Methanol Purification via Mid-Column Acid Addition
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Solution Overview
Problem
Existing methanol purification systems from kraft pulping processes face challenges in separating methanol due to the presence of azeotropes like dimethyl disulphide and dissociable sulphur compounds, which are difficult to remove through distillation, and risk column fouling from acid addition.
Innovation Solution
A method and apparatus that involves a dedicated condensing system, acid addition at the mid-point of a topping column to control pH without reacting with ammonia, followed by a rectification section with countercurrent steam flow through packing to achieve high-purity methanol recovery, avoiding column fouling and effectively removing impurities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If acid is added to the liquid feed to the distillation column to lower pH and remove dissociable sulphur compounds, then the removal of sulphur compounds is improved, but column fouling occurs due to reaction with ammonia
Solution Approach 1:
The acid is added at a location above the feed introduction point, performing the pH adjustment action before the liquid reaches the section where ammonia concentration is highest. This preliminary acidification allows sulphur compound removal while preventing excessive fouling in the lower column sections.
Solution Approach 2:
Different pH conditions are created at different locations in the column. The upper section maintains higher pH for ammonia removal, while the lower section has lowered pH for sulphur compound removal, allowing both functions to occur simultaneously without mutual interference.
2Quantity of substance
If distillation is used to separate methanol from foul condensate, then methanol concentration is improved, but separation is inhibited by azeotropes with dimethyl disulphide
Solution Approach 1:
The pH parameter is changed and controlled at different locations in the distillation column to alter the chemical state of sulphur compounds. By lowering pH in the lower section, dissociable sulphur compounds are converted to non-dissociated forms that can be separated, breaking the azeotropic relationship and enabling high-purity methanol separation.
3Quantity of substance
If steam stripping system is used to remove methanol from foul condensate, then methanol recovery is improved, but fluctuations in evaporator operation affect SOG quantity and quality
Solution Approach 1:
The distillation column is divided into functionally distinct sections: an upper section for ammonia removal and a lower section for sulphur compound removal and methanol concentration. This segmentation allows each section to handle specific contaminants independently, stabilizing the overall SOG composition against evaporator fluctuations.
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 recovery and purification of methanol to at least 99.85 wt% purity, enabling its use within the kraft pulping process and potential sale, while maintaining system stability and preventing column fouling.
Implementation Method 1
Most such systems use some form of distillation to separate methanol from other compounds. Distillation separates the components of a solution by partial vapourization of the mixture and separate recovery of vapour and residual liquid.
Implementation Method 2
These compounds can dissociate under certain conditions, making them all but impossible to remove from SOG by simple distillation. Controlling the pH of the liquid phase in the distillation column is therefore an effective way to remove these compounds in a distillation process.
Implementation Method 3
a rectification section with countercurrent steam flow through packing to achieve high-purity methanol recovery
Data Source
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AI summary
The invention relates to a method and apparatus to recover and purify methanol from gases produced in the digester during the kraft pulping process. The gas is typically recovered as a foul gas (called stripper off gas or SOG) comprising methanol, water and various other contaminants. The gas is then treated with successive decanting and distillation steps to remove impurities, thereby producing highly purified methanol.