Key Takeaways & Executive Findings
- •• A novel hyperbranched polymer (HBP) hollow-fiber composite membrane was fabricated via a facile dip-coating method on a PVDF ultrafiltration membrane. • The optimized membrane achieved a high permeation flux of 1766 g·m⁻²·h⁻¹ and a separation factor of 4.1 for a 50/50 wt% toluene/n-heptane mixture at 60 °C. • The study demonstrates the potential of HBP/PVDF hollow-fiber membranes for industrial pervaporation separation of aromatic/aliphatic hydrocarbons. • The membrane offers advantages of self-supporting structure, high packing density, and ease of scale-up compared to flat-sheet and tubular modules.
Abstract
The separation of aromatic/aliphatic hydrocarbon mixtures is crucial in the petrochemical industry. Pervaporation is regarded as a promising approach for the separation of aromatic compounds from alkanes. Developing membrane materials with efficient separation performance is still the main task since the membrane should provide chemical stability, high permeation flux, and selectivity. In this study, the hyperbranched polymer (HBP) was deposited on the outer surface of a polyvinylidene fluoride (PVDF) hollow-fiber ultrafiltration membrane by a facile dip-coating method. The dip-coating rate, HBP concentration, and thermal cross-linking temperature were regulated to optimize the membrane structure. The obtained HBP/PVDF hollow-fiber-composite membrane had a good separation performance for aromatic/aliphatic hydrocarbon mixtures. For the 50%/50% (mass) toluene/n-heptane mixture, the permeation flux of optimized composite membranes could reach 1766 g·m⁻²·h⁻¹, with a separation factor of 4.1 at 60 °C. Therefore, the HBP/PVDF hollow-fiber-composite membrane has great application prospects in the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures.
1. Introduction
The separation of aromatic/aliphatic hydrocarbon mixtures is of great significance in the petrochemical industry, chemical production, and environmental protection. However, the separation of aromatic compounds from alkanes is very difficult due to their similar chemical and physical properties. As an efficient membrane separation technique, pervaporation has great advantages in economy and environment because of its environment-friendly nature, low energy consumption, compact equipment, and easy coupling with other techniques.
The development of pervaporation membranes depends on their separation performance and its longevity. High-performance polymeric membrane material often requires a complicated synthesis process. The most reported membrane materials for separating mixtures of aromatic and aliphatic hydrocarbons via pervaporation are polymers, such as polyimide, polyurethane, polyacrylate, poly(ether amide), polysiloxane amide, poly(vinyl alcohol), poly(methyl methacrylate), and hyperbranched polymer (HBP). They have been widely used because of their effective membrane-forming abilities, functional versatility, and low cost. In our previous study, HBP emulsion was prepared in aqueous solution and then deposited on the surface of a tubular porous ceramic substrate by a negative-pressure-driven assembly method. The green preparation method exhibited excellent application prospects. However, since the HBP was deposited inside the pores of the ceramic tubular porous substrate, the flux of the membrane was only 238 g·m⁻²·h⁻¹, which should be further improved to meet the requirement in the industry. To increase permeation flux, it is necessary to regulate the structure of the HBP-composite membrane.
The membrane module also has a significant influence on the application in industry. Most of the polymers were deposited on the surface of organic flat sheet and ceramic tubular substrate in the field of aromatic/aliphatic separation. Compared with the flat-sheet and tubular membrane modules, the hollow fiber membrane module has the advantage of self-supporting, high packing density, and ease to scale-up. Therefore, the hollow fiber membrane modules have a promising future in the pervaporation separation industry. However, to the best of our knowledge, there is only one report on the fabrication of hollow fiber membrane for the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures. Commercial polybenzimidazole (PBI) and polyimide Matrimid were used to prepare an asymmetric hollow fiber membrane using a non-solvent induced phase separation method. Expanding membrane materials and preparation methods is still the main task. Thin film composite membrane, which is constructed by ultrathin separation layer and porous substrate, has been considered as the promising membrane in industry. However, it is challenging to form an intact and effective separation layer on the three-dimensional substrate surface of hollow fiber.
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Tong Liu, Hao Sun, Xiangqiong Wang, Jie Li, Zhanquan Zhang, Pei Wu, Naixin Wang, Quanfu An (2023). Hyperbranched polymer hollow-fiber-composite membranes for pervaporation separation of aromatic/aliphatic hydrocarbon mixtures. Chinese Journal of Chemical Engineering. https://doi.org/10.1016/j_cjche_144878161
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Frequently Asked Questions
What is the main challenge in separating aromatic/aliphatic hydrocarbon mixtures?
The main challenge is the similar chemical and physical properties of aromatic and aliphatic hydrocarbons, making their separation difficult. Pervaporation is a promising membrane-based technique for this separation.
How was the hyperbranched polymer (HBP) membrane fabricated in this study?
The HBP was deposited on the outer surface of a polyvinylidene fluoride (PVDF) hollow-fiber ultrafiltration membrane using a facile dip-coating method. The dip-coating rate, HBP concentration, and thermal cross-linking temperature were optimized.
What separation performance did the optimized HBP/PVDF membrane achieve?
For a 50/50 wt% toluene/n-heptane mixture at 60 °C, the optimized membrane achieved a permeation flux of 1766 g·m⁻²·h⁻¹ and a separation factor of 4.1.
What are the advantages of hollow fiber membranes over flat-sheet or tubular membranes?
Hollow fiber membranes offer self-supporting structure, high packing density, and ease of scale-up, making them promising for industrial pervaporation applications.
What is the significance of this study for the petrochemical industry?
The study provides a novel and efficient membrane material and fabrication method for pervaporation separation of aromatic/aliphatic mixtures, which is crucial in petrochemical processes, offering potential for energy savings and environmental benefits.
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