The present study investigates the oxidative dehydrogenation of propane-butane (C3–C4) fraction over mono (Cr or Mo) and bi-metal (Cr-Mo) loaded SiO2 catalysts. The catalysts were prepared by sequential impregnation method at 500oC calcination temperature. Experiments were performed by feeding C3–C4 fraction, oxygen, nitrogen, and steam into a continuous flow quartz reactor at an atmospheric pressure (P = 1 atm.), reaction temperatures between 500 – 650oC, gas hourly space velocity (GHSV) within 100 – 400 h-1, and at reaction time (tr) = 2h. Appropriate water vapor addition to the feed sinificantly minimizes oxidation into coke deposits on the catalyst surface, and also prevents further olefin conversion into undesirable product. The physicochemical properties were evaluated by BET, XRD, IR, and EPR characterization techniques. The major oxidation products are ethylene, propylene, isobutylene, butylene. This paper reports that the total yield of olefins (Ʃ C2-C4) = 66.0 % was achieved at 83.5 % conversion level of C3–C4 at 630oC. The results indicate that the addition of Mo to catalysts of Cr/SiO2 modifies its catalytic activity for the ODH reaction. Mono-metallic catalysts (Cr/SiO2 and Mo/SiO2) were prepared for comparison purposes.
Table of Contents
1. Introduction
2. Experimental
2.1 Materials and Methods:
2.2 Catalysts Preparation:
2.3 Catalysts Treatment:
2.4 Catalysts Test:
2.5 Oxidative De-hydrogenation of C3–C4:
3. Results and Discussion
3.1 Catalysts Characterization:
3.2 x-ray diffraction of calcined catalysts:
3.3 NH3 adsorption sites of catalysts:
3.4 Oxidative de-hydrogenation of C3–C4:
4. Conclusion
Research Objectives and Topics
The primary objective of this study is to investigate the oxidative dehydrogenation of a propane-butane (C3–C4) fraction into valuable olefins using mono-metallic (Cr or Mo) and bi-metallic (Cr-Mo) loaded SiO2 catalysts, aiming to identify optimal conditions for high catalytic activity and selectivity while minimizing undesirable side reactions and coke formation.
- Synthesis and characterization of Cr/SiO2, Mo/SiO2, and Cr-Mo/SiO2 catalysts.
- Evaluation of catalytic performance under varying temperature and gas hourly space velocity (GHSV) conditions.
- Analysis of reaction mechanism and the impact of catalyst surface acidity and morphological alterations.
- Optimization of olefin yield through bimetallic synergistic effects.
- Assessment of industrial viability regarding material cost and environmental impact.
Excerpt from the Book
3.4 Oxidative de-hydrogenation of C3–C4:
During oxidation, the alkane molecule is adsorbed to the surface of oxygen atom [Eq. (5)], followed by the cleavage of C–H bond to form an alkyl intermediate, and a hydroxyl group on the catalyst surface [Eq. (6)]. The adsorbed alkyl specie looses a second hydrogen atom, thus, forming alkene, and another hydroxyl group on the catalyst surface [Eq. (7)]. Two hydroxyl groups combine to form water and lattice vacancy [Eq. (8)]. The oxidative dehydrogenation reaction is postulated to occur via a redox cycle, where the catalysts lattice oxygen takes part in the oxidation reaction [Eq. (9)], and then the reduced catalyst is re-oxidized following a Mars-van Krevelen mechanism.[45]
The catalytic performances of samples, as well as the effect of external mass transfer on C3–C4 oxidation was studied by varying stirrer speed from 100 – 400 h-1, T = 500 – 650oC, and P = 1 atm. Since the pore structure of catalyst surface vary at different reaction temperatures, any impurity generated at different temperatures blocks the catalyst pore structure, resulting in lower catalytic activity and shorter catalyst effective time. Therefore, five different temperatures ranging from 500 to 650oC were selected to investigate the optimum reaction temperature. The optimum reaction temperature was therefore, carefully determined by COx removal efficiency and effective time of catalyst.
Summary of Chapters
1. Introduction: Outlines the importance of olefins in modern chemistry, discusses current industrial production limitations, and establishes the rationale for using oxidative dehydrogenation.
2. Experimental: Details the materials, catalyst preparation methods (wet impregnation), treatment processes, and the experimental setup for testing catalytic activity.
3. Results and Discussion: Presents the characterization of catalyst samples (BET, XRD, SEM, NH3 adsorption) and discusses their performance in C3–C4 conversion, including reaction parameters and mechanistic insights.
4. Conclusion: Summarizes the key findings, confirming that the 15 %wt. Cr-Mo/SiO2 catalyst exhibits the best catalytic performance and highlights the potential for industrial application.
Keywords
oxidative de-hydrogenation, propane-butane, C3–C4 conversion, catalyst selectivity, olefin yield, Cr-Mo/SiO2, SiO2 support, catalytic activity, Mars-van Krevelen mechanism, surface acidity, heterogeneous catalysis, gas hourly space velocity.
Frequently Asked Questions
What is the primary focus of this research?
The research focuses on the oxidative dehydrogenation of propane-butane (C3–C4) fractions into lighter olefins like ethylene and propylene using chromium and molybdenum-loaded silica catalysts.
What are the main thematic areas covered?
The study covers catalyst synthesis and characterization, the effect of bi-metallic synergy on catalytic activity, the influence of reaction parameters like temperature and GHSV, and mechanistic studies on coke formation and catalyst regeneration.
What is the main goal or research question?
The goal is to determine if bi-metallic Cr-Mo/SiO2 catalysts provide superior performance for olefin production compared to mono-metallic variants and to identify the optimal operating conditions for efficiency.
Which scientific methods are employed?
The study uses experimental wet impregnation for catalyst preparation and various analytical techniques including BET, XRD, IR spectroscopy, and XPS for surface and structural characterization, alongside GC-MS for product analysis.
What is treated in the main body?
The main body examines the physiochemical properties of the synthesized catalysts, the experimental results regarding conversion and selectivity under different temperatures, and the post-reaction analysis of the catalysts.
Which keywords characterize the work?
Key terms include oxidative dehydrogenation, C3–C4 conversion, olefin yield, bimetallic catalysts (Cr-Mo), silica support, and reaction selectivity.
How does the addition of Mo affect the Cr/SiO2 catalyst?
The addition of Mo to the Cr/SiO2 catalyst significantly improves its specific activity toward olefin formation and enhances the total yield of olefins compared to the mono-metallic catalysts.
Why is steam used during the reaction?
Steam is added to the feed as a diluent to minimize oxidation into coke deposits on the catalyst surface and to facilitate catalyst regeneration after reaction cycles.
What makes the Cr-Mo/SiO2 catalyst superior?
It exhibits enhanced surface acidity, improved reducibility, and a synergistic interaction between MoOx species and Cr crystallites, which optimizes the dehydrogenation process.
- Citation du texte
- Ayodeji Ijagbuji (Auteur), I. I. Zakharov (Auteur), T. C. Philips (Auteur), M. G. Loriya (Auteur), M. B. Saltzberg (Auteur), A. B. Tselishtev (Auteur), R. J. Taylor (Auteur), B.V. Shevchenko (Auteur), K. M. Jackson (Auteur), D. B. Woods (Auteur), J. K. Johnson (Auteur), 2015, Production of olefins via oxidative de-hydrogenation of C3‒C4 fraction by O2 over (Cr‒Mo)SiO2, Munich, GRIN Verlag, https://www.grin.com/document/292808
