Catalysis, today the workhorse of the chemical industry, plays a crucial role in the development of new products. Catalysis plays an important role in the production of MA to meet the demanding market. Selective oxidation of n-butane over vanadyl pyrophosphate (VPO) as a catalyst in the reaction results in the formation of MA.
Catalysis and Catalysts
The catalysts can thus be reused for the next reaction cycle, provided they have not been deactivated. Moreover, the overall free energy change of the catalytic process and the uncatalyzed process is the same. In other words, catalysts affect the kinetics of the reaction, but not the thermodynamics.
Types of Catalysis
Homogeneous Catalysis
Heterogeneous Catalysis
Energy Profiles of Reaction with Catalysts
However, for a collision to occur, the reactant molecules must encounter a certain energy barrier. Nevertheless, it is not necessary to change high temperature or other physical conditions for every chemical reaction. Therefore, the probability that molecules of significant energy collide with each other increases, resulting in a high productivity of the desired products.
Essential Properties of Good Catalysts
This technique uses mercury to be forced into the pores on the surface of the catalyst under a pressure of approx. 700 atm. The mercury applied under this pressure is required to fill a pore with a diameter of about 10 nm. The amount of uptake as a function of pressure determines the pore size distribution of the larger pores.
Importance and Uses of Catalysts
Again, catalysis is considered in the effort to improve the environmental quality. The biological reactions in our body are catalyzed by enzymes, as referred to earlier as nature's catalysts. Biological processes such as respiration must occur rapidly at ambient temperatures and pressures in order for the material in our body to survive.
Problem Statements
The discovery of the high selectivity VPO enabled the direct oxidation of n-butane to MA to be practiced by industry. According to the senior manager of process optimization department of BASF PETRONAS, the selectivity and activity of the VPO catalyst is approximately 82 % and 65 % respectively. In order to meet the demand of MA, the improvement of the physical and chemical performance of VPO catalyst for selective oxidation of n-butane to MA is desirable.
World Consumption of Maleic Anhydride- 2008
Objectives of Research
To investigate the effect of calcination durations on the physical and chemical properties of VPO catalysts.
These factors can be manipulated while generating the VPO catalyst and the physical, chemical and catalytic performance can be investigated to determine the appropriate conditions for the optimal performance of the VPO catalyst. However, in this report the variable being manipulated is the calcination durations of the precursor, vanadyl (IV) hydrogen phosphate hemihydrates, VOHPO4·0.5H2O.
Preparation of Vanadium Phosphorus Oxide Catalyst
- Aqueous Medium
- Organic Medium
- Dihydrate Precursor Route
- Hemihydrate Precursor Route
- Sesquihydrate Precursor Route
This solution was boiled for 2 hours and concentrated to a volume of 20 ml, to which hot water was then added to obtain blue vanadyl orthophosphate. It was then calcined in air at 673 K for 18 hours with a stream of a mixture comprising 0.75% n-butane and air, after which it was allowed to cool for 4 hours. Organic medium produces a higher surface area than aqueous medium due to the nature of the alcohol.
The slurry was then centrifuged and filtered, washed and dried overnight in an oven at 423 K. Vanadyl(IV) hydrogen phosphate hemihydrate, VOHPO4·0.5H2O, is one of the accepted precursors of commercial VPO catalysts for the selective oxidation of n-butane. to MA. 85% ortho-phosphoric acid solution was then added to the vanadium suspension and refluxed for another 2 h.
The sesquihydrate precursor was obtained by reducing VOPO4·2H2O in 1-butanol and calcined at 753 K for 10 h in a flow of n-butane/air mixture (0.75 % n-butane in air). The resulting yellow solid (VOPO4·2H2O phase) was then recovered using the centrifuge technique and then washed extensively with distilled water and dried in an oven at 353 K for 16 h. The formation of a new phase (V5+) and the reduction of the surface area of the catalysts were observed by prolonging the calcination duration of the vanadyl pyrophosphate catalysts prepared via the sesquihydrate precursor in the n-butane/air mixture at 673 K.
However, significant changes were observed where the surface of the crystal plate became cracked and rougher as the calcination duration increased.
Parameters of Vanadium Phosphorus Oxide Catalyst
- Parameter: Calcination Condition
- Parameter: Support System
- Parameter: Dopant
In addition, the sesquihydrate could be cross-linked with cobalt acetate to provide high-activity modified (VO)2P2O7, but both the selectivity to MA and the surface area decreased with increasing cobalt content. The most active phase used in the reaction is (VO)2P2O7 which is well crystallized. VO)2P2O7 can be generated via calcinations of precursor VOHPO4·0.5H2O prepared via reduction of VOPO4·2H2O using isobutanol as reducing agent followed by heat treatment in a reaction medium.
As can be seen from the description of the process, the transformation from the precursor to the active phase can be influenced by three main conditions of the calcinations: temperature, environment and duration. The temperature of the calcination could be adjusted so that the intervals between all experiments are the same for ease of research. It has been reported that V5+-containing phases, such as α1-VOPO4 or γ-VOPO4, exist in supported VPO catalysts, especially those prepared in aqueous media, and that the presence of such phases may inhibit the conversion of n-butane and/or MA can decrease. selectivity.
The presence of dopant can enhance the surface phosphorus enrichment, which changed the surface acidity. 2003) suggested that the addition of cobalt can stabilize the catalyst performance by forming cobalt phosphate, which improves its catalytic properties. Moreover, they used in situ laser Raman spectroscopy to study the evolution of the catalyst structure for materials derived from Co-VOHPO4·0.5H2O formed by the reaction with isobutanol. They found that the incorporation of Co could alter the V4+/V5+ balance during the activation period and thus change the catalytic performance in the steady state.
2003) used NMR techniques and it was observed that the presence of the Co dopant inhibits and stabilizes the transformation of the precursor onto amorphous vanadium phosphate.
Maleic Anhydride
- Uses of Maleic Anhydride
- Oxidation of n-butane to Maleic Anhydride
The demand for MA comes primarily from the manufacture of unsaturated polyester resins, agricultural chemicals, food-dependent substances, lubricating oil-dependent substances and pharmaceuticals. Therefore, it is crucial that MA's productivity can be enhanced and improved to meet the demanding market. In general, it is widely used in the production of unsaturated polyester resins, lubricating oil additives, alkyd resins, etc.
In the manufacturing process, resin is usually integrated into glass fiber reinforced plastic to meet the three basic requirements mentioned above. On the other hand, MA is also an important source of material used in the production of varnishes, lubricating oil-dependent substances and agricultural products. In the lubricating oil industry, the addition of MA reduces the required drying time for oils and improves the coating quality of varnishes.
Catalyst, being the workhorse of almost the complete range of the chemical industry, attracts a lot of attention from the researchers. The transformation of MA from n-butane requires the withdrawal of eight hydrogen atoms, the insertion of three oxygen atoms and a ring closure. Moreover, this catalyst is the only commercially viable system that enables the selective production of MA from n-butane.
As the following chemical equations show, the energy released in the oxidation of n-butane exceeds that of benzene, which is reflected in the co-product steam.
Materials and Gases used
- Preparation of the Vanadyl Phosphate Dihydrate
In general, the preparation of the bulk vanadyl pyrophosphate catalysts can be done by several routes; notably the sesquihydrate pathway (VPOs), the organic pathway (VPOo) and the reduction of vanadyl phosphate dihydrate, VOPO4·2H2O phase (VPOd). The preparation of the doped vanadyl pyrophosphate catalysts can take place via the organic route and the reduction of the VOPO4·2H2O phase. In this study, the preparation of the vanadium phosphorus oxide catalyst takes place via the sesquihydrate precursor VOHPO4·1.5H2O.
The production of vanadyl pyrophosphate catalyst has been developed via the vanadyl hydrogen phosphate sesquihydrate precursor, VOHPO4·1.5H2O. The synthesis of sesquihydrate precursor has been divided into two-step procedure, which involves vanadyl phosphate dihydrate, VOPO4·2H2O as an intermediate before obtaining the precursor. Yellow solids recovered by centrifugation technique, were washed sparingly with acetone and were oven dried (~80 °C) for 24 h.
- X-Ray Diffraction (XRD) Analysis
- BET Surface Area Measurements
- Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometer (SEM-EDX)
- Introduction
- Brunauer-Emmer-Teller Single Point Surface Area (BET)
- Scanning Electron Microscopy (SEM)
- Inductively- Coupled Plasma- Optical Emission Spectrometer (ICP- OES)
- Energy Dispersive X-Ray Diffraction (EDX)
- Conclusions
- Recommendations
Several instruments are included throughout the research to study the physical and chemical properties of the produced catalysts. In this research, a redox titration was performed to determine the average vanadium valence (AV) of VPO catalysts and/or to obtain the average oxidation state of vanadium. The endpoint is reached when the purple color of the solution disappears and becomes colorless.
Then another 25 ml of the original solution was titrated with 0.01 N ammonium iron(II) sulfate solution. First, a thin layer of gold metal must be applied to the surface of the catalyst sample during analysis for conductive purposes. The interaction between the beam and the sample results in the emission of the electrons and photons as the electrons penetrate the surface of the sample.
Quantitative and qualitative analysis of VPO catalysts was carried out on a Perkin-Elmer Emission Spectrometer Model Plasma 1000. By increasing the duration of calcination, we observed an increase in the specific surface area of VPO catalysts. Line electron microscopy shows the surface morphology of the catalysts obtained with different calcination durations.
ICP-OES requires the catalysts to be in the solution phase, which could ensure a more accurate measurement, while EDX only detects on the surface of the catalysts. In this technical report, the physico-chemical properties of the VPO catalysts, obtained through different calcination times, are presented. The effect of n-butane/air pretreatment duration on the morphology and reactivity of (VO)2P2O7 catalysts.
