Ambient carbon dioxide capture and conversion via membranes
- Autores: Adrianna Nogalska
- Directores de la Tesis: Ricard Garcia Valls (dir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Veronica Ambrogi (presid.), Bartosz Tylkowski (secret.), Alberto Vaca Puga (voc.)
- Programa de doctorado: Programa de Doctorado en Nanociencia, Materiales e Ingeniería Química por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX hdl.handle.net
- Resumen
The climate change caused by the increased CO2 content in the atmosphere is raising a lot of concern nowadays. The constant need for sustainable green energy generation inspired us to develop an artificial photosynthetic system. The system works as a leaf, where CO2 is captured directly from air through the membrane pores and passes to the next compartments to be finally converted to methanol or other hydrocarbons and to be further used as fuel in fuel cells.
The main scope of the work is to reveal the influence of polysulfone -based membrane contactors on atmospheric CO2 capture rate by chemical sorption into absorbent aqueous solutions. Flat sheet membranes that vary in morphology were prepared by immersion precipitation and undergo internal morphology and surface characterization. Moreover, the compatibility between membranes and absorbent solution was evaluated in terms of swelling and contact angle measurements. According to the results, it can be concluded that polysulfone membranes is suitable for use with potassium hydroxide solutions. The study indicates that the CO2 flux increases when increasing the absorbent flow rate over the range of liquid velocities investigated. Moreover, the flux grows with the increase of membrane macrovoids size, due to decrease of the membrane mass transfer resistance. Results obtained during dynamic module operations revealed a superior CO2 assimilation abilities of the unit as compared to a natural leaf.
In order to evaluate the impact of liquid flow on the system performance, the subsequent experiments were carry out in static conditions – without the use of a pump, with the solution being mixed only by a stirrer. The influence of the solution’s mass transfer resistance during static operation of the module is low, as the solution remains in the same container. Still, the CO2 assimilation results were similar to a leaf performance.
The polysulfone membrane was modified with a number of additives. Copper-ferrite nanoparticles were firstly added to the membrane bulk in the concentration of 5%. Studies showed that the incorporation of nanoparticles does not change the membrane internal morphology. However, it increased surface roughness and CO2 permeability. CuFeO3 nanoparticles proved to be capable of capturing CO2, but when introduced to the polymeric membrane and tested in contactor systems they influenced the CO2 flux negatively.
The polysulfone flat sheet membranes were modified with activated carbon following two approaches: i) bulk modification by adding AC into the polymeric solution used for membrane preparation and ii) spraying of the carbon-containing ink on the blank polysulfone membrane top surface. In the case of surface modification, the amount of introduced AC was determined by elemental analysis and calculation of change in membrane mass and thickness. The incorporation of AC into the polymeric bulk caused an increase of the membrane thickness and contributed to pores formation on the bottom surface of the membrane. The hydrophilicity was not improved and the gas absorption test results showed no improvement of the membrane performance.
Modification of the polysulfone surface by coating it with active carbon layer was accomplished. The cross section images of the modified membranes showed that the layer was not penetrating into the membrane. Unfortunately, the additional layer increased membrane mass transfer resistance without no active passage of the CO2 to absorbent solution, which decreased its effectiveness as a membrane contactor.
Another tested solution for improving CO2 capture was the combination of the polymeric membrane with enzymes involved in the nature carbon fixation: RuBisCo and CA. Two approaches were studied: physical attachment by adsorption and chemical attachment by covalent binding to amine terminated magnetic nanoparticles dispersed within the membrane. In order to evaluate the real influence of covalent binding on the immobilization, the adsorption studies were performed on both blank and nanocomposite membranes. The structural changes of the enzyme induced by the immobilization, as well as its activity and CO2 solubility was determined. It was observed that RuBisCo immobilization is favourable to more hydrophilic surfaces. The solubilized CA was attached to the hydrophilic membrane and -NH2 terminated nanoparticles, but there was no evidence of covalent binding. Fluorescence analyses did not reveal any structural changes in the case of CA immobilization, while the RuBisCo structure was altered during the process. Nevertheless, polysulfone based bio-mimetic membranes showed slight increase in the nanocomposite membrane CO2 absorption, although the blank membrane still shows the best performance.
In addition, PVA-based membranes were studied for the development of the biomimetic membranes. The PVA membranes were found to be good supports for enzyme immobilization due to their high hydrophilicity. Unfortunately, enzyme immobilization did not improve the CO2 sorption of the membrane, independently on the enzyme used – CA or RuBisCo - or its concentration. Moreover, both enzymes show signs of a molecular unfolding, which could change the availability of the active center and cause the decrease of activity.
As the captured CO2 takes form of bicarbonate or carbonate accordingly to the pH, bicarbonate conversion to fuel was also studied. The working electrode was prepared by electro-polishing copper foil followed by annealing, and characterized by LSV. The conversion of bicarbonate to formic acid by electro-reduction was achieved in potentiostatic conditions at -1.6 V.
An artificial stomata for ambient CO2 capture was designed and developed. Studies showed that the polysulfone based system has superior CO2 assimilation compared to a leaf performance. Moreover, the best results were obtained using blank and unmodified membrane, providing a low production cost. Furthermore, the conversion of bicarbonate to formic acid was achieved, giving a promising start to be improved in future work.
