Core challenges and corresponding requirements

1. Physical property degradation and poisoning caused by high temperature and high humidity

Main issues :

When humidity remains between 70% and 95% and temperature between 35 and 45°C , water molecules strongly adsorb onto the catalyst surface, competing with target pollutants (such as VOCs) for active sites, leading to a significant decrease in low-temperature activity. For some metal oxide catalysts, prolonged high humidity may cause loss of active components or aging of the support structure , such as decreased strength and pore collapse.

Requirements for catalysts:

needs to be hydrophobically treated , for example, by using silane coupling agents to reduce the physical and chemical adsorption of water molecules on the surface. Additionally, it is recommended to use hydrothermal resistant materials for the support (such as TiO₂ with specific crystal forms, or partially modified alumina) . Finally, regarding the active catalyst component , manganese-based (MnO₂) and noble metal (Pt/Pd) catalysts are recommended, as their resistance to moisture is generally superior to some copper-based or iron-based catalysts .

2. Chemical poisoning caused by biological and industrial sources.

Main issues :

The humid and hot environment fosters active microbial activity, potentially leading to the presence of malodorous and toxic gases in exhaust gases, such as hydrogen sulfide, ammonia, and thiols, produced by biological metabolism. Furthermore, regional development is accompanied by various large-scale industrial activities, resulting in complex industrial exhaust gas compositions that may contain elements like chlorine, sulfur, and phosphorus . The combined effects of biological and industrial sources pose a serious threat of chemical poisoning to catalysts, especially precious metal catalysts.

Requirements for catalytic reactions :

with high poisoning resistance , sulfur- and chlorine-resistant catalysts are recommended . For example, in VOCs oxidation catalysts, palladium-based catalysts may exhibit slightly better sulfur resistance than platinum-based catalysts. Additionally, multiple transition metal oxides (such as Mn-Ce, Mn-Fe) can be incorporated to disperse the effects of poisons. Along the overall catalytic reaction pathway, an additional protective layer is recommended , such as a replaceable adsorption or reaction protective layer at the catalyst front end, which preferentially adsorbs or decomposes the main poisons.

3. Resistant to clogging by dust and complex impurities

Main issues :

The large-scale industrial activities accompanying regional development can lead to complex industrial emissions , which may include dust, oil mist, salt (in coastal areas) , and even biological impurities such as insects. These substances can physically clog the pores of honeycomb catalysts or the bed of granular catalysts.

Requirements for catalysts:

Prioritize the use of honeycomb catalysts or structured packing materials with fewer pores , larger pore sizes, and open structures to reduce the risk of clogging , and avoid using microporous catalysts as much as possible. In addition, the catalyst must have high mechanical strength to withstand physical cleaning such as high-pressure water jet washing or compressed air blowing , and the adhesion between the carrier and the coating must be strong to withstand washing and erosion.

4. Frequent equipment start-ups and shutdowns and load fluctuations

Main issues :

Temporary power outages or reduced loads in factories due to various reasons cause catalysts to frequently undergo heating and cooling cycles, which , combined with the influence of air humidity , result in thermal stress and condensation risks that can affect the catalyst's lifespan to some extent .

Requirements for catalytic reactions :

Excellent thermal shock resistance is essential ; the catalyst support (especially honeycomb ceramic) must have a low coefficient of thermal expansion to withstand rapid temperature changes without cracking. The catalytic reaction system must also be designed to prevent condensation ; during shutdown, the system program must ensure that the catalyst bed is thoroughly purged with hot air to remove moisture and prevent condensation buildup.

Design recommendations for catalytic reaction systems

High-efficiency emission of industrial waste gas under high humidity and high heat conditions faces multiple difficulties and challenges. Improving catalyst conditions alone is not enough; the entire waste gas treatment system needs to be designed in a coordinated manner and operated in a coordinated manner.

1. Enhance the preprocessing unit

01 High-efficiency dehumidification:

A "cooling + demisting" or "rotor/solution dehumidification" device must be added before the catalyst reactor to control the relative humidity of the exhaust gas to below 70% or even 50% .

02 Multi-stage filtration:

It adopts a three-stage filtration system of "pre-filter (to prevent biological impurities ) + medium-efficiency filter (to prevent dust) + high-efficiency filter (to prevent oil mist and micron particles)" to provide a clean gas source for the catalyst .

03 Preheating Guarantee:

The power of the preheater (such as a heat exchanger or electric heater) needs to have sufficient margin to ensure that the exhaust gas can still be heated above the catalyst ignition temperature when high humidity air is drawn in.

2. Assemble an intelligent control system

If conditions permit, it is recommended to integrate temperature and humidity sensors into the entire system to monitor and automatically adjust the preheating power and bypass valve in real time . Set an automatic purging program to start immediately upon shutdown, using dry, hot air to protect the catalyst.

3. Regular maintenance checks

Hot and humid environments can exacerbate corrosion of industrial equipment . Therefore, it's crucial to select corrosion-resistant materials for equipment to minimize replacement frequency . Furthermore, regular inspections and maintenance of the equipment's operating conditions and the catalyst's status are necessary.