Valorization of a Byproduct for Sustainable Formulations: Preparation of an Alcohol Gel Hand Sanitizer Containing Glycerol and Methyl Salicylate

Advancements in production techniques have markedly enhanced potential glycerol applications across various sectors. The present study describes the purification of two different samples of crude glycerol obtained from industrial processes. First, the purification of crude glycerol (pH = 5) was achieved by treatment with KOH and subsequent adsorption on commercial activated charcoal. K2SO4 was also obtained as a byproduct of the process. The purification of crude glycerol (pH = 12) was also achieved by treatment with H3PO4 and subsequent adsorption on commercial activated charcoal. KH2PO4 was also obtained as a byproduct of the process. The purified glycerol was analyzed by IR, 1H and 13C NMR, and the ASTM D4176–22 method (standard test method for free water and particulate contamination). ASTM D874 is the standard test method for determining the sulfated ash content. The test is used to measure the amount of inorganic contaminants (ash-forming materials) such as abrasive solids and catalyst residues that might remain in glycerol after the purification process. These materials often contain metals such as calcium, potassium, and sodium, and ASTM D664 is a standard potentiometric titration method to determine the total acid number in fatty acid methyl esters (biodiesel or biofuel) by measuring free fatty acids and mineral acids, expressed as mg KOH/g; while not directly used for glycerol, it is crucial for determining glycerol quality because crude glycerol from biodiesel production contains impurities such as free fatty acids that ASTM D664 quantifies, helping to determine if glycerol is suitable for further processing. Subsequently, glycerol was applied directly in the formulation of a hand sanitizer. The hand sanitizer was prepared by mixing water, glycerol, hydroxyethylcellulose, and a solution of methylparaben-ethanol. Methyl salicylate was added to the formulation after the homogenization process, and a hand sanitizer without methyl salicylate was prepared for comparison. In the context of ecosustainable formulation design, this study addresses the self-aggregation of glycerol and methyl salicylate with a wide range of physicochemical and biological activities in hand sanitizer. The physicochemical properties of the formulation were determined in a preliminary analysis of the properties of the hand sanitizer. The pH of the hand sanitizers was slightly acidic (5.7), and despite their high viscosities, the formulations had a high degree of spreadability. The aggregation of methyl salicylate was determined at concentrations up to 40–50 wt %. These results provide basic knowledge to promote the exploration of glycerol and methyl salicylate as valuable ingredients in formulations for various applications.