高熔点蜡合成技术的研究进展

Approaches for the Synthesis of High-Melting Waxes:A Review

高熔点蜡(熔点>80℃)具有高熔点、高稳定性、低针入度、低迁移率以及耐磨坚硬等特点,在食品化妆、材料加工、电子机械、国防航空以及医疗领域有着重要的应用。但目前市场上的蜡产品熔点(50–70℃)较低。而我国高熔点蜡和特种蜡的需求量日益增加,预计缺口将突破70万吨。本文详细综述国内外合成高熔点蜡(熔点>80℃)的技术和工艺,包括聚乙烯蜡、费托蜡和生物质基蜡等,尤其对工艺涉及的催化剂和反应机理等进行了分析。聚乙烯裂解制备具有成本低、可以有效解决“白色污染”等优点,并且可以直接利用现有的催化裂化装置。但这一过程需要在高温的苛刻条件下进行,得到的蜡产品碳数分布较广、杂质较多,性能和色泽等方面不如直接乙烯聚合工艺的蜡产品。乙烯聚合蜡工艺则主要受限于复杂的工艺和昂贵的茂金属及非茂金属的配合物催化剂。高熔点费托蜡虽然性能优异并且技术也逐渐成熟,但其不同熔点的产品是通过不同长度碳链的精馏得到,产品是混合碳链的烷烃,仍然存在相对较宽的熔程。虽然生物质基蜡的合成研究刚起步,但其产物碳数单一,具有更窄的熔程;在合成过程中可根据需求选取特殊官能团的生物质平台小分子,还可根据特殊的使用场景对产品进行官能团化等。更重要的是,生物质基高熔点蜡更加契合世界各国的能源绿色可再生化和低碳化政策。展望了高熔点合成蜡的未来发展趋势,以期促进新的工艺和技术路线的涌现。

High-melting hydrocarbon waxes(melting point:>80℃),consisting of saturated alkanes with carbon numbers greater than 40,exhibit unique features including high melting points,high stability,low penetration,high viscosity,as well as good wear resistance and hardness.These features make high-melting waxes suitable for use in foods,cosmetics,materials processing,electronic machinery,national defense,aviation,medical fields,etc.Considering the fast growth of technology and the electronics industry,the world’s economy relies on the production and utilization of high-quality high-melting waxes.However,most waxes in the world’s current markets are prepared from mineral oils,and such commercial waxes have melting points in the range of 50–70℃.Considering the rapid consumption of high-melting waxes and specialty waxes,their supply insufficiency is anticipated to exceed 700000 t.High-melting waxes are divided into polyethylene(PE)wax and Fischer-Tropsch synthesis(FTS)wax,based on synthesis methodology.PE wax can be obtained via the polymerization of ethylene and can also be prepared via the thermal or catalytic cracking of plastics.PE cracking to form waxes,with the advantage of low cost,can effectively solve the problem of“white pollution”and make use of existing catalytic cracking units.However,this process results in high energy consumption to achieve waste polymer depolymerization and exhibits some drawbacks,such as a wide carbon number distribution and high impurity content in the obtained PE waxes.However,there are some new methods for synthesizing PE waxes,such as cross alkane metathesis.The FTS,which uses carbon monoxide and hydrogen as raw materials,realizes the synthesis of waxes through carbon chain growth.Although the highmelting FTS waxes display excellent performance and the technology is gradually maturing,FTS waxes with different melting points are produced by rectification of products with various carbon chain lengths.Nonetheless,PE and FTS waxes are widely used in various industries because of their excellent properties.However,their synthesis is based on petroleum and coal-derived chemical products.Biomass-derived waxes have a narrow melting range due to their precise carbon chain growth process.Based on different application demands,small biomass platform molecules can be functionalized to fabricate biomass-derived waxes with special functions.More importantly,the biomass-based synthesis route is sustainable and in-line with the global values for mitigating carbon dioxide emissions and achieving carbon neutrality.This review discusses the recent advances in the synthesis techniques for high-melting waxes,including PE waxes,FTS waxes,and biomass-derived waxes.Furthermore,the catalysts and reaction mechanisms involved in the synthesis of high-melting waxes are discussed in detail.Finally,the perspectives and trends of high-melting waxes are reviewed to promote the emergence of new processes and technical routes.