Melamine Purification via CO2 Stripping and NH3 Segmentation
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Solution Overview
Problem
Current industrial processes for producing high-purity melamine through urea pyrolysis consume high amounts of raw materials and utilities, such as vapor, cooling water, and electric energy, primarily due to inefficient CO2 removal and recycling methods.
Innovation Solution
A low-energy-consumption process involving separate treatment of the biphasic liquid/gas effluent from urea pyrolysis, where CO2 is removed from both the anhydrous off-gas and raw melamine using anhydrous NH3, followed by washing with an aqueous solution to recover melamine, and subsequent crystallization to achieve high-purity melamine production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If CO2 is removed from the aqueous effluent using conventional stripping methods, then melamine purity is improved, but energy consumption increases
Solution Approach 1:
The effluent stream is segmented into two separate streams: an aqueous stream containing melamine and impurities, and a gas stream containing CO2 and NH3. CO2 removal is applied selectively to the aqueous stream through targeted stripping, while the gas stream is routed to the urea plant for ammonia recovery. This segmentation avoids the energy-intensive conventional approach of stripping CO2 from the entire effluent mixture, reducing vapor consumption while maintaining melamine purity.
Solution Approach 2:
CO2 is extracted and removed from the aqueous effluent stream using a stripping column where ammonia gas is introduced to strip CO2 from the liquid phase. The extracted CO2 is then separated and routed to the urea plant, while the depleted aqueous stream proceeds to crystallization. This selective extraction of CO2 from the aqueous phase eliminates the need for energy-intensive removal from the entire biphasic effluent.
2Quantity of substance
If the entire biphasic effluent is cooled and collected in aqueous ammonia medium, then melamine recovery is improved, but cooling water consumption and process complexity increase
Solution Approach 1:
The gas phase containing CO2 and NH3 is separated and extracted from the biphasic effluent before the aqueous phase undergoes cooling and crystallization. This extraction eliminates the need to cool the entire biphasic mixture, reducing cooling water consumption. The separated gas stream is directly routed to the urea plant for ammonia recovery, while only the aqueous stream requiring cooling proceeds to the crystallization section.
Solution Approach 2:
The effluent is segmented into gas and liquid phases that are treated separately. The gas phase is diverted to the urea plant without requiring extensive cooling, while the liquid phase undergoes targeted cooling and crystallization. This segmentation reduces the total volume requiring cooling water, thereby reducing energy loss while maintaining melamine recovery efficiency.
3Manufacturing precision
If CO2 is removed from the effluent, then melamine purity is improved, but process complexity and equipment investment increase
Solution Approach 1:
The stripping column serves multiple functions: it removes CO2 from the aqueous effluent to improve melamine purity, simultaneously generates ammonia gas that is routed to the urea plant for ammonia recovery, and prepares the depleted aqueous stream for crystallization. This multi-functionality eliminates the need for separate equipment for CO2 removal and ammonia recovery, reducing overall process complexity and equipment investment.
Solution Approach 2:
The CO2 removal process is merged with the existing urea plant ammonia recovery system. The stripping column integrates CO2 stripping with ammonia generation, and the resulting gas stream is directly fed to the urea plant. This merging eliminates redundant equipment and simplifies the overall process while maintaining high melamine purity through effective CO2 removal.
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 process significantly reduces energy consumption by 60% for vapor and 55% for cooling water, simplifies purification, and increases melamine yield, while using more economical materials and reducing investment costs.
Implementation Method 1
putting the above liquid stream of raw melamine in contact with a stream of gaseous anhydrous NH3 and forming a liquid stream of raw melamine impoverished in CO2 and a second stream of anhydrous off-gas comprising NH3, CO2 and melamine vapour
Implementation Method 2
putting the above first and second anhydrous off-gas streams in contact with at least one aqueous washing stream and forming an aqueous stream comprising melamine, NH3 and CO2
Implementation Method 3
removing from said aqueous stream comprising melamine, NH3 and CO2, at least a part of the CO2 contained therein
Implementation Method 4
recovering the melamine contained in said liquid stream of raw melamine impoverished in CO2 and the melamine contained in said aqueous stream comprising melamine and impoverished in CO2 through crystallization by cooling
Data Source
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AI summary
A process for the production of high-purity melamine comprising: a) separating a biphasic liquid-gas effluent product in a pyrolysis reaction of urea in a liquid stream of raw melamine (3) and a first stream of anhydrous off-gas (15); b) putting said liquid stream (3) in contact with a stream of gaseous anhydrous NH3 (13) and forming a liquid stream of raw melamine impoverished in CO2 (4) and a second stream of anhydrous off-gas (16); c) putting said first and second anhydrous off-gas streams (15,16) in contact with at least one aqueous washing stream (32) and forming an aqueous stream (20) and a stream of damp off-gas (19); d) removing from said aqueous stream (20) at least a part of the CO2 contained therein, and forming a stream (22) comprising the CO2 removed and an aqueous stream (21) comprising melamine and impoverished in CO2; e) recovering the melamine contained in said liquid stream (4) and the melamine contained in said aqueous stream (21) through crystallization by cooling, with the formation of a stream (10) of crystallized melamine and a stream (23) of mother liquor. The present invention also relates to the equipment for effecting the above process. img id="iaf01" file="imgaf001.tif" wi="247" he="132" img-content="drawing" img-format="tif"/>