ChE453 – Capstone Project (Group 4)
Department of Chemical Engineering, Indian Institute of Technology Kanpur
✨ This project presents the design, simulation, and optimisation of a continuous industrial process for the production of Methyl Benzoate via the esterification of Benzoic Acid with Methanol.
Methyl Benzoate is a high-value aromatic ester widely used in fragrances, flavouring agents, solvents, and as an intermediate in pharmaceutical and agrochemical industries.
🔁 The project evolves systematically from process selection and thermodynamic validation to flowsheet development, separation sequencing, energy integration, cogeneration, and economic optimisation, culminating in a technically feasible and economically attractive plant design.
Core Reaction:
Benzoic Acid + Methanol ⇌ Methyl Benzoate + Water
🔬 Key characteristics:
- Reversible, equilibrium-limited esterification
- Acid-catalysed (HCl); molar ratio Methanol : Benzoic Acid : HCl = 16.59 : 2.7 : 0.1215 (Roberts & Urey, 1938)
- Liquid-phase operation at 25 °C, 1 bar
- Excess methanol used to shift equilibrium toward ester formation and act as solvent/carrier
✅ Identify and justify a suitable industrial process route for Methyl Benzoate production
✅ Select and validate an appropriate thermodynamic model
✅ Develop and compare alternative separation sequences
✅ Integrate reactor, distillation, heat exchangers, and utilities into a unified flowsheet
✅ Apply pinch analysis for heat exchanger network (HEN) design
✅ Integrate a cogeneration (Rankine cycle) system for energy recovery
✅ Perform economic and sensitivity analysis to maximise profitability
| Stream | Component | Flow |
|---|---|---|
| Feed | Methanol | 61.37 kmol/hr (fresh) |
| Feed | Benzoic Acid (0.5 mass% Phthalic Acid impurity) | 57.81 kmol/hr (fresh) |
| Product | Methyl Benzoate | 57.77 kmol/hr |
Market prices (used in economic analysis):
- Methanol: USD 370/MT (Asia Pacific, 2025)
- Benzoic Acid: USD 1,010/MT (FOB Shanghai, Q1 2025)
- Methyl Benzoate: USD 2,200/MT (industrial-grade, Q4 2023)
- Esterification route selected based on industrial relevance
- Feed specified: Methanol (16.95k moles), Benzoic Acid (2.7k moles with 0.5 mass% Phthalic Acid)
- Reactor converts feeds to ~7,435 moles each of Methyl Benzoate and Water at 80% single-pass conversion (assumed pending kinetics)
- Market study conducted — Methyl Benzoate market projected to reach USD 2.26 billion by 2032 at 6% CAGR
- Preliminary break-even analysis: k ≈ 437 (scaling factor), profit multiplier ≈ 1.74×
- Thermodynamic models evaluated: NRTL, Peng–Robinson, UNIQUAC
- ⭐ UNIQUAC selected based on best fit to experimental Txy data for Water–Methanol binary
- Azeotrope analysis (UNIQUAC, 1 bar): No azeotropes found — confirms conventional distillation feasibility
- Operating conditions fixed: 25 °C, 1 bar, high methanol excess (molar ratio 16.59 : 2.7 : 0.1215)
- Two four-column distillation sequences developed and compared in Aspen (shortcut method):
Method 1 — Early Methanol Recovery:
- C1 strips methanol overhead; C2 removes water; C3 recovers MEB; C4 polishes benzoic acid/PTH
- Methanol recovery: ~99.0% | MEB recovery: ~98.01% | Benzoic acid recovery: ~98.01%
- Total reboiler duty: 49,902 kW (C1 bears ~80% of load at 40,099 kW)
Method 2 — Load-Distributed Separation:
- C1 sends MeOH+H₂O overhead; C2 is main methanol column; C3 and C4 target MEB and benzoic acid
- Methanol recovery: ~98.90% | MEB recovery: ~98.01% | Benzoic acid recovery: ~98.01%
- Total reboiler duty: 48,931 kW (~2% lower than Method 1, more evenly split between C1 and C2)
- 🏆 Method 2 selected due to ~971 kW lower total reboiler duty, reduced peak column load, and better utility integration potential
Complete material flowsheet developed in Aspen Plus with:
Distillation Columns (all 20 trays, rigorous RadFrac):
| Column | Separation | Feed Stage | Reflux Ratio | Reboiler Duty | Condenser Duty |
|---|---|---|---|---|---|
| C1 | MEB + Benzoic acid from MeOH + Water | 11 | 0.0187 | 22,532 kW | −17,596 kW |
| C2 | Methanol (distillate) from Water (bottoms) | 14 | 1.7256 | 38,340 kW | −38,109 kW |
| C3 | Methyl Benzoate (distillate) from Benzoic acid + PTH | 11 | 0.3033 | 4,291 kW | −4,436 kW |
| C4 | Benzoic acid (distillate) from Phthalic acid | 10 | 1.1913 | 25 kW | −19 kW |
Heat Exchangers:
| Unit | Duty | Hot Side → Cold Side |
|---|---|---|
| HX1 | ~1,205 kW | Mixed water stream → Cooling water recycle |
| HX2 | 9,983 kW | Methanol distillate D2 (64 → 35 °C) → Rankine condensate |
| HX3 | ~2,792 kW | MEB distillate D3 (191 → 30 °C) → Cooling water recycle |
⚡ Cogeneration (Rankine Cycle) — Three-stage steam turbine system:
| Stage | Pressure Out | Power Generated |
|---|---|---|
| HP Turbine | 40 bar | 1,540 kW |
| MP Turbine | 10 bar | 7,013 kW |
| LP Turbine | 3 bar | 4,693 kW |
| LLP Turbine | 1 bar | 3,372 kW |
| Total | — | ~16,618 kW |
- Mass balance verified across all columns and heat exchangers (total in = total out)
- Cooling water loop designed with recycle; makeup stream required to maintain 40 °C return temperature
- Practical challenges documented: lack of detailed reaction kinetics limited reactor–HEN coupling
- Type: Plug Flow Reactor (PFR) with recycle
- Dimensions: Length = 40 m, Diameter = 8 m
- Operating temperature: 63.4 °C (isothermal)
- Heat duty: −285.4 kW (exothermic)
- Residence time: 2.57 hr (within typical industrial range of 1–5 hr)
- Average velocity: 0.00433 m/s | Reynolds number: 36,961 → Turbulent flow (Re ≥ 4,000) ✅
- Single-pass conversion: 58% | Overall conversion with recycle: 99.63%
- Fresh feeds: Methanol 61.37 kmol/hr, Benzoic Acid 57.81 kmol/hr | Product: 57.77 kmol/hr MEB
| Parameter | Value |
|---|---|
| Shell type | E-type (single pass) |
| Tube OD / ID | 20 mm / 16 mm |
| Tube length | 4.88 m (standard) |
| Number of tubes | 2,425 (triangular pitch, 25 mm) |
| Number of baffles | 5 (single segmental, 25% cut, 288 mm spacing) |
| Shell diameter | 1,441 mm |
| Tube-side fluid | Methanol (hot), 64.2 → 35 °C |
| Shell-side fluid | Cooling water, 25 → 40 °C |
| Heat duty | 9,983 kW |
| HX area (calculated) | 735.3 m² |
| UA (calculated) | 625 kW/K |
| Tube material | CuNi 90/10 (TEMA Class B, ASME Code Sec VIII Div 1) |
Manual calculations closely matched Aspen EDR results (within ~2%).
- ΔT_min chosen: 10 °C
- 5 process streams included:
| Stream | Type | mCp (kW/°C) | Tin | Tout | Duty (kW) |
|---|---|---|---|---|---|
| D2 (Methanol distillate) | Hot | 341.89 | 64 °C | 35 °C | 9,915 |
| D3 (MEB distillate) | Hot | 4.668 | 191 °C | 35 °C | 728 |
| D4 (Benzoic acid distillate) | Hot | 1.733 | 248 °C | 35 °C | 369 |
| LIQOUT (Reactor outlet) | Cold | 374.54 | 50 °C | 54 °C | 1,498 |
| MIXOUT (Reactor inlet) | Cold | 348.69 | 25 °C | 50 °C | 8,717 |
- Cascade diagram result: No pinch point — net excess energy throughout; all surplus transferred to cold utility
- Minimum heat exchangers required: 5 (= N_streams + N_utilities − 1)
- HEN designed with 5 exchangers (HEN1–HEN5); streams matched by mCp_hot ≤ mCp_cold rule
- Cooling water loop optimised with makeup block to achieve zero fresh cooling water requirement
- Makeup block targets: BACWH = 40 °C, MBCWH = 40 °C, net fresh water makeup = 0 tonne/hr
- Cooling tower simulated with air/water mass balance verified (total in = 25,082,416 kg/hr = total out)
Dominant design variables explored via Fortran-coded objective function in Aspen:
| Variable | Optimum Value | Observation |
|---|---|---|
| Reactor diameter | 13.68 m | Clear profit maximum |
| Reactor length | 59.46 m | Broad optimum |
| Column 2 bottom purity | 0.95 | Higher purity reduces profit (higher reboiler duty) |
| Column 1 top purity | 0.95 | Same trend; minimum purity constraint applied |
| Column 2 top purity | 0.99 | Higher methanol recovery improves profit monotonically |
- Plug Flow Reactor (PFR) with recycle — turbulent regime (Re = 36,961), residence time 2.57 hr
- Four-column distillation train (Method 2 sequence)
- Shell-and-tube HX designed to TEMA Class B / ASME standards (CuNi 90/10, 2,425 tubes)
- Heat exchanger network with ΔT_min = 10 °C, 5 exchangers, no pinch point
- Three-stage Rankine cogeneration generating ~16,618 kW of electricity
- Cooling water loop with zero freshwater makeup at steady state
- Aspen Plus simulation (UNIQUAC thermodynamics) supported by manual design validation
| Metric | Value |
|---|---|
| Total Capital Cost (TCC) | $2.98 × 10⁷ |
| Yearly Operating Cost (YOC) | $1.39 × 10⁸ |
| Raw Materials Cost | $1.06 × 10⁸ |
| Annual Revenue | $2.14 × 10⁸ |
| Total Annualised Cost (TAC) | $1.49 × 10⁸ |
| Total Annual Profit (TAP) | $6.46 × 10⁷ |
| Payback Period | ~3 years |
The process is economically viable under realistic market assumptions (methanol at $370/MT, benzoic acid at $1,010/MT, methyl benzoate at $2,200/MT, operating 7,200 hr/yr).
Limitations:
- Lack of detailed reaction kinetics prevented accurate temperature-dependent reactor–HEN coupling; equilibrium reactor (R-Equil) used as approximation
- Some Aspen EDR settings could not be fully replicated in manual heat exchanger calculations
- Cooling water loop closure required simplifying assumptions (makeup block approach)
Future work:
- Kinetic parameter estimation (rate constant k, activation energy Ea) for Fischer esterification
- Rigorous PFR modelling with temperature profiles
- Dynamic simulation and process control studies
- Optimisation of HEN retrofit to incorporate reactor heat duties more accurately
▶ Watch Endterm Presentation video
| Member | Roll No. |
|---|---|
| Aaditya Amlan Panda | 220007 |
| Abhijit Dalai | 220030 |
| Adarsh Pal | 220054 |
| Akash Kumar Gupta | 220095 |
| Kushagra Tiwari | 220574 |
| Saurabh Yadav | 220991 |
| Snehil Tripathi | 221071 |
| Tushar Verma | 221147 |
✨ This repository documents the complete academic capstone journey — from conceptual process selection to final techno-economic evaluation.