A review of biodiesel production by integrated reactive separation technologies

Abstract

Biodiesel is a biodegradable and renewable fuel, emerging as a viable alternative to petroleum diesel. Conventional biodiesel processes still suffer from problems associated with the use of homogeneous catalysts and the limitations imposed by the chemical reaction equilibrium, thus leading to severe economic and environmental penalties. This work provides a detailed review—illustrated with relevant examples—of novel reactive separation technologies used in biodiesel production: reactive distillation/absorption/extraction, and membrane reactors. Reactive separation offers new and exciting opportunities for manufacturing the fatty acid alkyl esters involved in the industrial production of biodiesel and specialty chemicals. The integration of reaction and separation into one operating unit overcomes equilibrium limitations and provides major benefits such as low capital investment and operating costs. These reactive separation processes can be further enhanced by heat‐integration and powered by heterogeneous catalysts, to eliminate all conventional catalyst related operations, using efficiently the raw materials and the reaction volume, while offering higher conversion and selectivity, as well as significant energy savings compared with conventional biodiesel processes. Remarkable, in spite of the high degree of integration, such integrated reactive‐separation processes are still very well controllable as illustrated by the included examples. Copyright © 2012 Society of Chemical Industry

Potential of Pervaporation and Vapor Separation with Water Selective Membranes for an Optimized Production of Biofuels—A Review

“…This integration may offer major benefits such as process efficiency and compactness along with flexibility due to its modular design, with consequent reduction in energy input, capital investment, and process costs. Moreover, these reactive separation technologies could be improved by heat-integration, and the use of solid catalysts could avoid the conventional operations related to homogeneous catalysis, with consequent advantages in the efficient use of raw materials and reaction volume and, at the same time, enhanced conversion and selectivity values [4]. Usually, the batch processes are more advantageous when a variety of different products are produced in relatively small volumes using the same equipment, whereas continuous processes are employed for large volume products since these processes are less labor intensive.…”

“…The use of a large excess of one reactant could cause inefficient exploitation of the reactor volume and a higher cost of subsequent separation steps to recover the reactant. As regards reactive separation processes for biodiesel production, an overview was provided by Kiss et al [4], while the main applications of membrane technology for biodiesel production and refining technology were reviewed by Atadashi et al [108] and Shuit et al [109]. By comparing the energy requirements for a conventional two-step process based on FFAs pre-treatment and TGs transesterification (acid and basic catalysis respectively) with a reactive separations process, it is possible to verify that the specific energy use in reactive separation processes is significantly lower than that required for the FAAE purification step alone [3,4].…”

“…In the first case, the reaction products (FAAEs and glycerol) and the catalyst are soluble in the alcoholic phase. Considering the molecular sizes, the methanol/FAME/glycerol phase selectively passes through the membrane into the permeate stream, while the larger oil droplets are retained [4]. The FAAE synthesized by employing the membrane reactor easily meets both the free and total glycerine ASTM standards, even when low-grade lipid feedstock is processed [110].…”

Systematic Sustainable Process Design and Analysis of Biodiesel Processes

“…The process synthesis problem is represented mathematically by Equations (1)(2)(3)(4)(5)(6)(7)(8). Equation (1) represents the objective function, which can either be maximized or minimized.…”

“…For example, it is non-toxic, biodegradable and has a very low concentration of sulfur. In addition it has a high cetane number (above 60 as compared to 40 for regular diesel), a high flash point (<130 °C) and it emits ~70% fewer hydrocarbons, ~80% less carbon dioxide and ~50% less particulates [3]. The interest in biodiesel can also be understood from its global production in recent years.…”