Chemical Engineering Sustainable Manufacturing Processes Engineering Design ASPEN Plus V15

Novel Sustainable Process Designfor Production of Adipic Acid

An alternative approach to industrially produce Adipic Acid in an operationally and environmnentally safer way through Cyclohexene & H2O2 pathway.

The Problem With Conventional Process
~12.3%
Global N₂O Share
of all global N₂O emissions are driven by Adipic Acid production alone.
(~0.3kg N₂O / kg of AA)
~370M Tonnes
Annual CO₂-e Emissions
It is equivalent to the entire carbon footprint of the Netherlands !
Photochemical Smog1.02 kg O₃-e / kg of AA
Acidification0.06 kg SO₂-e / kg of AA
⚠ Conventional Route Operational Hazards
Generation of highly toxic NOₓ gases
Extremely corrosive operational environment
High risk of exothermic thermal runaway
APPROACH & ENGINEERING DESIGN
Designed & Simulated in ASPEN Plus V15
01
Foundation
  • Thermodynamic Property Package selection and VLE validation for complex non-ideal mixtures involved in our plant.
  • Binary interaction parameter estimation and tuning via regression.
  • Integrated sub-critical Co-Generation Power Plant & Cooling Water loop for Plant's utility needs.
  • Implemented Heat Exchangers across the plant & utilised Heat Integration to minimise external energy needs.
02
Core Process Synthesis
  • Engineered an Multi-Tubular Capillary Microreactor utilising the principle of Process Intensification for enhanced HT-MT for given reaction kinetics.
  • Designed a Heterogeneous Azeotropic Distillation setup for complex Cyclohexene-Water separation.
  • Established plant-wide recycle loops & purge streams for maximising closed-loop raw materials recovery.
03
Process Dynamics, Economics & Safety
  • Conducted rigorous equipment sizing along with detailed Techno-Economic Analysis to assess economic feasibility.
  • Implemented plant-wide control architectures along with dynamic simulation of the PFD to validate operational stability.
  • Evaluated environmental impact and operational hazards against the conventional route using the Inherent Safety Design framework.
If I were to talk about only one technique which sits at the heart of this Process Design, it's going to be Sensitivity Analysis. It was utilised at every major cornerstone of this process, be it deciding the operating temperature or number of capillaries in the Microreactor, or optimising recycle loops to minimise feed wastage.

It tells you how the output variables (e.g. reactor conversion) of the model (e.g. the microreactor) respond on changing the inputs (e.g. Temperature, Pressure, No. Of Capillaries, etc.). It aids the user in getting more out of less by making better data-driven design tradeoffs & removing the guesswork.
Outcomes & Takeaways
Key Performance Indicators
99.8%
Polymer-Grade Purity
100%
NOₓ Elimination
96.7%
H₂O₂ Conversion
98.0%
Cyclohexene Recovery
Economic Feasibility
2.5 Years
Capital Payback Period
Profit/Investment Ratio (POI) 7.7x
Microreactor Design
245x Intensification
Surface-Area-to-Volume Ratio
Single Tube4.08 m⁻¹
60k Capillaries 1,000 m⁻¹
Bottlenecks In The Alternative Route

If this alternative chemistry is potentially highly profitable and eliminates NOₓ why hasn't the industry tried to adopt this pathway? The simulation represents an idealized thermodynamic envelope, but physical pilot scale-up will introduce some major problems:

  • Capillary Fouling: The 245x intensification relies on 60,000 micro-tubes. Even minor catalyst degradation or Adipic Acid solidification will cause fouling, leading to high pressure drops and plant downtime.
  • H2O2 Logistics: While a ‘green’ oxidant, sourcing, transporting, and storing industrial volumes of 90% conc H2O2 is very expensive (& dangerous on par) compared to legacy HNO3 feed.
  • Azeotropic Column Stability & Operation: The heterogeneous azeotropic separation of Cyclohexene/Water is highly sensitive. Minor fluctuations in a pilot plant could easily destabilize the column. This was evident in the ASPEN Plus simulation as well where it took a lots of efforts to converge the column properly as well as the dynamic PFD simulation.

Conclusion & Further Takeaways: This simulation successfully validates the potential technical and economic viability of this alternate route to produce adipic acid in a zero-emission fashion. While the capillary microreactor provides the massive process intensification required to make the phase transfer catalysis feasible, to move beyond the PFDs in ASPEN, further experimental pilot-scale studies are necessary to assess real-world operations and practicality of the process.


If you have access to ASPEN Plus software, then do check out the simulation file in the GitHub repository below.

GitHub Repository →