What is the feed composition and what is your temperature?

please check cold properties including critical pressure/temperature ... of the components and also their phase envelope and thermodynamic model

@ Antonin Chapoy

Dear Professor Chapoy

My overall composition is:

z=[0.3 0.6 0.1]. The first array is for H2O. The second is for CO2 and the third is for NC5. T=312 K

Use your calculation results at 12 bar to initialize all the variables of your computations at higher pressures.

Also, try to initialize relaxations parameters. Even, if you have problem in first iterations.

What is the 2-phase dew point  (V-L-L -> V-L) pressure that you are predicting with your parameters? I would expect problem at pressure closer to the dew point when molar volume of the liquid organic phase  is small not at higher pressure. You should try to do check the CO2-C5 system first.

Below are some data you could use to check your parameters on the CO2-C5 system.

Besserer G.J., Robinson D.B., J.Chem.Eng.Data, 18(4), p416-419, 1973

T/K P/bar x y

311.04 4.6195 0.0344 0.7421

311.04 8.4806 0.0739 0.8598

311.04 15.859 0.1689 0.9202

311.04 21.788 0.2379 0.9401

311.04 29.51 0.3357 0.9527

311.04 36.405 0.4223 0.955

311.04 43.851 0.5321 0.9575

311.04 53.09 0.6674 0.9663

311.04 59.226 0.7702 0.9692

311.04 62.33 0.8109 0.9699

311.04 65.363 0.8553 0.9704

311.04 67.982 0.8763 0.9701

311.04 69.982 0.8963 0.9745

311.04 73.843 0.9416 0.9724

Cheng H., Pozo De Fernandez M.E., Zollweg J.A., ..., J.Chem.Eng.Data, 34, p319, 1989

T/K P/bar x y

311.59 4.1 0.037 0.7458

311.59 8.41 0.079 0.8647

311.59 13.65 0.1297 0.9119

311.59 20.68 0.2135 0.9372

311.59 28.13 0.3123 0.9495

311.59 35.03 0.391 0.9557

311.59 41.92 0.4871 0.9602

311.59 49.3 0.5994 0.9599

311.59 55.64 0.6903 0.9642

311.59 61.98 0.7746 0.9669

311.59 65.36 0.8258 0.968

311.59 68.46 0.8664 0.9689

311.59 69.84 0.8853 0.9697

311.59 71.36 0.9026 0.9703