Calibration strategies, digital images and microfluidic device for quality control of biodiesel

Author(s)

Samara Soares

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB)
• Defense date: 2023-04-12

Examining board members

Fabio Rodrigo Piovezani Rocha; Joaquim de Araujo Nobrega; Thiago Regis Longo Cesar da Paixão; Alex Virgilio

• Advisor: Fabio Rodrigo Piovezani Rocha

Abstract

This Thesis presents the development of analytical procedures for the quantification of methanol, alkyl ester and Ca and Mg contents in biodiesel as well as biodiesel in diesel or vegetable oil blends, and the evaluation of calibration strategies to circumvent matrix effects in these analyses. Procedures for quantification of methanol, Ca and Mg and biodiesel in diesel blends were based on DIP exploiting a smartphone camera. Methanol quantification was based on oxidation to formaldehyde and subsequent reaction with Schiff reagent. Two linear responses were obtained from 75500 mg kg1 and 5002000 mg kg1 methanol, with a coefficient of variation (CV, n = 10) of 5% and detection limit (LD) of 25 mg kg1. A simple and low-cost alternative procedure for methanol microdistillation from biodiesel was also developed. It was based on the discoloration of an acid potassium permanganate solution, caused by the oxidation of methanol to formaldehyde. A linear response was obtained from 2502000 mg kg1, with CV (n = 10) and LD estimated at 3.7% and 90 mg kg1. The analytical method for determining Ca and Mg was based on the discoloration of an alkaline Eriochrome black T solution. A linear response was obtained from 1075 mol L1, with CV (n = 10) and LD estimated at 1.0% and 3 mol L1, respectively. A novel volumetric procedure was also developed for the quantification of biodiesel in diesel or vegetable oil blends, using and aquo-ethanol solution as titrant. Linear responses were obtained up to 25 %(v/v) (diesel:biodiesel) and up to 80 %(v/v) (biodiesel:vegetable oil). The CV (n = 10) and LD were 6.8% and 2 %(v/v) for diesel samples and 5.8% and 7 %(v/v) for vegetable oil samples. Multi-energy calibration (MEC) was explored to circumvent matrix effects and the feasibility was demonstrated for iodine value and free glycerol quantification in biodiesel. The CV (n = 8) and LD were estimated at 1.7% and 5 g I2/100 g for iodine value and 3.0% and 10 mg kg1 for free glycerol. In another approach, MEC was pioneering associated to DIP to circumvent glycerol interference on methanol quantification in biodiesel. A linear response was obtained within 20500 mg L1 methanol, with CV (n = 10) and LD estimated at 3.5% and 7 mg L1, respectively. A microfluidic device was developed for the quantification of biodiesel in diesel blends, based on the reaction of alkyl esters with hydroxylamine, in a basic medium, to form hydroxamate, which formed a violet complex with Fe(III) in an acidic medium. A linear response was obtained within 0.10.6 %(v/v) of methyl linoleate, with CV (n = 10) and LD estimated at 4.0% and 0.04 %(v/v), respectively. The mentioned procedures stand out by practicality, cost-effectiveness, and greenness, consuming low amounts of organic solvents and reagents, and generating low waste amounts. Matrix effects were circumvented, and accuracy was demonstrated in comparison with reference procedures (AU)

• FAPESP's process: 18/07687-5 - Exploitation of novel calibration strategies, digital images and flow analysis for biodiesel quality control
• Grantee: Samara Soares
• Support Opportunities: Scholarships in Brazil - Doctorate