The removal of organic micropollutants (OMPs) in the aquatic environment is crucial to avoid health hazards. Zeolites have been confirmed as a selective adsorbent and can effectively remove target OMPs. To achieve sustainable application of adsorbents, regeneration of zeolites is required.
The objective of this study was to investigate the regeneration performance of dried OMP-loaded granular zeolites through gaseous ozonation process, and the regeneration feasibility in long-term adsorption-regeneration processes. Three types of zeolites (MOR, MFI and BEA) were applied for target OMP (benzotriazole, methyl-benzotriazole, carbamazepine, diclofenac hydrochlorothiazide, sulfamethoxazole, metoprolol, sotalol, trimethoprim, propranolol, and clarithromycin) removal. A sequential process coupling zeolite adsorption and oxidation by gaseous ozone was established in batch mode. To assess the ozone effect on OMP degradation and zeolite itself, ozone bubbling tests and adsorption isotherm experiments were executed as pre-experiments. The relative adsorption capacity obtained through regeneration was used to demonstrate regeneration performance. Operating conditions, adsorption duration and regeneration duration were determined and applied. Ultimately the regeneration performance in long-term adsorption-regeneration processes was investigated.
Experimental results showed that all target OMPs were not resistant to ozonation in the water phase. Gaseous ozone was showed no influence on the adsorption capacities of zeolite granules. 120 hours and 500 mgL-1 zeolite granules were applied in OMP-loading adsorption experiments. Zeolites always showed high adsorption capacities of metoprolol, trimethoprim and sotalol, which regeneration effect was not evidenced. 60 minutes of ozonation was effective and sufficient for regenerating low and medium adsorption OMPs, except for carbamazepine. The regeneration of carbamazepine probably required a longer regeneration duration. In four cycles of adsorption-regeneration experiments, regeneration of sulfamethoxazole could be achieved after four rounds of ozonation. Regarding carbamazepine, diclofenac, benzotriazole, and methyl-benzotriazole, the regeneration performance were significantly reduced after the first cycle of regeneration. The ozonation duration is supposed to be extended above 60 min in long-term regeneration experiments. Intermediates were potentially responsible for the reduction of regeneration performance in ozonation and adsorption processes. Particularly, the effect of intermediates accumulation might be the main factor that hampered the regeneration performance of low and medium adsorption OMPs in long-term operation. ... Read more

Searching for better ways to store the excess renewable energy at large scale, the topic regarding sorption enhanced methanation of CO2 is researched, pushing the Sabatier reaction over the theoretical equilibrium by means of different water-absorbing zeolites. Till now zeolites and catalyst were mixed separately in the reactor for sorption enhancement. In this thesis, the focus is on impregnating the catalyst on the zeolite as the support, so as to shorten the diffusion path length of water vapour. This material will be called ‘the bifunctional material’. This report covers 2 subtopics: Firstly, do bigger pore sized zeolites improve the sorption enhanced CO2 methanation? An appropriate zeolite is searched, resulting in just one zeolite found from the 237, namely the zeolite L. Thereafter, the zeolite L, 13X and 5A zeolites, were impregnated with nickel citrate or nickel nitrate. These bifunctional materials are characterized with the XRD, SEM/EDX and H2-TPR. In addition, two distinct tests in a fixed bed Sabatier setup were executed: The activity and sorption enhanced methanation tests. Overall, the results show that the nickel impregnated zeolite L activity is between impregnated 13X and the 5A activity (13X < L < 5A). The sorption enhanced test reveals that impregnated 13X and 5A did have sorption enhancement but not for impregnated zeolite L. Secondly, how do cleaned bifunctional materials affect the activity compared to regular bifunctional material from evaporation impregnation? Here, the influence of washing on the nickel loading is examined with SEM/EDX. Thereafter, the activity test shows the effect of cleaning on the activity. Finally, the activity of various bifunctional samples (zeolite supports) are compared with reference samples (impregnated Al2O3 supports), based on comparable support’s pore structure. The results show the following: Increasing the amount of washing did not have a noticeable effect on the nickel loading. Just by changing the impregnation method from evaporative impregnation method to filtered impregnation method without additional washing (1,2,3,4 or 5x) is sufficient to prepare clean bifunctional material, containing only little precipitated salt precursor material. Furthermore, by comparing regular and cleaned bifunctional material per zeolite, reveals that the 5A is impregnated primarily on the outside surface of the zeolite followed by L and 13X (nickel on the outside surface: 13X = 51.3%, L =58.1% & 5A = 84.9%). The activity test displays that the effective activity (conversion per gram nickel catalyst) of cleaned impregnated 13X and 5A are the highest in H2 conversion. This makes it interesting for further research since separation enhancement of the Sabatier reaction reduces byproduct formation (CO) to a very large extent. The activity test comparing bifunctional samples with reference samples result that, supports with similar-looking pore structures do not lead to comparable activity. ... Read more

Rising CO2 levels in the atmosphere are becoming increasingly problematic, due to the effect of CO2 on climate change. CO2 capture and utilization has high potential as strategy to close the carbon cycle. An example of utilization of CO2 is the electrochemical reduction of CO2 to more valuable compounds. This thesis discusses the electrochemical reduction of CO2 to oxalic acid. Until now, oxalic acid as target product of the electrochemical CO2 reduction has not been studied in great depth, mainly because it only forms in non-aqueous solutions. The influence on several parameters, namely cathode material, applied potential,
anolyte, catholyte, membrane, supporting electrolyte, and temperature, on the electrochemical conversion of CO2 to oxalic acid has been studied. The first step in scaling-up has been taken, from a batch reactor (H-cell reactor) to a semi-continuous system (flow-cell reactor). In order to investigate the feasibility and its implementation in the industry, several options for the downstream processing of oxalic acid are discussed and a techno-economic analysis is performed on the proposed process design.

From the parametric study that was carried out, the parameters that had a considerable effect on the performance of the electrochemical reduction of CO2 to oxalic acid were cathode and anode material, catholyte and anolyte, membrane, applied potential and temperature. With the batch reactor optimal results in terms of faradaic efficiency and current density have been found, using lead as cathode, platinumas anode, propylene carbonate+0.7M tetraethylammonium chloride as catholyte and 0.5M H2SO4 as anolyte in which the cathodic and anodic compartment are separated by a Nafion 117 membrane. At higher temperatures, higher current densities were induced by reduction of mass transfer limitations. Within the range of -2.2V to -2.7V vs Ag/AgCl, increasing current densities and decreasing faradaic efficiencies were found with increasing applied potential. Semi-continuous flow-cell was investigated as a strategy to increase the mass transfer in the system. Although higher reduction currents were measured during CO2 reduction in a flow-cell compared
to the batch reactor, the faradaic efficiency towards oxalic acid was lower. The oxalic acid produced during CO2 reduction in the electrochemical reactor is dissolved in the liquid electrolyte. A further separation step of the oxalic acid from the liquid needs to be present to recover the product in a solid state. In order to assess the feasibility of the separation of oxalic acid, several technologies were addressed. Liquid-liquid extraction followed by crystallization is experimentally proved to be a suitable method for the separation and recovery
of oxalic acid from the electrolyte. Based on this separation method, a process design is proposed and a techno-economic analysis has been performed. The techno-economic analysis showed a favorable economic potential for this technology if certain key performance indicators can be achieved. However, the maturity level of this process is still in early stages. Some of those key performance indicators still need to be experimentally improved, further research should focus on increasing the obtained current densities and obtaining
stable faradaic efficiencies. ... Read more