Kinetic modeling conversion of carboxylic acids with Hydrogen, over a Zirconium and Cobalt based catalyst into alcohols with application in the Mixalco® process

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(1)KINETIC MODELING CONVERSION OF CARBOXYLIC ACIDS WITH HYDROGEN, OVER A ZIRCONIUM AND COBALT BASED CATALYST INTO ALCOHOLS WITH APPLICATION IN THE MIXALCO® PROCESS.. Degree Project By. RAFAEL AMAYA GÓMEZ CAROLINA JIMÉNEZ PEÑA. Submitted to the office of Graduate Studies of Universidad de los Andes In partial fulfillment to the requirements for the degree of. B.S. CHEMICAL ENGINEERING. Advisor ROCIO SIERRA, M.Sc, Ph.D. UNIVERSIDAD DE LOS ANDES ENGINEERING FACULTY CHEMICAL ENGINEERING DEPARTMENT BOGOTA D.C 2012.

(2) KINETIC MODELING CONVERSION OF CARBOXYLIC ACIDS WITH HYDROGEN, OVER A ZIRCONIUM AND COBALT BASED CATALYST INTO ALCOHOLS WITH APPLICATION IN THE MIXALCO® PROCESS.. Degree Project By. RAFAEL AMAYA GÓMEZ CAROLINA JIMÉNEZ PEÑA. _____________________________________________ ROCÍO SIERRA RAMÍREZ, M.Sc., Ph.D Advisor. _____________________________________________ PABLO ORTIZ, Ph.D Committee member. UNIVERSIDAD DE LOS ANDES ENGINEERING FACULTY CHEMICAL ENGINEERING DEPARTMENT BOGOTA D.C 2012. 2.

(3) ABSTRACT Kinetic modeling conversion of carboxylic acids with hydrogen, over a zirconium and cobalt based catalyst into alcohols with application in the MixAlco® process. Rafael Amaya Gómez & Carolina Jiménez Peña, Universidad de los Andes, Colombia. Advisor: Rocío Sierra Ramirez, PhD.. The goal of this project was to evaluate the production of alcohols during the ketonization of carboxylic acids over a series of metal oxide based catalysts on a laboratory scale and develop a kinetic model to fit data for alcohols formation in order to be applied in the MixAlco® process. The reaction was performed in a fixedbed catalytic reactor, feeding concentrated Acetic Acid and using metal oxide catalysts, specifically zirconium. and a cobalt-chromium based catalyst. The. influence of the catalyst composition was tested, obtaining that the the only catalyst with which alcohols were obtained is C4 (cobalt-chromium based catalyst), due to the fact that it was the only one that worked with a sufficient source of hydrogen to favor the alcohols production. Regarding the Zirconium catalysts (C1, C2 and C3) acetone was the only product obtained. The experimental model was based on the factor levels used previously by Huertas (Huertas, 2011) and based on Huertas it was designed the next experimental model: a pressure of 14.7. , four temperatures. (300, 325, 350, and 380°C) and a feed flow of 1 mL/min. In this work the production of alcohols using the above mentioned catalysts was validated due to the fqact that Huertas results (Huertas, 2011) generated doubt regarding its validity It was concluded then that the conditions at which it was obtained the biggest ethanol production were the use of catalyst C4 at a temperature of 380°C. Furthermore with the help of the software MATLAB, optimized kinetic models for the production of 3.

(4) acetone and ethanol were developed by means of a combination of literature review and parameters adjusted to the experimental data. The model was statistically validated, calculating the residual norms, the confidence intervals and regression coefficient. All the previous indicators demonstrated to be satisfactory, thereby confirming a good accommodation of the experimental data with the models built. Finally, different analyses were performed for the characterization of various zirconium catalysts such as XRD, FTIR, surface area and SEM.. Keywords: Acetic Acid, Cobalt and Zirconium Catalyst, Ethanol, MixAlco® Process, PBR.. 4.

(5) RESUMEN Conversión del modelaje cinético de ácidos carboxílicos con hidrógeno, sobre un catalizador basado en cobalto y circonio en alcoholes con aplicación en el proceso MixAlco ®. Rafael Amaya Gómez & Carolina Jiménez Peña, Universidad de los Andes, Colombia. Asesora: Rocío Sierra Ramírez, PhD. El objetivo de este proyecto fue evaluar la producción de alcoholes durante la cetonización de ácidos carboxílicos sobre una serie de catalizadores de óxidos de metales en una escala de laboratorio y desarrollar un modelo cinético para ajustar los datos para la formación de alcoholes, todo esto para una posterior aplicación en el proceso de MixAlco®. La reacción se realizó en un reactor de lecho catalítico alimentando ácido acético glacial como reactivo y usando catalizadores de óxidos de metales, específicamente zirconio (ZrO2) y un catalizador basado en cobalto y cromo (C4). La influencia de la composición del catalizador fue evaluada obteniendo que el único catalizador con el cual se obtuvieron alcoholes es el C4 (catalizador de Cobalto y Cromo), ya que fue el único que trabajó con una fuente suficiente de hidrógeno para llegar a la formación de alcoholes. En cuanto a los catalizadores de Zirconio (C1, C2 y C3) solo se obtuvo acetona. El modelo experimental se estructuró a partir de los niveles utilizados previamente por Huertas (Huertas, 2011) y con base a Huertas se desarrollo el siguiente modelo experimental: una presión de 14.7. ,. cuatro temperaturas (300, 325, 350, y 380°C) y un caudal de alimentación de 1 mL/min. En este trabajo se validó la obtención de alcoholes utilizando los catalizadores anteriormente mencionados debido a que los resultados obtenidos por Huertas (Huertas, 2011) generaban dudas en su validez. Se concluyó entonces que 5.

(6) las condiciones a las cuales se obtuvo una mayor producción de etanol son el uso del catalizador C4 a una temperatura de 380°C. Además, con la ayuda de la herramienta computacional MATLAB se desarrollaron modelos cinéticos optimizados para la producción de Acetona y Etanol por medio de una combinación de revisión de literatura y parámetros que se ajustaron a los datos experimentales. El modelo se validó estadísticamente, calculando las normas de los residuales, los intervalos de confianza y el coeficiente de regresión. Todos estos indicadores demostraron ser satisfactorios y confirman una buena acomodación de los datos experimentales al modelo construido. Finalmente, se realizaron análisis de caracterización para los diferentes catalizadores de Zirconio tales como XRD, FTIR, área superficial y SEM.. Palabras claves: Ácido acético, Catalizador de Zirconio y Cobalto, Etanol, Proceso MixAlco®, PBR.. 6.

(7) DEDICATIONS. I would like to dedicate this work to all my family and loved ones which in the course of my life unfortunately have died and are now beside God guiding my way and protecting me from all evil, especially to mi aunts Mª Elvira Amaya Perry and Mª Eugenia Gómez Ortega, which sadly died the last few years, leaving from our side. I would also like to dedicate this work to my family, who supported me unconditionally throughout the process, especially my parents and my sister, I love them and they are one of the best gifts that God could made me when I came into this world. And finally to my friends, who showed me the light in the darkness, giving me calm and patience, thanks a lot.. Rafael Amaya Gómez. I would like to dedicate not only this work but all my work, acknowledgements and goals I have achieved during this career to all the people that supported me always and in every situation. Thank you mommy, I don’t know what I would do without you. Dad, in spite of everything you know I love you and you have taught me beautiful and valuable things. My love, thanks for making my life so happy, I know our life together is going to be awesome. Abuelita Esther and Abuelito Rafael, thanks, I love you and I know that you are and will be always beside me. And last but never least, this and all my goals forever will be for you, my beautiful Celeste or Dante. I love you so so much!. Carolina Jiménez Peña. 7.

(8) ACKNOWLEDGEMENTS. The authors want to thank first Dr. Rocío Sierra for their support in the course of all this work, her leadership and commitment to research was a guide to promote the work done in this degree project. We also want to thank Dr. Juan Carlos Moreno for his help in the obtaining of heavy metals (indispensables for this work), as well as for his help to characterize the catalyst of zirconium implemented. We also wish to thank Dr. Edgar Vargas and Professor Rigoberto Gómez for their contributions to this project. Similarly we warmly thank the laboratory technicians of the department of chemical engineering, who in the course of the semester supported us and guided us to complete the entire experimental model raised, in particular we want to thank Deicy Tique and Mauricio Gomez for their constant help and support. We also wish to acknowledge the support and the work provided by the graduate student Nicolas Auza, with his help we were able to complete the experimental design.. Acknowledgements of Rafael Amaya: I want to thank my family, without their support and help could not have accomplished this project. I want to thank my parents for being a guide in my way all my life, you are a role model and I hope to be one day, half person of who you are today. I want to thank you deeply because without your help I could not be able to study in this incredible university and had not been able to realize this degree project. I love you very much. I want to thank my sister, because with her help and love could get this job finished, she developed all isometric drawings, thanks. I love you with all my heart, you are invaluable! You make. my life something unique and sublime. Similarly I want to thank all my friends, which they were and will be one of the most precious things that I have. I thank God for having such a good friends, they give me their support in good as in bad times, they are people with a unique human value, thank you very much for being by my side. I especially want to thank Luz Alba Gallo, Juan Sebastián Peña, Miguel Suarez, Luisa F. Soto, Daniel Lozano, Juliana. 8.

(9) Pinzón, Nicolás Gómez, Rubén Vargas, Manuel F. Giraldo, Vanessa Núñez, Carlos Murillo, Paola Díaz, Diana Salas and Sonia Calero. Finally, I want to thank my colleague and friend Carolina Jimenez for the work she did, without her contribution thanks for you this work could not be done.. Acknowledgements of Carolina Jiménez: I would like to thank my family and friends for all the support and love you have given me since always. Thank you mom, dad, Buli, Abuelito and Cata. Thanks to my love, Richi, for you unconditional support and for the best gift someone can ever give me! Thanks Glori because in this complicated week you were there for us giving us calm and taking care of us. Tia Diana, thanks for everything I love you. Thanks to my friends at Dow, Caris, Thani and Andresito. Rafis! Nothing could have been possible without your friendship and support. I know this is one more step in my life and I’m grateful of have lived it in this university and surrounded with the people I love.. 9.

(10) TABLE OF CONTENTS. DEDICATIONS…………………………………………………………………....7 ACKNOWLEDGEMENTS………………………………………………………..8 LIST OF FIGURES……….……………………………………………………….13 LIST OF TABLES…………………………………………………………………17 1. INTRODUCTION………………………………………………………………19 1.1. Kinetic model fundamentals…………………………………………….......21 2. OBJECTIVES…………………………………………………………………...23 2.1 GENERAL OBJECTIVE…………………………………………………...23 2.2 SPECIFIC OBJECTIVES………………………………………………......23 3. LITERATURE REVIEW…………………………………………………….....24 3.1 REGENERATION OF THE CATALYST……………………………….....24 3.2 CATALYST PROPERTIES………………………………………………...26 3.2.1 Fourier Transform Infrared (FTIR)………………………………........26 3.2.2 X-ray Diffraction……………………………………………………....28 3.2.3 Surface Area Analysis……………………………………………….....29 3.2.4 Scanning Electron Microscopy (SEM)…………………………………31 3.3 THERMODYNAMIC ANALYSIS………………………………………....33 3.4 KINETIC MODEL…………………………………………………………...49 3.4.1 Rate Controlling Step……………………………………………………49 Adsorption……………………………………………………………….50 Surface Reaction………………………………………………………….51 10.

(11) Desorption………………………………………………………………..52 3.4.2. Optimization model…………………………………………………….53 4. METHODOLOGY………………………………………………………………55 4.1. Overall experimental methodology…………………………………………..57 4.2. Experimental Design………………………………………………………....58 4.3. Zirconium Based Catalyst…………………………………………………...60 4.4. Cobalt Based Catalyst……………………………………………………….60 4.5. GC Analysis………………………………………………………………….61 5. RESULTS AND RESULTS ANALYSIS………………………………………65 5.1 CATALYST CHARACTERIZATION…………………………………….65 5.1.1 Surface Area results…………………………………………………..65 5.1.2 XRD results…………………………………………………………..74 5.1.3 FTIR results…………………………………………………………..82 5.1.4 Scanning Electron Microscopy (SEM)...……………………………..88 5.2 ETHANOL AND ACETONE RESULTS..………………………………..89 5.3 KINETIC MODEL…………………………………………………………95 Ketones kinetics................................................................................…...95 Alcohols kinetics…..…………………………………………………….95 5.3.1 Initial Parameters Estimation…………………………………………97 6. CONCLUSIONS………………………………………………………………..104 APPENDIX 1: Pictures of catalysts preparation and samples from C1, C2 and C3…………………………………………………………………………………..107 APPENDIX 2: Thermodynamic Analysis………………………………………....114 APPENDIX 3: Chromium and Cobalt nitrates preparation……………………….118 APPENDIX 4: Process Flow Diagram and the Isometric Plane of the Fixed Bed Tubular Reactor……………………………………………………………………122 11.

(12) APPENDIX 4: GC – MS results for the samples made of C1, C2, C3, and the replicates of C1 and C3……………………………………………………………124 APPENDIX 5: GC – MS results for the samples made of C4- C4 replicate and samples take for the kinetic model…………………………………………………148 APPENDIX 6: Results of XRD and Surface Area………………………………..156 APPENDIX 7: Kinetic’s calculations……………………………………………..166 APPENDIX 8: MATLAB® Codes………………………………………………..172 APPENDIX 9: GC for C4, C4 replicate and C4 at 380°C (For 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 minutes)…………………………………………………………178 APPENDIX 10: SEM pictures.......………………………………………………...181 REFERENCES…………………………………………………………………….185. 12.

(13) LIST OF FIGURES. FIGURE. DESCRIPTION. PAGE. 1. Diagram of MixAlco® Process (Huertas, 2011). 20. 2. 24. 3. A schematic representation of a catalyst deactivation front moving through a fixed bed reactor. (Jackson, 2006) A Simple Spectrometer Layout. (Thermo Nicolet Corporation, 2001). 4. Bragg’s Law representation (Dr. Falak Sher, 2007).. 29. 5. 32. 6. Schematic Drawing of the electron and the x-ray optics of a SEM (The Science Education Resource Center at Carleton College, 2012) Equilibrium constant for the first reaction against the temperature. 7. Equilibrium constant for the second reaction against the temperature.. 36. 8. Equilibrium constant for the third reaction against the temperature.. 36. 9. Equilibrium constant for the fourth reaction against the temperature.. 37. 10. Gibbs free energy for the first reaction against the temperature.. 39. 11. Gibbs free energy for the second reaction against the temperature.. 40. 12. Gibbs free energy for the third reaction against the temperature.. 40. 13. Gibbs free energy for the fourth reaction against the temperature.. 41. 14. Enthalpy for the first reaction against the temperature.. 42. 15. Enthalpy for the second reaction against the temperature.. 43. 16. Enthalpy for the third reaction against the temperature.. 43. 17. Enthalpy for the fourth reaction against the temperature.. 44. 18. Extent of the firth reaction against the temperature. 46. 19. Extent of the second reaction against the temperature. 47. 20. Extent of the third reaction against the temperature. 48. 21. Extent of the fourth reaction against the temperature. 49. 22. Adsorption representation (Departamento de Ing. Qca, Universidad Nacional del Sur, 2012). 50. 28. 35. 13.

(14) 23. Initial rate versus total pressure for absorption rate-controlling step.. 51. 24. Surface Reaction representation (Departamento de Ing. Qca, Universidad. 51. Nacional del Sur, 2012) 25. Initial rate versus total pressure for surface reaction rate-controlling step.. 52. 26. Desorption representation (Departamento de Ing. Qca, Universidad Nacional del Sur, 2012) Initial rate versus total pressure for desorption rate-controlling step.. 52. 56. 29. Experimental system: fixed bed tubular reactor, metric pump and a controller of pressure and temperature. Isometric plane of the fixed bed tubular reactor and the jacket.. 30. Isometric plane in 3D of the fixed bed tubular reactor and the jacket. 57. 31. PBR packed. 58. 32. Proposed experimental design.. 59. 33. 62. 34. GCMS-QP2010s Shimadzu Gas Chromatograph Mass Spectrometer. (SHIMADZU, 2007) Quadrupole Analyzer. (espectrometria0de0masas, 2011). 35. Isotherm of type II. (Hwang & Barron, 2011). 66. 36. Estimation of Micropores DR Plot. (Quantanchrome Instruments , 2011). 68. 37. Isotherm C1 Before. 68. 38. Isotherm C1 After. 70. 39. Isotherm C1 Before-C1 After. 72. 40. Isotherm C3 After. 72. 41. Isotherm C1 After-C3 After. 74. 42. X-ray diffraction of rutile TiO2 (a) micropowders and (b) nanopowders. (Thamaphat, Limsuwan, & Ngotawornchai, 2008) Conventional XRD profile of α-quartz of different particle size of silica. (Takeyoshi, 2006) X-ray diffraction pattern of Metco-8 sample (Zirconium Oxide) (Dercz, Prusik, & Pająk, 2008) X-ray diffraction patterns of powdered ZrO2 and Zr/Si binary oxides: (a) Zr/Si binary oxide of 17.0 wt % as ZrO2 (Zr/Si ) 0.19), (b) 45.1 wt % (Zr/Si ) 0.4), (c) 55.2 wt % (Zr/Si ) 0.6), (d) 67.2 wt % (Zr/Si ) 1.0), and. 74. 27 28. 43 44 45. 53. 56. 63. 75 75 75. 14.

(15) 47. (e) powdered ZrO2 catalyst. (Moon, Fujino, Yamashita, & Anpo, 1997) The XRD patterns of the hydrous-zirconia particles after calcinations at 600 ◦C for 1 h. (Tai, Hsiao, & Chiu, 2004) XRD C1 Before. 48. XRD C1 After. 77. 49. XRD a) C1 before b) C1 after. 78. 50. XRD C3 After. 79. 51. XRD a) C1 after b) C3 after. 80. 52. IR Spectra of zirconium oxide (Morales, et al., 2011). 83. 53. 83. 55. IR Spectra of composites and individual titanium and silicon oxides. : 1 (0:100), 2 (12:88), 3 (50:50), 4 (92:8) and 5 (100:0) (Murashkevich, Lavitskaya, Barannikova, & Zharskii, 2008) The FT–IR spectrum for the zirconia particles: (a) ZrO(NO3)2 raw material, (b) zirconia powder synthesized before, and (c) after calcinations at 600 ◦C for 1 h. (Tai, Hsiao, & Chiu, 2004) FTIR Spectra C1 Before. 56. FTIR Spectra C1 After. 86. 57. FTIR Spectra C1 before- C1 After. 87. 58. FTIR Spectra C3 After. 87. 59. FTIR Spectra C1 after- C3 After. 88. 60. SEM image of the C1. 88. 61. SEM image of the C1. 89. 62. Acetone concentration in C4 and C4R. 90. 63. Ethanol concentration in C4 and C4R. 90. 64. Ethanol and Acetone concentration in C4. 90. 65. Ethanol and Acetone concentration in C4R. 90. 66. Rate ketonization with respect to temperature. (Gaertner, Serrano-Ruiz, Braden, & Dumesic, 2009) Ethanol concentration with respect to temperature in ethanol production from jackfruit seeds. (Adapted form: (S. Chongkhong, 2012) ). 91. 46. 54. 67. 76 77. 85. 85. 92. 15.

(16) 68 69 70 71 72 73. Ethanol yield with respect to temperature in ethanol production from 93 molasses from sugar cane. (Adapted form: (D.B. Hughes, 1984)) Ethanol concentration with respect to temperature in ethanol production 93 from cashew apple juice. (Adapted form: (Usharani, 2009) ) 100 Arrhenius Plot for ketones production Comparison between the experimental data and the theoretical data 101 obtained with the kinetic model of ketones production. 102 Arrhenius Plot for alcohols production Comparison between the experimental data and the theoretical data 103 obtained with the kinetic model of alcohols production.. 16.

(17) LIST OF TABLES. TABLE. DESCRIPTION. PAGE. 1. Initial moles of the system. 45. 2. Surface Area Data of the sample C1 before. 69. 3. Pore Volume Data of the sample C1 before. 69. 4. Pore Size Data of the sample C1 before. 69. 5. Surface Area Data of the sample C1 after. 71. 6. Pore Volume Data of the sample C1 after. 71. 7. Pore Size Data of the sample C1 after. 71. 8. Surface Area Data of the sample C3 after. 73. 9. Pore Volume Data of the sample C3 after. 73. 10. Pore Size Data of the sample C3 after. 73. 11. Results of particle size in the main peaks of the XRD results.. 81. 12. 84. 13. IR Spectral data and band assignments of (Jose, Bushiri, Jayakumar, & Vaidyan, 2008) Conversion Results. 14. Formation Enthalpies Constants for 653.15 K. For ketones production. 98. 15. Formation Entropies Constants for 653.15 K. For ketones production. 98. 16. 98. 17. Formation Enthalpies Constants for 653.15 K. For alcohols production Formation Entropies Constants for 653.15 K. For alcohols production. 18. Initial parameters of the kinetic model. For ketones production.. 100. 19. Final parameters for the kinetic model of the ketones production.. 101. 20. Initial parameters of the kinetic model. For alcohols production. 102. 21. Final parameters for the kinetic model of the alcohols production.. 102. 89. 98. 17.

(18) A.2.1 Ideal gas heat capacities constants. 116. A.2.2 Ideal gas enthalpy of formation and the ideal gas Gibbs energy of formation A.6.1 Results XRD of C1 Before. 117. A.6.2 Results XRD of C1 After. 159. A.6.3 Results XRD of C3 After. 163. A.9.1 Calibration results for the acetone. 178. A.9.2 Calibration results for the ethanol. 178. A.9.3 Calibration results for the acetic acid. 179. 156. 18.

(19) 1. INTRODUCTION According to Zah et al, biofuels made from first generation renewable resources (currently, the most applied technology for bioethanol worldwide) are object of strong debate. Energy crops stand in direct competition with food production or biodiversity conservation, and the environmental impacts of biofuels production are often greater than those of fossil fuels. Second generation biofuels have become the most promising option for transportation fuels in the foreseeable future, while other promising technologies (such solar, electric cars, and hydrogen) surpass the research and development stage. Even though second generation fuels suffer from lower conversion efficiency than first generation fuels, they facilitate the use of alternative feedstocks such as wood, grass or biowaste, highly sustainable feedstocks. (Zah, Binder, Bringezu, Reinhard, Schmid, & Schütz, 2010).. Due to the last advances in biofuel research, there are different and new processes for biofuel production involving the combination of biological and chemical processes (Vieira Costa & Greque de Morais, 2010) (Zenga, Danquah, Dong Chen, & Lu, 2011) (Jin, Yao, Liu, Lee, & Ji, 2011). One of them is the MixAlco® Process developed by Dr. Mark Holtzapple at the Chemical Engineering Department of Texas A&M University. A diagram including major stages of several routes that convert trash into alcohols within the framework of the MixAlco® process is depicted in Figure 1. In this study, the route that includes alcohols and ketones (Route 1) will be followed considering only the stage that converts organic acids into ketones. A previous study, unintentionally showed that the conversion of acids directly into alcohols (i.e., without passing through ketones) is possible. (Huertas, 2011) This study is aimed to confirm this result or discharge it.. 19.

(20) Figure 1: Diagram of MixAlco® Process (Huertas, 2011). Although seldom reported in the literature, it would be interesting to test the production of alcohols during ketonization. A literature review shows that the path for such reaction is possible over a zirconium or cobalt based catalyst (C. Osorio et al, 2010). The zirconium catalyst selection is based on a previous work (Huertas, 2011) in order to confirm the alcohols formation reported in that work. The cobaltchromium catalyst selection follows a patent where the production of alcohols is obtained using this catalyst at 250°C and 319 psi (Johnston, et al., 2009). Thus, the presence of alcohols will be tested for experiments ran at different catalyst composition and temperatures.. The samples collected in this project will be analyzed by gas chromatography coupled with a mass spectrometer (GC-MS) in order to gather more information about the molecular structure and confirm the production of alcohols through the ketonization process.. Taking into account the molecular structure of acids, alcohols derived directly from them, require the presence of hydrogen. Alcohols can be obtained from carboxylic acids by chemical reactions with the implementation of a catalyst and a 20.

(21) hydrogen source. One way to provide this hydrogen is water decomposition, which may be accomplished using a Zirconium Nickel Alloy catalyst. Water vapor decomposition reaction on. was identified with an X-ray diffraction spectrum. (Kawano, 2005). The experiment was carried out at a temperature of 873 K, and 35 standard. gas flow rate. About 5 g. meshes that had been submitted to. -4. alloy with granular size of 70 to 200 Pa vacuum was used (Kawano, 2005).. Alternatively, the hydrogen molecule can be obtained using metal oxides as catalysts. The general reaction is shown below:. Various kinds of metal oxides can be used for the reaction including Cobalt, Iron, Zirconium, Magnesium and Zinc. The thermal conditions under which this reaction is favorable are in the range of 780 to 1200 K (Seok Go, Real Son, & Done Kim, 2008).. 1.1. Kinetic model fundamentals As the development of a reaction kinetic model is one of the objectives on this research, the most optioned model to study is based on the main chemical reaction proposed by (Johnston, et al., 2009):. (1). From Equation (1), the conversion of Acetic Acid will be defined as:. 21.

(22) The concentration. will be the concentration of the feed stream and the. final concentration. can be measured from the results obtained using gas. chromatography. (Johnston, et al., 2009) Using both Equations (1) and (2), the kinetic model will be developed.. The aim of this project is to establish the kinetic model for the alcohols production process. Afterwards, experiments were performed to determine the most appropriate reaction conditions based on the kinetic model. Finally these reaction conditions were tested. Furthermore, the effect of control variables such as temperature and the catalyst composition was studied to obtain a global optimum condition.. 22.

(23) 2. OBJECTIVES 2.1 GENERAL OBJECTIVE. Evaluate the production of alcohols during the ketonization of carboxylic acids over a metal oxide based catalyst on a laboratory scale and develop a kinetic model to fit data for alcohols formation.. 2.2 SPECIFIC OBJECTIVES. . Determine best operating conditions to produce ethanol from acetic acid within the ranges of variables established for this project by using the surface response methodology at varying catalysts composition and temperatures.. . Obtain kinetic models parameters for formation reactions and use them to optimize process conditions.. 23.

(24) 3. LITERATURE REVIEW 3.1 REGENERATION OF THE CATALYST Catalyst deactivation occurs eventually during any chemical process; catalysts do not maintain their activity and selectivity permanently. All catalysts deactivate and become less effective with time and generate undesired byproducts that would need an appropriate disposal that can increase production costs. This limits its use in commercial or lab-scale. Several factors may cause catalyst deactivation, like deposition on the catalyst surface of material from the reaction, sintering/restructuring or poisoning. Figure 2, shows a representation of catalyst deactivation front moving through a fixed bed reactor. (Jackson, 2006). Figure 2: A schematic representation of a catalyst deactivation front moving through a fixed bed reactor. (Jackson, 2006). The activity of the catalyst can be periodically regenerated or restored, which is an advantage since it would not be necessary to constantly buy more catalyst and costs on catalyst disposal would not be necessary. There are many ways that a catalyst may be regenerated, some of the include air, oxygen and nitrogen treatments.. As reported in literature, some of the most efficient ways to regenerate a catalyst include hydrogen and high pressure regeneration. An example is a study 24.

(25) made on regeneration of an Al-promoted sulfated zirconia (AL/SZ) catalyst after coke deposition. This work tries hydrogen for regenerating fouled catalysts; nevertheless, regaining activity is low when introducing atmospheric hydrogen as a regenerating gas, and it take about 20 to 30h to regain between 43 and 46% of initial activity. Fortunately, over 98% of original activity can be regained using high pressure hydrogen (2.1 MPa) at 250 °C within 8 h. (Ying-Chieh Yang; Hung-Shan Weng Department of Chemical Engineering, National Cheng Kung University, Taiwan, 2010). Another study made on regeneration of metal and metal oxide catalyst showed that as long as the temperature is above 500°C full activity can be restored but if a temperature of 400°C is used then there is irreversible loss in activity. (Jackson, 2006). The method for these types of catalyst involves calcining a used catalyst comprising a noble metal and a transition metal support on an inorganic carrier in an oxygen-containing gas to produce a calcined catalyst; and contacting the calcined catalyst with a hydrogen-containing gas at a temperature higher than 430° C. The calcination may be carried out in a stationary furnace, a fixed-bed reactor, a rotary kiln, or a belt calciner. A rotary kiln is a cylindrical vessel, inclined slightly to the horizontal, which is rotated slowly about its axis. The material to be processed is fed into the upper end of the cylinder. As the kiln rotates, material gradually moves down towards the lower end, and undergoes a certain amount of mixing. Hot gases pass along the kiln, sometimes in the same direction as the catalyst (co-current), but usually in the opposite direction (counter-current). (Sun & Nowowiejski, 2010) The catalyst-regeneration method comprises contacting the calcined catalyst with a 25.

(26) hydrogen-containing gas at a temperature higher than 430° C. (hydrogen treatment). Preferably the hydrogen treatment is performed at a temperature in the range of 450 to 550° C.. Regardless of the chemical path used for the production of ketones and alcohols, the catalyst regeneration step needs to be addressed. In the chemistry proposed in this paper for the production of alcohols, an external regeneration of the catalyst would be proposed using a rotary kiln with hydrogen treatment. Direct hydrogenation into the reactor would not be recommended because the conditions for the regeneration of the catalyst involve higher pressures (of about 304.5 psi) for best results in catalyst activation. 3.2 CATALYST PROPERTIES There are several methods for evaluating the physical properties of a catalyst. In this project, were chosen the Fourier Transform Infrared (FTIR), the X-Ray Diffraction, the Surface Area Analysis and Scanning Electron Microscopy (SEM).. 3.2.1 Fourier Transform Infrared (FTIR): It works to determine the chemical composition and show the chemical changes, polymerization and impurities with known samples. FTIR is based on the interactions of electromagnetic radiation and molecules. These interactions will be of a different nature depending on the region of the spectrum in which they are occurring; these interactions comprise electron excitation, molecular vibrations and molecular rotations. This technique uses an interferometer, for example the Michelson interferometer, which consists of two mirrors facing each other at a 90 degree angle. Furthermore, the interferometer has a ray refractor which is positioned 26.

(27) at a 45 degree angle from the mirrors. One of these mirrors is located at a stationary position, while the other one can move at a constant speed in a direction perpendicular to the frontal plane.. The device that is in charge of splitting the rays allows the mirrors to capture the light emanating from the source. Fifty percent of the light it absorbs is transmitted while the rest is reflected. The interferometer also has information about the intensity of all the frequencies in the light spectra. The information that comes out of the detector is digitalized and transformed to the Fourier series. Then the signals are converted to the conventional infrared spectra. FTIR has different applications:. 1. Characterization and identification of materials. 2. Polymers and plastics. 3. Inorganic solids (minerals, catalyst ) 4. Analysis and synthesis of pharmaceutical products. 5. Analysis of impurities 6. Tracking of chemical processes 7. Polymerization. 8. Catalytic reactions. 9. Analysis of oils and fuels.. 27.

(28) Figure 3: A Simple Spectrometer Layout. (Thermo Nicolet Corporation, 2001). 3.2.2 X-ray Diffraction X-ray diffraction (XRD) is a versatile, non-destructive technique that reveals detailed information about the chemical composition and crystallographic structure of natural and manufactured materials. (PANalytical, 2012). A crystal lattice is a regular three-dimensional distribution (cubic, rhombic, etc.) of atoms in space. These are arranged so that they form a series of parallel planes separated from one another by a distance d, which varies according to the nature of the material. For any crystal, planes exist in a number of different orientations - each with its own specific d-spacing. (PANalytical, 2012). When x-rays are scattered from a crystal lattice, peaks of scattered intensity are observed which correspond to the following conditions: First the angle of incidence is equal to the angle of scattering, second the path length difference is equal to an 28.

(29) integer number of wavelengths. The condition for maximum intensity contained in Bragg’s law above allows us to calculate details about the crystal structure. (Dr. Falak Sher, 2007). Figure 4: Bragg’s Law representation (Dr. Falak Sher, 2007).. Plotting the angular positions and intensities of the resultant diffracted peaks of radiation produces a pattern, which is characteristic of the sample. Where a mixture of different phases is present, the resultant diffractogram is formed by addition of the individual patterns. (PANalytical, 2012). 3.2.3 Surface Area Analysis: This technique is referenced by several standard organizations such as ISO, USP and ASTM. Pharmaceuticals, catalysts, activated carbons, pigments and numerous other materials exhibit varying physical properties and effectiveness depending on their surface area. (Particle Tech Labs , 2012). The surface area of a powder is determined by the physical adsorption of a gas (usually Nitrogen or Krypton) onto the surface of the sample at liquid nitrogen temperatures. The choice of gas to be used depends on the expected surface area and the properties of the sample. Once the amount of adsorbate gas has been measured. 29.

(30) (either by a volumetric or continuous flow technique), calculations which assume a monomolecular layer of the known gas are applied. (Particle Tech Labs , 2012) The BET (Brunauer, Emmett and Teller) Theory is commonly used to evaluate the gas adsorption data and generate a Specific Surface Area result expressed in units of area per mass of sample (m2/g). (Brunauer, Emmett, & Teller, 1938). The data from certain sample types such as zeolites, activated carbon, catalysts and various nanoparticles often use an alternative theory referred to as the Langmuir equation for the data reduction process. Additional data processing can provide information on mean pore size and distribution of the substrate if sufficient data points are collected. (Particle Tech Labs , 2012). The Langmuir equation relates the coverage or adsorption of molecules on a solid surface to gas pressure or concentration of a medium above the solid surface at a fixed temperature. (Langmuir, 1916). Prior to analysis, the sample must be preconditioned to remove physically bonded impurities from the surface of the powder. This is typically accomplished by applying elevated temperature to the sample in conjunction with vacuum or continuously flowing inert gas. This process must be carefully controlled and monitored in order to generate the most accurate and repeatable results. (Particle Tech Labs , 2012). 30.

(31) 3.2.4 Scanning Electron Microscopy (SEM): The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens. The signals that derive from electron-sample interactions reveal information about the sample including external morphology (texture), chemical composition, and crystalline structure and orientation of materials. (The Science Education Resource Center at Carleton College, 2012). Accelerated electrons in an SEM carry significant amounts of kinetic energy, and this energy is dissipated as a variety of signals produced by electron-sample interactions when the incident electrons are decelerated in the solid sample. These signals include secondary electrons, backscattered electrons, diffracted backscattered electrons, photons, visible light, and heat. Secondary electrons and backscattered electrons are commonly used for imaging samples: secondary electrons are most valuable for showing morphology and topography on samples and backscattered electrons are most valuable for illustrating contrasts in composition in multiphase samples. (The Science Education Resource Center at Carleton College, 2012). SEM analysis is considered to be "non-destructive"; that is, x-rays generated by electron interactions do not lead to volume loss of the sample, so it is possible to analyze the same materials repeatedly. (The Science Education Resource Center at Carleton College, 2012). 31.

(32) Figure 5: Schematic Drawing of the electron and the x-ray optics of a SEM (The Science Education Resource Center at Carleton College, 2012). Essential components of all SEMs include the following: (The Science Education Resource Center at Carleton College, 2012) . Electron Source ("Gun"). . Electron Lenses. . Sample Stage. . Detectors for all signals of interest. . Display / Data output devices. . Infrastructure Requirements:  Power Supply  Vacuum System  Cooling system  Vibration-free floor  Room free of ambient magnetic and electric fields. 32.

(33) 3.3 THERMODYNAMIC ANALYSIS. The following procedure shows the thermodynamic analysis done on the system composed of the following reactions:. Note that the compound reaction from the reactions and. gives the main reaction:. In this analysis we will evaluate the possibility of the production of acetaldehyde, acetone and an alternating reaction to produce ethyl acetate, which occurs spontaneously.. The first tool used to develop a thermodynamic analysis was the equilibrium constant of each of the three reactions separately, in order to determine if the reaction is exothermic or endothermic.. In an exothermic reaction, the total energy released in the formation of new bonds is greater than the total energy used to break the bonds. In contrast, chemical reactions that require energy are called endothermic reactions. (Walker, 2007). 33.

(34) The equilibrium constant is defined by: (Smith, Van Ness, & Abbott, Cambio en la energía de Gibbs estándar y la constante de equilibrio, 2007). Where. represents the change of the standard Gibbs free energy of the reaction,. R the ideal gases constant. and T the temperature in K.. The equation (4) shows the result of a rigorous development of equation (3). This development is shown in detail in Appendix 2.. Where: (Smith, Van Ness, & Abbott, Efecto de la temperatura en la constante de equilibrio, 2007). . : Is the change of the standard Gibbs free energy of the reaction at the temperature. .  . : Is the change of the standard enthalpy of the reaction at the temperature. : Is the reference temperature (298,15 K) : Is the change of the heat capacities in. 34.

(35) To determine if the reaction is exothermic or endothermic, the behavior of the equilibrium constant will be evaluated as the temperature increases. If the equilibrium constant decrease as the temperature increase, then the reaction is exothermic, otherwise if the equilibrium constant increase as the temperature increase then the reaction is endothermic. (Smith, Van Ness, & Abbott, Efecto de la temperatura en la constante de equilibrio, 2007). The constants of the heat capacities, as the Gibbs free energy of formation and the enthalpy of formation of each component are in the Appendix 2. As is shown in Figure 6 and Figure 9 the first and the fourth reaction are endothermic, in contrast with the reaction II and III both exothermic as is shown in the Figure 7 and Figure 8.. Figure 6: Equilibrium constant for the first reaction against the temperature.. In the Figure 7 is shown the behavior of the equilibrium constant through different temperatures. Clearly the equilibrium constant decrease as the temperature increase thus as is mentioned before, the second reaction that represent the ethanol formation by the acetaldehyde in presence of hydrogen is exothermic. 35.

(36) Figure 7: Equilibrium constant for the second reaction against the temperature.. Figure 8: Equilibrium constant for the third reaction against the temperature.. Similar as in the Figure 7 and Figure 6, in Figure 8 the behavior of the equilibrium constant as the temperature increases in the third reaction was evaluated. The behavior shown represents that as in Figure 7, this reaction is exothermic.. 36.

(37) Figure 9: Equilibrium constant for the fourth reaction against the temperature.. When deciding whether a reaction is favored, i.e. spontaneous, we need to consider both the energy (enthalpy) change, and the entropy change. Reactions which release energy, and increase disorder will be spontaneous, feasible, and will occur. Those which both increase order and take up energy will never occur spontaneously: they must be coupled to some other spontaneous process in order to be made to occur. (Department of Mechanical Science and Engineering, University of Illinois ar Urbana-Champaign, 2007). A reaction with negative. is termed exergonic, and will be spontaneous, although. it may not occur at any appreciable rate. One with positive. is termed endergonic,. will not be spontaneous, and will not go ahead, unless coupled to another reaction with negative. . (Department of Mechanical Science and Engineering, University. of Illinois ar Urbana-Champaign, 2007). The standard free energy change. is defined as the free energy change associated. for example with the reaction: 37.

(38) If we set up a reaction under. conditions, and we find it has a positive sign, we. know the forward reaction will not be energetically favored with these concentrations of products and reactants. However, the reverse reaction has the same value of but the opposite sign, hence the reverse reaction will be favored. (Department of Mechanical Science and Engineering, University of Illinois ar Urbana-Champaign, 2007). To evaluate the free Gibbs energy over time with the changes of concentration let use the following equation:. Where R is the universal constant of gases, T is the absolute temperature in K and Q is the mass action ratio. The mass action ratio is defined as the multiplication of the molar concentration of the products divided by the multiplication of the molar concentration of the reactants.. In equilibrium (. ):. 38.

(39) The mass action law states that the value of the mass action ratio is: (Department of Mechanical Science and Engineering, University of Illinois ar Urbana-Champaign, 2007). With the previous equilibrium constants of the reactions I-IV from Figure 6 to 9, and using (7), the Gibbs free energy of every reaction was evaluated in order to determined if the reaction is spontaneous or not.. Figure 10: Gibbs free energy for the first reaction against the temperature.. Based on the above explanation, it is clear that in Figure 10 the first reaction is not spontaneous. Similarly, it’s shown that the reaction is favored for higher temperatures and it tends to be spontaneously as the temperature increases. Similarly in Figure 11, the second reaction is not spontaneous for temperatures higher than 590ºC and tends to be spontaneous at lower temperatures.. 39.

(40) Figure 11: Gibbs free energy for the second reaction against the temperature.. In Figure 12 and Figure 13, the third and fourth reactions are clearly spontaneous reactions. Both reactions have a negative Gibbs free energy which means that are favored in contrast with the first two reactions.. Figure 12: Gibbs free energy for the third reaction against the temperature.. Figure 12 shows that the reaction is favored for lower temperatures in contrast with the fourth reaction in Figure 13, which is favored for higher temperatures. In 40.

(41) addition, the fourth reaction is more favorable than the third taking into account the values of Gibbs free energy obtained.. Figure 13: Gibbs free energy for the fourth reaction against the temperature.. Another important tool developed to complete the thermodynamic analysis was the enthalpy. As is mentioned before, the enthalpy quantifies the energy from the reaction or the required energy to be performed.. The standard heat of reaction is related as follows:. Using the integral method explained in Appendix 2 for the resolution of (8), were obtained the following figures.. 41.

(42) Figure 14 shows that the first reaction required energy to be performed. Also, shows that as the temperature increases requires less energy and tends to be spontaneous which is consistent with the respective Gibbs free energy and equilibrium constant figures, Figure 10 and Figure 6 respectively.. Figure 14: Enthalpy for the first reaction against the temperature.. Even though that the second reaction is not spontaneous (based on the equilibrium constant and the Gibbs free energy), but tends to be at lower temperatures in Figure 15 shows that the reaction releases energy, and the amount of energy released increases for higher temperatures, it means that the reaction don’t need much energy to be performed.. 42.

(43) Figure 15: Enthalpy for the second reaction against the temperature.. Figure 16 shows that the third reaction releases energy and as the temperature increases the energy released decreases which is consistent with the respective Gibbs free energy and equilibrium constant figures, Figure 12 and Figure 8 respectively.. Figure 16: Enthalpy for the third reaction against the temperature.. 43.

(44) Finally Figure 17 shows that the fourth reaction requires energy to be performed. Also shows that as the temperature increase the energy required decreases. Even though the reaction is very spontaneous requires energy to be performed.. Figure 17: Enthalpy for the fourth reaction against the temperature. The last tool used in this thermodynamic analysis was the extent of the reaction. First of all suppose that the following general reaction takes place: (Smith, Van Ness, & Abbott, Coordenada de la reacción, 2007). Where:. represents the stoichiometric coefficient. For the reactants the. stoichiometric coefficient is negative and for products positive. (Smith, Van Ness, & Abbott, Coordenada de la reacción, 2007). The extent of the reaction is a quantity that measures the extent in which the reaction proceeds. By definition de change of the extent of the reaction (usually denoted as ) is as follows: 44.

(45) Where. denote the moles change. Using (9) the mol fraction. of a species is. related to the extent of the reaction as is shown in equation (10). (Smith, Van Ness, & Abbott, Coordenada de la reacción, 2007). Where:   . is the initial mol of the specie. . Based on the previous information of the extent of the reaction, were obtained the following equations for every of the four reactions. Considering the experimental procedure performed, the initial moles of the system were obtained as follows: Table 1: Initial moles of the system. Compound Name. (mol) 0,1 1,7 0,55. The way the initial moles from the Table 1 were obtained, is shown in the Appendix 2. In order to establish the extent of the reaction results of and. and. was necessary to use the. of acetaldehyde and ethanol, respectively.. 45.

(46) . For the first reaction:. Using the results of Figure 6 (which corresponds of the equilibrium constant for the first reaction) and (15) was obtained their extent of the reaction against the temperature. Figure 18 shows the results. In this figure it is clear that as the temperature increases the extent of the reaction also increases, so the reaction is favorable as the temperature increases.. Figure 18: Extent of the firth reaction against the temperature. . For the second reaction:. 46.

(47) Figure 19: Extent of the second reaction against the temperature. Similarly as in the first reaction, it was obtained the extent of the second reaction. The results are shown in Figure 19. In contrast with the first reaction, the second reaction is more favorable at lower temperatures. The foregoing result confirmed previous findings regarding the second reaction (from the equilibrium constant so as the Gibbs free energy), that at lower temperatures the reaction tends to be spontaneous.. . For the third reaction:. 47.

(48) Figure 20: Extent of the third reaction against the temperature. In Figure 20 and Figure 21 shows the extension of the third and fourth reaction, respectively. Both figures follow the same tendency as in Figure 19 that for lower temperatures, the reaction tends to be spontaneous and therefore favorable.. . For the fourth reaction:. 48.

(49) Figure 21: Extent of the fourth reaction against the temperature. 3.4 KINETIC MODEL. Based on Huertas (Huertas, 2011) and Osorio (C. Osorio et al, 2010) was implemented an integral reactor. There is more contact between the reactant and catalyst in the integral reactor than in the differential reactor, owing to its greater length. Consequently, more amount of product will be formed, and the problems encountered in the differential reactor in analyzing small or trace amounts of product in the effluent stream are eliminated. (Michigan Engineering, University of Michigan, 2006). In catalytic reactions kinetics it is important to define the rate controlling step. This is the step with the slowest rate of reaction in a multi-step chemical reaction. This 49.

(50) step's rate will set the overall rate of reaction for the multi-step reaction. (Anne Marie Helmenstine, Ph.D.,, 2013). 3.4.1 Rate Controlling Step:. There are three possible rate controlling steps in catalytic reactions: adsorption, surface reaction and desorption. In order to determine which phase is the ratecontrolling step in this case, there is a simple but trustable method to follow. It consists on defining various graphics of Initial rate against the total pressure of the system and compare the curves obtained to the ones presented in the figures 23, 25 and 27 (Froment & Kenneth., 1990). . Adsorption. The adsorption of a reactive A over a site S can be represented as: (Departamento de Ing. Qca, Universidad Nacional del Sur, 2012) Where AS represents new specie “. ”.. Figure 22: Adsorption representation (Departamento de Ing. Qca, Universidad Nacional del Sur, 2012). If the rate controlling step is the Adsorption, the curves or isotherms obtained are as shown in figure 23.. 50.

(51) Figure 23: Initial rate versus total pressure for absorption rate-controlling step.. When the adsorption is the rate-controlling stage the initial velocity is a lineal function of the pressure. (Huertas, 2011). . Surface Reaction. After a reactive is adsorbed over the surface, the reaction or surface reaction to the products takes place. In this stage, the reactive. absorbed is taken to the product. still absorbed in the site S. (Departamento de Ing. Qca, Universidad Nacional del Sur, 2012). Figure 24: Surface Reaction representation (Departamento de Ing. Qca, Universidad Nacional del Sur, 2012) 51.

(52) If the rate controlling step is the Surface Reaction, the curves or isotherms obtained are as shown in figure 25.. Figure 25: Initial rate versus total pressure for surface reaction rate-controlling step.. When the surface reaction is the rate-controlling stage, the initial velocity increases when the total pressure increases, until the saturation point, later the speed falls. (Huertas, 2011). . Desorption. The adsorbed products generated in the surface reaction need to be desorpted. Here the product B is taken off the site S and the sites is freed. (Departamento de Ing. Qca, Universidad Nacional del Sur, 2012). Figure 26: Desorption representation (Departamento de Ing. Qca, Universidad Nacional del Sur, 2012) 52.

(53) If the rate controlling step is the Desorption, the curves or isotherms obtained are as shown in figure 27.. Figure 27: Initial rate versus total pressure for desorption rate-controlling step.. When desorption is the rate-controlling stage, the velocity doesn’t depend on the total pressure. (Huertas, 2011). 3.4.2. Optimization model:. In order to calculate the parameters required for these reactions, which involve nonlinear parameters will be implemented The Levenberg-Marquardt method. These estimates will be obtained through Matlab® and will be necessary a vector of observation or initial parameters to complete a correct estimation.. The Levenberg-Marquardt method is a standard technique used to solve nonlinear least squares problems (Gavin, 2011). Nonlinear least squares methods involve an iterative improvement to parameter values in order to reduce the sum of the squares. 53.

(54) of the errors or residuals between the function and the measured data points. (Gavin, 2011). The Levenberg-Marquardt curve-fitting method is a combination of two minimization methods: the gradient descent method and the Gauss-Newton method. In the gradient descent method, the sum of the squared errors is reduced by updating the parameters in the direction of the greatest reduction of the least squares objective. In the Gauss-Newton method, the sum of the squared errors is reduced by assuming the least squares function is locally quadratic, and finding the minimum of the quadratic. The Levenberg-Marquardt method acts more like a gradient-descent method when the parameters are far from their optimal value, and act more like the Gauss-Newton method when the parameters are close to their optimal value. (Gavin, 2011). Based on Huertas (Huertas, 2011) was implemented the following equation for the resolution and minimization of the nonlinear least square problem: Where RSS is the residual sum of squares, for a sample of size m.. 54.

(55) 4. METHODOLOGY. Reactions will be carried in a fixed bed tubular reactor. A constant metric pump will be used to drive the feed made of acetic acid (glacial) from Merck© into the system; stainless steel tubing will be used throughout. The reactor has a jacket where two resistances are used in order to graduate the temperature of the system; both resistances are located in a ceramic insulation of the same jacket. The resistances have a power of 700 W each one and are made of bronze. The temperature is measured by a thermocouple type K that is located throughout the packed bed. Another thermocouple type J is located in the ceramic insulation with the purpose of measure the temperature of both resistances, to be lower than the ceiling. A temperature controller establishes the set point and the temperature achieved in the system is shown by an indicator in the control panel located besides the reactor.. The acid will then pass into the reactor where it contacts the zirconium or cobaltchromium catalyst and reacts. Later, the reaction products pass through a condenser (shell and tube heat exchanger) that uses water at approximately 4°C in order to condense the products action which permits the sample to be taken. The samples are collected and frozen in order to maintain their initial properties. Product analysis is done through gas chromatography (GC) every week. For this analysis the samples should be thawed.. In Figure 28 and 29 are shown the isometric plane of the fixed bed tubular reactor with the corresponding jacket in two dimensions and in three dimensions, respectively.. 55.

(56) Figure 28: Experimental system: fixed bed tubular reactor, metric pump and a controller of pressure and temperature.. Figure 29: Isometric plane of the fixed bed tubular reactor and the jacket.. 56.

(57) Figure 30: Isometric plane in 3D of the fixed bed tubular reactor and the jacket.. 4.1. Overall experimental methodology. Catalyst is weighed and loaded into the reactor. The catalyst is supported by glass pearls and glass wool (Panreac®). The reactor temperature controller is set to the desired value. The system has a Type-K thermocouple as sensor with a digital reading for verification of a constant temperature. The liquid reactants are fed to the system with a HPLC pump. After the reaction temperature is stabilized (after 45 minutes of feeding), the liquid products are collected every 30 min. The liquid sample is collected and analyzed through a GC-MS technique, explained below in Section 4.5.. 57.

(58) Figure 31 shows how the PBR was packed in order to run the different experiments.. Figure 31: PBR packed.. Reactions are terminated by cutting off the feed. A water feed is necessary to wash the system due to the high corrosive properties of concentrated acetic acid. Finally, air is fed into the system to regenerate the catalyst (return to Step 1). (Taco, 2009) (Nieves & Holtzapple, 2010). 4.2. Experimental Design. A factorial design was selected because it allows development of response surfaces. This type of design is an experimental strategy in which the factors are varied together, rather than one at a time (Montgomery, 2009), thus the set of experiments is formed by all combinations of the different levels of the factors involved in the study (Cochran & Cox, 1995).. Because the main goal is to determine the effect that the composition of the catalyst 58.

(59) has in the production of alcohols, and because temperature is important for the kinetic model, in the experimental design two factors were accounted for: catalyst composition (C1 to C4 as shown below) and temperature chosen according to previous results and equipment limitations (300, 325, 350, and 380°C).. The pressure (14.7 psi) was taken from the optimal results in previous work (Huertas, 2011). The flow feed of acetic acid (1 mL/min) was chosen on the basis of equipment (pump) limitations.. The proposed combination of the experimental conditions is shown in the Figure 32, shown below:. T1. P = 14,7 psia F= 1mL /min T2 T3. T4. T1. P = 14,7 psia F= 1mL /min T2 T3. T4. Test C1 C2 C3 C4 Replicate C1 C2 C3 C4. Figure 32: Proposed experimental design.. 59.

(60) 4.3. Zirconium Based Catalyst. The following procedure was used for the preparation of 30 g of C1: Solution A is prepared with 12 g of Zirconium (IV) Oxide from Sigma Aldrich® (. ) on distilled water. Solution B is then prepared by mixing 6 g of Titanium. Dioxide from J.T. Baker®. , 6 Silica Fumed from Sigma Aldrich®. and. 6 g Zirconium (IV) Oxynitrate Hydrate from Sigma Aldrich® (. ). and diluting it with distilled water. The solutions A and B are mixed, and water is added until a uniform gel is formed. The mixture is dried at 120°C on an oven for approximately 24 hours. Finally it is calcined in a furnace at 450 °C for approximately 8 hours (C. Osorio et al, 2010) and the size of the particles obtained was controlled by sieving it in a Tyler Mesh 5 (Opening 4 mm) (AZoM.com, 2012). In Appendix 1 are the photos of the catalyst C1, C2, C3 preparation and the samples taken so far are shown.. 4.4. Cobalt Based Catalyst. The procedure to prepare a 10% (w/w) Co and 1% (w/w) Cr catalyst based on is explained next1:. 14.7 g of. is dried at 120°C and the cooled to room temperature. A. solution of 6.5 g of Chromium Nitrate diluted in 13 mL of distilled water is added.. 1. Johnston (Johnston, et al., 2009) explained their catalyst using graphite as support. In order to avoid the nitrogen atmosphere was used silica fumed, because as is explained by Lloyd (Lloyd, 2011) the silica is a modern support with the essential properties. Also, because one of the main characteristics that a support should have is the surface area, the conversion of the corresponding volume is shown below the cobalt-chromium catalyst production explanation.. 60.

(61) The resulting slurry is dried in an oven at a rate of 10°C per minute until a temperature of 110°C is reached. The mixture obtained is calcined at 500°C for 6 hours. Finally a solution of 49.9 g of Cobalt Nitrate in 50 mL of distilled water is added to the calcined and cooled mixture above and the resulting slurry is dried again in an oven at a rate of 10°C per minute until 110°C. The mixture obtained is calcined again at 500°C for 6 hours and the size of the particles obtained was controlled by sieving it in a Tyler Mesh 5 (Opening 4 mm) (AZoM.com, 2012).. (Johnston, et al., 2009) Because some administrative problems, it was necessary for the elaboration of the current catalyst, the production of the chromium and cobalt nitrate starting from their respective metals. Their production are explained in the Appendix 3. The calculi of the equivalent catalyst volumen is shown below:. 4.5. GC Analysis. First, standard solutions of acetone in water, ethanol in water and acetic acid in water are injected. A full pattern is introduced, using five different concentrations of each substance mentioned before in order to quantify the amount of acetic acid, acetone and ethanol present in each sample vial. The gases flows are established by setting the regulators to 40 psig for H2, 60 psig for He, and 50 psig for air. It is important to make sure the column head pressure gauge on the GC indicates the proper pressure of 15 psig in order to verify that no septum is damaged. The samples are placed in the auto sampler racks, not leaving empty spaces between samples. The GC is started on the computer then the sequence of samples is set and loaded. Once the setup is 61.

(62) ready, the sequence is run. The column is a TRB-FFAP (treated polyethyleneglycol for acidic compounds) from Teknokroma® with USP code G25, G35 (Teknokroma, 2010). This column use and injection of. , carrier gas of Helium at 4 psi, the oven. temperature is 120°C, can rise at a rate of 4°C/min to 220°C and has a FID (Flame Ionization Detector). (Teknokroma, 2010) The operation of the Flame Ionization Detector is principally based on the phenomenon of the appearance of charged particles in a hydrogen burner flame if traces of organic compounds are present. This ionization process results in a sharp increase in the electric current between the burner jet playing the role of one electrode and a second electrode located above the flame. The strength of the induced current is proportional to the flow-rate of organic material through the hydrogen burner flame of the detector. (Berezkin & Drugov, 1991). A Gas Chromatograph-Mass Spectrometer was also used in the Department of Chemistry in order to analyze the presence of alcohols and ketones and to quantify the amount of alcohols obtained in the samples. The instrument is a GCMS-QP2010s SHIMADZU GAS CHROMATOGRAPH MASS SPECTROMETER.. Figure 33: GCMS-QP2010s Shimadzu Gas Chromatograph Mass Spectrometer. (SHIMADZU, 2007). 62.

(63) The GCMS-QP2010s enables an accurate identification and quantification of substances at low levels, produces classical, library searchable spectra with a dynamic range of 106 and scan speeds of up to. AMU/sec and. .. It has a Patented Constant Linear Velocity of Carrier Gas and 20 Temperature Ramps. The high-quality mass spectra are generated by high precision quadrupoles and computer-designed ion transfer optics. Pre-quadrupoles stabilize the created ions, minimizing losses in transit to the quadrupoles. (SHIMADZU, 2007) This instrument exposes the ions present in a volume to an electromagnetic field in order for them to follow different trajectories according to their different mass-tocharge (. ) ratio. The quadrupole analyzer employs a quadrupole that generates a. variable electric field.. Figure 34: Quadrupole Analyzer. (espectrometria0de0masas, 2011). It consists basically of a source that produces ions, a quadrupole which produces variations in the ion trajectories depending on their charge to mass ratio and a detector that measures the number of ions (intensity) that have not been deflected.. 63.

(64) Depending on the frequency set, the quadrupole permits or not the ions to pass. It acts like an ion filter. This is very useful because it allows the user to select what to pass, in this case the analyte of interest, and what to not, that is waste and is threw out to the vacuum system. (espectrometria0de0masas, 2011). 64.

(65) 5. Results and results analysis 5.1 CATALYST CHARACTERIZATION: In order to establish correct characterizations of the catalysts were implemented the following analyses: Surface Area (BET), X-Ray Diffraction, Fourier Transform Infrared and SEM. Their results are shown below.. 5.1.1 Surface Area results: For all the analyses of surface area, nitrogen was used to determine the surface area by the physical adsorption of this gas onto the surface of the sample at liquid nitrogen temperatures. The method used in order to determine surface area was the BET method.. BET Method: The amount of gas adsorbed depends on the exposed surface area. In the BET method nitrogen is usually used because of its availability in high purity and its strong interaction with most solids. Known amounts of nitrogen gas are released into the sample cell. After the saturation pressure, no more adsorption occurs regardless of any further increase in pressure. After the adsorption layers are formed, the sample is removed from the nitrogen atmosphere and heated to cause the adsorbed nitrogen to be released from the material and then be quantified. The data collected is displayed in the form of a BET isotherm, which plots the amount of gas adsorbed as a function of the relative pressure as it is shown in the results shown below. (Hwang & Barron, 2011). Results obtained and showed in figures 37 through 41, have the behavior of a type II 65.

(66) BET isotherm as the one showed below.. Figure 35: Isotherm of type II. (Hwang & Barron, 2011). This is the most common isotherm obtained when using the BET method. The large uptake of nitrogen at low P/Po indicates filling of the micropores (< 20 Angstrom) in the catalyst. The linear portion of the curve represents multilayer adsorption of nitrogen on the surface of the catalyst, and the concave upward portion of the curve represents filling of meso- (20 - 500 Angstrom) and macropores (>500 Angstrom). (BASF Corporation, Catalysts Division's FCC Knowledge Base., 2013). The BET equation or equation (33) uses the information from the isotherm to determine the surface area of the sample, where X is the weight of nitrogen adsorbed at a given relative pressure (P/Po),. is monolayer capacity, which is the volume of. gas adsorbed at standard temperature and pressure (STP), and C is constant. STP is defined as 273 K and 1 atm.. When the BET equation is plotted, the graph should be of linear with a positive slope. 66.

(67) The slope and y-intercept can be obtained using least squares regression. monolayer capacity. Once. The. can be calculated with equation (34).. is determined, the total surface area S can be calculated with the equation. (35), where. is Avogadro’s number, Am is the cross sectional area of the. adsorbate and equals 0.162 nm2 for an adsorbed nitrogen molecule, and. is the. molar volume and equals 22414 mL.. DR Method: The method used in order to determine the pore volume and size was the DR method. The Dr or. method is a simple. relationship which linearizes the isotherm based on micropore filling principles. The best fit is extrapolated to. (where P/Po = 1) in order to find micropore. volume. (Quantachrome Instruments, 2004). Where: (Quantanchrome Instruments , 2011) . : Volume of the liquid adsorbate.. . : Total volume of the micropores. 67.