Dual Catalyst System for Aldehyde Reduction in Acrylic Acid Production
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Solution Overview
Problem
Existing catalysts used in the production of acrylic acid suffer from deactivation due to high temperatures and 'hot spots,' leading to decreased yield and frequent catalyst replacement, while also producing significant aldehyde byproducts that are difficult to separate.
Innovation Solution
A dual catalyst system comprising an acrolein-oxidizing catalyst with a mixed metal oxide composition and a finishing catalyst with a different composition, specifically a MoVTeNb or MoVNbSb-based oxide, which reduces aldehyde byproducts and extends catalyst lifetime by lowering reaction temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If mixed metal oxide catalyst is used at elevated temperatures for acrylic acid production, then oxidation reaction rate is improved, but catalyst deactivation occurs due to hot spots leading to decreased yield and frequent catalyst replacement
Solution Approach 1:
The patent applies local quality by creating a gradient structure where catalyst pellets of different sizes are arranged in sequence, and by incorporating inactive material layers at specific locations within the catalyst bed. This ensures that hot spots are addressed locally without compromising the overall reaction rate, as each zone is optimized for its specific function (conversion vs. temperature control).
Solution Approach 2:
The patent introduces an intermediary approach by using a two-stage catalyst system where the first stage uses traditional mixed metal oxide catalyst for high conversion, and the second stage uses a different catalyst formulation designed to reduce hot spots. This intermediary stage acts as a buffer to manage temperature issues while maintaining overall process efficiency.
2Productivity
If mixed metal oxide catalyst is used for acrolein oxidation, then acrylic acid yield is improved to 92% and above, but aldehyde byproducts are formed that are difficult to separate from acrylic acid
Solution Approach 1:
The patent applies parameter changes by optimizing the catalyst composition with specific ratios of Mo, V, W, Cu, and Ni, and by controlling the size distribution of catalyst pellets. These parameter changes enable the catalyst to selectively promote acrylic acid formation while minimizing aldehyde byproduct formation, and facilitate easier separation of byproducts from the main product.
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 dual catalyst system effectively reduces the weight percentage of aldehyde byproducts, increases the yield of acrylic acid, and prolongs the catalyst's operational life by mitigating temperature-related deactivation issues.
Implementation Method 1
catalytic gas-phase oxidation of alkanes, alkanols, alkenes, or alkenals
Implementation Method 2
contacted with a mixed metal oxide catalyst to be oxidized into acrylic acid
Implementation Method 3
formation of 'hot spots' (i.e., locations within the catalyst bed where the temperature is higher than the bath temperature) from such an exothermic reaction
Data Source
AI summary
A catalyst composition comprises an acrolein-oxidizing catalyst comprising a mixed metal oxide catalyst of general formula (1):MoVaA1bA2cA3dOm (I)in which A1 comprises at least one element selected from the group consisting of W and Cu; A2 comprises at least one element selected from the group consisting of Sb, Fe, and Nb; A3 comprises at least one element selected from the group consisting of Y, Ti, Zr, Hf, Ta, Cr, Mn, Re, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Si, Te, Pb, P, As, Bi, Se, rare earth elements, alkaline elements, and alkaline earth elements; a ranges from 0.01 to 1.0; b ranges from 0.01 to 1.5; c ranges from 0 to 1.5; d ranges from 0 to 1.0; and m is dependent on the oxidation state of the other elements. The catalyst composition further comprises a finishing catalyst comprising a mixed metal oxide catalyst of general formula (II):MoVwNbxX1yX2zOn (II)in which X1 comprises at least one element selected from the group consisting of Te and Sb; X2 comprises at least one an element selected from the group consisting of Y, Ti, Zr, Hf, Nb, Ta, Cr, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Ag, Au, Zn, B, Al, Ga, In, Ge, Sn, Pb, P, As, Bi, Se, rare earth elements and alkaline earth elements; w ranges from 0.01 to 1.0; x ranges from 0.01 to 1.0; y ranges from 0.01 to 1.0; z ranges from 0 to 1.0; and n is depended on the oxidation state of the other elements. The finishing catalyst does not contain W or Cu, and has an X-ray diffraction pattern showing an orthorhombic phase as the major crystal phase with main peaks with 2θ at 6.7°, 7.8°, 22.1°, and 27.2°. The acrolein-oxidizing catalyst has a different chemical composition than the finishing catalyst. A process for producing acrylic acid is also disclosed.