Abstract

Microwave assisted glycerol acetylation reactions in a monomode pilot reactor were performed in order to obtain glycerol derivatives as potential biodiesel additives. The reactions were carried out with acetic acid and acetic anhydride using sulfuric acid, pyridine and triethylamine as catalysts. The acetylation reactions yielded a mixture of mono, di and triacetin respectively with short irradiation time and high selectivity to triacetin. Pyridine exhibits 100% of selectivity to triacetin in 30 min of microwave heating with 0.88% (w/w_T) of catalyst concentration. Microwave-heating technology has been demonstrated as an alternative to reach a green chemistry and to this end becomes essential the knowledge of the dielectric properties of the materials involved in microwave heating in order to operate under optimal conditions. Dielectric properties of the pure reagents and during the glycerol acetylation under conventional heating were measured. High loss tangent were obtained for reactions mixtures employing H₂SO₄ and triethylamine and dielectric heating is dominated by ionic conductivity whereas with pyridine the dielectric heating of the reaction mixture is governed by dielectric relaxation process. Physical–chemical analysis of blended biodiesel with triacetin show values for viscosity, flash point, water content, density and acid number in accordance with current international standards. Gaseous emissions analyses of blended biodiesel showed significant reduction of CO emission (50%), CO₂ (25%) and 30% reduction in unburned hydrocarbon (UBHC) and 50% of NOx emissions. The best values were observed in the samples containing 5 and 10% of triacetin.

Graphical abstract

中文翻译：

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介电特性在微波甘油乙酰化和混合生物柴油气体排放中的作用

摘要

在单模中试反应器中进行微波辅助甘油乙酰化反应，以获得作为潜在生物柴油添加剂的甘油衍生物。该反应以乙酸和乙酸酐为原料，以硫酸、吡啶和三乙胺为催化剂进行。乙酰化反应分别产生单、双和三醋精的混合物，照射时间短，对三醋精的选择性高。在微波加热 30 分钟、催化剂浓度为 0.88% ( w / w _{T ) 的情况下，吡啶对三醋精的选择性为 100%。}微波加热技术已被证明是实现绿色化学的替代方案，为此，了解微波加热所涉及材料的介电性能至关重要，以便在最佳条件下运行。测量了纯试剂的介电性能以及常规加热下甘油乙酰化过程中的介电性能。使用H ₂ SO ₄和三乙胺的反应混合物获得高损耗角正切，并且介电加热由离子电导率主导，而使用吡啶时，反应混合物的介电加热由介电弛豫过程控制。对含有三醋精的混合生物柴油进行物理化学分析，显示粘度、闪点、含水量、密度和酸值符合现行国际标准。混合生物柴油的气体排放分析显示，CO 排放量 (50%)、CO ₂ (25%) 显着减少，未燃烧碳氢化合物 (UBHC) 排放量减少 30%，NOx 排放量减少 50%。在含有 5% 和 10% 三醋精的样品中观察到了最佳值。

图形概要