Hydrogenation of Sunflower Oil in Pd Catalysts at Single‐Phase Conditions

Contribution to the Study of Heterogeneous Catalytic Reactions in SCFs: Hydrogenation of Sunflower Oil in Pd Catalysts at Single‐Phase Conditions. by Eliana Ramírez Rangel December 2005 Submitted to the Department of Chemical Engineering in partial fulfillment of The requirements for the degree of Doctor at the Universitat Politècnica de Catalunya Supervised by: Dr. Francesc Recasens Dr. M. A. Larrayoz Department of Chemical Engineering Universitat Politècnica de Catalunya To my Mom and my Grandmother To Oscar Mauricio Summary Hydrogenation is a major industrial chemical process. A wide variety of chemicals is obtained by catalytic hydrogenation. One typical heterogeneous catalytic hydrogenation process is the production of margarine and shortenings from vegetable oils. The hydrogenation of double bonds in fats and oils has the purpose of providing products with the desired melting profile and texture, according to their final use. The hydrogenated oil is more stable and less sensitive to oxidation. The classic process is carried out in batch reactors where the oil, hydrogen, and catalyst nickel powder are mixed intensively at temperatures between 373 K and 423 K. In this case, the compound to be hydrogenated and or the reaction products are liquid at process conditions; the reaction rate is limited by the concentration of hydrogen on the catalyst surface. The low reaction rate is caused by the low solubility of hydrogen and the high mass‐transfer resistance in the liquid phase, which leads to a depletion of hydrogen at the catalyst surface. In the presence of double bonds, this lack of hydrogen also gives rise to double‐bond migration and cis‐trans‐isomerization. Despite of the fact that isomerization of cis‐trans configuration increases the melting point, conflicting conclusions have resulted from studies on trans fatty acids. In several studies, these isomers formed during hydrogenation of fatty edible oils have shown to have similar effects as saturated fats increasing serum cholesterol levels in the blood, believed to be a major cause of heart desease. For this reason, apprehension and public awareness have risen regarding the potential health hazards of trans fatty acids intake in the human diet. The aim of this research is to study continuous single‐phase hydrogenation of sunflower oil on supported palladium catalysts using supercritical fluids as a reaction solvent. This would be an alternative process for producing a wide variety of end products having different characteristics (iodine value, trans‐fatty acid content and saturated content mainly) of industrial foodstuffs interest to be used as low cholesterol precursors for margarine and shortening bases in the next few years. In addition, the objective of the study is to show, on a lab‐scale, the potential of heterogeneous catalytic reactions under supercritical single‐phase conditions. i Summary This thesis is based on the material published in several technical papers and one patent, which can be found at the end of the thesis. The tesis is structured as follows: Chapter 1 consists of a background, to explain the idea of use supercritical fluids in the hydrogenation of fats and oils, to describe the state of the art and what are the aims of this research. Chapter 2 presents a theoretical study for modelling the vapor‐liquid high pressure equilibrium for sunflower oil/hydrogen/C3H8 system as well as for sunflower oil/hydrogen/DME in order to determine suitable operating conditions (concentrations, temperatures and pressures) which can bring all hydrogenation reactants and products into a homogeneous reactive fluid phase. Chapter 3 establishes a better understanding of how operating variables affect the rate of reaction, conversion and final product distribution in a continuous recycle reactor as well as the experimental conditions where a potential CSTR process could be operated to obtain end‐products with industrial foodstuff of interest. As an extension of these results, the kinetics of the reaction is worked out. Chapter 4 it is a consequence of the results of the previous chapter and develops the study of the intraparticle diffusion‐reaction mechanisms in supercritical sunflower oil hydrogenation on Pd/C catalyst. The final chapter contains the experimental details of this thesis. The last part gathers the main conclusions, discusses the prospects for further investigations and presents the bibliopraphy and the appendixes. ii Acknowledgements I want to thank Professor Francesc Recasens and Professor M. Angels Larrayoz for the supervision of this Thesis. I really appreciate your advices and support throughout my research work. I thank professors José Luis Cortina and Jordi Bou for sharing with me different stages during these years of intensive work. I also thank people of mechanics laboratory for your attention and your help. I would like to express my appreciation for my lab‐mates (Nancy, Fakher, Kamal, Alfredo and Aline) and for the students that have realised final projects or made an intership (Susana, Joan, Rubén, Silvia, Jordi, Mónica, Cristina, Ana Sofía, Sara, Tiff, Thierry, Mathew and Marine) who made all together an enjoyable space for work. To all the administrative staff my sincere thanks. I thank Generalitat de Catalunya as well as The Spanish Ministry of Science and Technology for the financial support during my doctoral studies. I wish to express my gratitude to people of The Clean Technology Research Group in The University of Nottingham especially to professors Martyn Poliakoff and Paul Hamley. I thank Eduardo, Maia, Joan, Lu, Pete, Jason, Silvia, Su, Rodrigo, Gonzalo and Tomás not only for sharing with me your scientific knowlegde but also for having fun. I also thank all my friends (Lili, Iván, Laura, Dionisio, Humberto, Leonardo, people from Santa Teresita Church, Silvia, Tiff and Aline) for the prayers and for the support that I have received from them. My eternal gratitude goes to my family for its continued love and support. I also would like to mention the love that every day I receive from Oscar and my puppies Paca and Coco that has supported me all the time. iii Contents Contents List of Figures ix List of Tables xv List of Schemes xix Chapter One Introduction. 1 1.1 Physical and Chemical Process in Heterogeneous Catalyst Reactions. 1 1.2 Hydrogenation. 2 1.2.1 Hydrogenation of Fats and Oils. 3 1.2.2 Fats and Oil Hydrogenation Mechanism. 7 1.2.3 Fats and Oil Conventional Hydrogenation Process. 8 1.3 Supercritical Fluids. 11 1.3.1 Definition and Properties. 11 1.3.2 SCFs in Heterogeneous Catalysis. 12 1.3.3 SCFs in Fats and Oil Hydrogenation. 21 1.4 Objectives and Scope of this Thesis. 27 1.5 Thesis Structure. 28 1.6 Nomenclature. 29 Chapter Two High‐Pressure Equilibria. 31 2.1 Introduction. 31 2.2 Objectives and Strategy. 40 2.3 Theoretical Determination of L‐V High Pressure Equilibria. 41 2.4 Results and Discussion. 45 2.5 Conclusions. 55 2.6 Nomenclature. 56 v Contents Chapter Three Kinetics of the Sunflower Oil Hydrogenation Process over Palladium‐Based Catalysts using SC propane or SC DME as Reaction Solvent. 59 3.1 Introduction. 59 3.2 Objectives. 72 3.3 Sunflower Oil Hydrogenation on Pd/C using SC Propane as Reaction Solvent. 73 3.3.1 Study of the Effect of Operating Variables on Hydrogenation Reaction by means of the Experimental Design. 73 3.3.1.1 Creating the Central Composite Experimental Design. 73 3.3.1.2 Results and Discussion. 77 3.3.2 Kinetic Analysis of CSTR Data: Modeling and Results. 84 3.4 Sunflower Oil Hydrogenation over Pd/Al2O3 using SC DME as Reaction Solvent. 90 3.4.1 Experimental Considerations. 90 3.4.2 Kinetic Analysis of CSTR Data: Results and Modeling. 92 3.5 Final Discussion. 98 3.6 Conclusions. 99 3.7 Nomenclature. 100 Chapter Four Intraparticle Diffusion in Porous Catalyst Particles used in Supercritical Sunflower Oil Hydrogenation. 105 4.1 Introduction. 105 4.2 Objectives and Strategy. 113 4.3 Detection of the Internal Mass Transport Resistance. 113 4.4 Determination of Effective Diffusion Coefficients. 114 4.4.1 Experimental Measurements. 114 4.4.2 Steady‐State Diffusion and Chemical Reaction in Porous Catalyst Particle Model under Isothermal Conditions. 115 4.4.3 Results and Discussion. 119 4.5 Conclusions. 134 4.6 Nomenclature. 135 Chapter Five vi Contents Experimental. 139 5.1 Introduction. 139 5.2 Raw Materials. 139 5.2.1 Sunflower Seed Oil. 139 5.2.2 Hydrogen. 139 5.2.3 Propane. 139 5.2.4 Dimethyl ether (DME). 139 5.2.5 Catalysts. 140 5.2.5.1 Activation Procedure. 140 5.2.5.2 Test of the Stability of Catalyst Activity. 140 5.3 Safety Procedures and Devices. 140 5.4 Supercritical Fluid Continuous Flow Apparatus. 142 5.4.1 Process and Instrumentation Diagram (P&ID). 142 5.4.2 Equipment List. 145 5.4.3 Experimental Apparatus Description. 146 5.4.3.1 The Gradientless Reactor. 146 5.4.4 Modifications Made to the Supercritical Flow Apparatus. 148 5.4.4.1 The Replacement of the Reactor. 148 5.4.5 Standard Operating Procedure for the Supercritical Continuous Flow Apparatus. 150 5.5 Analytical Techniques. 152 5.5.1 Iodine Value. 152 5.5.2 Preparation of Methyl Esters of Fatty Acids. 153 5.5.3 Silver ion High‐Performance Liquid Chromatography. 153 5.6 Nomenclature. 159 Chapter Six Conclusions and Prospects for Further Investigations. 161 Chapter Seven Bibliography. 165 Appendix A vii Contents Survey of Heterogeneous Catalytic Reactions carried out under SC Conditions or in SCF solvents (Baiker, 1999, Ramírez et al. 2002). 187 Appendix B Hydrogenation of Aromatic Compounds in High‐Temperature Water. 191 Appendix C Estimation of Thermodynamic Properties for Sunflower Vegetable Oil. 207 Appendix D Calculating Binary, Vapor‐Liquid Equilibria Using The Peng Robinson Equation of State.

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