Low-concentration VOCs treatment in printing and packaging: zeolite rotor and catalytic combustion

The printing and packaging industry uses large amounts of solvent-based inks, diluents, adhesives, and cleaning agents during production. Volatile organic compounds (VOCs) such as ethyl acetate, toluene, methyl ethyl ketone (MEK), and isopropyl alcohol are released into the atmosphere during drying or volatilization stages. This type of exhaust gas features typical high-volume, low-concentration characteristics. A single production line can generate airflow rates of 30,000 to 100,000 m³/h, while VOC concentrations typically range from 200 to 1,000 mg/m³, far below the concentration required for self-sustaining combustion. Additionally, the gas composition is complex and fluctuates dramatically, posing severe challenges for treatment technologies. Traditional single adsorption or direct combustion methods suffer from high energy consumption, frequent media replacement, and secondary pollution. This article focuses on the combined process of zeolite rotor adsorption concentration and regenerative catalytic combustion (RCO), systematically explaining its technical principles, key control parameters, and engineering considerations, providing a scientifically feasible technical pathway for the industry.

1. Exhaust Gas Characteristics and Technical Requirements Analysis

VOC emissions from the printing and packaging industry mainly originate from gravure printing, dry lamination, coating, and cleaning operations. Their core characteristics can be summarized as follows:

1. High air volume: To ensure workshop safety and operational environment, exhaust systems typically use general or local ventilation, with air volumes generally in the range of 3×10⁴ to 1×10⁵ m³/h.
2. Low concentration: Large amounts of dilution air cause low VOC concentrations, typically 200 to 1,000 mg/m³.
3. Complex composition: Common components include benzene series (toluene, xylene), esters (ethyl acetate, butyl acetate), ketones (MEK, acetone), alcohols (isopropyl alcohol), etc., with significant differences depending on ink formulations.
4. Intermittent fluctuations: Operations such as start-up, shut-down, plate changes, and cleaning cause periodic or random fluctuations in exhaust concentration and flow rate.
5. Moderate temperature and humidity: Exhaust temperature is generally room temperature to 60°C, with relative humidity of 40%–70%.

To address the above characteristics, an ideal treatment technology must: handle high-volume, low-concentration conditions; resist fluctuations; operate with low energy consumption; produce no secondary pollution; and maintain manageable capital and operating costs. The "adsorption concentration + catalytic combustion" combined process is a mature solution that meets these requirements, with the combination of zeolite rotor and regenerative catalytic combustion (RCO) being particularly outstanding.

2. Core Process Principles

2.1 Zeolite Rotor Adsorption Concentration System

The core of the zeolite rotor is a honeycomb ceramic disk filled with hydrophobic zeolite molecular sieves, divided circumferentially into adsorption, desorption, and cooling zones. The rotor rotates continuously at a very low speed (typically 1–5 revolutions per hour), with each zone connected to different air ducts.

• Adsorption zone: Pretreated printing exhaust passes through the adsorption zone, where VOC molecules are captured by the zeolite micropores (mainly physical adsorption), and the purified gas is directly discharged. The hydrophobic nature of zeolite allows it to maintain 80%–95% adsorption efficiency at relative humidity below 70%, significantly outperforming activated carbon.
• Desorption zone: The saturated rotor rotates into the desorption zone, where it is counter-currently swept by hot air at 180–220°C. The high temperature desorbs VOCs into the gas phase, forming a low-volume (only 1/10 to 1/20 of the original exhaust volume), high-concentration (concentration factor of 5 to 25 times) desorption gas stream, which is sent to the subsequent catalytic combustion unit.
• Cooling zone: The rotor after desorption is at an elevated temperature and must be cooled by ambient air or purified cooling gas to restore its adsorption capacity before re‑entering the adsorption zone to continue the cycle.

Through this continuous cycle, a low-concentration exhaust stream of 8×10⁴ m³/h is concentrated into a high-concentration stream of approximately 5,000 m³/h, greatly reducing the scale and energy consumption of downstream combustion equipment.

2.2 Regenerative Catalytic Combustion (RCO) System

The concentrated high-concentration exhaust gas enters the RCO system. The RCO consists of a combustion chamber, catalyst bed, and ceramic heat recuperator. The exhaust gas is first preheated by passing through the ceramic heat recuperator to 250–350°C, then enters the catalyst bed. On the surface of a catalyst loaded with precious metals (e.g., platinum, palladium) or transition metal oxides (e.g., copper‑manganese composites), VOCs undergo deep oxidation with oxygen, producing carbon dioxide and water and releasing substantial heat. The resulting high-temperature flue gas (typically 400–500°C) passes through another set of ceramic heat recuperators, where most of the heat is stored and used to preheat the incoming cold exhaust gas for the next cycle, achieving heat recovery efficiency exceeding 95%.

Compared to direct combustion (requiring 700–850°C), catalytic combustion lowers the reaction temperature by about 400–500°C, reducing auxiliary fuel consumption by 40%–60%. Moreover, because the entire oxidation process occurs on the catalyst surface without an open flame, system safety is significantly improved. When the desorption gas concentration is sufficiently high (typically no less than 1,500 mg/m³), the exothermic heat from VOC oxidation can sustain the system’s self‑thermal balance without external heating.

3. Key Engineering Control Points

3.1 Exhaust Gas Pretreatment

Printing exhaust inevitably contains particulate or sticky substances such as ink dust, paper lint, fibers, and high‑boiling‑point oil mists. If these substances enter the zeolite rotor, they will clog the micropores or cover the surface, causing irreversible loss of adsorption capacity. If they enter the catalyst bed, they will cover active sites, leading to permanent deactivation. Therefore, at least two stages of dry filtration (e.g., G4 coarse + F7 medium efficiency) must be installed to ensure that the particulate concentration entering the rotor is below 1 mg/m³. For exhaust containing high‑boiling‑point components (e.g., plasticizers, varnish ingredients), a cooler or oil removal device should be added upstream of the filtration.

3.2 Desorption Temperature and Concentration Ratio Control

If the desorption temperature is too low, high‑boiling‑point VOCs will not be completely desorbed, gradually accumulating and causing a "memory effect" that progressively reduces the effective adsorption capacity of the zeolite. If the desorption temperature is too high (exceeding 250°C), it may damage the zeolite crystal structure or cause aging of the rotor seals. In practice, the desorption temperature is typically controlled at 180–220°C. The concentration ratio (ratio of original exhaust flow rate to desorption gas flow rate) should be reasonably set based on the downstream RCO’s light‑off concentration and thermal balance requirements, generally ranging from 5 to 15 times. If the concentration ratio is too low, RCO energy consumption becomes high; if too high, the desorption gas concentration may exceed the lower explosion limit, requiring online monitoring of combustible gas concentration and interlock dilution protection.

3.3 Catalyst Activity Protection and Poisoning Prevention

VOC catalysts are highly sensitive to poisons such as sulfur, phosphorus, chlorine, silicon, and heavy metals. If the printing exhaust contains chlorinated solvents (e.g., dichloromethane, trichloroethane), silicon‑containing ink additives, or phosphorus‑containing flame retardants, a dedicated detoxification unit (e.g., an alkaline scrubber or special adsorption media) must be installed upstream, or a poison‑resistant catalyst should be selected. Furthermore, after long‑term operation, catalysts may lose activity due to carbon deposition or thermal sintering. Regular checks of bed pressure drop and purification efficiency (e.g., every six months) should be performed, and online or offline regeneration should be carried out according to the regeneration process guidance provided by the manufacturer (e.g., Minstrong). When catalyst activity drops below 60% of the design value and cannot be restored, full replacement is required.

3.4 Automatic Control and Safety Interlocks

Because printing production involves intermittent fluctuations, the treatment system must be equipped with a PLC or DCS automatic control system. Key parameters such as rotor pressure drop, desorption temperature, RCO combustion chamber temperature, catalyst bed temperature, and outlet VOC concentration should be monitored in real time, and fan VFDs, electric valve positions, and burner power should be automatically adjusted. Multiple safety interlocks should also be established: when the desorption gas concentration approaches 25% of the lower explosion limit, fresh air is automatically added for dilution; when the RCO inlet temperature exceeds a set upper limit (e.g., 450°C) or the outlet temperature exceeds a warning value (e.g., 650°C), the system automatically cuts off the exhaust feed and initiates emergency venting.

4. Technical Advantages and Applicability

The combined process of zeolite rotor adsorption concentration and RCO catalytic combustion provides a mature, reliable, and cost‑effective technical solution for treating low‑concentration, high‑volume VOCs in the printing and packaging industry. Its core advantages are summarized as follows:

• Efficient concentration: Compresses large air volumes into small‑volume, high‑concentration gas, significantly reducing downstream combustion equipment investment and operating energy consumption.
• Low‑temperature oxidation: Catalytic combustion operates at low temperatures (300–400°C), consumes little auxiliary fuel, produces no open flame, and poses low safety risks.
• Long‑life core components: Zeolite rotor is non‑flammable, high‑temperature resistant, with a design life of 8–10 years; precious metal catalysts typically last 2–3 years under proper use and can be partially regenerated.
• Fully automatic operation: The system adapts to periodic fluctuations in exhaust concentration and flow rate, maintaining stable compliance.

When implementing the project, enterprises should scientifically design pretreatment and process parameters based on their specific exhaust composition, humidity, particulate content, and production patterns, and strictly follow a regular maintenance schedule. For the selection of catalysts and core system components, high‑quality, field‑proven products (e.g., Minstrong series catalysts) can be adopted to ensure long‑term efficient and stable operation of the system.

5. Conclusion

The printing and packaging industry is facing increasingly stringent environmental requirements for VOC control. The combined process of zeolite rotor adsorption concentration and regenerative catalytic combustion enables efficient, low‑energy, and safe exhaust gas purification under conditions of high volume, low concentration, and complex composition. Through proper pretreatment design, precise control of desorption temperature and concentration ratio, strict protection of catalyst activity, and the aid of automatic control systems, this technical route is ready for large‑scale engineering application. In the future, with advances in materials science and control technology, treatment systems will evolve toward greater intelligence, lower energy consumption, and longer service life, providing solid support for the green transformation of the printing and packaging industry.

author：Gloria
date:2026-05-20