Allyl Alcohol Alkoxylates Process Segmentation Safety
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Solution Overview
Problem
The existing processes for alkoxylating unsaturated starters face safety risks due to exothermic secondary reactions at high temperatures, leading to potential reactor ruptures and low reaction rates, while also resulting in undesirable by-products and impaired economics due to low reaction temperatures.
Innovation Solution
Regulating the introduction of alkylene oxides based on the degree of alkoxylation to maximize concentration in the liquid phase, ensuring the temperature at the end of a runaway reaction is at least 100 K below the onset temperature of decomposition, thereby increasing space-time yield and product quality while ensuring safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the temperature is increased to accelerate the alkoxylation reaction, then the reaction rate is improved, but exothermic secondary reactions occur that pose safety risks
Solution Approach 1:
The alkoxylation reaction is divided into multiple stages with different temperature profiles. The reaction proceeds through distinct phases: initial alkoxylation at moderate temperature, then a second alkoxylation stage at higher temperature after water removal. This segmentation allows the system to achieve high reaction rates when safe, while avoiding dangerous exothermic secondary reactions by controlling temperature in each stage.
Solution Approach 2:
Water is removed from the reaction mixture before conducting the second alkoxylation stage at higher temperature. This preliminary action of water removal prevents the occurrence of exothermic secondary reactions that would otherwise occur at elevated temperatures, thereby enabling safe high-temperature operation in the second stage.
2Reliability
If the temperature is decreased to prevent exothermic secondary reactions, then reactor safety is improved, but the reaction rate decreases and space-time yield is reduced
Solution Approach 1:
The reaction is divided into two temperature stages: a first stage at moderate temperature (80-120°C) for initial alkoxylation, and a second stage at higher temperature (120-180°C) for further alkoxylation after water removal. This segmentation enables the system to achieve high space-time yield in the second stage while maintaining safety by controlling temperature and water content in each respective stage.
Solution Approach 2:
Water is removed from the reaction mixture before conducting the second alkoxylation stage at higher temperature. This preliminary water removal creates conditions that allow high-temperature operation without triggering exothermic secondary reactions, thereby achieving both high productivity and reactor safety.
3Ease of manufacture
If solid alkali metal hydroxide catalyst is used, then the catalyst is easier to handle, but water content in the catalyst forms diols as undesirable by-products
Solution Approach 1:
The catalyst is changed from solid alkali metal hydroxide to alkali metal alkoxide. This parameter change eliminates the water content issue inherent in solid hydroxides, preventing diol by-product formation while maintaining catalytic activity for the alkoxylation reaction.
4Productivity
If high concentration of alkylene oxide is used to increase reaction rate, then productivity is improved, but the temperature at the end of runaway reaction approaches the decomposition onset temperature, reducing safety margin
Solution Approach 1:
The alkoxylation is divided into two stages with different alkylene oxide concentrations. The first stage uses moderate alkylene oxide concentration to build up conversion safely. The second stage, conducted after water removal, uses higher alkylene oxide concentration to achieve high reaction rates and productivity while maintaining safety through the lower water content that prevents exothermic secondary reactions.
Solution Approach 2:
Water is removed before conducting the second alkoxylation stage with high alkylene oxide concentration. This preliminary water removal enables the system to tolerate higher alkylene oxide concentrations without creating unsafe conditions, as the reduced water content prevents exothermic secondary reactions even at elevated temperatures.
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 enhances the space-time yield and product quality while ensuring reactor safety by maintaining the temperature below the decomposition onset, allowing for efficient and safe alkoxylation with increased alkylene oxide concentration.
Implementation Method 1
reacting one or more unsaturated starters having at least one active hydrogen atom per molecule with one or more alkylene oxides in the presence of a basic catalyst
Implementation Method 2
unsaturated starters in the presence of bases as are used for the above-described alkoxylations undergo, at relatively high temperatures, secondary reactions which are so strongly exothermic that they represent a safety risk
Data Source
AI summary
A process for preparing polyether alcohols by reacting one or more unsaturated starters having at least one active hydrogen atom per molecule with one or more alkylene oxides in the liquid phase in the presence of a basic catalyst in a reactor, wherein the one or more alkylene oxides are introduced into the reactor in such a way that the concentration of unreacted alkylene oxide in the liquid reaction mixture in the reactor is increased as far as possible with increasing degree of addition of the alkylene oxide onto the starter, with the proviso that the temperature at the end of a runaway reaction is at any point in time at least 100 K below the onset temperature of the decomposition reaction of the liquid reaction mixture, is proposed.