1,2-Propanediol Process Pressure Control for Safe Oxygen Purging
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Solution Overview
Problem
The existing process for producing 1,2-propanediol from propene and hydrogen peroxide is hazardous due to the formation of a flammable gas phase containing oxygen, which poses an explosion risk, and requires additional equipment for propene recovery.
Innovation Solution
The process is modified by operating in vessels flooded with a liquid reaction mixture at high pressure to suppress gas desorption, using a catalyst mixture with a phase transfer catalyst and heteropolytungstate, and desorbing only a portion of dissolved oxygen into a non-flammable gas, allowing for efficient propene recycling and reducing propane loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reaction is carried out at high pressure to suppress gas desorption, then safety is improved by preventing flammable gas phase formation, but equipment complexity increases due to additional pressure control requirements
Solution Approach 1:
The patent applies parameter changes by operating the reaction and separation steps at elevated pressures (e.g., 4.2 MPa in step a, 1.6 MPa in step b) to suppress gas desorption and prevent flammable gas phase formation. This pressure parameter modification directly addresses the safety concern while the patent notes that standard pressure control equipment suffices, limiting the increase in device complexity.
2Reliability
If complete oxygen desorption is performed to prevent flammable gas phase, then safety is improved, but propene loss increases requiring additional recovery equipment
Solution Approach 1:
The patent applies partial action by desorbing only a portion of the dissolved oxygen from the organic phase (step c) rather than complete desorption. This partial oxygen removal is sufficient to prevent flammable gas phase formation while minimizing propene co-desorption and associated losses. The patent explicitly states that only a part of the oxygen needs to be desorbed, avoiding the need for extensive propene recovery equipment.
3Manufacturing precision
If propane separation from propene is implemented to improve product purity, then manufacturing precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies the extraction principle by removing propane from the process stream through the off-gas of the oxygen desorption step (step c). Propane, being more soluble in the liquid phase than oxygen, remains in the liquid stream while oxygen is extracted into the gas phase for removal. This selective extraction achieves product purity without requiring separate propane-propene separation equipment, as the patent notes propane is purged with the off-gas with little loss of propene.
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 safety by minimizing the formation of a flammable gas phase and reduces propene loss, enabling an economically viable and resource-efficient production of 1,2-propanediol without additional recovery steps.
Implementation Method 1
oxygen, formed by decomposition of hydrogen peroxide in step a)
Implementation Method 2
desorption of oxygen from the separated organic phase into a non-flammable gas such as nitrogen
Data Source
AI summary
A method for preparing 1,2-propanediol involves reacting propene with hydrogen peroxide, in the presence of a phase transfer catalyst and a heteropolytungstate, in a liquid two phase reaction mixture with an organic phase containing an alkylaromatic hydrocarbon solvent. The method then involves separating the reaction mixture into an aqueous phase containing 1,2-propanediol and an organic phase, recycling the oxygen depleted organic phase to the reaction, and recovering 1,2 propanediol from the aqueous phase. The reaction and separation are carried out in liquid flooded vessels at a pressure high enough to suppress desorption of gas from the liquid reaction mixture. The separated organic phase is contacted with a stream of a non-flammable gas to desorb from 10 to 75% of the oxygen dissolved in the organic phase into the stream of non-flammable gas, before recycling the organic phase which purges oxygen safely with little loss of propene.