Key Takeaways & Executive Findings
- •• Hydrophilic ZSM-5 zeolite membranes exhibit excellent stability and dehydration performance for concentrating and dehydrating H2SO4 solutions, even at high concentrations (6 M) and temperatures (90 °C). • The membranes achieve near-complete rejection of inorganic salts (natrium, iron, magnesium) in acid/salt mixtures, demonstrating high desalination efficiency. • Pervaporation with ZSM-5 membranes offers an energy-efficient and environmentally friendly alternative for treating acidic wastewater, addressing a critical industrial need. • The membranes maintain neutral permeate pH even under harsh acidic conditions, confirming their acid resistance and potential for long-term industrial application.
Abstract
The hydrophilic ZSM-5 zeolite membranes are applied to separate the inorganic acid solutions and inorganic acid/inorganic salt mixtures by pervaporation, and the membrane presents good stability, dehydration, and desalination performance. Influences of inorganic acid type (H2SO4, H3PO4, HNO3, and HCl), H2SO4 concentration (1e6 mol$L−1), test temperature (60e90 °C) and inorganic acid/inorganic salt type (2 mol$L−1 H2SO4 and sulfate, 2 mol$L−1 H3PO4 and phosphate) on the pervaporation performance are investigated in this work. Either for concentrating 3% (mass) H2SO4 solution or consecutive dehydrating 20% (mass) H2SO4 solution, the hydrophilic ZSM-5 zeolite membrane has a good dehydration performance and stability. Even though the H2SO4 concentration and test temperature are increased to 6 M and 90 °C, only H2O molecules could pass through the membrane and pH value of the permeation is kept neutral. Besides, the membrane has good dehydration and desalination performance for H2SO4/sulfates and H3PO4/phosphate mixtures, and the rejection of natrium salt, molysite, and magnesium is almost 100%.
1. Introduction
With the development and large-scale expansion of industrial productions, many industrial processes have produced a large amount of acidic wastewater, such as mining plants, chemical plants, chemical fiber plants, electroplating plants, coal processing plants, and metal pickling workshops [1e4]. The output of waste acid in China is more than 100 million tons every year, and this acidic wastewater contains a large number of free acids, sulfate ions, chloride ions, and various metal ions [5e7]. If the untreated acid wastewater is directly discharged, it has a great impact on the ecosystem on the earth and even human life safety. It is urgent to improve the utilization rate of waste acid resource for the sustainable development of the acidic industry [8,9].
Because waste acid aqueous mixtures have various concentrations, wide sources, and complex components, it is a great challenge to separate and recycle the waste acid. Currently, separation methods of waste acid aqueous mixtures include distillation, concentration, extraction, high-temperature cracking, chemical oxidation, polymerization, and membrane separation technologies [10e12]. Membrane separation technology is energy-saving, efficient, environmental-friendly, simple, and convenient, which has become a hot spot in recovering waste acid in recent [13e15]. Polyacrylonitrile-based composite membrane was applied to purify sulfuric acid aqueous from copper-refining sulfuric acid wastewater, the membrane showed excellent acid stability and evaluated the recovery performance in 1 t$d−1 pilot-scale process [13]. TiO2 ceramic and MPF-34 (proprietary layer) composite membrane exhibited the transport of H+ cations and negative rejections, and the performance of the membranes was related to the metallic ions transport [14]. The poly amide-sulfonamide membrane had impressive long-term stability for dehydrating 20% (mass) H2SO4 wastewater mixture [15].
Pervaporation (PV) is an efficient, energy-saving, and environmental-friendly membrane separation technology, which has a great potential value in the separation of acidic liquid mixtures and desalination. Because of the excellent acid resistance and adjustable hydrophilicity, zeolite membranes could be used to separate acidic systems [16,17]. Yao et al. [16] prepared a novel UZM-5 zeolite membrane with UFI crystal phase, which had good acid-resistance and dehydration performance for 90% (mass) HAc aqueous mixture by PV. Yang et al. [18] used OH− and F− ions as co-minerals to prepare ZSM-5 zeolite membranes, which had high acid resistance to HAc aqueous solution in a wide concentration range. The hydrophilic and acid-stable ZSM-5 zeolite membranes were successfully prepared in our previous studies, and the membrane had good stability, dehydration, and PV performance for high-concentration acetic acid solution and esterification product [19,20]. In order to enlarge the applied range of the membrane, the hydrophilic ZSM-5 zeolite membranes are applied to dehydration of the inorganic acid solutions and inorganic acid/inorganic salt mixtures by PV, influence...
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Huanxu Teng, Ronghui You, Huanyi Li, Siqi Shao, Qi Zhou, Ying Yang, Ting Wu, Meihua Zhu, Xiangshu Chen, Hidetoshi Kita (2023). Pervaporation performance and characterization of hydrophilic ZSM-5 zeolite membranes for high inorganic acid and inorganic salts. Chinese Journal of Chemical Engineering. https://doi.org/10.1016/j_cjche_144878383
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Frequently Asked Questions
What is the main application of hydrophilic ZSM-5 zeolite membranes in this study?
The membranes are used for pervaporation separation of inorganic acid solutions and inorganic acid/inorganic salt mixtures, achieving dehydration and desalination.
How do the ZSM-5 membranes perform under high acid concentrations and temperatures?
They maintain good dehydration performance and stability even at 6 M H2SO4 and 90 °C, with only water molecules permeating and neutral permeate pH.
What is the rejection rate for inorganic salts in the mixtures?
The rejection of sodium, iron, and magnesium salts is almost 100%.
Why is pervaporation considered an advantageous technology for acid wastewater treatment?
Pervaporation is energy-efficient, environmentally friendly, and simple, offering a sustainable alternative to conventional methods like distillation.
What types of inorganic acids were tested in this study?
The study tested H2SO4, H3PO4, HNO3, and HCl, with detailed investigation on H2SO4 concentration and temperature effects.
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