA-ODA increased between 25 to 100% at the expense of CO2 permeance. We observed the similar trend for 6FDA-ODA:DABA EGmSal-crosslinked with 143% selectivity enhancement. FeAc-crosslinked membranes showed an increment in both selectivity and CO2 permeability by 126% and 29% respectively. Interestingly, FeAc acted as both cross-linker which reduces chain mobility; consequently improving the selectivity and as micro-pore former; thus increases the gas permeability. The separation stability was further evaluated using 25–75% CO2 in the feed with CH4 as the remaining, between 2 and 8 bar at 25 °C. We also observed no CO2-induced plasticization to the measured pressure with high CO2 content (max. 75%).