Hollow fiber membrane contactor as a gas-liquid model contactor

Microporous hollow fiber gas-liquid membrane contactors have a fixed and well-defined gas-liquid interfacial area. The liquid flow through the hollow fiber is laminar, thus the liquid side hydrodynamics are well known. This allows the accurate calculation of the fiber side physical mass transfer coefficient from first principles. Moreover, in the case of gas-liquid membrane contactor, the gas-liquid exposure time can be varied easily and independently without disturbing the gas-liquid interfacial area. These features of the hollow fiber membrane contactor make it very suitable as a gas-liquid model contactor and offer numerous advantages over the conventional model contactors. The applicability and the limitations of this novel model contactor for the determination of physico-chemical properties of non-reactive and reactive gas-liquid systems are investigated in the present work. Absorption of CO 2 into water and into aqueous NaOH solutions are chosen as model systems to determine the physico-chemical properties for non-reactive and reactive conditions, respectively. The experimental findings for these systems show that a hollow fiber membrane contactor can be used successfully as a model contactor for the determination of various gas-liquid physico-chemical properties. Moreover, since the membrane contactor facilitates indirect contact between the two phases, the application of hollow fiber model contactor can possibly be extended to liquid-liquid systems and/or heterogeneous catalyzed gas-liquid systems

Ammonium removal by liquid–liquid membrane contactors in water purification process for hydrogen production

© 2014 Balaban Desalination Publications. All rights reserved. In this work, a liquid–liquid membrane contactor (LLMC) was evaluated to remove ammonia traces from water used for hydrogen production by electrolysis. Three operational parameters were evaluated: the feed flow rate, the initial ammonia concentration in the water stream, and the pH of solution. Synthetic aqueous solutions with ammonium concentration of 5–25 mg L-1 and a sulfuric acid solution (pH 2) were supplied to the LLMC in countercurrent and open-loop configuration with flow rates between 2.72 × 10-6 and 22.6 × 10-6 m3 s-1 and the pH values of the solution with ammonium between 8 and 11. A 2D numerical model was developed considering advection–diffusion equation inside a single fiber of the lumen with fully developed laminar flow and liquid–gas equilibrium in the membrane–solution interface. Predictions of the model were then validated against experimental data, which were found to be in good agreement. According to both, experimental data and numerical predictions, the hollow-fiber membrane contactor technology is a suitable alternative to remove ammonium from water and to feed the membrane distillation unit in order to fulfill water quality requirements for electrolysis-based hydrogen production.Peer ReviewedPostprint (author's final draft

Mathematical Modelling and Simulation of Carbon Dioxide Absorption from N2 Using Hollow Fiber Membrane Contactor

In this work, hollow fiber membrane contactor was used to theoretically study absorption carbon dioxide using water. Governing equations were solved by finite element method. The impact of temperature and velocity of liquid phase and velocity of gas phase on CO2 absorption flux has been investigated. Results showed that by increasing liquid phase velocity, CO2 absorption flux increases remarkably. Also, CO2 absorption flux increases only 6 % by increasing gas phase velocity from 0.02 to 0.06. Thus, liquid phase is the controller of mass transfer in gas absorption process. The results also showed that CO2 absorption flux decreases by increasing liquid phase temperature, due to the reduction of gas solubility in liquid phase, and outlet CO2 concentration of liquid phase decreases too. To validate of model’s results, the data of two experimental works have been used

Trace ammonium removal by liquid-liquid membrane contactors as water polishing step of water electrolysis for hydrogen production from a wastewater treatment plant effluent

© 2016 Society of Chemical Industry. BACKGROUND: This work evaluates hollow fiber liquid-liquid membrane contactors (HFMC) as a polishing step for the removal of low levels of ammonium from water purified by (or being supplied to) a membrane distillation unit in order to fulfil the conductivity requirements of hydrogen production by water electrolysis. RESULTS: The influence of the operating conditions (flow, pH, ammonium concentration, buffer capacity) were evaluated under a closed-loop setup in order to achieve a reduction of total ammonia concentration in water, from 15 to 1mgL-1 to assure the production of water in the membrane distillation with a conductivity lower than 1 µS cm-1. These values were used to validate a numerical algorithm describing the system performance. In order to reach the ammonia concentration requirements and considering the low concentration of bicarbonate (low pH buffer capacity) in the treated water a buffer agent was added to the working solution. CONCLUSIONS: HFMC technology is a suitable solution to remove low levels of ammonium from water to values as low as 1mgL- 1NH3 through appropriate control of pH. The ammonium removal efficiency of the HFMC was improved by raising the pH or the flow rate. Finally, the model proposed provides a good description of the membrane contactor performance with minimal deviations when compared with experimental results.Peer ReviewedPostprint (published version

Carbon dioxide removal from anaesthetic gas circuits using absorbent membrane contactors

Tese de doutoramento. Engenharia Química e Biológica. Faculdade de Engenharia. Universidade do Porto. 200

Analysis of heat and mass transfer in membrane-based absorbers with new working fluid mixtures for absorption cooling systems

Absorption refrigeration technology, which has the ability to utilize heat directly for cooling purposes, has been one of the most widely used technologies for refrigeration and cooling applications since the early stages of refrigeration technology. Working fluid mixtures employed in the absorption cooling systems are environmental friendly and do not contribute in green house gas emission when compared to vapour compression systems which also use costly mechanical energy input. However, high initial costs and bigger size are some of the main obstacles that impede their wide use in small scale residential buildings and transport sector. In order to overcome these obstacles, design and configuration of the system and its components need to be reinvestigated in order to achieve compact components and reduce the size of the system. Use of membrane contactors in the form of hollow fiber membrane module or plate-and-frame membrane module is one of the alternatives to achieve compact components. Absorber is an important component of the absorption refrigeration system and plays a critical role in the overall performance, size, and capital cost of the system. In this study, numerical analyses are performed to evaluate the performance of a plate-and-frame membrane contactor based absorber employing water/(LiBr + LiI + LiNO3 + LiCl) and water/(LiNO3+KNO3+NaNO3) working fluid mixtures for air cooled absorption cooling systems and multi-stage high temperature heat sources applications, respectively. CFD tool ANSYS/FLUENT 14.0 is used to perform the simulation and investigate in detail the heat and mass transfer mechanisms and the fluid dynamics behaviour at local levels in the channels. Moreover, a MATLAB code is developed to investigate the effect of membrane material characteristics and operating conditions on the absorption performance of the absorber. This study recommends optimum operating and design parameters to effectively utilize the membrane based absorber

Enhancement of CO2 removal by promoted MDEA solution in a hollow fiber membrane contactor: A numerical and experimental study

In this work, carbon dioxide (CO2) loading capacity of methyldiethanolamine (MDEA) solution promoted by potassium lysinate (KLys) was experimentally measured by using a gas absorption setup at different concentrations and temperatures. The CO2 removal efficiency of the MDEA + KLys solution was investigated for a CO2/N2 gas mixture by using computational fluid dynamic (CFD) simulations in a hollow fiber membrane contactor (HFMC). The effects of operating conditions including solvent concentration, solvent flow rate, gas flow rate, inlet CO2 concentration and module length on the CO2 removal efficiency were also studied. The experimental results revealed that CO2 loading capacity increases with increasing KLys concentration in the solution, while decreases as temperature increases. The simulation results indicated that MDEA + KLys solution has higher CO2 removal efficiency compared to pristine MDEA and MEA solutions. The CO2 removal efficiency increases with increasing solvent concentration, solvent flow rate and module length, whereas decreases as gas flow rate increases. The zeolitic imidazolate framework-8 (ZIF-8), as sorbent, was then incorporated into the MDEA + KLys solution and its effect on the CO2 removal efficiency was also examined. The MDEA + KLys + ZIF-8 nano-absorbent showed higher CO2 removal efficiency than that of MDEA + KLys absorbent, where introducing 0.4 wt.% ZIF-8 enhanced CO2 removal from ⁓96% to ⁓99%. The results of this work suggest that both MDEA + KLys absorbent and MDEA + KLys + ZIF-8 nano-absorbent are promising candidates for CO2 absorption processes. However, for practical use as well as a complete investigation, their behavior should be assessed by using other parameters of solvent such as reactivity with CO2, corrosion rate, and regeneration performance

A Simple Solution of Dissolved Ammonia Recovery Process in a Hollow-Fiber Membrane Contactor: Comparison with Experimental and Numerical Results

Ammonia in gaseous form is one of the major pollutants in waters and wastewaters. Of all the processes studied so far for the removal of dissolved ammonia from aqueous solution, hollow fiber membrane contactor-based processes have shown great potential. This method has shown to be effective to substantially reducing ammonia concentration to an acceptable value economically and efficiently. Mathematical analysis is presented in this report for the removal of ammonia dissolved in an aqueous phase to a recovery/stripping solution in a hollow fiber membrane contactor (HFMC). The membrane contactor is considered to consist of the lumen side (allowing aqueous flow) and shell side (allowing the flow of the stripping/recovery solution). An approximate analytical solution is derived for the simplified model that does not include radial diffusion of solutes (only axial mass flux is included). The predicted results of this solution are compared with the experimental data and with the numerical results in the literature over a range of operating conditions. The flow rates of the feed solution covered: 2.01 x 10 -9 to 4.7 x 10 -6 m3/s, initial concentration: 50 – 800 ppm and pH values of the solution containing ammonia: 8 - 11. The agreement is very good between the profiles of the simplified analytical solution and the earlier published experimental data. In addition, the results obtained by the analytical solution are close to the numerical solution of the complete model over a good range of operating conditions

3D-CFD analysis of the effect of cooling via minitubes on the performance of a three-fluid combined membrane contactor

Abstract A 3D computational fluid dynamics model was adopted to study the effects of internal cooling on the performance of a three-fluid combined membrane contactor (3F-CMC), in the presence of minitubes in solution and a spacer in the air channel. This compact 3F-CMC is part of a hybrid climate-control system, recently developed for serving in electric vehicles. For the studied operating conditions, results show that the absorption and sensible effectiveness parameters increase up to 77% and 124% by internal cooling, respectively. This study also reports 3D flow effects on the heat and mass transfer enhancement inside the contactor, with implications for further design improvements