Liquid Phase Catalytic Exchange Research Articles

Synthesis and characterization of hydrophobic nickel catalyst supported on different oxides for continuous liquid phase catalytic exchange reaction

Hydrophobic Ni catalysts supported on three metal oxides coated with PTFE namely Ni/SiO2/PTFE, Ni/Cr2O3/PTFE, and Ni/Al2O3/PTFE were used in liquid-phase catalytic exchange (LPCE) reactions to enrich hydrogen isotope and produce deuterium oxide (heavy water). Wet impregnation method was employed to prepare the Ni/SiO2, Ni/Cr2O3, and Ni/Al2O3 before PTFE coating. The as prepared catalysts were characterized using different characterization techniques and their performances were evaluated in LPCE reaction using a continuous reactor. The performance evaluation based on the D2O yield can be ranked as Ni/Al2O3/PTFE > Ni/Cr2O3/PTFE > Ni/SiO2/PTFE > Ni/PTFE. The catalysts’ performances are strongly associated with the crystallite size, particle size, hydrophobicity, surface area, pore size, and metal-support interaction. Since isotope exchange requires a dry catalyst surface, the catalyst’s hydrophobicity plays a crucial role. In addition, the catalyst support improves the LPCE reaction efficiency, as the most efficient catalyst, Ni/Al2O3/PTFE, yielded 1220 ppm D2O, compared to 520 ppm for the benchmark catalyst, Ni/PTFE. The characterization results reveal that Ni/Al2O3/PTFE outperformed the other catalysts due to its low crystallite size (D = 23.04 nm), high hydrophobicity (WCA = 139.23°), higher surface area (16.31 m2g−1), small pores (pore size = 6.18 nm), and lowest average Ni particle size (40.89 nm).

Liquid phase catalytic exchange column of water detritiation system: Steady-state modeling, simulation, and optimization

This paper presents a steady-state modeling, simulations, and optimization for an LPCE column of water detritiation system. It introduces a three-fluid model that integrates isotopic exchange, equilibrium-stage, and hydrodynamic models, considering energy balance and multiple feeds with adaptable feed location. The models were implemented in Pyomo, an equation-oriented, Python-based optimization modeling framework. Parametric studies are presented to analyze the effects on the detritiation factor and deuterium concentration resulting from changes in the gas to liquid feed mole ratio, gas feed composition, heat duty distribution, and gas feed location. Using the three most commonly employed catalysts, a design study investigates the minimal number of hypothetical stages required to meet the defined annual tritium discharge levels.

Superwetting metal-organic frameworks optimized interface for high-performance hydrogen-water isotopic exchange for tritiated water treatment

A metal-organic frameworks (MOFs) modified interface with superhydrophilic and superaerophobic properties was successfully prepared via the solution process for tritiated nuclear wastewater (HTO) treatment. The superwetting performance of the packing surface which facilitated the liquid phase catalytic exchange was discussed in detail for the hydrogen-water isotope exchange reaction. Superhydrophilic property originated from the microporous hydrophilic nature of MOFs resulting in a rapid spreading and phase-transfer process of the tritiated water droplet, and superaerophobic property accompanied by superhydrophilic water thin film favored the effective exchange between gaseous reactants. Computational fluid dynamic (CFD) simulations revealed the influence of contact angle and liquid flow rate on the gas-liquid two-phase interface and catalytic performance. High performance with the lowest height equivalent to a theoretical plate (HETP) and long-term stability is achieved for this superwetting packing, which holds promise for the detritiation of nuclear wastewater with higher performance and stability.

Hydrophilic Amino Groups Acted in the Hydrophobic Reaction Environment for Efficient Hydrogen Isotopes Enrichment.

Hydrogen isotope enrichment through liquid-phase catalytic exchange (LPCE) technology is achieved in a hydrophobic reaction environment to avoid liquid water poisoning, but the usage of hydrophobic support severely inhibits the internal diffusion of water molecules to decrease the catalytic efficiency. Herein, we encapsulate platinum active sites into a metal organic framework (Pt@NH2-UiO-66) as the efficient catalyst for LPCE via introducing hydrophilic amino groups. Experiments and density functional theory simulation reveal amino groups in the channel as the adsorption site of water molecules accelerates the internal diffusion and slows down the accumulation on the platinum sites. Meanwhile, the amino groups interact with the Pt site bridge electron transfer from active sites to support the host, thus decreasing the catalytic reaction and generated water desorption barrier. Due to these positive roles, the turnover frequency of Pt@NH2-UiO-66 reaches 2272 h-1 in a microchannel reactor. This work provides a novel design strategy of catalysts in LPCE.

NiAl-layered double hydroxides stabilized Pt clusters with enhanced metal-support interaction: Boosting hydrogen isotope separation

Metal-support interaction plays a key role and remains a challenge in exploring highly efficient heterogeneous catalysts, especially for hydrophobic catalysts in Liquid Phase Catalytic Exchange (LPCE) process for water detritiation. In this work, supported Pt catalysts using layered double hydroxides (LDHs) as supports are featured by highly dispersed Pt nanoparticles, water resisting property, and strong interaction of Pt with LDHs, exhibiting excellent anti-aggregation of Pt nanoparticles and catalytic performance over traditional Pt/C at high temperature and humidity conditions. Density Functional Theory calculations show that there is strong interaction between Pt nanoclusters and hydrogen defective LDHs surface, together with significant interfacial charge transfer and metal electronic structure modification, which can restrain the aggregation of Pt on LDHs and enhance catalytic activity. These findings are helpful to deepen understandings of the effects of metal-support interactions in LPCE process, which shed valuable insights for the design and preparation of highly-efficient hydrophobic catalysts on LDHs with prospective applications in water detritiation.

Functionalized graphene modified styrene-divinylbenzene copolymer as a superhydrophobic catalyst carrier for hydrogen-water liquid phase catalytic exchange

Styrene-divinylbenzene (SDB) catalyst carrier is the key material for hydrogen-water liquid phase catalytic exchange (LPCE) reaction. However, currently available SDB generally has drawbacks such as low hydrophobicity, small particle size, and poor strength. Therefore, it is interesting to obtain SDB carriers with large particle size, superhydrophobicity and high strength. Herein, modification of graphene with hexadecyltrimethoxysilane (HDTMS) and γ-methylallyl oxypropyl (KH570) respectively gave KH570-GNS and HDTMS-GNS with a good lipophilicity and a uniform dispersity. Then, terpolymerization of KH570-GNS with styrene and divinylbenzene provided KH570-GNS-SDB; In-situ polymerization of HDTMS-GNS with styrene and divinylbenzene in oil phase gave HDTMS-GNS-SDB. Data show that catalyst carriers KH570-GNS-SDB and HDTMS-GNS-SDB have a suitable particle size (up to 3.5–4.5 mm), as well as a higher strength and a better hydrophobicity (152.36°) than reported for SDB. Interestingly, the hardness of the modified SDBs with a graphene-content of 1% is 189% greater than that of normal SDB with the same diameter, according to particle hardness test. Furthermore, KH570-GNS-SDB exhibits a high stability more than 11 h at 80 °C.Generally, the modified SDB carriers have excellent properties such as superhydrophobicity, high strength and high specific surface area. Hence, they have certain application prospects in the treatment of tritium-containing wastewater.

Superhydrophobic Pt@SBA-15 catalyst for tritium separation in liquid phase catalytic exchange

Through the modification of mesoporous silica (SBA-15), a hydrophobic microscopic reaction environment was constructed, which was beneficial to improve the catalytic activity of the LPCE reaction. The Pt@SBA-15-tetramethyldisilazane catalyst is prepared by the modification of the SBA-15 carrier and the loading of metal Pt, with a water contact angle of 158°. This superhydrophobic structure can enhance the catalytic performance and can prevent the deactivation of the catalyst. By measuring the actual catalytic performance of tritium water under different conditions, we found that it has good catalytic activity, and the catalyst can still maintain a high catalytic activity after 30 days in tritium water environment.

Superhydrophobic Pt@SBA-15 catalyst for hydrogen water isotope exchange reactions

In this work, Santa Barbara amorphous-15 (SBA-15) mesoporous silica was modified to fabricate hydrophobic microscopic reaction environments that enhanced the catalytic activity of the liquid phase catalytic exchange (LPCE) reaction. The hydrophobicity or hydrophilicity of the environments synthesized using modified SBA-15 was verified by conducting N2 and water vapor adsorption-desorption experiments. A porous composite catalyst, Pt@SBA-15-x/PVDF, was synthesized via a two-solvent method. The water contact angle of Pt-modified SBA-15 was 152°, proving its superhydrophobicity and granting it excellent catalytic performance for LPCE techniques in hydrogen-water isotope exchange processes. The catalytic performance of the hydrophobic catalyst did not decrease significantly after 30 days of usage.

MICRO-CHANNEL REACTOR FOR LOW LEVEL H2 OXIDATION WITHIN AN O2 STREAM: PRELIMINARY TESTS IN VIEW OF INTEGRATION IN A H2 GENERATOR WITHIN CECE PROCESS

CECE (Combined Electrolysis Catalytic Exchange) process is the candidate for low level tritiated water detritiation within any application. The process consists mainly of a H2 generator, a LPCE (Liquid Phase Catalytic Exchange) column and an O2 striping column. During operation, tritium is being accumulated within the H2 generator in the form of tritiated water and the effluent streams (hydrogen and oxygen) show in time an increase concentration in tritium in the form of both tritiated water vapors and gas, which needs to be recovered. The tritium in the H2 stream is recovered in a LPCE column, while the tritium in the O2 stream is recovered in a striping column. In view of lowering the load onto the striping column and to recover the tritium in gas form, a micro-channel reactor is proposed to be included for H2 oxidation followed by vapor recovery. The design of the equipment together with the preliminary results of the tests done with H2 and air will be shown, prior to integration in the CECE process.

Liquid-Phase Catalytic Exchange of Hydrogen Isotopes over Platinum on Dual-Modified Graphene.

Although liquid-phase catalytic exchange is an environmentally friendly treatment of hydrogen isotopes in recycled water of a nuclear power station, the successive development of hydrophobic catalysts is still needed to meet much higher catalytic exchange efficiency and stability. Herein, a dual-modified graphene with Pt loading was designed by amination and silanization to anchor Pt nanoparticles uniformly, as well as obtain higher hydrophobicity. After coating the reactor walls with poly(dimethylsiloxane), the catalytic exchange efficiency of the dual-modified graphene with lower Pt loadings (Pt/200-S-NH2-GR) improved up to 91% at 80 °C, which was higher than 80% of only animated graphene (Pt/NH2-GR) at the same condition. Furthermore, the Pt/200-S-NH2-GR maintained high stability for at least 10 h in the temperature range of 40-80 °C, while the Pt/NH2-GR decreased 17% of catalytic exchange efficiency at 80 °C within 10 h. Using the dual-modified strategy for graphene support, high efficiency and stability was achieved for heavy water dedeuteration.

Residence time distribution study in a pilot-scale liquid phase catalytic exchange (LPCE) column packed with a mixture of hydrophobic and hydrophilic catalysts

Residence time distribution (RTD) measurements were carried out in a packed bed column designed for exchange of hydrogen isotopes. The main objective of the study was to characterize the liquid phase mixing under various processes and operating conditions. The packed bed was composed of a mixture of two different types of catalytic packing materials, i.e., a hydrophobic material and a hydrophilic material. Technitium-99m (99mTc) as sodium pertechnetate was used as a radiotracer for RTD measurements. From the measured RTD curves, mean residence times (MRTs), liquid holdup and degree of mixing of liquid phase were evaluated. An axial dispersion model exchange with stagnant zones was used to simulate the measured RTD curves. The results of model simulation showed that volume fraction of hydrophobic to hydrophilic packing and gas/liquid superficial velocities affect the liquid holdup, bed pressure drop and liquid phase dispersion/mixing characteristics. The results of the present study will help to screen packing, optimize the volume of the packing fractions, design and construct the catalyst and optimize the operating conditions for scale up of the isotope exchange process.

A highly efficient and stable catalyst for liquid phase catalytic exchange of hydrogen isotopes in a microchannel reactor

The liquid phase catalytic exchange of hydrogen isotopes is a promising process for upgrading recycle water in nuclear power station. To facilitate the isotope catalytic reaction, a series of two-dimensional hydrophobic catalysts of Pt/modified carbon nitride (Pt/s-C3N4) with different Pt loadings were fabricated and applied in microchannel reactor. Their excellent catalytic performances were found in our experiments by comparing with purchased Pt/activated carbon (Pt/AC), the Turn-Over-Frequency (TOF) of Pt/s-C3N4 is 3 times higher than Pt/AC. Because the Pt clusters of 0.82 ± 0.08 nm were uniformly distributed on the support of two-dimensional carbon nitride (C3N4) to improve availability of the Pt catalyst by exposing more active sites and decreasing effect of the internal diffusion. The catalytic activity of Pt/s-C3N4 catalysts remained stable after 1800 min reaction, whereas Pt/AC displayed a 20% drop. Hydrophobicity of the catalyst maintained its high activity and stability in the liquid phase catalytic exchange reaction.

Thermodynamics Study on Liquid Phase Catalytic Exchange for Water Detritiation

Liquid phase catalytic exchange (LPCE) is one of the key technologies for tritium removal of tritiated water, such as effluents from Fukushima nuclear power plant. Although former researchers have widely studied this process theoretically, the reported results differ from each other due to different assumptions and parameters adopted. In this work, the principle of Gibbs free energy minimization is applied, with only basic physical properties and no more other assumptions involved. The predictions of isotope exchange are more accurate, and the average error between calculation results and experimental data reduces from 4.45%~6.65% to 2.17%. Then the catalytic exchange behaviors are systematically investigated in the protium-deuterium (H-D) system, and the influence of the cascade processes are emphatically analyzed. The method established in this paper could be applied to catalytic exchange systems for tritium separation, which is essential for the development of water detritiation.

Commissioning of the LPCE and purification systems as front-end of the experimental pilot plant for D-T separation

Abstract Liquid Phase Catalytic Exchange (LPCE) as front-end process and Cryogenic Distillation (CD) as back-end process are key processes in detritiation of heavy water used in Cernavoda CANDU-type Nuclear Power Plant (NPP) from Romania as neutron moderator and in the primary heat transfer system. Same technology is used in the Water Detritiation System (WDS) of International Thermonuclear Experimental Reactor (ITER) from Cadarache, France, in order to recover tritium from moderately tritiated water. The purpose of this paper is to give a detailed overview of the current status for the front-end of the ICSI pilot plant, LPCE and purification systems, including all process components. Additionally, the paper will present the results of the non-radiological commissioning of the actual LPCE. The tests were made using protium and deuterium in order to have the confirmation of fully availability for all systems, to verify the operability in manual and automate mode for all sequences involved by start-up, normal operation and safe shut-down of the installation. The principal results consist in the safety and operability design confirmation. Secondly we present the mass transfer data of LPCE column equipped with catalytic package COMPACK C–P 001 consisting of the structured B7 stainless steel packing manufactured and patented by ICSI and a Pt/C/PTFE hydrophobic catalyst at the commissioning low concentration heavy water tests.

Nano-silica hybrid SDB carriers with high strength and hydrophobicity: synthesis, characterization and their application as sorbents of Ni2+

In Liquid Phase Catalytic Exchange (LPCE), the strength and hydrophobicity of styrene-divinylbenzene copolymer (SDB) carrier are key limitation factors for practical applications. In this paper, a surface-modified nano-SiO2 (KH570-SiO2) was used to improve the strength and hydrophobicity of SDB. Then, copolymerization of KH570SiO2 with St, DVB to produce KH570-SiO2/SDB, Divinyl benzene (DVB), styrene (St) glycidyl methacrylate (GMA) to produce KH570-SiO2/GMA/SDB. The two kinds of new carriers were characterized by scanning electron microscope, static water contact angle, N2 adsorption–desorption, transform infrared spectrometry and thermogravimetric analysis. Compared with SDB, both KH570-SiO2/SDB and KH570SiO2/GMA/SDB show better performances, such as a higher hydrophobicity(147° and 145°, respective), a higher strength(107.11 N and 115.37 N, respectively), a better thermal stability(373.8 and 435.67 ℃, respectively), and a larger specific surface area(487.253 and 463.673 m2/g, respective). The Nickel ion was uesd as the model ion of Platinum ion. And then the Ni2+ adsorption performances of KH570-SiO2/SDB and KH570-SiO2/GMA/SDB were studied. Experiments show that KH570-SiO2/GMA/SDB has a much higher adsorption rate and a bigger adsorption amount. Refinement indicates that the adsorption behaviors of SDB, KH570-SiO2/SDB and KH570-SiO2/GMA/SDB with Ni2+ are according to pseudo-first-order kinetic. The adsorption of SDB and KH570-SiO2/GMA/SDB obeyed Freundlich isotherm, while the adsorption of KH570-SiO2/SDB obeyed Langmuir isotherm.

Overview about cryogenic distillation control and safety approach for Isotopes Separation Facility (ISF)

Abstract Isotopes separation technologies are used in both Tritium Removal Facilities associated with CANDU reactors (to remove tritium from heavy water) and fusion applications (eq. ITER Isotope Separation System) to recover and enrich tritium for further operation. The expertise gained during design, manufacturing, building, commissioning and operation of the Cryogenic Distillation System (CDS) with proprietary four column design built at ICSI Rm. Valcea, could be applied for various tritium recovery applications, regardless of the type of front-end process used, Liquid Phase Catalytic Exchange or Combined Electrolysis and Catalytic Exchange. Cryogenic Distillation feed is a mixture of hydrogen isotopes which presents hazards in operation (explosion and tritium contamination), therefore the CDS of PESTD was designed to meet industrial and nuclear applicable standards. In this paper we present an overview of the CDS focusing on the process control and safety approach which meet specific conditions of Romanian codes and standards required for operation. However, specific information may be used later as reference for design consideration for other CDS. The cryogenic distillation process from ICSI Rm. Valcea is designed as four columns cascade inside a cold-box which acts as second barrier against hydrogen release and thermal insulation. The CDS process control is based on a Programmable Automation Controller (PACs), a Supervisory Control and Data Acquisition (SCADA) and specific low temperature field equipment and devices. The control room operator supervises the process using a specific designed Human Machine Interface (HMI) which permits to monitor process parameters, alarms acknowledgment and acts to adjust the process or override normal PACs control.

The Study of CECE Process for Low-Tritiated Liquid Waste Prior to Experimental Phase

In order to ensure the efficient management of radioactive waste in the form of tritiated light water and tritiated heavy water with low tritium and/or deuterium concentration, Institute for Cryogenics and Isotopic Technologies (ICSI) Rm.Valcea is developing an experimental demonstration facility based on the combined electrolysis catalytic exchange (CECE) separation process. The facility is completing the experimental pilot plant for tritium and deuterium separation—the installation support for heavy water detritiation from the CANDU reactors in Romania. The concentration of deuterium from low-concentrated waste extends the recovery area from below 1% D2O/(D2O + H2O), corresponding to the minimum threshold of the Cernavoda Upgrading Facility, thus contributing to the reduction of heavy water losses. At the same time the tritium recovery process will be increased. The experimental installation has an innovative solution that reconfigures a proton exchange membrane (PEM) electrolyzer for tritium qualification thereby improving equipment specific to hydrogen isotope separation processes. This paper presents the experimental installation conceptual scheme, including the measurement and control elements. A modeling software for simulation of the nonsteady-state regime of the CECE separation process, specific to the deuterium/tritium isotopes concentration process in the liquid phase, is also presented. The mathematical model integrates the characteristic equations of separation by liquid phase catalytic exchange (LPCE), the mathematical representation of isotope separation by electrolysis, and the water distillation from the oxygen purification process in a nonstationary regime. An analysis is presented for the concentration of various low-concentrated tritium waste. We also investigate the influence of the electrolyzer liquid holdup and the isotopic separation column holdup on concentrated water production.

Experimental Results and Experience with the LPCE Process

This paper presents further investigation of the liquid phase catalytic exchange (LPCE) process on the LPCE-3 column (50-mm inner diameter and 2-m height) of the EVIO pilot plant. The characteristics of the column filled with alternating layers of RCTU-3SM hydrophobic catalyst and stainless steel spiral-prismatic packing have been studied at a catalyst/packing volume ratio of 2:1 and compared to a ratio of 4:1. The EVIO-5 computer model is used for the column performance evaluation (as before) but this time the mass transfer coefficient for phase exchange Bx is not fixed. Due to the unequivocal separation of the catalytic and phase exchange with the help of the EVIO-5 code, the comparison of catalyst activity given by mass transfer coefficient Kc has been made for the experiments at two different catalyst/packing volume ratios. The column performance has also been expressed by the value of the height-equivalent-to-theoretical-plate average along the column. Some experience concerning the control of an LPCE column operating at the mode “with independent flows” is discussed.

Catalytic exchange of hydrogen isotopes intensified by two-phase stratified flow in wettability designable microchannels.

This work develops a reliable method to achieve stratified flow in squared cross-section microchannels by endowing the four channel walls with very different wettabilities. The gas-liquid flows are studied experimentally in six kinds of microchannels with different wetting partitions on the channel walls, where occurrence of the stratified flow is found to strongly depend on the wetting partition and the individual flow rate of gas or liquid. Among them, the microchannel possessing three hydrophobic and one hydrophilic walls (3S1H) shows great potential in facilitating liquid phase catalytic exchange (LPCE) of hydrogen isotopes. Subsequently, a 3S1H microchannel reactor coated with hydrophobic Pt/activated carbon/polydimethylsiloxane (Pt/AC/PDMS) is fabricated to perform the LPCE at 30-80 °C and in a wide range of flow rates of hydrogen and water. The experimental outcomes not only unveil the relationship of the isotopic exchange performance with the temperature and flow pattern but also exhibit an outstanding isotopic exchange performance under the stratified flow.

Rigorous Dynamic Simulation of Cryogenic Distillation of Hydrogen Isotopologues in the Fuel Cycle of a Thermonuclear Reactor Based on UV Flash

Operation of the fuel cycle of a thermonuclear fusion reactor naturally leads to accumulation of surplus protium, but in some cases it can also lead to accumulation of surplus deuterium. Both surplus protium and deuterium have to be separated, detritiated, and discharged to the environment, normally passing a final detritiation stage based on either the liquid phase catalytic exchange or water distillation process. The concept of a multicolumn cryogenic distillation (CD) system capable of discharging a time-varying surplus of deuterium is presented in this paper. A model of a CD column based on a UV (internal energy U – volume V) flash formulation and equation of state (EOS) thermodynamic model for hydrogen isotopologue mixtures is also presented at the principal step to a comprehensive model of the isotope separation system. Although fundamental for constant volume systems, the UV formulation of the thermodynamic state has not been widely used in transient simulations; in particular, for distillation dynamics modeling, other approaches are much more common. At the same time, in helium cryogenics the UV formulation has gained wide usage in large-scale dynamic simulations. It is known from the literature that a UV formulation of the distillation problem is very challenging for a numerically stable implementation. To cope with this situation, we present our findings on the sources of numerical instabilities and approaches.