Polyol Purification Reducing 2-Methyl-2-Pentenal via Dilute Acid Neutralization
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Solution Overview
Problem
The production of long chain, low hydroxyl number polyether polyols often results in undesirable levels of 2-Methyl-2-Pentenal (2M2P) and residual alkalinity, which can catalyze subsequent urethane-forming reactions and affect the quality of polyurethane foams, particularly in flexible foam applications where odor and chemical stability are concerns.
Innovation Solution
A method involving the neutralization of alkali metal ions in polyols using a dilute sulfuric acid solution with sulfuric acid concentrations no more than 5% by weight, and using 2% to 10% more acid than theoretically necessary to neutralize all alkali metal ions, effectively reducing 2M2P content to 10 ppm or less and minimizing residual alkalinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sulfuric acid is used to neutralize alkaline catalyst in polyether polyol, then residual alkalinity is removed, but 2M2P content increases due to acid-catalyzed condensation reaction
Solution Approach 1:
The patent changes the concentration parameter of sulfuric acid from traditional high concentrations (10-20% or higher) to a low concentration range of 0.1-5% (preferably 0.5-2%). This parameter change reduces the acid-catalyzed condensation reaction that forms 2M2P while still effectively neutralizing the alkaline catalyst, thus resolving the contradiction between removing residual alkalinity and minimizing 2M2P formation
Solution Approach 2:
The patent applies partial neutralization by using sulfuric acid in an amount of 0.95 to 1.05 equivalents relative to the alkaline catalyst, rather than complete or excessive neutralization. This partial action approach is sufficient to remove residual alkalinity that would catalyze urethane-forming reactions, while avoiding the excessive acid exposure that would promote 2M2P formation through condensation reactions
2Productivity
If higher concentration sulfuric acid is used for neutralization, then neutralization efficiency is improved, but odor body formation increases
Solution Approach 1:
The patent changes the concentration parameter of sulfuric acid from traditional high concentrations (10-20% or higher) to a low concentration range of 0.1-5% (preferably 0.5-2%). This parameter change reduces the acid-catalyzed condensation reaction that forms 2M2P while still effectively neutralizing the alkaline catalyst, thus resolving the contradiction between removing residual alkalinity and minimizing 2M2P formation
Solution Approach 2:
The patent converts the potentially harmful effect of acid concentration (which causes 2M2P formation) into a beneficial outcome by using low concentration sulfuric acid. This approach maintains the useful neutralization function while eliminating the harmful condensation reaction, effectively turning the limitation of low concentration into an advantage for reducing odor bodies
3Reliability
If sulfuric acid amount is increased to ensure sufficient neutralization, then residual alkalinity is minimized, but acid number becomes too high causing decomposition or undesired catalysis
Solution Approach 1:
The patent applies partial neutralization by using sulfuric acid in an amount of 0.95 to 1.05 equivalents relative to the alkaline catalyst, rather than complete or excessive neutralization. This partial action approach is sufficient to remove residual alkalinity that would catalyze urethane-forming reactions, while avoiding the excessive acid exposure that would promote 2M2P formation through condensation reactions
Solution Approach 2:
The patent changes the concentration parameter of sulfuric acid from traditional high concentrations (10-20% or higher) to a low concentration range of 0.1-5% (preferably 0.5-2%). This parameter change reduces the acid-catalyzed condensation reaction that forms 2M2P while still effectively neutralizing the alkaline catalyst, thus resolving the contradiction between removing residual alkalinity and minimizing 2M2P formation
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 significantly reduces 2M2P levels in polyols to 10 ppm or less, eliminates residual alkalinity, and maintains a low acid number, improving the quality and stability of polyurethane foams by ensuring minimal interference in subsequent reactions and odor issues.
Implementation Method 1
neutralizing the alkali metal ions with an acid to neutralize the alkaline catalyst
Implementation Method 2
to minimize the amount of water that is used that must be later removed, such as by distillation
Data Source
AI summary
Disclosed are methods for purifying polyols containing oxyalkylene units that is an alkali metal catalyzed alkoxylation reaction product of an alkylene oxide and an H-functional starter. The methods include neutralizing the alkali metal ions with an aqueous solution comprising water and sulfuric acid, in which: (i) the sulfuric acid is present in an amount of no more than 5% by weight, based on the total weight of the aqueous solution, and (ii) the sulfuric acid is used in an amount of 2% to 10% more than the theoretical amount necessary to neutralize all of the alkali metal ions present. The methods can produce polyols having a low content of 2-methyl-2-pentenal.