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Process Optimization of UV-Based Advanced Oxidation Processes in VOC Removal Applications
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Process Technology.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Air pollution is a major concern in developed countries due to its hazardous health effects. Recent studies by the WHO (World Health Organization) estimate that urban air pollution causes a number of diseases of the respiratory tract and is associated with 150,000 deaths each year. Volatile organic compounds (VOCs) are among the major pollutants affecting the outdoor air quality. Given that industrial processes are the main source of atmospheric VOC emissions, national and international authorities have issued regulations to limit such emissions. However, traditional removal technologies such as incineration, have low energy efficiency and high investment costs. AOPs (advanced oxidation processes) offer a promising alternative in which very reactive conditions can be achieved at room temperature, thus greatly increasing energy efficiency. However, this is still not a mature technology due to challenges that limit the range of applications.

This thesis focuses on two types of UV-based AOP: photocatalysis and UV-ozone. The goal is to improve VOC conversion and achieve a process that is competitive with traditional technologies. The research on photocatalysis presents an innovative UV reactor design that is closer to industrial conditions and has the ability to effectively screen different samples. Effort was put into finding a metallic support for the photocatalyst without using additional adhesives. Several electrochemical treatments were performed on metals to restructure the surface. One treatment proved to be superior when it came to stabilizing the TiO2 coating, especially when compared with the traditional ceramic support.

Research on UV-ozone AOPs focused on reactor modelling, developing a numerical and a fluid dynamics model. The goal was to gain a deep understanding of the governing phenomena of UV-ozone reactors so as to optimize the reactor configuration. The numerical model created described the UV irradiation and the reaction kinetics accurately, while a computational fluid dynamics (CFD) simulator modelled the fluid a larger scale, simulating two prototypes. The work resulted in general guidelines for the design of UV-ozone UV reactors as well as for full-scale units. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. , p. 92
Series
TRITA-CBH-FOU ; 2018:35
Keywords [en]
AOP, UV, photocatalysis, ozone, air pollution, VOC abatement, reactor design, reactor modelling, photocatalyst support, electrochemical treatment, electrochemical etching, irradiation modelling, kinetics modelling, fluid dynamics simulation, prototype, full-scale, CFD simulation
National Category
Chemical Process Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-233386ISBN: 978-91-7729-911-0 (print)OAI: oai:DiVA.org:kth-233386DiVA, id: diva2:1239852
Public defence
2018-09-28, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research, MI15.14
Note

QC 20180820

Available from: 2018-08-20 Created: 2018-08-18 Last updated: 2018-08-20Bibliographically approved
List of papers
1. Development of a stagnation point flow system to screen and test TiO2-based photocatalysts in air purification applications
Open this publication in new window or tab >>Development of a stagnation point flow system to screen and test TiO2-based photocatalysts in air purification applications
Show others...
2016 (English)In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 306, p. 734-744Article in journal (Refereed) Published
Abstract [en]

An innovative system suitable for the abatement of VOCs (Volatile Organic Compounds), using photo catalysis under UV light, was designed and built. The design of the reactor is based on the stagnation point flow geometry and the fluid dynamics of the system was carefully investigated in order to avoid mass transfer limitations. The proportions of the elements in the reactor were adjusted in order to homogenize the UV irradiation on the catalyst surface. The supports used for the coating of the catalysts were aluminum plates in order to accurately reproduce industrial conditions. After each test, the catalytic plate was examined to evaluate the mechanical strength of the bonding between the catalyst powder and the metallic support. The coating proved to be sufficiently stable for tests in the designed set up. The potential scale-up of the features of the system was considered throughout the design and especially the power of the UV lamps was decided in order to be representative of the industrial cases. In order to evaluate the suitability of the system for catalysis investigations, various photocatalysts, both synthesized and commercial, were screened. Analyzing the activity results, using acetyl aldehyde as a model VOC, it was possible to evaluate clear differences between the samples and P90 proved to be the most active sample. All the aspects investigated in this work demonstrate that the design of the reactor is in accordance with the expectations and that the system is suitable for screening and testing of photocatalysts for VOCs removal applications.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
VOC abatement, Photocatalysis Reactor engineering, Computational Fluid Dynamics, UV irradiation, Stagnation point flow
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-196585 (URN)10.1016/j.cej.2016.07.117 (DOI)000386420700080 ()2-s2.0-84980619175 (Scopus ID)
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research
Note

QC 20161118

Available from: 2016-11-18 Created: 2016-11-17 Last updated: 2018-08-18Bibliographically approved
2. Surface treatments of metal supports for photocatalysis applications
Open this publication in new window or tab >>Surface treatments of metal supports for photocatalysis applications
2017 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 401, p. 283-296Article in journal (Refereed) Published
Abstract [en]

One of the most important challenges, for scaling up a photocatalytic system for VOCs abatement to full-scale, is the design of a suitable photocatalyst support. The support has to firmly immobilize the photocatalyst, without using an organic adhesive, and should also withstand relatively high mechanical stresses. Metals may be effectively implemented as a support material, after a corrugation of the surface with electrochemical treatments. In the present work, we treated stainless steel and aluminum supports, evaluating the surface modifications due to the electrochemical treatments, with scanning electron microscopy (SEM) and confocal microscopy. Five samples showing the highest degree of restructuring were selected and spray coated with P25, a TiO2 photocatalyst, evaluating the mechanical stability of the coating with a standard tape test method. One particular stainless steel sample presented a superior surface restructuring and coating stability. The photocatalytic activity of this sample, evaluated measuring the complete oxidation of acetaldehyde, was tested for 15 h, and compared with sample of TiO2-P25 on a ceramic support. The stainless steel exhibited a constant performance after an initial stabilization period. The stainless steel sample showed a slightly higher activity, due to the surface restructuring, increasing the irradiated area available for the coated photocatalyst.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Coating stability, Electrochemical treatments, Photocatalysis, Photocatalytic support, Surface restructuring, VOCs abatement
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-200852 (URN)10.1016/j.apsusc.2016.12.233 (DOI)000394074300034 ()2-s2.0-85009128693 (Scopus ID)
Note

QC 20170203

Available from: 2017-02-03 Created: 2017-02-03 Last updated: 2018-08-18Bibliographically approved
3. Development of an irradiation and kinetic model for UV processes in volatile organic compounds abatement applications
Open this publication in new window or tab >>Development of an irradiation and kinetic model for UV processes in volatile organic compounds abatement applications
2018 (English)In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 348, p. 569-582Article in journal (Refereed) Published
Abstract [en]

Air pollution from volatile organic compounds (VOCs) is one of the most important environmental hazards. Advanced oxidation processes (AOPs) with UV systems have been showing high potential for the abatement of VOCs. This work is aimed at modeling UV reactors for scaling-up AOPs from lab-scale to full-scale. The proposed model has a novel approach coupling the UV fluence rate to the photo-kinetic mechanism, for a robust understanding of the phenomena involved. The results show that the 185 nm wavelength is deeply absorbed within few centimeters by oxygen, while the 254 nm wavelength is weakly absorbed by the ozone generated in the reactor. Based on the fluence rate calculations, the reactions of ozone generation and depletion were modeled. The ozone net concentration was compared to the experimental results, for model verification. The model accurately predicts the effect of the airflow rate and reactor diameter for the tested cases. The acetaldehyde oxidation reaction was modeled using a simplified kinetic mechanism, using the experimental data of VOC conversion for a further model verification. The suggested reactor models accurately predicted the effect of airflow rate, while exhibiting limitations for the effect of different reactor diameters. Therefore, a computational fluid dynamics (CFD) investigation is needed for an accurate modeling of the VOCs oxidation reaction, implementing the developed analytical expression for reducing the computational workload. By combining the developed model with a CFD simulator, it would be possible to simulate several reactors, also at full-scale, for predicting their performance and identifying optimal configurations.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Air treatment, AOPs, Reaction modeling, Reactor scale-up, UV irradiation, VOCs abatement
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-228697 (URN)10.1016/j.cej.2018.05.009 (DOI)000434467000056 ()2-s2.0-85046649604 (Scopus ID)
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research
Note

QC 20180530

Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2018-08-18Bibliographically approved
4. Fluid dynamics model development for scaling-up UV reactors in VOC abatement applications
Open this publication in new window or tab >>Fluid dynamics model development for scaling-up UV reactors in VOC abatement applications
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The present work focuses on the treatment of VOC emissions from industrial processes, since they represent a very severe environmental hazard. For removing the VOC, an AOP (Advanced Oxidation Process) stage based on UV light and ozone was considered, analyzing the methods for the unit scale-up. An innovative CFD (Computational Fluid Dynamics) model, combining UV irradiation, reaction kinetics and fluid dynamics, describing the behavior of UV reactors in the laboratory scale, was developed. This model was verified against experimental results, displaying good agreement. Therefore, we concluded the CFD model could adequately describe relevant features regarding the performance of UV reactors. After analyzing the laboratory reactors, two designed and scaled up prototypes, were simulated using the CFD model. While the first prototype has a standard lamps configuration, the second presents an innovative lamps distribution. As for the laboratory cases, the most relevant features in terms of irradiation and reaction were described for the prototypes, comparing their performance. We evaluated both the overall VOC conversion and VOC conversion per UV lamp, analyzing the energy efficiency of each configuration with adequately accuracy. Therefore, we conclude the CFD model to be an important tool for reactor scale-up as a result of the good prediction of experimental results and the accurate description of the governing phenomena. By using the developed model, the scale-up process of UV reactors can be quickly improved, by screening various configurations with the simulator before testing them, saving significant time and effort in the development of full-scale reactors.

Keywords
CFD simulation; reactor modelling; reactor scale-up; air treatment; UV reactor; VOC abatement;
National Category
Chemical Process Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-233384 (URN)
Funder
Mistra - The Swedish Foundation for Strategic Environmental Research, MI15.14
Note

QC 20180820

Available from: 2018-08-18 Created: 2018-08-18 Last updated: 2018-08-20Bibliographically approved

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