Ultrathin Microporous Metal Oxide Coatings: Preparation by Molecular Layer Deposition, Characterization And Application

Molecular layer deposition (MLD), a gas phase deposition technique, was applied to deposit conformal organic-inorganic hybrid coatings by conducting a series of sequential, self-limiting surface reactions on substrates with exquisite thickness control at the sub-nanometer level. Obtained organic-inorganic hybrid coatings can subsequently be converted into porous coatings by removing the organic compound. Potential of functional coatings and membranes prepared by MLD was explored for applications from adsorptive separation, water purification, to gas storage. We demonstrated a new concept, pore misalignment, to continuously fine tune the molecular-sieving “gate” of 5A zeolite by adjusting the external porous Al2O3 MLD coating thickness. For the first time, small organic molecules with sub-0.01 nm size differences were effectively distinguished by size. As an extension of the pore misalignment concept, a composite zeolite adsorbent was prepared by depositing an ultrathin porous TiO2 coating on 5A zeolite by MLD. This composite adsorbent showed great potential for effective C3H6/C3H8 separation based on both equilibrium and adsorption kinetics differences (approximately 5 times higher ideal adsorption selectivity and 44 times higher diffusivity, compared to uncoated 5A zeolite). MLD coated zeolite (5A and 13X) composite adsorbents were also found to have great potential for CO2 capture from flue gases; greatly enhanced CO2/N2 ideal adsorption selectivity was obtained, while maintaining high CO2 adsorption capacity, by controlling calcination conditions. Molecular layer deposition was also used as a highly controllable method to prepare TiO2 nanofiltration membranes by depositing microporous TiO2 coating on mesoporous anodic aluminum oxide (AAO) support with excellent control of coating quality, thickness and nanometer-sized membrane pores for water purification. Optimized TiO2 nanofiltration membranes had a pure water permeability as high as ~48 L/(m2∙h∙bar). Salt and dye rejection measurements showed moderate rejection of Na2SO4 (43%) and MgSO4 (35%) and high rejection of methylene blue (~96%). In addition, natural organic matter (NOM) removal testing showed high rejection (~99%) as well as significantly improved antifouling performance and recovery capability. A novel concept of utilizing nanoporous coatings as effective nano-valves on microporous adsorbents was developed for high capacity natural gas storage at low storage pressure. For the first time, the concept of nano-valved adsorbents capable of sealing high pressure CH4 inside the adsorbents and storing it at low pressure was demonstrated. Traditional natural gas storage tanks are thick and heavy, which makes them expensive to manufacture and highly energy-consuming to carry around. Our design uses unique adsorbent pellets with nano-scale pores surrounded by a coating that functions as a valve to help manage the pressure of the gas and facilitate more efficient storage and transportation. The optimal nano-valved adsorbents comprise of a ~7.5 μm thick MCM-48 mesoporous layer coated on the outer surface of 5A beads. After modification by 3 cycles of MLD, the steady state CH4 storage capacity of MLD-MCM-48-5A adsorbent (loading pressure 50 bar, storage pressure 1 bar) was about 55.8-58.4% (40.7-42.6 V/V) of the maximum capacity of the uncoated 5A beads in three CH4 storage cycles, which is about 200% higher than storage capacity of the uncoated 5A beads at the same storage pressure

3D-printed adsorbents for gas separations: A material development, kinetic assessment, and process performance investigation

“Adsorbent materials are promising for various gas purification processes, however, forming them into structured contactors is paramount in enhancing mass transfer properties and reducing pressure losses. In this research, various adsorbents were engineered into structured contactors with 3D printing. The overall goal of this research was to improve the formulation methods of 3D-printed adsorbents and understand their performances in gas separation processes. The specific objectives were to 1) develop new adsorbent 3D-printing strategies, 2) understand the kinetic properties of printed adsorbent monoliths, and 3) assess their process performances. Objective one was addressed by developing five 3D printing techniques: i) oxide seeding and secondary MOF growth (Paper I), ii) direct ink writing of amine-modified MOFs (Paper II), iii) polymer seeding with MOF growth (Paper III), IV) MOF precursor incorporation into printable sol-gels with thermal coordination (Paper V), and v) binderless zeolite printing with sacrificial pectin and gelatin biopolymers (Paper VI). Objective two was addressed by varying the monolith cell density (Paper IV), adsorbent loading method (Papers II-III, V-VI) and macropore space (Paper IV-VI) to determine how these properties relate to printed monoliths’ mass transfer rates. Objective three was addressed by varying the process conditions in a PSA system over a 3D-printed MOF-74 (Ni) monolith for CO2/H2 separation (Paper VII) and over an activated carbon monolith bed for CO2/CH4 separation (Paper VIII). Overall, this research indicated that developing new printing methods can enhance the physiochemical and kinetic properties of printed adsorbent monoliths, established that printed monoliths’ kinetic rates are limited by molecular diffusion, and demonstrated that printed adsorbent monoliths can achieve comparable PSA separation performance to established benchmarks”--Abstract, page iv

Efficient targeted optimisation for the design of pressure swing adsorption systems for CO2 capture in power plants

Pressure swing adsorption (PSA) is a cyclic adsorption process for gas separation and purification, and can be used in a variety of industrial applications, for example, hydrogen purification and dehydration. PSA is, due to its low operational cost and its ability to efficiently separate CO2 from flue gas, a promising candidate for post-combustion carbon capture in power plants, which is an important link in the Carbon Capture and Storage technology chain. PSA offers many design possibilities, but to optimise the performance of a PSA system over a wide range of design choices, by experimental means, is typically too costly, in terms of time and resources required. To address this challenge, computer experiments are used to emulate the real system and to predict the performance. The system of PDAEs that describes the PSA process behaviour is however typically computationally expensive to simulate, especially as the cyclic steady state condition has to be met. Over the past decade, significant progress has been made in computational strategies for PSA design, but more efficient optimisation procedures are needed. One popular class of optimisation methods are the Evolutionary algorithms (EAs). EAs are however less efficient for computationally expensive models. The use of surrogate models in optimisation is an exciting research direction that allows the strengths of EAs to be used for expensive models. A surrogate based optimisation (SBO) procedure is here developed for the design of PSA systems. The procedure is applicable for constrained and multi-objective optimisation. This SBO procedure relies on Kriging, a popular surrogate model, and is used with EAs. The main application of this work is the design of PSA systems for CO2 capture. A 2- bed/6-step PSA system for CO2 separation is used as an example. The cycle configuration used is sufficiently complex to provide a challenging, multi-criteria example

An Investigation into the use of Coated Vanadium Alloys for the Purpose of Hydrogen Separation

A need for a new energy vector is highlighted, as carbon-based transport fuels are identified as producing sub-micron particulate causing both environmental and health issues. It is suggested that this energy vector should be hydrogen, however current commercial hydrogen production relies on the use of expensive hydrogen separation technologies such as amine separation and pressure swing adsorption. It is suggested in this work that a focus be put on the development of hydrogen separation membranes, and in particular a focus on metallic membranes due to their potential for delivering a large hydrogen flux at a high purity and low operating cost. The major barrier to utilisation is identified as cost and thus motivation is provided for the need to develop a new generation of membrane. The problem is identified as having two parts: identifying suitable surface catalysts and bulk membrane materials. Theoretical modelling was used to investigate the design of idealised membranes before tests were conducted. A number of membranes were tested in a bespoke enclosure under conditions designed to mimic real-life operation, with tests undertaken under non-dilute hydrogen conditions and with a mixed CO2/H2 feed. Tests on a non-palladium containing surface catalyst, oxidised silver, proved to show no positive results. Pd-Ag Coated V-Ni and V-Ni-Al membranes are shown to have a maximum apparent permeability of 3.3 x10-8 mol m-1 s-1 Pa-0.5 and 4.1 x10-8 mol m-1 s-1 Pa-0.5 when tested at 300 °C with a binary feed mixture of CO2 and H2. In both instances the purity of the permeate was found to be 99.9% hydrogen. The permeability of both membranes under these conditions warrants further study

ESSE 2017. Proceedings of the International Conference on Environmental Science and Sustainable Energy

Environmental science is an interdisciplinary academic field that integrates physical-, biological-, and information sciences to study and solve environmental problems. ESSE - The International Conference on Environmental Science and Sustainable Energy provides a platform for experts, professionals, and researchers to share updated information and stimulate the communication with each other. In 2017 it was held in Suzhou, China June 23-25, 2017

An investigation of the feasibility of a process-intensified differential temperature water-gas shift reactor with integrated Pt/Al2O3 catalyst

There has been serious interest in hydrogen as a source of energy in the United States due to its capability of delivering a sustainable, carbon-free energy future. Currently, most hydrogen in the United States is produced via the steam methane reforming of natural gas, which converts methane to hydrogen through a series of energy-intensive and carbon-producing reactions, one being the water-gas shift (WGS) reaction. Previous research suggests that the implementation of a differential temperature WGS reactor operating under optimal temperature conditions reduces the required reactor volume to achieve a specific CO conversion level and the hydrogen production cost associated with the overall steam reforming process. This thesis investigates the feasibility of utilizing a plate architecture WGS microreactor with integrated platinum-ceria catalyst to intensify the WGS reaction with the goal of increasing overall hydrogen yield of the steam-methane reforming process and bridging the gap towards a sustainable hydrogen future. First, modeling from previous research was used to inform the design and manufacture of a sub-scale WGS microreactor prototype. Next, a catalyst recipe for a platinum catalyst with ceria precursor supported on washcoated alumina was developed and coated onto the walls of the reaction channels in the prototype. Finally, an experimental test set-up with a reacting gas loop and integrated cooling loop was designed, constructed, and configured to enable chemical testing of the WGS reactor prototype. The WGS reactor prototype with integrated catalyst was assembled and integrated onto the test loop. The thermal behavior of the prototype was validated using inert gases, but sealing challenges arose due to the high number of mechanically sealed surfaces. The results of catalyst adhesion characterization studies suggest that enhancing the surface roughness of the substrate's surface greatly improves the adhesion of the platinum catalyst. The results of the test loop experiments suggest that difficulties in sealing plate architecture-style reactors make this type of design mechanically feasible but impractical for realizing the potential of the intensified water-gas shift reaction