Denis Rodrigue

Membrane gas separation technologies for biogas upgrading

Biogas is a renewable energy source like solar and wind energies and mostly produced from anaerobic digestion (AD). The production of biogas is a well-established technology, but its commercial utilization is limited because on-site purification is needed before its transport or use. Biogas composition varies with the biomass digested and contains mainly methane (CH4) and carbon dioxide (CO2), as well as traces of hydrogen sulfide (H2S), ammonia (NH3), hydrogen (H2), nitrogen (N2), carbon monoxide (CO), oxygen (O2). In some cases dust particles and siloxanes are present. Several purification processes including pressurized water scrubbing, amine swing absorption, pressure swing adsorption, temperature swing adsorption, cryogenic separation and membrane technologies have been developed. Nevertheless, membrane technology is a relatively recent but very promising technology. Also, hybrid processes where membranes are combined with other processes are believed to have lower investment and operation costs compared with other processes. In this report, a discussion on the different materials used to produce membranes for gas separation is given including inorganic, organic and mixed matrix membranes, as well as polymer of intrinsic microporosity (PIM). Advantages and limitations for each type are discussed and comparisons are made in terms of permeability and diffusivity for a range of operating conditions.

Optimization of continuous phase in amino-functionalized metal–organic framework (MIL-53) based co-polyimide mixed matrix membranes for CO2/CH4 separation

Nano-size non- and amino-functionalized flexible crystalline metal-organic frameworks (MOFs) MIL-53(Al) and NH2-MIL-53(Al), two co-polyimides 6FDA/ODA-DAM (1 : 1 and 1 : 4) and cross-linked co-polyimide 6FDA-ODA-DAM (1 : 1, 2% agent cross-linking APTMDS) were used to prepare mixed matrix membranes (MMMs) whilst membranes consisting of MIL-53(Al) and commercial polyimides (Matrimid 5218 and Ultem 1000) were also fabricated for comparison. Pure gases and blends of CO2 and CH4 permeation tests showed enhanced separation performance of MMMs with relatively high NH2-MIL-53(Al) loadings (CO2 permeability up to 65 Barrer, ideal selectivity up to 36.5). A detailed study of the relation between MMM properties and their morphology as affected by the nature of continuous polyimide phase was performed. The separation factor increased with MOF loading. Furthermore, these materials showed stable CO2/CH4 selectivity at increasing feed pressure, in contrast to the traditional polymer membranes. The separation performances as functions of operation temperature and composition of gas mixture were also studied. Experimental permeation data of MMMs with 6FDA-ODA-DAM (1 : 1, 2% agent cross-linking APTMDS) and up to 35 wt% NH2-MIL-53(Al) loading are in excellent agreement with the modeling predictions by both the Maxwell model and the modified Maxwell model. An approximately ideal morphology was reached when preparing MMMs. A computational optimized process was proposed in order to estimate simultaneously three independent parameters, including gas permeability of dispersed filler, interphase thickness and polymer chain rigidification factors, which would be applied for non-ideal MMM systems.

Polymer functionalization to enhance interface quality of mixed matrix membranes for high CO2/CH4 gas separation

Hydroxyl-functionalized homo- and co-polyimides 6FDA–(DAM)x–(HAB)y (with x : y molar ratio of 1 : 0; 2 : 1; 1 : 1; 1 : 2) and two metal–organic frameworks (MOFs), MIL-53(Al) and NH2-MIL-53(Al) were synthesized for preparation of mixed matrix membranes (MMMs). The MOF loadings were varied over the range of 10–20 wt% for NH2-MIL-53(Al) and 10–15 wt% for MIL-53(Al). The incorporation of hydroxyl groups into the polyimide backbone is expected to improve the interfacial interaction between the polymer matrix and fillers, consequently, enhancing gas separation performance of MMMs. A big increase in glass transition temperature (Tg) for MMMs confirmed the polymer chain rigidification, which was caused by a strong interaction between the hydroxyl groups in the copolyimides and the amine groups in NH2-MIL-53(Al). Additionally, SEM results showed that the hydroxyl groups facilitated the particle dispersion in the MMMs, either was NH2-MIL-53(Al) or MIL-53 used as filler. Gas separation performances of MMMs were characterized by both CO2/CH4 pure gas and binary permeation measurements at 35 °C and 150 psi. The incorporation of NH2-MIL-53(Al) in the hydroxyl-copolyimides was found to significantly improve the CO2/CH4 separation factor while maintaining CO2 permeability of the MMMs as high as those of the neat corresponding copolyimides, therefore greatly enhancing the MMM separation performance. For example, the MMM prepared from 6FDA–DAM–HAB (1 : 1) copolyimide and 10 wt% NH2-MIL-53(Al) showed a permeability/selectivity behavior approaching the 2008 Robesons upper bound making it attractive for practical usage. The significant improvement in CO2/CH4 separation factor observed for the MMMs made of the hydroxyl-copolyimides and the amine-functionalized MOFs was due to (i) the enhanced polymer–filler compatibility originating from a mutual interaction between the polymer-functional moieties and the amine-functionalized MOF surface yielding defect-free MMMs and (ii) the high CO2/CH4 selective adsorption in the NH2-MIL-53(Al) framework.

Effect of Mold Temperature on Morphology and Mechanical Properties of Injection Molded HDPE Structural Foams

In this study, HDPE structural foams are produced by injection molding under different mold temperatures to study the effect of this variable on average cell dimension, cell density, and skin thickness ratio. Samples are also produced by setting independently the temperature of the fixed and moving plate of the mold to detect the sensitivity of foam structure to a temperature gradient in processing. The resulting foams are also characterized in terms of mechanical properties including impact and flexural tests. It has been found that for homogeneous mold temperatures, symmetrical skin thicknesses are obtained, which increase with decreasing mold temperature. On the other hand, by keeping one mold face at a constant temperature and varying the second one, asymmetric skin thicknesses are obtained. The degree of asymmetry is found to increase as the temperature difference between both molds increased. Furthermore, decreasing mold temperature produces a small increase in average cell sizes and reduced cell density. In general, both impact strength and flexural moduli of the structural foams increase with increasing skin thickness. For the particular case of asymmetric foams, the flexural moduli are slightly higher when the load is applied on the thicker skin; while much higher impact strength is obtained when the falling weight strikes the samples on the face having the smaller skin thickness.

Injection Molding of Postconsumer Wood-Plastic Composites I: Morphology

In this study, fiber-reinforced microcellular foams are produced via injection molding and studied as a function of mold temperature as well as wood, blowing agent, and coupling agent concentrations. Birch wood fibers are added to a post-consumer recycled HDPE/PP matrix (85: 15 ratio) in proportions ranging from 0 to 40 wt% and then foamed. Maleic-anhydride-polypropylene copolymer (MAPP) is also used as a coupling agent in proportions ranging from 0 to 10 wt% of wood content. In this first part, the morphological analysis of composite foams is presented including cell roundness, cell size, skin thickness, void fraction, and fiber aspect ratio.

Morphology and Mechanical Properties of Foamed Polyethylene-Polypropylene Blends

Blends of high-density polyethylene and polypropylene are foamed by means of extrusion using azodicarbonamide as a chemical blowing agent to study the effect of blending on the morphological and mechanical properties. At 0.5 wt% of blowing agent, optimum foam density is found to be around 417 kg/m3 for each blend composition, but the average cell size ranges between 130 and 301 mm depending on the blend composition. It is believed that the dispersed polymer phase acts as nucleating sites producing foams with smaller cell sizes. Owing to the incompatibility between both the polymers, the best tensile and impact properties are obtained for neat polymers. Simple semi-empirical models are proposed to predict the tensile and impact properties of the foams.

Injection Molding of Postconsumer Wood–Plastic Composites II: Mechanical Properties

ABSTRACT: In the first part of this study, fiber-reinforced microcellular foams were produced via injection molding to study their morphological properties as a function of mold temperature as well as wood, blowing agent, and coupling agent concentrations. Yellow birch wood fibers are added to a recycled postconsumer HDPE/PP matrix (85: 15 ratio) in proportions ranging from 0 to 40 wt% and then foamed with a chemical blowing agent. Maleic-anhydride-polypropylene copolymer (MAPP) is also used as a coupling agent in proportions ranging from 0 to 10 wt% of wood content. In this second part, the mechanical properties in flexion, torsion, and traction are presented.

Bubble velocities : further developments on the jump discontinuity

Abstract The motion of a gas bubble in a non-Newtonian fluid has been further examined in order to determine the conditions for the possible existence of a discontinuity in the bubble velocity-bubble volume log–log plot. It has been proposed in the past that this phenomenon was the result of a sudden change in the hydrodynamics of the moving bubble, resulting in a transition from a Stroke to a Hadamard regime. Furthermore, this abrupt transition was only qualitatively attributed to the elasticity of the fluid. Using our data as well as those of Leal et al., we demonstrate here that the discontinuity results as a balance between elastic and Marangoni instabilities, providing another major difference between Newtonian and non-Newtonian hydrodynamics.

The effect of fibre and coupling agent content on the mechanical properties of hemp/polypropylene composites

Composites made from hemp and polypropylene were prepared in order to determine the effect of fibre and coupling agent content on their mechanical properties. The samples were prepared by compression molding after an initial melt blending and homogenization step in an internal batch mixer. Different fibre contents (0, 10, 20 and 30 wt%) and sizes (355 and 500 μm) were used with two coupling agents: maleic anhydride polypropylene (MAPP) pellets and wax. For each case, MAPP concentrations between 0 and 7 wt% (fibre basis) were added to determine the optimum amount maximizing mechanical properties. The fractured surfaces of these composites were investigated by scanning electron microscopic technique (SEM) to investigate the fibre/matrix interfacial bonding. The mechanical properties of the composites were characterized in tensile, torsion, and flexion and the results showed that coupling agent addition has a positive effect on all moduli with an optimum content ranging between 2 and 4 wt%. It was also found that the coupling agent wax was more effective that the pellets.

Tensile properties of polymerization-filled Kevlar pulp/polyethylene composites

Polymerization-filled composites (PFC) and melt-blended composites (MBC) of Kevlar pulp/high density polyethylene composites were prepared to compare their mechanical properties. It was found that break strains of PFC composites were by far higher than MBC composites for a similar fiber concentration. Tensile data were then used to compare several models of short fiber polymer composites. Of all the models tested, it was found that Berlins approach in combination with Rosens model for critical aspect ratio give reasonable prediction. It was also found that fibers aspect ratio in composites is strongly related to the processing technique used.