Kinetics and Mass Transfer of Free Fatty Acids Esterification with Methanol in a Tubular Packed Bed Reactor:  A Key Pretreatment in Biodiesel Production

Abstract

Biodiesel can be easily obtained starting from high-quality or refined vegetable oils and performing on these feedstocks a transesterification reaction usually promoted by alkaline catalysts in the homogeneous phase. In this production scheme the employment of low-quality or waste raw materials, as cheap as possible, must be carefully considered to strongly improve the economic competitiveness of this biofuel with respect to the petroleum-derived diesel. In the case of raw materials characterized by a high content of free fatty acids (FFAs), a preliminary esterification treatment with methanol or ethanol is necessary for the abatement of the FFA concentration below the threshold limit value of 0.5-1.0% by weight that is tolerable by the subsequent process step of alkaline transesterification. In the present work the esterification reaction in tubular packed bed reactors, operating under pressure and using a sulfonic acid resin as catalyst, has been extensively studied. As it is well-known, sulfonic exchange resins are subjected to an impressive swelling phenomenon, and it is difficult to obtain, in this case, a dimensionally stable packed bed reactor. A particular solution to this problem has been proposed by the authors using springs of suitable size and shape as catalyst diluent. The influence of operative conditions like overall feed flow rate, reactants feed molar ratio, reactor aspect ratio L/D R , and mixture viscosity in the described reactors has been investigated. The collected experimental data have been interpreted by means of a mono-dimensional packed bed reactor model in which the external mass-transfer limitation (fluid-to-particle) has been accounted for.

Vegetable Oil Deacidification by Methanol Heterogeneously Catalyzed Esterification in (Monophasic Liquid)/Solid Batch and Continuous Reactors

“…For this reason, in the typical reaction conditions 8,[11][12] there are two liquid phases, being the methanol soluble in oil up to about 6-8% by weight, depending on the operative conditions and on the oil type. The presence of a double liquid phase (plus the solid catalyst) makes much more difficult the design and operation of the different types of reactors, either batch or continuous, for different reasons.…”

Heterogeneous Catalysis in Biodiesel Production: The Influence of Leaching

“…glycerol) and the separation of glycerol becomes difficult. Therefore, a preliminary stage for free fatty acid elimination is necessary for this process [1,[6][7][8][9][10][11]. Moreover, alkaline catalyst must be neutralized with mineral acids and the recovered glycerol containing dissolved formed salts, is difficult to purify.…”

Influence of Mass Transfer and Kinetics on Biodiesel Production Process

“…Yet another possibility is a packed bed reactor, in which kinetics and mass transfer of free fatty acids esterification with methanol are a key pre-treatment in biodiesel production. The collected experimental data may be interpreted by means of a mono-dimensional packed bed reactor model in which the external mass transfer limitation (fluid-to-particle) is accounted for (Santacesaria et al, 2007a). Experiments were performed by Ataya et al (2008a) to study the mass-transfer limitations during the acid-catalyzed transesterification reaction of triglyceride with methanol (CH 3 OH) to fatty acid methyl ester (biodiesel).…”

“…The common acid-catalyzed processes of the biodiesel production from low-cost raw materials involve the use of mineral acids; this is due to the large amounts of the edible resources with free fatty acids, which are not compatible with the use of base-catalyzed methods. The acid-catalyzed processes and the corresponding kinetic studies included the use of sulphuric acid as the catalyst (Santacesaria et al, 2007b), whereas in another study of Santacesaria et al (2007a), a sulphonic active group-functionalized copolymer matrix gel was applied as a catalyst as well. It must be pointed out, however; that major drawbacks -such as reactor corrosion and the substantial generation of by-products and waste materials, including the salts formed as a result of mineral acid neutralization, which must be disposed of in the environmentrepresent insurmountable problems for the mineral-acid-catalyzed process.…”