Methanol Separation from Oxygenates via Water Extractive Distillation
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Solution Overview
Problem
The methanol-to-olefins (MTO) process generates significant quantities of water and oxygenate byproducts, such as acetone, acetaldehyde, and methyl ethyl ketone, which are difficult to separate from methanol due to similar volatilities, leading to operational difficulties and increased recovery costs.
Innovation Solution
The process involves adding water to separate streams to enhance the volatility of oxygenate byproducts relative to methanol, using distillation columns to separate methanol from these byproducts, with initial water separation concentrating hydrocarbon oxygenates and subsequent water addition in distillation columns facilitating their separation from methanol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional distillation is used to separate methanol from oxygenate byproducts, then separation is attempted, but the similar volatilities of methanol and byproducts like acetone, acetaldehyde, and MEK make separation difficult and inefficient
Solution Approach 1:
The patent uses water as an intermediary substance in extractive distillation. Water is introduced into the distillation column to selectively interact with methanol through hydrogen bonding, changing the relative volatility relationships. This intermediary substance enables separation of methanol from oxygenate byproducts that have similar volatilities, resolving the technical contradiction between separation efficiency and process complexity.
Solution Approach 2:
The patent changes the physical-chemical parameters of the separation system by introducing water, which alters the volatility parameters of the components. The relative volatility between methanol and oxygenate byproducts is modified through the presence of water, enabling effective separation that would not be achievable with conventional distillation alone.
2Productivity
If water is removed from the MTO process stream, then olefin production is maintained, but significant quantities of water are released (2 mols per mol of ethylene, 3 mols per mol of propylene)
Solution Approach 1:
The patent converts the harmful effect of water release into a beneficial separation mechanism. The water that would normally be a waste product or operational difficulty is instead utilized as the separating agent in extractive distillation. This transforms the water release issue from a disadvantage into the key mechanism enabling efficient methanol recovery and oxygenate byproduct separation.
3Productivity
If unconverted methanol and DME are recovered for recycle, then overall high yields are achieved, but oxygenate byproducts are also recycled and build up in the recycle streams
Solution Approach 1:
The patent extracts oxygenate byproducts from the recycle stream using extractive distillation with water. By taking out the byproducts (acetone, acetaldehyde, MEK) that do not readily convert over MTO catalyst, the system prevents their accumulation in the recycle streams while maintaining high methanol recovery for continuous recycling, thus resolving the contradiction between productivity and byproduct accumulation.
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 efficient recovery of methanol and oxygenates, achieving at least 99 wt% recovery of hydrocarbon oxygenates and 95 wt% recovery of methanol, reducing operational challenges and increasing separation efficiency.
Implementation Method 1
addition of water to a mixture of oxygenates increases their volatility relative to methanol
Implementation Method 2
using distillation columns to separate methanol from these byproducts
Data Source
AI summary
We have discovered that addition of water to a mixture of oxygenates increases their volatility relative to methanol. A process and apparatus are disclosed for separating methanol from other oxygenates. Water is separated from a stream comprising water, methanol and at least one other oxygenate to provide a water rich stream and a methanol and oxygenate rich stream. The methanol and oxygenate rich stream and water are fed to a column to provide an oxygenate rich stream and a methanol and water extract stream. The methanol and water can then be readily separated from each other.