The present study investigates the oxidative de-hydrogenation of propane-butane (C3-C4) fraction over mono (Cr, Mo) and bi-metal (Cr-Mo) loaded MCM–41catalysts. The catalysts were prepared by sequential impregnation method at 500oC calcination temperature. Experiments were performed by feeding C3-C4 fraction and CO2 into a continuous flow quartz reactor at atmospheric pressure (P = 1 atm.), reaction temperatures between 500 – 650oC, gas hourly space velocity within 100 – 400 h-1, and at reaction time (tr) = 2h. The physicochemical properties and performance of catalysts were evaluated by BET, XRD, H2–TPR, and NH3–TPD characterization techniques. The major products are ethylene, propylene, isobutylene, butylene. This paper reports that the total yield of olefins (Ʃ C2-C4) = 71.6 % was achieved at 89.5 % conversion level of C3–C4 at 630oC. The results indicate that the addition of Mo to Cr/MCM–41 modifies its catalytic activity. The Cr/MCM–41 and Mo/MCM–41 catalysts 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 Temperature-programmed analysis of calcined catalysts:
3.4 Oxidative de-hydrogenation of C3–C4:
4. Conclusion
Research Objectives and Key Themes
This study aims to investigate the catalytic performance of mono-metallic (Cr, Mo) and bi-metallic (Cr-Mo) loaded MCM-41 catalysts for the oxidative dehydrogenation of propane-butane (C3-C4) fractions into olefins. The research evaluates optimal operating conditions—specifically temperature, gas hourly space velocity, and reactant composition—to maximize olefin yield and selectivity while minimizing over-oxidation to carbon oxides.
- Synthesis and physicochemical characterization of Cr, Mo, and Cr-Mo impregnated MCM-41 catalysts.
- Evaluation of catalytic activity, stability, and selectivity in a continuous flow quartz reactor.
- Impact of bi-metallic synergy (Cr-Mo) on catalyst reducibility and surface acidity.
- Optimization of reaction parameters to enhance conversion efficiency and reduce byproduct formation.
Excerpt from the Book
3.1 Catalysts Characterization:
The Textural characteristics such as metallic composition, BET surface area and pore distributions of catalyst samples are compiled in Table 1. Atomic absorption spectroscopy by «Accu-sorb» was used to measure the elemental composition of catalysts. The BET surface areas (determined by N2 physi-sorption) and the pore size distributions of all the catalyst samples were calculated using the Brunauer-Emmett-Teller (BET) and the Barrett-Joyner-Halenda (BJH) methods, respectively. The N2 adsorption-desorption isotherms on catalyst samples show a characteristic capillary condensation pore-filling step of a typical reversible type IV adsorption isotherm as defined by IUPAC for mesoporous materials.[15] After calcinations, the observed surface area of parent MCM–41 (1238.6 m2/g) may be attributed to the removal of organic template, and CTABr from the material which, consequently, resulted in an increase in the adsorption site for the nitrogen molecules. Upon Cr, Mo, and Cr-Mo incorporation on MCM–41 support, it can be seen that the surface areas of catalyst samples show a similar trend: being maximum for the 1.2Cr-2.8Mo/MCM–41 impregnated sample (1098.4 m2/g), and minimum for the 4Mo/MCM–41 (932 m2/g) upon calcination. The pore size distribution curves of samples as calculated by BJH method centered between Vp = 0.652 – 0.948 cm3/g (pore volume) and d = 2.6 – 3.2 nm (pore diameter) are presented in Figure 2. Nevertheless, the observed slight reductions in textural characterization, in comparison to values of the parent MCM–41, may be attributed to modification of the pore wall with metal precursor which reduces the scattering contrast between the pores and the walls of the molecular sieve.
Summary of Chapters
1. Introduction: Provides an overview of the petrochemical demand for olefins and the current limitations of traditional steam cracking, identifying oxidative dehydrogenation as a promising alternative.
2. Experimental: Details the systematic preparation of MCM-41 supported catalysts, the impregnation procedures for mono and bi-metallic samples, and the setup of the catalytic reactor tests.
3. Results and Discussion: Analyzes the characterization data (XRD, TPR, TPD) and discusses the catalytic performance regarding conversion levels, olefin selectivity, and the synergistic effects of Cr and Mo.
4. Conclusion: Summarizes the optimal operating parameters for the Cr-Mo/MCM-41 catalyst and reaffirms its superior performance and cost-effectiveness compared to mono-metallic catalysts.
Keywords
oxidative de-hydrogenation, C3–C4 conversion, selectivity to olefin, olefin yield, olefin production, MCM–41 catalysts, chromium, molybdenum, bi-metallic catalysts, catalytic performance, pore distribution, surface acidity, propane-butane fraction, gas hourly space velocity, petrochemical industry
Frequently Asked Questions
What is the core focus of this research?
The research focuses on developing effective bi-metallic (Cr-Mo) catalysts supported on mesoporous MCM-41 to convert propane-butane fractions into valuable olefins through oxidative dehydrogenation.
What are the primary thematic fields covered?
The work covers heterogeneous catalysis, material science (specifically mesoporous silica), chemical reaction engineering, and the optimization of petrochemical feedstock conversion.
What is the main objective of the study?
The primary goal is to find an efficient, cost-effective catalytic process that maintains high olefin selectivity while minimizing undesirable side reactions like coke formation and over-oxidation.
Which scientific methods were employed?
The study utilizes synthesis methods like incipient wetness impregnation, and characterization techniques including BET surface area analysis, XRD, H2–TPR, NH3–TPD, and TEM, alongside gas chromatography for product analysis.
What does the main body address?
The main body examines the structural properties of synthesized catalysts and discusses the experimental results of catalytic tests conducted under varying temperatures and gas hourly space velocities.
Which keywords define this work?
Key terms include oxidative de-hydrogenation, C3–C4 conversion, olefin selectivity, Cr-Mo/MCM–41 catalysts, and catalytic synergy.
Why is the Cr-Mo/MCM-41 catalyst more effective than mono-metallic versions?
The bi-metallic system exhibits a synergistic effect where the interaction between Cr and Mo species enhances reducibility and surface acidity, leading to better catalyst performance and tolerance to carbonaceous deposits.
How does reaction temperature affect the outcome?
Increasing the reaction temperature raises the conversion level but can lead to lower selectivity for propylene and butylene due to secondary cracking and the formation of methane or carbon oxides.
What role does gas hourly space velocity play?
Gas hourly space velocity acts as a critical parameter; an optimum value of 250 h⁻¹ was determined to balance conversion efficiency with the retention time required to prevent incomplete reactions.
What are the implications for industrial application?
The findings suggest that this technology is an environmentally benign route for converting light paraffins, provided that heat management and catalyst durability are further refined for large-scale operations.
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- A. A. Ijagbuji (Autor:in), V. V. Schwarzkopf (Autor:in), I. I. Zakharov (Autor:in), D. B. Woods (Autor:in), T. C. Philips (Autor:in), K. M. Jackson (Autor:in), M. B. Saltzberg (Autor:in), B.V. Shevchenko (Autor:in), J. K. Johnson (Autor:in), 2015, Production of olefins via oxidative de-hydrogenation of C3‒C4 fraction by CO2 over Cr‒Mo/MCM‒41, München, GRIN Verlag, https://www.grin.com/document/294184
