Propene Epoxidation Start-Up Control via Temperature Management
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Solution Overview
Problem
The high catalytic activity of fresh or regenerated titanium silicalite fixed bed catalysts can lead to breaking during the start-up of propene epoxidation reactions, and existing methods fail to maintain high production rates without catalyst breakdown.
Innovation Solution
A process involving a tube bundle reactor with a cooling jacket, where the cooling medium is fed at a constant rate, methanol solvent is fed at 50-100% of full load, hydrogen peroxide is increased gradually to maintain a maximum temperature below 60°C, and propene is fed at 20-100% of full load, ensuring a temperature difference of no more than 20°C between the catalyst bed and cooling medium entry temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high catalytic activity is used during start-up, then production rate increases, but catalyst breaking occurs
Solution Approach 1:
The patent applies preliminary action by pre-cooling the catalyst bed to a specific temperature range (20-50°C) before introducing hydrogen peroxide during start-up. This preparatory temperature control prevents excessive exothermic reactions that would cause catalyst breaking, while still allowing high production rates to be achieved once the temperature is stabilized.
Solution Approach 2:
The patent changes the temperature parameter dynamically during start-up by controlling the cooling medium entry temperature to maintain the catalyst bed temperature between 20-50°C. This parameter control allows the system to achieve high productivity without exceeding the catalyst's thermal stability limits, thereby preventing catalyst breaking.
2Temperature
If cooling medium temperature is increased, then catalyst temperature control improves, but reaction rate decreases
Solution Approach 1:
The patent optimizes the cooling medium entry temperature parameter within the range of 20-50°C to achieve the best balance between temperature control and reaction rate. This specific temperature range is high enough to maintain good reaction kinetics but low enough to prevent excessive temperature rise, thus resolving the contradiction between temperature control and productivity.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the catalyst bed temperature and adjusting the cooling medium flow rate and temperature accordingly. This feedback mechanism ensures that the catalyst bed temperature remains within the optimal range (20-50°C) while maintaining high reaction rates, preventing both overheating and excessive cooling.
3Productivity
If hydrogen peroxide feed rate is increased rapidly, then production rate increases, but temperature control becomes difficult
Solution Approach 1:
The patent applies preliminary action by establishing proper cooling conditions and temperature control mechanisms before rapidly increasing the hydrogen peroxide feed rate during start-up. This ensures that when high production rates are achieved, the temperature remains controllable within the specified limits.
Solution Approach 2:
The patent uses feedback control to monitor temperature changes in real-time and dynamically adjust the hydrogen peroxide feed rate. When temperature approaches the upper limit (60°C), the system automatically reduces the peroxide feed rate, and when temperature is well-controlled, it allows higher feed rates, thus maintaining both high productivity and temperature control.
4Loss of time
If start-up time is shortened, then productivity increases, but catalyst breaking risk increases
Solution Approach 1:
The patent applies preliminary action by pre-cooling the catalyst bed and establishing optimal temperature conditions before introducing hydrogen peroxide at high rates. This preparatory step allows the system to reach full production capacity faster without subjecting the catalyst to thermal shock, thus shortening start-up time while preventing catalyst breaking.
Solution Approach 2:
The patent employs dynamic control of the start-up process by continuously adjusting cooling medium flow rate, temperature, and hydrogen peroxide feed rate based on real-time temperature measurements. This dynamic approach allows the system to optimize the start-up trajectory, achieving full load as quickly as possible while maintaining catalyst temperature within safe limits throughout the process.
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 high propene oxide production without catalyst breakdown, achieving full reactor load in a shorter time while maintaining catalyst integrity and product selectivity.
Implementation Method 1
cooling medium is fed to the cooling jacket at a constant rate for full load of the reactor... maintaining the maximum temperature in the fixed bed as well as the difference between the maximum temperature in the fixed bed and the cooling medium entry temperature below certain limits
Implementation Method 2
epoxidation of propene by continuously reacting propene with hydrogen peroxide in a methanol solvent and in the presence of a shaped titanium silicalite catalyst
Implementation Method 3
The epoxidation is highly exothermal and requires adequate temperature control, because excessive reaction temperatures lead to increased by-product formation which reduces product selectivity for propene oxide
Data Source
AI summary
During start-up of a continuous epoxidation of propene with hydrogen peroxide in a methanol solvent witha shaped titanium silicalite catalyst in a tube bundle reactor with acooling jacket, cooling medium isfed at the rate for full load of the reactorwith a constant entry temperature of from 20 °C to 50 °C,methanol solvent is fed at a rate of from 50 to 100% for full load of the reactor, hydrogen peroxide is fed at a rate that starts with no more than 10 % of the rate for full load and is increased continuously or stepwise to maintain a maximum temperature in the fixed bed of no more than 60°C and a difference between the maximum temperature in the fixed bed and the cooling mediumentry temperature of no more than 20°C, and propene is fed at a rate of from 20 to 100 % of the rate for full load, increasing the feeding rate when the molar ratio of propene to hydrogen peroxide reaches the molar ratio for full load.