Acrylic Acid Start-Up Control via Acrolein Loading
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Solution Overview
Problem
The production of acrylic acid by catalytic vapor-phase oxidation of acrolein faces challenges with unstable catalytic activity during start-up, leading to reduced yield and catalyst deterioration, especially when using reactors with multiple reaction zones of varying catalytic activity.
Innovation Solution
A process is developed where acrolein supply is gradually increased during start-up, adjusting reaction conditions such as temperature and gas composition to maintain acrolein conversion above 90% and peak catalyst temperatures below 400°C, ensuring stable operation and high yield in reactors with multiple reaction zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the acrolein supply rate is rapidly increased during start-up to achieve high productivity, then the acrylic acid production rate increases, but abnormal heat generation occurs in the catalyst layer leading to reduced yield and catalyst deterioration
Solution Approach 1:
The patent applies preliminary action by pre-heating the catalyst to the reaction temperature before introducing acrolein, and by gradually increasing the acrolein supply rate in a controlled manner during start-up. This gradual increase allows the catalyst to activate progressively without generating abnormal heat, thereby preventing hot spots and catalyst deterioration while still achieving high productivity once stable operation is reached.
2Reliability
If the acrolein supply rate is kept low during start-up to suppress abnormal heat generation, then catalyst deterioration is prevented, but the acrylic acid production rate drops and catalyst activation becomes insufficient
Solution Approach 1:
The patent applies dynamics by implementing a dynamic control strategy where the acrolein supply rate is gradually increased over time during the start-up period. The supply rate transitions from low to high in a controlled manner, allowing the catalyst to activate progressively. This dynamic adjustment optimizes both catalyst stability during the transition and productivity once stable operation is achieved, resolving the contradiction between maintaining low supply for stability and high supply for productivity.
3Loss of time
If the acrolein supply rate is increased to reach prescribed reaction conditions quickly, then start-up time is reduced, but localized heat generation occurs causing catalyst deterioration
Solution Approach 1:
The patent applies feedback by implementing temperature monitoring and control mechanisms that detect temperature changes in the catalyst layer during start-up. Based on this feedback, the acrolein supply rate is dynamically adjusted to prevent localized heat generation. This feedback control allows for faster start-up by permitting higher supply rates when temperatures are stable, while automatically reducing supply rates when temperature rise is detected, thus preventing catalyst deterioration.
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
This approach allows for quick attainment of stable reaction conditions, preventing catalyst deterioration and achieving high acrylic acid yield from the start of the reaction, even under high load conditions.
Implementation Method 1
catalytic vapor-phase oxidation of acrolein
Implementation Method 2
The catalytic vapor-phase oxidation of acrolein, however, is exothermic
Data Source
AI summary
The invention offers an improvement in a process for start-up in the occasion of producing acrylic acid by catalytically oxidizing acrolein at vapor phase under high load conditions, the start-up meaning the step of increasing the acrolein supply rate (loading) from the non-reacting condition to the prescribed reaction conditions. This process is characterized in that the acrolein supply rate is increased in the start-up stage of the reaction until the prescribed composition of starting reactant gas and the flow rate of the starting reactant gas are obtained, while adjusting at least one of the reaction temperature, the composition of the starting reactant gas and the flow rate of the starting reactant gas, so as to maintain the acrolein conversion at not lower than 90 mol %, the maximum peak temperature of the catalyst layer in each reaction zone at no higher than 400° C., and the sum of each ΔT (maximum peak temperature of a catalyst layer-reaction temperature) at the catalyst layer in each of the reaction zones to be no more than 150° C., respectively. According to this process, the reaction speedily reaches the steady state (standard operating conditions) and a high acrylic acid yield is stably achieved from the start of the reaction.