Maximizing liquid fertilizer concentration during ammoniacal nitrogen recovery using hollow fiber membrane contactors

A kinetic model has been developed to predict the distribution of wetness along a hollow fiber and the average wetness as a function of time in hollow fiber membrane (HFM) contactors. The membrane absorption experiments were conducted using the diethanolamine (DEA) solution as absorbent to absorb CO2 in polyvinylidene fluoride (PVDF) and polypropylene (PP) HFM contactors. The influences of operating conditions (such as solution concentration, temperature, liquid and gas flow rates) on the membrane wetting process in a HFM contactor were also investigated in experiments. The experimental data were fitted to the proposed kinetic equations. The fitting results indicate that the proposed kinetic equation successfully described the membrane wetting process and prove that the membrane wetting rate was controlled by the solute adsorption on the bare pore wall. Therefore, this model may provide support for the design of membrane contactors suffering from membrane wetting.

Removal of percentile level of H 2S from pressurized H 2S–CH 4 gas mixture using hollow fiber membrane contactors and absorption solvents

A dynamic model of mass transfer was developed with mass transfer equation and mass transfer differential equation according to two film theory for the simultaneous transport of hydrogen sulfide through hollow fiber membrane (HFM) contactors while using N-methyldiethanolamine (MDEA) as the chemical solvent. The model results are in excellent agreement with the experimental data. The results indicate that the removal of H2S increased while increasing concentration of MDEA and gas pressure, however, the removal of H2S decreases while increasing gas velocity. The concentration of H2S increases at the same place in the lumen while increasing gas velocity. There is serious decreasing amplitude of axial concentration of H2S during the initial stage, but it slows down at half of the length and a great reduction of H2S concentration in radial direction with the increase of the length. The decreasing amplitude is dropped due to the concentration of H2S decreased in radial direction. The model can indicate H2S removal rate in given operational conditions and offer theory evidence for the design of membrane contactor. Natural gas is believed to play a vital role in the next few decades for industrial and domestic utilization. It is considered as one of the cleanest and safest of all energy sources. However, nature gas is not a pure hydrocarbon and sometimes it has some sour gases such as hydrogen sulfide which has high toxicity. Hydrogen sulfide can not only corrode equipment and transmission pipeline under aerobic and hot humid conditions but also cause catalyst poisoning, even serious threaten the safety of human. Wet desulphurization is widely used for natural gas treatment and aqueous solutions of alkanolamines are often used as absorption solvent. Among these alkanolamines, MDEA as an absorption solvent of acid gases is widely used today because it possesses the characteristics such as higher H2S selectivity, bigger absorption capacity, lower regeneration energy, smaller hot-degradation and lower circulating load. But desulphurization unit can be seriously corroded in the sulfur removal process. On the other hand, these conventional processes such as absorption towers, packed and plate columns possess many disadvantages such as flooding, foam formation, and demand high capital and operating costs. So the technology meets a certain obstacles. Recently, new processes using gas–liquid membrane contactors as gas absorption devices have been a subject of great interest. Among the diversity of membrane geometries available for membrane contactors, hollow-fiber membrane contactors are favored due to their high surface/volume ratio for separation which is 30-50 times compared with traditional absorbers. This type of process offers several practical advantages including low energy and operating costs, simplicity and occupying small area. In addition, membrane contactors as unit equipment can be combined according to actual need. [4~5] used polypropylene hollow fiber membrane as the absorber and MDEA as the chemical solvent for the absorption of H2S via changing operating conditions (e.g. temperature, pressure, the concentration of the solvent, flux of gas-liquid phase) and studied the influence of the changes to mass transfer coefficient and sulfur removal efficiency. The results indicate that the sulfur removal efficiency can be 95% above by optimizing the operating conditions. At home and abroad, comprehensive two-dimensional mathematical models were developed based on differential equation. Wang [6] simulated the absorption of CO2 using different absorption medium in hollow fiber membrane contactors. But they did not consider the effect of mixed gas. Chen [7] modeled the distribution of reactants and products concentration in the shell side in different typ es of reaction. However, the model can not obtain the concentration of H2S in the lumen. Rami Faiz [8] modeled the distribution of acid gas, but the mathematical model was not validated by the experimental work.

Experimental and modeling of CO2 removal from gas mixtures using membrane contactors packed with glass beads

Effect of long-term operations on the performance of hollow fiber membrane contactor (HFMC) in recovering dissolved methane from anaerobic effluent

Removal of carbon dioxide from pressurized CO 2–CH 4 gas mixture using hollow fiber membrane contactors

Amine CO2 solvents undergo oxidative degradation with the formation of heat stable salts (HSS). These HSS reduce the sorption capacity of amines and lead to intense corrosion of the equipment. In our work, we propose a membrane-supported liquid-liquid extraction of the HSS from alkanolamines. For this purpose, a hollow fiber membrane contactor was used for the first time. A lab-scale extraction system on the basis of a hollow-fiber liquid-liquid membrane contactor with hollow fiber ultrafiltration polyvinylidenefluoride and polysulfone membranes has been studied. The extraction of the HSS-ions from a 30 wt.% solution of monoethanolamine was carried out using a 0.25–1 M solution of OH-modified methyltrioctylammonium chloride in 1-octanol as an extractant. It has been shown that >90% of HSS ions can be extracted from the alkanolamine solvent within 8 h after extraction. The results obtained confirm the possibility of using membrane extraction with a liquid-liquid membrane contactor for the reclaiming of amine CO2 solvents to increase the general efficiency of carbon dioxide capture.

Mathematical modeling for the simultaneous absorption of CO 2 and H 2S using MEA in hollow fiber membrane contactors

Global warming, driven significantly by carbon dioxide (CO2) emissions, necessitates immediate climate action. Consequently, CO2 capture is essential for mitigating carbon output from industrial and power generation processes. This study investigates the effect of absorbent temperature on CO2 separation performance using gas-liquid polymeric hollow fiber membrane (HFM) contactors. It summarizes the relationship between liquid-phase temperature and CO2 capture efficiency across various physical and chemical absorption processes. Twelve relevant studies (nine experimental, three mathematical), providing a comprehensive database of 104 individual measurements, were rigorously analyzed. Liquid-phase temperature significantly influences CO2 separation performance in HFM contactors. In particular, the present analysis reveals that, overall, for every 10 °C temperature increase, physical absorption performance decreases by approximately 3%, while chemical absorption performance improves by 3%, regardless of other parameters. This empirical law was confirmed by direct comparisons with additional experimental results. Strategies for further development of these processes are also proposed.

Mathematical modeling and simulation of carbon dioxide stripping from water using hollow fiber membrane contactors

GTI Energy and Air Liquide Advanced Separations (ALaS) have been developing a novel hollow fiber membrane contactor (HFMC) technology for post-combustion CO2 capture. The process combines advantageous features of both absorption and membrane-based separation processes to separate CO2 from flue gas cost-effectively. The key component of the HFMC technology is the super-hydrophobic, porous hollow fiber, which is made from polyether ether ketone (PEEK). Compared to conventional absorption/desorption technologies, the critical advantage of the HFMC process is the high contact surface area provided by the hollow fibers enabling an increased volumetric mass-transfer rate. In the PEEK HFMC process, the specific surface area has been increased by an order of magnitude over structurally packed or trayed columns, resulting in compact systems with small footprints. A pilot-scale demonstration of the HFMC process on coal-fired power plant flue gas has been performed in Wilsonville, AL at the National Carbon Capture Center (NCCC) treating flue gas from pulverized coal-fired Alabama Power’s Gaston Power Station. A 90% CO2 removal rate was achieved by the HFMC using a 50 wt.% aMDEA solvent during the initial tests with 4 modules and actual coal-fired flue gas at NCCC. The stripped stream from the two-stage flash desorber had a CO2 concentration of >98.6 vol%. Further tests indicated an issue of liquid-side concentration polarization – higher CO2 concentration in the fluid boundary layer (next to the fiber) relative to the bulk flow stream. This issue was resolved by decreasing the aMDEA concentration from 50 wt.% to 35 wt.%. Continuous testing with 28 membrane modules, however, did not match the single module results; the CO2 capture performance declined with time. Quantitative analysis as well as inspection and measurements of the spent modules were conducted to investigate the potential causes. The major issue identified was the tubesheet leaking from patch points and potentially from fiber/epoxy separation. Future steps would include: 1) resolving technical hurdles in materials and manufacturing; 2) increasing the inner diameter of the hollow fibers to achieve a low pressure drop (when flue gas flows through the hollow fibers); and 3) consideration of inclusion of multiple membrane cartridges in one housing. Overall, this project has advanced the HFMC technology to a high TRL level and resolved a number of technical issues (e.g. concentration polarization) that other researchers have not dealt with to date. The project results and publications is a significant contribution to the literature and for other technology developers.

The absorption efficiencies of CO2 in hollow-fiber membrane contactors using an ethanolamine (MEA) solvent under both concurrent- and countercurrent-flow operations were investigated theoretically and experimentally. Two-dimensional mathematical modeling was developed by Happel’s free surface model, and the resultant partial differential equations were solved analytically using the separated variables method with the use of an orthogonal expansion technique. A simplified expression of Sherwood number variations was reported by employing the relevant operations conditions and expressed in terms of the computed eigenvalues for predicting concentration distribution and absorption efficiency. It is emphasized that, in comparing various fiber packing configurations, both theoretical predictions and experimental results should be compared to find the absorption flux increment accomplished by the CO2/N2 stream passing through the fiber cells under the same mass flow rate. The value of the present mathematical treatment is evident to propose a simplified expression of the averaged Sherwood number variations, and provides the predictions of the absorption flux, absorption efficiency, average Sherwood number with the absorbent Graetz number, inlet CO2 concentration, and absorbent flow rates as parameters. The availability of such concise expressions, as developed directly from the analytical formulations, is the value of the present study. The experiments of the CO2 absorption using MEA with alumina (Al2O3) hollow fiber membranes are also set up to confirm the accuracy of the theoretical predictions. The accuracy derivations between the experimental results and theoretical predictions for concurrent- and countercurrent-flow operations are and , respectively. The operations of the hollow-fiber membrane contactor implementing N = 7 fiber cells and N = 19 fiber cells offer an inexpensive method of improving absorption efficiency by increasing fiber numbers with consideration of device performance.

Contaminant removal from natural gas using dual hollow fiber membrane contactors

Membrane technology scientists proposed hollow fiber membrane contactors (HFMCs) as an alternative to conventional CO2 absorption-desorption columns due to their promising advantages and outstanding performance for CO2 capture. However, the HFMC systems suffer from wetting phenomena; hence, the HFMC studies focus on optimizing the membrane material, liquid absorber, and operating conditions. As scientists have addressed the wetting phenomenon with these solutions, new issues have emerged. In addition, the feedback loop between the lab and the industrial scale has been ignored. In this review, the characteristics of different HFMC systems based on their membrane types, including porous, dense, and composite (e.g., thin-film composite and mixed matrix) membranes, are compared to clarify their advantages and disadvantages. Also, the scale-up and economic conditions were discussed in terms of HFMC's feasibility to highlight the importance of the lab and industry loop. Furthermore, the future direction is stated to accelerate the HFMCs’ development and provide a clear strategy for achieving practical and theatrical CO2 absorption through HFMCs.

Optimization of hollow fiber membrane contactor system for CO2 mineralization using seawater brine: Comparative analysis of performance and transport mechanisms