Abstract
Serious environmental concerns regarding the use of fossil-based fuels have raised awareness regarding the necessity of alternative clean fuels and energy carriers. Biodiesel is considered a clean, biodegradable, and non-toxic diesel substitute produced via the transesterification of triglycerides with an alcohol in the presence of a proper catalyst. After initial separation of the by-product (glycerol), the crude biodiesel needs to be purified to meet the standard specifications prior to marketing. The presence of impurities in the biodiesel not only significantly affects its engine performance but also complicates its handling and storage. Therefore, biodiesel purification is an essential step prior to marketing. Biodiesel purification methods can be classified based on the nature of the process into equilibrium-based, affinity-based, membrane-based, reaction-based, and solid-liquid separation processes. The main adverse properties of biodiesel – namely moisture absorption, corrosiveness, and high viscosity – primarily arise from the presence of oxygen. To address these issues, several upgrading techniques have been proposed, among which catalytic (hydro)deoxygenation using conventional hydrotreating catalysts, supported metallic materials, and most recently transition metals in various forms appear promising. Nevertheless, catalyst deactivation (via coking) and/or inadequacy of product yields necessitate further research. This paper provides a comprehensive overview on the techniques and methods used for biodiesel purification and upgrading.
Highlights
Bateni et al / Biofuel Research Journal 15 (2017) 668 -690 are distinct enough from one another to be separated via gravitational settling and centrifugation (Van Gerpen et al, 2004; Atadashi et al, 2011b), further purification is required to remove impurities and meet the standard specifications introduced in ASTM D6571 or EN14214
According to the results presented by Coelho et al (2011) for purification of ethyl esters of castor oil, decreasing the pH of water used in the washing step decreased the amount of water required for neutralization
Biodiesel has been introduced as a clean, biodegradable, and biocompatible diesel substitute produced via transesterification of fresh vegetable oil, animal fats, waste cooking oil, and microalgae oil
Summary
Absorption and distillation, as well as supercritical fluid extraction and liquid-liquid extraction (LLE), are some of the most common equilibriumbased separation processes (Huang and Ramaswamy, 2013; Lei and Chen, 2013). Absorption is commonly utilized for separating particles and impurities from a gaseous mixture (Treybal, 1980; De Haan and Bosch, 2013; Huang and Ramaswamy, 2013); it does not have a major application in biodiesel separation
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