How to simulate cold-methanol co2 absorption at 30 bar (srk + huron-vidal)
The Rectisol idea — CO₂ dissolves strongly in methanol at -35 C and 30 bar while methane does not — on the one Gᴱ-mixing package whose parameters were regressed for the rule: SRK with Huron-Vidal mixing driven by Equinor NeqSim's Apache-2.0 set (methanol/CO₂, methanol/methane fitted at infinite pressure), not by the low-pressure NRTL binaries the other Gᴱ packages borrow. 100 mol/s of 30% CO₂ gas against 150 mol/s of cold methanol: the treated gas comes out at 99.9% methane with 0.08% CO₂, the rich methanol holds 17 mol% CO₂, and a first-stage flash to 2 bar releases 6.3 mol/s of 97% CO₂ — a real Rectisol regenerates in several flash stages plus stripping, which is why this solvent still carries 14% CO₂. K-values on the package: CO₂ 0.60 at 238 K against plain SRK's 1.64 (the mixing rule is the whole difference), methane 3100. Two things worth knowing: the lean methanol carries 0.1% dissolved methane on purpose — the cubic K-value refinement collapses onto the trivial solution when a gas is seeded at the 1e-4 placeholder the Kremser absorber uses, and that K of 1 sent 27 mol/s of methane into the solvent before the seed was made physical (recorded in flowsim/solver/ as an open item); and the absorber is a Kremser stage model at the mean of the two inlet temperatures.
- 1Open the ready-made model
Open the "Cold-methanol CO2 absorption at 30 bar (SRK + Huron-Vidal)" model in the MaximaLabs workspace — no install, no license. It loads live on the canvas, ready to edit and run.
- 2Confirm the thermodynamics
This process is modeled with the SRK-HURON-VIDAL property package over methane, co2, methanol — already selected, so the phase equilibrium and enthalpy are physically consistent from the first run.
- 3Review the flowsheet
The flowsheet chains ABS, Letdown, Flash Regen. Every block is a real, solvable unit op you can reconfigure on the canvas.
- 4Run the simulation
Click Run. The deterministic solver converges the material and energy balances (recycles included) and fills the live stream table — the AI never invents a number.
- 5Read the results and iterate
Inspect the converged streams, tweak a spec, and re-run — or ask the AI copilot to explain a result or diagnose a failed solve in plain English.
- Thermodynamics
- SRK-HURON-VIDAL
- Components
- methane, co2, methanol
- Unit operations
- ABSLetdownFlash Regen
Opens live on the canvas — free, no install.
Explore the model & flowsheetFrequently asked questions
- What does the Cold-methanol CO2 absorption at 30 bar (SRK + Huron-Vidal) model simulate?
- The Rectisol idea — CO₂ dissolves strongly in methanol at -35 C and 30 bar while methane does not — on the one Gᴱ-mixing package whose parameters were regressed for the rule: SRK with Huron-Vidal mixing driven by Equinor NeqSim's Apache-2.0 set (methanol/CO₂, methanol/methane fitted at infinite pressure), not by the low-pressure NRTL binaries the other Gᴱ packages borrow. 100 mol/s of 30% CO₂ gas against 150 mol/s of cold methanol: the treated gas comes out at 99.9% methane with 0.08% CO₂, the rich methanol holds 17 mol% CO₂, and a first-stage flash to 2 bar releases 6.3 mol/s of 97% CO₂ — a real Rectisol regenerates in several flash stages plus stripping, which is why this solvent still carries 14% CO₂. K-values on the package: CO₂ 0.60 at 238 K against plain SRK's 1.64 (the mixing rule is the whole difference), methane 3100. Two things worth knowing: the lean methanol carries 0.1% dissolved methane on purpose — the cubic K-value refinement collapses onto the trivial solution when a gas is seeded at the 1e-4 placeholder the Kremser absorber uses, and that K of 1 sent 27 mol/s of methane into the solvent before the seed was made physical (recorded in flowsim/solver/ as an open item); and the absorber is a Kremser stage model at the mean of the two inlet temperatures.
- Which thermodynamic method does it use?
- The SRK-HURON-VIDAL property package, over methane, co2, methanol — already selected. You can switch the method on the canvas before running.
- Which unit operations are in the flowsheet?
- It chains ABS, Letdown, Flash Regen. Every block is a real, solvable unit operation you can reconfigure, add to, or remove.
- Do I need to install software or buy a license?
- No. Cold-methanol CO2 absorption at 30 bar (SRK + Huron-Vidal) runs entirely in your browser on MaximaLabs — free, no install, no license. Open the model to load it live and run the deterministic solver.
More guides like this
Methanol-water column at 10 atm (PR + Huron-Vidal)
A methanol-water column at 10 atm on Peng-Robinson with the original Huron-Vidal (1979) infinite-pressure Gᴱ mixing rule, driven by the fitted methanol/water NRTL binary. 30 mol% feed, 16 stages, reflux 2, 30% distillate: 96.2 mol% methanol overhead, 1.6% in the bottoms, 3.4 MW on the reboiler at 452 K. The point is the pressure: at 10 atm a gamma-phi activity model is at the edge of its ~10 bar envelope, and a cubic with a Gᴱ rule carries no such ceiling. Bound, as the package's own description says: Huron-Vidal wants activity parameters regressed at infinite pressure, and these are the low-pressure DECHEMA ones, so treat the split as the rule's reading of that binary rather than a validated high-pressure number (the SRK + NeqSim card is the one with parameters fitted for the rule).
Deep ethane recovery with propane-refrigerated feed chilling
Associated gas is chilled by an external propane refrigeration package before a demethanizer recovers ethane and heavier as NGL bottoms from a methane-rich residue gas overhead — the cryogenic-chilling role Ortloff's CCS/GSP processes play ahead of the turboexpander in a real deep-ethane-recovery plant. The mechanical refrigeration loop itself (compressor/condenser/valve) isn't separately modeled here; the chiller's duty is represented directly as the feed's cooled outlet temperature (the same honest-simplification pattern used for LNG cold-box examples elsewhere in this library).
Pressure-swing ethanol dehydration (Gᴱ mixing rule)
Ethanol–water is the classic azeotrope, and pressure-swing distillation breaks it without an entrainer: the azeotrope moves with pressure, so a low-pressure column and a high-pressure column pass each other's azeotropic distillate and each recovers a pure product. The whole process only works if the property package tracks that shift — which is exactly where a conventional package choice falls between two chairs. This flowsheet runs the high-pressure column at 15 bar on pr-mhv1: Peng-Robinson with an MHV1 excess-Gibbs mixing rule, so the cubic equation of state gets its attraction parameter from NRTL's excess Gibbs energy instead of from a single binary interaction constant. Switch the thermo package (Solver menu) and compare the predicted azeotrope: | package | 1 atm | 15 bar | valid at 15 bar? | |---|---|---|---| | NRTL | 0.891 | 0.802 | no — γ-φ is a low-pressure formulation (~10 bar) | | Peng-Robinson (kij) | 0.586 | 0.613 | yes, but a kij cannot represent this azeotrope | | pr-mhv1 | 0.949 | 0.798 | yes | (mole fraction ethanol; the repo's DECHEMA-validated 1 atm anchor is 0.894.) At 15 bar pr-mhv1 lands within 0.005 of NRTL while remaining a genuine equation of state, whereas plain Peng-Robinson is off by ~0.19 and puts the azeotrope in the wrong place entirely. Selecting nrtl here also trips the applicability guard, which warns that the activity model is past its pressure ceiling and names the fix. The flowsheet demonstrates the mechanism on itself. Drop the column pressure to 1 atm and re-run, changing nothing else: the solve fails with SPEC_THERMODYNAMICALLY_IMPOSSIBLE, because at atmospheric pressure the requested bottoms purity sits beyond the azeotrope and no column can reach it. At 15 bar the same specification converges and the bottoms leaves at x_EtOH ≈ 0.924 — past the atmospheric azeotrope of 0.894, which is precisely the composition an atmospheric column cannot cross.
CO2 removal from syngas (Rectisol-style physical solvent)
A CO₂-laden syngas stream from gasification/reforming (H₂/CO with 25% CO₂, the actual Rectisol duty — scrubbing raw syngas ahead of methanol/ammonia synthesis, not treating pipeline natural gas) is sweetened by a cold-methanol physical-solvent absorber (chosen because chemical amine reactions aren't modeled here) down toward synthesis-loop spec, then the rich solvent is regenerated by a pressure letdown into a second flash that flashes the bulk of the absorbed CO₂ back off — the same letdown-valve-plus-flash regeneration pattern used for HDA's and methanol synthesis's own dissolved-gas trains. No solvent recycle loop (an honest simplification: the regenerated solvent is reported as a product stream rather than closed back onto the absorber feed). From the ChemSep casebook (CO₂ removal from natural gas), adapted to Rectisol's real syngas duty.
Ethanol-water column at 6 atm (SRK + MHV1)
The ethanol-water column everyone knows, run at 6 atm on the Gᴱ-mixing-rule package: Soave-Redlich-Kwong whose mixture energy parameter comes from NRTL's excess Gibbs energy through the MHV1 rule (Michelsen 1990) instead of a kij — the package built for polar, hydrogen-bonding mixtures at pressure, where a γ-φ activity model is past its ~10 bar ceiling and a plain cubic with van der Waals mixing has no hydrogen bonding at all. A 10 mol% ethanol feed through 16 stages at a reflux ratio of 2.5 gives a 66.7 mol% distillate and an ethanol-free bottoms, 2.6 MW on the reboiler. Read it against NRTL, which at 6 atm is still inside its own range: the two packages put the pressure-shifted azeotrope in different places — 0.88 mol fraction ethanol here, 0.84 on NRTL at 6 atm (0.97 against 0.89 at 1 atm) — so this card shows where the MHV1 rule sits, not a number to prefer over the fitted binary at low pressure. The cut is kept well short of the azeotrope on purpose: at a distillate ratio of 0.12 the profile pinched against it and the column reported exactly that. Each solve is about a minute, because every stage K-value is a Gᴱ mixing-rule evaluation.
Acetone-water column at 3 atm (PR + Wong-Sandler)
An acetone recovery column at 3 atm on Peng-Robinson with the Wong-Sandler mixing rule — the one Gᴱ rule that keeps the quadratic composition dependence of the second virial coefficient, so it stays thermodynamically consistent at high pressure. 20 mol% acetone feed, 14 stages, reflux 2, 25% distillate: 80 mol% acetone overhead and acetone-free water in the bottoms, 2.65 MW on the reboiler. The cut is set at 0.25 rather than the feed's exact acetone fraction of 0.20, which pinned the column on a razor edge (temperature residual 2e-3, balance 3%); at 0.25 it closes to zero. Bound: the rule is driven by the low-pressure acetone/water NRTL binary and, as records, NeqSim's Wong-Sandler kij is deliberately not wired in, so the second-virial cross term uses the van der Waals kij.