THE EFFECT OF VARIOUS SOLVENTS ON THE PURIFICATION OF ZEOLITE WASTES

ABSTRACT

This study investigates the effect of various solvents on the purification of zeolite wastes. Zeolite waste was treated with monoethanolamide, methyl diethanolamine, and hydrogen peroxide at different concentrations. The results showed that increasing solvent concentration generally enhanced the reduction of zeolite contamination. MEA and MDEA demonstrated moderate cleaning efficiency, with optimal effects observed at intermediate concentrations. Hydrogen peroxide exhibited the highest purification performance, and an H₂O₂ concentration of about 3–4% was identified as optimal, providing the maximum reduction of contamination. These findings indicate that hydrogen peroxide is the most effective solvent among those studied for zeolite waste purification.

АННОТАЦИЯ

В данной работе изучено влияние различных растворителей на процесс очистки цеолитных отходов. В качестве основного сырья использовались цеолитные отходы, а в качестве очищающих агентов — водные растворы моноэтаноламина, метилдиэтаноламина и перекиси водорода в различных концентрациях. Установлено, что увеличение концентрации MEA и MDEA приводит к постепенному снижению степени загрязнения цеолита, однако эффект очистки ограничен. Наиболее выраженное снижение загрязнённости наблюдается при использовании перекиси водорода, что связано с её высокой окислительной способностью. Определено, что H₂O₂ является оптимальным реагентом для очистки цеолитных отходов, обеспечивая наибольшую эффективность процесса при сравнительно низких концентрациях.

Keywords: zeolite wastes, purification, monoethanolamide, methyl diethanolamine, hydrogen peroxide.

Ключевые слова: цеолитные отходы, очистка, моноэтаноламин, метилдиэтаноламин, перекись водорода.

Introduction

The rapid development of chemical, petrochemical, gas-processing, and environmental industries has led to a significant increase in the consumption of zeolite materials worldwide. Zeolites are widely used as adsorbents, ion-exchange materials, and heterogeneous catalysts due to their high surface area, well-defined pore structure, and strong affinity toward polar molecules [1]. According to recent industrial reports, global zeolite production exceeds 3.5–4.0 million tons per year, with natural zeolites accounting for nearly 70% and synthetic zeolites for about 30% of the total volume. A substantial portion of these materials becomes spent or waste zeolites after repeated operation cycles, particularly in gas purification, water treatment, and catalytic processes [2].

Statistical data indicate that up to 20–30% of zeolites used in industrial adsorption and catalysis are discarded annually due to pore blockage, surface fouling, or loss of activity. For example, in gas purification and drying units, zeolite adsorbents often lose 40–60% of their adsorption capacity after several regeneration cycles because of contamination with heavy hydrocarbons, resins, sulfur-containing compounds, and inorganic salts [3]. Disposal of such zeolite wastes without proper treatment not only leads to economic losses but also creates serious environmental concerns, including secondary pollution of soil and water resources.

In recent years, increasing attention has been paid to the purification and regeneration of zeolite wastes as an effective strategy for resource conservation and sustainable development [4]. Among the available methods, solvent-based purification has emerged as a promising approach due to its relative simplicity, flexibility, and potential for selective removal of organic and inorganic contaminants. Various solvents—such as water, alcohols, hydrocarbons, ketones, and polar aprotic solvents—have been investigated for their ability to dissolve and extract foulants from zeolite surfaces and pore systems.

However, the efficiency of zeolite waste purification strongly depends on the nature of the solvent, its polarity, boiling point, viscosity, and interaction with both the contaminant species and the zeolite framework [5]. Statistical analyses from experimental studies show that appropriate solvent selection can restore up to 70–90% of the original adsorption or ion-exchange capacity of spent zeolites, whereas unsuitable solvents may result in recovery efficiencies below 40%. Therefore, a systematic investigation of the effect of various solvents on zeolite waste purification is essential for optimizing regeneration processes and reducing industrial waste [6-7].

This study focuses on evaluating the influence of different solvents on the purification efficiency of zeolite wastes, with the aim of identifying optimal solvent systems that ensure high cleaning performance, minimal structural damage to the zeolite framework, and improved economic and environmental sustainability [8].

Material and methods

Materials

The primary raw material used in this study was zeolite waste, obtained from industrial gas and liquid purification processes. The spent zeolite mainly consisted of aluminosilicate phases and contained adsorbed organic impurities, sulfur-containing compounds, and residual hydrocarbons accumulated during long-term operation. Prior to use, the zeolite waste was air-dried at ambient temperature and mechanically crushed, followed by sieving to obtain a particle size fraction of 0.5–1.0 mm, ensuring uniform contact with the treating solvents.

The solvents selected for the purification process were:

• Monoethanolamine (MEA),
• Methyldiethanolamine (MDEA),
• Hydrogen peroxide (H₂O₂).

MEA and MDEA were chosen due to their well-known ability to dissolve acidic gases, polar organic compounds, and sulfur-containing impurities. Hydrogen peroxide was used as an oxidizing agent to promote the decomposition of organic contaminants and enhance surface regeneration of the zeolite.

All chemicals used in the experiments were of analytical grade and were applied without further purification. Aqueous solutions of MEA and MDEA with concentrations of 5, 10, and 20 wt.% were prepared using distilled water. Hydrogen peroxide solutions with concentrations of 3, 6, and 10 wt.% were employed to investigate the effect of oxidant strength on the purification efficiency.

Purification Procedure

The purification experiments were carried out in a batch mode using a thermostatically controlled glass reactor equipped with a mechanical stirrer. In each experiment, a fixed mass of zeolite waste (50 g) was mixed with the selected solvent at a solid-to-liquid ratio of 1:5 (w/v). The mixture was stirred at a constant speed of 300 rpm to ensure homogeneous contact between the zeolite particles and the solvent.

The treatment temperature was maintained at 60 ± 2 °C for MEA and MDEA solutions, while hydrogen peroxide treatments were conducted at 40 ± 2 °C to prevent excessive decomposition of the oxidant. The contact time for all experiments was set to 60 minutes, based on preliminary tests indicating that equilibrium purification conditions were achieved within this period.

After completion of the treatment, the suspension was filtered, and the solid zeolite was thoroughly washed with distilled water until neutral pH was reached. The purified zeolite samples were then dried in an oven at 105 °C for 12 hours and stored in airtight containers for further analysis.

Evaluation of Purification Efficiency

The effectiveness of the purification process was evaluated by comparing the physicochemical properties of the zeolite waste before and after treatment. The following parameters were assessed:

• Mass loss (%), used as an indirect indicator of impurity removal;
• by thermal analysis and loss-on-ignition measurements.

All experiments were performed in triplicate, and the average values were reported to ensure reproducibility and reliability of the results.

Result and discussion

Initially, the effect of monoethanolamine (MEA) aqueous solutions with concentrations ranging from 5 to 20% on zeolite waste was investigated. The obtained results are presented in Figure 1, illustrating the influence of MEA concentration on the purification efficiency and structural changes of the zeolite waste.

Figure 1. Effect of MEA concentration on the reduction of zeolite contamination (%)

The results indicate that increasing the concentration of the MEA solution from 5% to 20% leads to a gradual reduction in the contamination level of the zeolite waste. At low MEA concentration, the purification effect is limited, while a sharp improvement is observed as the concentration increases to the intermediate range. At higher concentrations, the rate of improvement slows down, suggesting that the purification process approaches a saturation region where further increases in MEA concentration result in only minor additional cleaning. This trend indicates that MEA is effective for zeolite waste purification, with optimal performance achieved in the medium-to-high concentration range.

The results indicate that increasing the MEA concentration from 5% to 20% leads to a gradual reduction in the contamination level of the zeolite waste. At low MEA concentrations, the purification efficiency is limited, while higher concentrations significantly enhance the removal of impurities. However, the rate of improvement decreases at concentrations above 15%, suggesting an approach to a saturation or equilibrium effect.

Figure 2. Effect of MDEA concentration on the reduction of zeolite contamination (%)

The effect of MDEA concentration on the purification efficiency of zeolite waste shows a pronounced dependence on solvent concentration. At low MDEA concentration, the reduction of zeolite contamination is limited and reaches only 1.8%. As the concentration increases, the purification efficiency rises significantly, achieving 2.2% at the intermediate level and reaching a maximum value of 3.1%. Further increase in MDEA concentration leads to a slight decrease in efficiency to 2.9%, indicating that excessively high concentrations may reduce solvent effectiveness due to saturation or diffusion limitations. Overall, MDEA demonstrates an optimal concentration range where the purification of zeolite waste is maximized.

At the next stage, the effect of hydrogen peroxide (H₂O₂) concentration on the purification of zeolite waste was investigated. Hydrogen peroxide was selected as an oxidizing agent due to its ability to decompose organic contaminants and promote the removal of surface-bound impurities without causing significant damage to the zeolite framework. The experiments were carried out using H₂O₂ solutions of different concentrations, allowing evaluation of the relationship between oxidant strength and contamination reduction efficiency. An increase in H₂O₂ concentration led to a noticeable decrease in the degree of zeolite contamination, indicating more effective oxidation and removal of residual organic and inorganic impurities. However, at higher concentrations, the improvement tended to level off, suggesting that an optimal H₂O₂ concentration exists beyond which further increases do not significantly enhance purification efficiency.

Figure 3. Effect of H₂O₂ concentration on the reduction of zeolite contamination (%)

Figure 3 illustrates the effect of hydrogen peroxide (H₂O₂) concentration on the reduction of zeolite contamination. As the H₂O₂ concentration increases, a gradual improvement in purification efficiency is observed. At the lowest concentration, the contamination reduction reaches 2.1%, which then increases to 2.6% at an intermediate concentration. Further increase in H₂O₂ concentration results in contamination reductions of 3.2% and finally 3.4%, indicating the highest purification efficiency within the studied range. This trend suggests that hydrogen peroxide effectively enhances the oxidative removal of impurities from zeolite waste, although the rate of improvement becomes less pronounced at higher concentrations, implying a tendency toward saturation of the oxidation process.

Conclusion

Based on the experimental results, hydrogen peroxide (H₂O₂) demonstrated the most stable and progressive effect on reducing the contamination level of zeolite waste. An increase in H₂O₂ concentration led to a consistent improvement in purification efficiency, rising from 2.1% at low concentration to a maximum of 3.4% at the highest studied concentration.

Compared with MEA and MDEA solutions, H₂O₂ provided a more predictable and monotonic cleaning behavior without a noticeable decline at higher concentrations. This indicates that the oxidative mechanism of hydrogen peroxide effectively decomposes organic and inorganic contaminants adsorbed on the zeolite surface, enhancing pore accessibility and surface cleanliness.

Therefore, H₂O₂ can be considered the optimal solvent among the studied reagents for the purification of zeolite waste, particularly when a balance between purification efficiency, process simplicity, and chemical stability is required. The obtained results confirm the feasibility of using hydrogen peroxide as an efficient and environmentally acceptable reagent for zeolite waste regeneration and reuse.

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