Acetonitrile Separation Using Dehydration and Extraction Columns
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Solution Overview
Problem
Conventional acetonitrile separation processes struggle to effectively isolate acetonitrile from industrial streams containing impurities like acrylonitrile, methanol, water, allyl alcohol, and oxazole due to azeotrope formation and similar physical properties, leading to reduced separation efficiencies and lower product purities.
Innovation Solution
A multi-step process involving dehydration, distillation, extraction, and caustic treatment to separate acetonitrile, including dehydrating a feedstock stream in a first column, distilling in a second column, extracting the distillation bottoms in a third column with caustic treatment, and purifying the raffinate stream in subsequent columns to achieve high-purity acetonitrile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional distillation schemes are used to recover acetonitrile, then the separation process is simple, but the presence of impurities like methanol, water, allyl alcohol, and oxazole complicates acetonitrile isolation due to azeotrope formation and similar physical properties
Solution Approach 1:
The patent divides the separation process into multiple sequential distillation zones (first, second, and third distillation zones) operating at different pressures. Each zone targets specific impurities: the first zone removes light ends and some water, the second zone handles acetonitrile-water azeotrope, and the third zone removes heavy ends. This segmentation allows systematic removal of different impurity groups that form azeotropes, achieving high purity without requiring a single complex distillation step.
Solution Approach 2:
The patent employs pressure swing distillation, operating different distillation zones at varying pressures (atmospheric, sub-atmospheric, and super-atmospheric). By changing operating pressure, the relative volatility between acetonitrile and its azeotropic partners (especially water) changes, enabling separation of azeotropic mixtures that cannot be separated by conventional constant-pressure distillation. This parameter change is critical for breaking azeotropes and achieving the required purity.
2Manufacturing precision
If multiple distillation zones at varying pressures are used to improve acetonitrile purity, then product purity increases, but process complexity increases
Solution Approach 1:
The patent combines multiple distillation operations with different pressure conditions into an integrated separation train. The first, second, and third distillation zones are connected in sequence, with intermediate streams being recycled or reprocessed. This merging of operations allows the system to handle multiple impurity removal functions (light ends removal, azeotrope breaking, heavy ends removal) in a coordinated manner, achieving high purity while managing complexity through systematic integration rather than separate standalone units.
Solution Approach 2:
The patent uses intermediate streams and recycle loops between distillation zones. For example, the bottoms from the first distillation zone are fed to the second zone, and side draws are recycled back to previous zones for further purification. These intermediary streams act as mediators that transfer material between zones, allowing progressive purification while managing the complexity of multi-pressure operations through controlled material flow and intermediate storage.
3Use of energy by moving object
If conventional distillation is used, then energy consumption is moderate, but separation efficiency decreases due to azeotrope formation
Solution Approach 1:
The patent exploits phase transitions during distillation, particularly utilizing the vapor-liquid equilibrium changes that occur at different pressures. By operating at varying pressures, the boiling points and relative volatilities of components change, enhancing the phase separation efficiency. The pressure swing causes azeotropic compositions to shift, allowing more efficient separation in each zone. This phase transition exploitation improves separation efficiency without requiring excessive energy input, as the pressure changes are achieved through controlled compression and expansion rather than extreme temperature differences.
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 effectively reduces acrylonitrile content to low levels, enhances separation efficiency, and increases the purity and yield of acetonitrile, overcoming the challenges posed by impurities in conventional methods.
Implementation Method 1
dehydrating, e.g., at a pressure less than 150 kPa, a feedstock stream comprising acetonitrile, acrylonitrile, allyl alcohol, and water (and optionally methanol and hydrogen cyanide), in a dehydration (first) column to yield a dehydrated acetonitrile stream
Implementation Method 2
distilling the dehydrated acetonitrile stream in a lights (second) column to yield a distillate stream comprising lights and optionally oxazole, methanol, and/or acrylonitrile
Implementation Method 3
extracting the distillation bottoms stream in an extraction (third) column, optionally wherein an accelerator, e.g., methanol, is utilized during the extracting, to yield a raffinate stream comprising acetonitrile and less than 200 ppm, e.g., less than 50 ppm, acrylonitrile
Data Source
AI summary
A process for producing acetonitrile, the process comprising dehydrating a feedstock stream comprising acetonitrile, acrylonitrile, allyl alcohol, and water (and optionally methanol) in a dehydration (first) column to yield a dehydrated acetonitrile stream comprising acetonitrile and acrylonitrile, less than 1 wt % allyl alcohol, and less than 50 wt % water, and optionally hydrogen cyanide; distilling the dehydrated acetonitrile stream in a lights (second) column to yield a distillate stream comprising lights, and a bottoms stream comprising acetonitrile, acrylonitrile, water, and optionally hydrogen cyanide and acrylonitrile; extracting the distillation bottoms stream in an extraction (third) column to yield a raffinate stream comprising acetonitrile and less than 200 ppm acrylonitrile and an extract stream comprising water and acrylonitrile; purifying the raffinate stream to yield a product acetonitrile stream.