Eco-efficient processes for biodiesel production from waste lipids

The paper proposes innovative eco-efficient processes for converting waste lipid feedstock with up to 35% free fatty acids into biodiesel. Free fatty acids pre-treatment is a key issue, which can be handled by esterification with methanol or glycerol, using hetero- or homogeneous catalyst. The integration with the transesterification stage is possible using methods based on process intensification and heterogeneous catalysis. Three integrated continuous processes are investigated. The first performs the esterification with methanol by reactive absorption and superacid solid catalyst, followed by transesterification by reactive distillation with alkali catalyst. The second method applies the esterification with glycerol at high temperature, coupled with transesterification by heterogeneous catalyst in a variable residence-time plug-flow reactor. The third alternative replaces the second reaction stage with vacuum distillation. In all cases, biodiesel fulfills the specifications of D6751 and EN14214 norms. This result is obtained by kinetic simulation of reactors including free fatty acids esterification and glycerides transesterification. A techno-economic analysis pinpoints the pros and cons of each process. The first process is suited for low free fatty acids content, as used cooking oils. The second and third processes can be applied for higher content of free fatty acids, such as animal fats and greases. Particularly the third process can deliver biodiesel of highest quality, conforming to the cold soak filtration test

Adhesion of solid particles to gas bubbles. Part 2: Experimental

In slurry bubble columns, the adhesion of solid catalyst particles to bubbles may significantly affect the G–L mass transfer and bubble size distribution. This feature may be exploited in design by modifying the hydrophilic or hydrophobic nature of the particles used. Previously we have proposed a generalised model, describing the adhesion of particles to G–L interface under stagnant conditions. In this work, we studied the adhesion of particles characterised by different degree of hydrophobicity and porosity: non-porous polystyrene and glass beads, unmodified and hydrophobised mesoporous silica, and activated carbon particles. Images recorded at high optical magnification show the particles adhering to gas bubbles individually or as aggregates. In aqueous media, higher liquid surface tension and particle surface hydrophobicity increase the adhesion strength and the tendency of particles to agglomerate, in agreement with the model. The adhesion of non-porous rough-surface particles to gas bubbles can be characterised by the receding contact angle. The advancing contact angle represents better the adhesion of the same particles to liquid droplets. We found that the “effective” contact angle of porous particles is much lower than an “intrinsic” contact angle calculated from the heat of immersion in water, or measured by sessile drop method. An equivalent contact angle derived from the Cassie rule explains the wetting behaviour of particles having the pores filled with liquid

Enhancing the Separation Efficiency in Acetic Acid Manufacturing by Methanol Carbonylation

Acetic acid is an essential chemical used in the production of many chemical products. Using methanol as bio-building block, the acetic acid produced may be incorporated in bio-based products. This study deals with enhancing the efficiency of separations in a process using a homogeneous catalyst, which is the most applied today industrially. Several configurations for downstream processing by distillation are investigated using effective combinations of fully thermally coupled columns, namely, dividing-wall columns, alone or combined with heat pumps. The results indicate that the three-column direct sequence may be effectively replaced by a two-column sequence. Overall, the total annual cost is reduced by 34 %. The cost of compressor may be paid back in 1.5 years by the saved energy. Low energy intensity is achieved by tight integration with the reaction section.Accepted Author ManuscriptChemE/Product and Process Engineerin

Adhesion of solid particles to gas bubbles. Part 1: Modelling

Particle-to-bubble adhesion is important in the areas of anti-foaming, in flotation processes and in multiphase slurry reactors. In the present work we particularly address the latter. The behaviour of fine catalyst particles adhering to gas bubbles in aqueous media is governed by the surface hydrophobicity. This adhesion on its turn influences the G–L mass transfer, bubble coalescence and the particle agglomeration. Existing models for the quantitative description of adhesion of particle to a G–L interface usually assume nonporous, spherical particles with a smooth surface and a well-defined contact angle. As catalyst particles are normally highly porous, have a rough surface, and an irregular shape, we developed a generalised model describing the adhesion of particles to a gas bubble based on maximum adhesive and cohesive forces as the main parameters. This model describes adhesion of: (i) a single spherical particle, (ii) a monolayer of particles, and (iii) a particle agglomerate. The cohesive forces between particles play a key role. For small cohesive forces, the particles can either adhere as a single particle or as a monolayer, while stronger cohesive forces allow multilayer adhesion or adhesion of particle clusters via one or few particles

Steady-state behaviour of PFR-separation-recycle systems with simultaneous exothermic and endothermic, first-order reactions

A systematic investigation of plug-flow reactor (PFR)-separation-recycle systems where first-order exothermic and endothermic reactions are simultaneously performed is presented. The nonlinear behaviour is analyzed for two flowsheet alternatives and four plantwide control structures. It is shown that the system can exhibit a complex nonlinear behaviour. For the parameter values used, regions of unfeasibility, two or three multiple steady states and branches of isolated solutions were found. The undesired nonlinear phenomena can be avoided by fixing the reactor-inlet flow rates of each reactant or, when this is impossible due to the flowsheet structure, by providing sufficient cooling capacity. © 2008 Elsevier Ltd. All rights reserved