Since Japanese scientist Akira Fujishima discovered the phenomenon of photocatalysis in 1972, photocatalysis has undergone a development journey of fifty years. In recent years, research in photocatalysis has gradually transitioned from laboratory-based fundamental research towards industrialization. Due to the limitations of traditional batch reactors, such as small illuminated surface area, uneven illumination of photocatalysts, low heat transfer efficiency, and issues like magnification effects, it has been challenging to achieve industrial-scale applications of photocatalysis.
Unlike traditional batch reactors, the structure of a flat-plate photochemical reaction apparatus is flat, and catalysts can be uniformly dispersed within the plate reactor. This design offers advantages including a larger illuminated surface area, higher uniformity of catalyst illumination, improved mass transfer efficiency between reactants and photocatalysts, reduced magnification effects, making it an optimal choice for outdoor applications of photocatalytic reaction systems.
However, most of the current research is still conducted within batch reactors. To transition from batch reactors to flat-plate reactors, the following issues need to be considered:
1. Fixation method and dosage of photocatalysts
2. Reactor material
3. Reactant concentration
4. Flow rate
5. Heat transfer within the flat-plate reactor
6. Bed thickness, and more
Nevertheless, conventional flat-plate reactors are generally large in volume and consume significant raw materials for each experiment, which makes them unsuitable for initial explorations, particularly when adjusting parameters such as catalyst fixation method, reactor material, and bed thickness.
PLR-SPRL Laboratory-Scale Photochemical Reaction Apparatus is used for initial experimental explorations. The reactor has a compact design, with a standard working area of only 10×10 cm2, and options for 5×5, 15×15, 20×20, and 25×25 cm2. Experimenters can replace different reactors according to experimental requirements, gradually increasing the reaction area to gather mass transfer, heat transfer, and reaction kinetics data during the scaling-up process.
In order to accommodate different types of photocatalysts and reactions, different substrates are typically chosen for fixing photocatalysts. Common materials for fixing photocatalysts include non-woven fabric, carbon paper, carbon cloth, high borosilicate glass, and organic glass.
| Material | Characteristic |
| Non-woven Fabric | Has excellent porous structure and high surface area, strong binding ability with photocatalysts, good load capacity, and provides a large active surface area |
| Carbon Paper, Carbon Cloth | Has good conductivity, aids in the separation of photogenerated charges in photocatalysis, and can be used in electrically assisted photocatalytic reaction systems |
| High Borosilicate Glass | Has good transparency and mechanical strength, longer lifespan, higher light absorption efficiency for photocatalysts, especially suitable for reactions with certain corrosiveness (acid, alkali, and strong oxidative conditions) |
| Organic Glass | Can be processed into different shapes and sizes, suitable for studying the effects of process on reactions |
PLR-SPRL Laboratory-Scale Photochemical Reaction Apparatus is designed with supporting blocks that can match the fixation of photocatalysts on various substrates, meeting the demands of different experimental scenarios.
Mass Transfer in Flat-Plate Reactors
When the reaction solution flows through a flat-plate reactor, as shown in the figure, laminar flow and turbulent flow occur. To enhance mass transfer between the reaction solution and the catalyst, the longitudinal flow rate of the fluid needs to be increased.
The Reynolds number (Re) is used to measure the state of fluid flow. For non-circular pipe fluid flow, its formula is as follows:
When Re > 500, the fluid begins to transition from laminar flow to turbulent flow.
Taking water as an example and using its kinematic viscosity V = 0.013 cm2/s, it can be calculated that for a 10×10 cm2 flat-plate reactor, when the flow rate v > 8000 mL/min, Re > 500. This means that under normal experimental conditions (0~200 mL/min), the flat-plate reactor is in a laminar flow state.
To improve mass transfer within the flat-plate reactor, the PLR-SPRL Laboratory-Scale Photochemical Reaction Apparatus limits the fluid layer thickness, dL, to within 3 mm, reducing the diffusion distance of reactants to the photocatalyst bed layer. Additionally, the flat-plate reactor is inclined and fluid enters from the bottom. On one hand, this approach increases the illuminated surface area and light intensity for the photocatalyst; on the other hand, gravity and frictional resistance with the bed layer disturb the fluid flow downward, increasing the probability of reactant diffusion to the photocatalyst bed layer, achieving high mass transfer efficiency at low flow rates.
For photocatalytic reactions with low mass transfer efficiency or low reaction rates, the PLR-SPRL Laboratory-Scale Photochemical Reaction Apparatus can be operated in a closed mode, or the reaction solution can be circulated into the flat-plate reactor multiple times through a storage tank and a circulation pump. This allows the accumulation of photocatalyst activity over time. With process optimization and increased production, the apparatus can gradually switch to continuous flow mode for calculating photocatalyst activity.
After obtaining suitable parameters through experimentation using laboratory-scale flat-plate reactors, such as optimizing catalyst loading and flow rate, as well as selecting appropriate reactor materials, verification at larger scales on flat-plate reactors is needed for large-scale production.
However, during actual scale-up production, the following issues need to be considered:
1. Impact of Heat Transfer
The cooling system used in laboratory flat-plate reactors, such as circulating water or ice baths, can quickly dissipate heat and have minimal impact on the reaction. However, once the reaction system is scaled up, timely heat dissipation becomes more challenging and can significantly affect the direction of the reaction;
2. Reaction Efficiency
Increasing the area of the flat-plate reactor affects the total residence time of the reaction and alters mass transfer efficiency, thus impacting reaction efficiency and yield;
3. Load Process
Scaling up the reaction process enlarges the area for catalyst loading on the substrate. This change affects the pressure resistance and stability of the substrate, requiring adjustments to the catalyst loading process and substrate fixation structure to meet the demands of large-sized reactions;
4. Dynamic Circulation System
As reactor volume increases, the processing capacity of reaction solution per unit time also increases. Corresponding dynamic circulation systems such as circulation pumps, conveyance pipelines, and storage pumps need to be appropriately scaled up to ensure efficient circulation, minimize structural energy losses, and reduce costs.
PLR-SPRF Pilot-Scale Flat-Plate Photochemical Reaction Apparatus offers three sizes (40×40, 60×60, and 80×80 cm2) of large-sized flat-plate reactors. The maximum effective illuminated area can reach 0.5 m2, and two flat-plate reactors can be connected in series with quick connectors to achieve an illuminated area of 1 m2.
For different-sized flat-plate reactors, Perfectlight Technology has made corresponding adjustments to reactor structure and photocatalyst substrate fixation.
To optimize mass transfer efficiency, the PLR-SPRF Pilot-Scale Flat-Plate Photochemical Reaction Apparatus incorporates disturbance structures at the inflow and outflow ports of the reactor. The fluid layer thickness in the reactor also includes an adjustable space of 1~5 mm, minimizing the impact of scaling up on mass transfer efficiency.
For reactors of different sizes, the PLR-SPRF Pilot-Scale Flat-Plate Photochemical Reaction Apparatus calculates the liquid holding volume of the reactor and optimizes the length and size of supporting equipment including storage tanks, liquid pumps, flow meters, and conveyance pipelines.
After confirming the final reaction conditions through scale-up experiments, the largest-sized (80×80 cm2, effective illuminated area of 0.5 m2) photochemical reactor can be connected in series or parallel for large-scale production.
PLR-SPRG Mass Production Photochemical Reaction Apparatus is designed for large-scale photocatalytic production. The apparatus consists of a reaction module, liquid driving module, gas-liquid separation module, and detection control module. It is controlled by a built-in PLC, allowing real-time monitoring and adjustment of reaction parameters through the touch screen interface. Monitored and adjustable parameters include solution state monitoring of the reaction system, such as reaction flow, pressure, pH, and ORP (Oxidation-Reduction Potential). Additionally, it can control reaction conditions, such as total flow rate, individual unit flow, and pressure.
| PLR-SPR Series Flat-Plate Photochemical Reaction Apparatus | |||
| Parameters | PLR-SPRL Laboratory-Scale | PLR-SPRF Pilot-Scale | PLR-SPRG Mass Production |
| Reactor Size | 10×10 cm², options for 5×5, 15×15, 20×20, 25×25 cm² | 0.1 m², options for 0.25, 0.5 m² | 0.5 m², options for 5 m², 10 m² |
| Flow Rate | 0~1 L/min | 5~10 L/min | 25~120 L/min |
| Storage Tank | 0.2~0.8 L | 10 L | 10~1000 L |
| Support Unit | Desktop | Free-standing | Outdoor |
| Pipelines | PU tubing, PTFE tubing, stainless steel tubing, PPR tubing | Stainless steel tubing | Stainless steel tubing |
| Application Setting | Indoor/Outdoor | Indoor/Outdoor | Outdoor |
| Required Area | 2 m² desktop | 5~10 m² floor | 10~100 m² floor |
| Application Field | Photocatalysis: Photocatalytic water splitting, liquid solar fuels, photocatalytic wastewater treatment Photoelectrocatalysis: Photovoltaic photocatalytic water splitting |
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