Rectisol Process Mercaptan Removal via Stripping Column
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Solution Overview
Problem
The existing Rectisol process for separating sulfur-containing components from methanol used as an absorbent in synthesis gas scrubbing struggles to effectively remove mercaptans and thiophenes, leading to continuous methanol losses due to reabsorption of mercaptans, necessitating a blow-down and make-up stream.
Innovation Solution
A plant and process incorporating a distillation column with a stripping column and heater to separate volatile components from the condensed top product, utilizing a stripping gas to strip mercaptans and thiophenes, and recycling condensed methanol to minimize methanol losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the existing Rectisol process is used to separate sulfur-containing components from methanol, then carbon dioxide and sulfur-containing accompanying gases can be separated from synthesis gas, but mercaptans and thiophenes cannot be effectively removed from the methanol
Solution Approach 1:
The separation process is divided into two distinct stages: a hot regeneration column for initial separation of sulfur-containing gases, followed by a stripping column for removal of mercaptans and thiophenes. This segmentation allows each column to be optimized for its specific function, achieving complete removal of all sulfur components including previously problematic mercaptans and thiophenes
Solution Approach 2:
A stripping gas is introduced as an intermediary substance in the stripping column to facilitate the removal of mercaptans and thiophenes from the methanol. The stripping gas acts as a mediator that selectively strips these components from the liquid methanol phase, enabling their separation without significant methanol loss
2Manufacturing precision
If a blow-down stream is continuously removed from methanol to limit mercaptan content, then mercaptan levels can be controlled, but methanol losses increase
Solution Approach 1:
The stripping column extracts mercaptans and thiophenes from the methanol using a stripping gas, separating these unwanted components without requiring continuous removal of methanol itself. This extraction process achieves mercaptan control while preserving methanol, eliminating the need for wasteful blow-down streams
Solution Approach 2:
The process changes the separation mechanism from physical blow-down to chemical stripping by introducing a stripping gas. This parameter change in the separation approach allows selective removal of mercaptans based on their chemical properties rather than simply venting methanol, thereby controlling mercaptan content while minimizing methanol loss
3Loss of energy
If the top product from hot regeneration column is condensed and recycled, then methanol can be recovered, but mercaptans are reabsorbed by the condensed methanol
Solution Approach 1:
The stripping column is positioned to act preliminarily on the condensed top product before it is recycled back to the hot regeneration column. By stripping mercaptans and thiophenes from the condensed methanol beforehand, the process prevents their reabsorption in the recycling loop, enabling both methanol recovery and mercaptan removal
Solution Approach 2:
The stripping column operates continuously on the condensed top product stream, ensuring that mercaptans are continuously removed from the recycled methanol. This continuous stripping action maintains mercaptan-free methanol in the recycling loop, allowing uninterrupted methanol recovery without mercaptan reabsorption
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 the efficient separation of mercaptans and thiophenes from methanol, reducing methanol losses and improving the economic viability of the Rectisol process by recycling condensed methanol back into the system.
Implementation Method 1
a distillation column (1) in which laden methanol is freed of its load by distillation
Implementation Method 2
The unwanted accompanying substances that are separated from the synthesis gas by the Rectisol process are mainly the accompanying gases carbonyl sulfide (COS), hydrogen sulfide (H2S) and carbon dioxide (CO2), but mercaptans are frequently also present in the synthesis gas, and are likewise absorbed by the methanol and hence separated from the synthesis gas
Implementation Method 3
a heat exchanger for the introduction of heat into the methanol
Implementation Method 4
heat exchangers for the cooling of the top product by cooling water, heat exchangers for the cooling of the top product by means of a coolant circuit
Implementation Method 5
liquid separators for separation of the condensate from the top product
Implementation Method 6
the circuit for the top product further comprises a stripping column (15) for separation of volatile components from the condensate
Data Source
AI summary
Plant and process for separation of sulfur-containing components, H2S, COS and mercaptans from methanol which is used as absorbent within the Rectisol process by hot regeneration of the methanol laden in the absorption and an additional step for separation of the mercaptans from the methanol by stripping.