Melamine Synthesis via Fluidized Bed Reactor and Low-Pressure Cycle Gas Recycling
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Solution Overview
Problem
Current melamine synthesis processes have limitations in single-line capacity, energy consumption, and product purity, with complex and energy-intensive removal processes, and unclear formation mechanisms of by-products and conversion products.
Innovation Solution
A modified low-pressure process using a fluidized bed reactor with a catalyst and a specific gas composition of ammonia and CO2, where the reaction gas is cooled and filtered to separate melamine from by-products, and a portion of the cycle gas is recycled as fluidizing gas to optimize melamine synthesis and reduce apparatus volume and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the Linz-Chemie process is used with a sand fluidized bed and fixed bed reactor, then melamine can be synthesized at low pressure, but the workup process becomes relatively complicated with multiple solid/liquid separation stages
Solution Approach 1:
The invention extracts and removes the complex solid/liquid separation stages from the workup process. By using a fluidized bed reactor that directly produces dry melamine powder, the process eliminates the need for multiple separation stages, simplifying the overall workflow while maintaining low pressure conditions.
Solution Approach 2:
The fluidized bed reactor performs both synthesis and product separation functions simultaneously. The reactor design allows melamine to be produced directly in a usable dry powder form, making the system self-sufficient and eliminating the need for separate complex workup equipment.
2Productivity
If the DSM-Stamicarbon process is used with aluminum silicates or zeolite-containing catalysts, then single-line capacity increases to approx. 80000 t/year, but the removal process becomes complicated requiring water quenching and multiple separation stages
Solution Approach 1:
The invention removes the water quenching and multiple separation stages from the process. By using a fluidized bed reactor with appropriate catalyst, melamine is produced directly as dry powder, eliminating the need for complex removal infrastructure while maintaining high productivity.
Solution Approach 2:
The invention changes the physical state parameter of the product output. Instead of producing gaseous melamine that requires water quenching to condense, the process produces dry melamine powder directly, fundamentally changing the workup requirements while maintaining high capacity.
3Manufacturing precision
If the BASF process is used with fluidized bed and crystallizer, then melamine can be desublimed to fine crystalline powder, but the process requires complex gas circulation systems with urea scrubbers and multiple cooling stages
Solution Approach 1:
The invention extracts and removes the complex gas circulation system, urea scrubbers, and multiple cooling stages. The fluidized bed reactor directly produces melamine with desired crystal morphology, eliminating the need for separate crystallization and gas treatment equipment.
Solution Approach 2:
The invention merges the synthesis and crystallization functions into a single fluidized bed reactor. The reactor conditions are optimized to produce melamine with fine crystalline powder morphology directly, combining multiple process steps into one operation.
4Ease of manufacture
If high-pressure process is used at more than approx. 80 bar and temperatures of more than 370° C., then melamine can be synthesized in a noncatalytic manner, but the single-line capacity remains comparatively low at approx. 30000 t/year
Solution Approach 1:
The invention changes the pressure parameter from high pressure (>80 bar) to low pressure conditions. By using a fluidized bed reactor with catalyst at low pressure, the process achieves both simplicity and high productivity, producing approx. 80000 t/year capacity.
Solution Approach 2:
The invention uses composite catalyst materials in the fluidized bed reactor that enable high productivity at low pressure. The catalyst composition is optimized to facilitate the reaction under milder conditions while maintaining high capacity.
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
The process achieves higher single-line capacities, reduced energy consumption, and maintains high melamine purity, with improved crystal morphology and reduced formation of by-products, enabling more efficient and cost-effective melamine production.
Implementation Method 1
The preparation of melamine by decomposition of urea is a known reaction which is utilized in several variants by the chemical industry... in a heterogeneous catalysis
Implementation Method 2
The low-pressure process is generally performed at pressures of from approx. 1 bar (abs.) to approx. 10 bar (abs.) and temperatures of from 370 to 430° C. in a heterogeneous catalysis
Implementation Method 3
The reaction gas comprising gaseous melamine is cooled ('quenched') with water and the melamine is thus removed from the reactor gas
Implementation Method 4
The hot, gaseous melamine, in contrast to the Linz-Chemie and DSM-Stamicarbon process, is desublimed in a crystallizing apparatus (also known as 'crystallizer') by cooling to approx. 200° C., and a fine crystalline powder is obtained
Data Source
AI summary
Process for preparing melamine by converting urea in the presence of a solid catalyst in one reactor or in a plurality of reactors connected in series in the temperature range from 370° C. to 430° C., cooling and filtering the gas formed in the urea conversion, removing the melamine by desublimation and recycling a portion of the gas present after the melamine removal (“cycle gas”) into the reactor or the reactors, which comprises performing all of the above stages at a pressure in the range from 4 bar abs. to 10 bar abs.