Molybdenum Catalyst Modifier Inhibits Oxide Loss
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Solution Overview
Problem
Current catalysts for the oxidation or ammoxidation of hydrocarbons face challenges in maintaining yield of desirable co-products like hydrogen cyanide without economically unacceptable losses in acrylonitrile production, and suffer from molybdenum oxide loss leading to catalyst deactivation and reactor scaling issues.
Innovation Solution
A molybdenum-based catalyst system modified with molybdates or polymolybdates of specific elements such as cesium, rubidium, potassium, and sodium, which are added in situ to inhibit molybdenum oxide loss and adjust selectivity, thereby enhancing hydrogen cyanide yield while maintaining acrylonitrile production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If operating conditions are changed to increase hydrogen cyanide yield, then hydrogen cyanide production increases, but acrylonitrile production yield decreases economically unacceptable
Solution Approach 1:
The patent applies parameter changes by introducing a catalyst modifier (alkali metal molybdate) that alters the catalytic properties of the molybdenum-based catalyst. This chemical parameter modification enables the system to achieve higher hydrogen cyanide yields without the need to change operating conditions, thereby maintaining economically acceptable acrylonitrile production yields while improving co-product yield
Solution Approach 2:
The catalyst modifier acts as an intermediary substance that mediates between the reactants and the catalyst. By adding alkali metal molybdate as a modifier, the system can adjust product distribution and increase hydrogen cyanide yield without directly changing operating parameters, thus resolving the contradiction between co-product yield and main product productivity
2Duration of action of moving object
If molybdenum-based catalyst is used for prolonged exposure to ammoxidation conditions, then catalyst activity declines, but molybdenum oxide loss occurs leading to reactor scaling
Solution Approach 1:
The patent applies beforehand cushioning by adding a catalyst modifier (alkali metal molybdate) that prevents molybdenum oxide loss before it can occur. The modifier creates a protective effect that cushions against the deactivation mechanism, reducing molybdenum oxide volatilization and preventing reactor scaling during prolonged catalyst operation
Solution Approach 2:
The catalyst modifier serves as an intermediary that protects the molybdenum-based catalyst from deactivation. By introducing alkali metal molybdate, the system creates a protective layer or modifies the catalyst surface to prevent molybdenum oxide loss, thereby extending catalyst life without directly addressing the prolonged exposure condition
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The catalyst modifier effectively increases hydrogen cyanide yield while reducing molybdenum oxide loss, minimizing reactor scaling and maintaining acrylonitrile production efficiency, thus improving overall process economics and catalyst longevity.
Implementation Method 1
Catalysts containing oxides of bismuth and molybdenum have long been used for the conversion of propylene at elevated temperatures in the presence of ammonia and oxygen to manufacture acrylonitrile
Implementation Method 2
a catalyst modifier that can be added in situ, to modify the performance of the catalyst in the reactor and inhibit molybdenum oxide loss from the base catalyst
Data Source
AI summary
A process for the conversion of a hydrocarbon selected from the group consisting of propylene, isobutylene, propane, isobutane or mixtures thereof, to acrylonitrile, methacrylonitrile, or mixtures thereof, the process comprising the step of reacting in the vapor phase at an elevated temperature and pressure said hydrocarbon with a molecular oxygen-containing gas and ammonia, in the presence of a molybdenum-based ammoxidation catalyst and a catalyst modifier, wherein said catalyst modifier comprises a molybdate or a polymolybdate of at least one element M selected from the group consisting of cesium, rubidium, potassium, sodium, thallium, lithium, nickel, cobalt, iron, chromium, copper, magnesium, manganese, cerium and phosporus, and wherein the ratio of the M elements to Mo in the molybdate or polymolybdate is greater than the ratio for these M elements to Mo in the molybdenum-based catalyst. The catalyst modifier is useful in modifying the performance of molybdenum-based catalyst and inhibiting molybdenum oxide loss for such catalysts.