1. Overview

For each component Rareytec Thermo assembles the constants and temperature-dependent correlations CHEMCAD needs, choosing for every slot between: your imported data, the company data bank, the shared core bank, a physical estimate, or a manual entry. You pick per slot; the choice is stored per project. The result is exported as a CHEMCAD neutral file (.nf) or written directly into a CHEMCAD simulation (.ccsim).

2. Projects & components

A project holds a set of components and (optionally) mixtures. Add components by search, manual identifiers, structure drawing, a CHEMCAD neutral/flat file, an IK-CAPE/PPDS file, a ThermoML archive, or by attaching a CHEMCAD .ccsim (its full property set is harvested in). Every added component is run through identification against the core registry, so the same substance is recognised across sources by InChIKey.

3. The CHEMCAD parameter block

The parameter block lists every scalar constant (MW, Tb, Tc, Pc, Vc, ω, and the secondary parameters Z_RA, UNIQUAC r/q, dipole moment, …). Each row shows the current value and where it comes from. Priority: your project choice → core DB → the rulebook-default estimate → component identity (MW). Click a row to see all candidate values (imported / company / core / estimate / internet) and pick or type one; that choice then applies to this project only. The provenance label always names the method that produced the number — e.g. Z_RA reads “Yamada-Gunn from estimated omega”, not a blanket method name.

3.1 One set of values, used everywhere

The component page is the authority for a component's pure-component properties. Whatever it shows is what every other part of Rareytec Thermo uses: the property and correlation pages, the vapour pressure behind the binary (VLE) pages and their regression, the electrolyte workbook, experimental-data plots, the gas-solubility classification, the Claude assistant, and every export (.nf, .ccsim, Aspen Plus). There is no second, hidden set of numbers anywhere.

Where the page values come from is set per component with the Parameters pulldown on the project page:

• This project (the default for a new component) — filled with the rulebook defaults: the estimate Rareytec Thermo currently judges best for this component (IAPWS for water; GRAPPA where it is the preferred method; Rarey-Nannoolal otherwise — see section 4). Different components may therefore carry different default methods; that is intended. Any value you choose or regress overrides the default. Derived quantities (ω, ΔH_vap, Z_RA, solubility parameter) are computed from the page's own vapour-pressure curve, Tc and Pc.
• Library — the page values of another project, write-protected.
• CHEMCAD databank — CHEMCAD's own pure-component record. It is used for every calculation, but its numbers are not displayed and are never written to a file: the .nf and Aspen exports stop with an explanation instead of substituting other values. To export such a component, switch it to This project or a library.

VLE regression keeps its own vapour-pressure shift factors (one overall and one per data set) to separate pure-component from mixture effects — authors differ in purity and in T/P calibration. These factors live only inside the regression; they never change the page's vapour pressure and are never folded into the binary interaction parameters.

4. Estimation methods

• Tb, Tc, Pc, Vc — the Rarey-Nannoolal group-contribution methods, directly from structure.
• T-dependent curves — vapour pressure and liquid viscosity by Rarey-Nannoolal, liquid thermal conductivity by Rarey-Govender, surface tension by Rarey-Olivier — each limited to its measured range of validity (section 4.1).
• Acentric factor ω — derived: ω = −1 − log₁₀(P_s(0.7·Tc)/Pc) on the Rarey-Nannoolal vapour-pressure curve.
• Z_RA (Rackett) — Yamada-Gunn: Z_RA = 0.29056 − 0.08775·ω.
• ΔH_vap(Tb) — Clausius-Clapeyron on the Rarey-Nannoolal P_s(T) curve (skipped for vapour-associating species — carboxylic acids, HF).
• UNIQUAC r/q — UNIFAC group contribution, as CHEMCAD itself does when the DECHEMA values are absent.
• Mixture activity coefficients (predicted) — the UNIFAC family (original, Modified UNIFAC (Dortmund), NIST-modified, UNIFAC 2.0, PSRK) and COSMO-SAC-dsp (2010 electrostatics with the 2014 dispersion term) from stored σ-profiles — fully implemented and fast (Newton segment solver, <1 ms per evaluation); available in every predicted-model list on the binary and ternary pages. When a component contains an atom the dispersion term has no parameter for (S, P, Br, I, …) the term is left out for that pair and the model label says so.
• HANNA (neural-net g^E) — a hard-constraint neural network for activity coefficients from the group of Fabian Jirasek and Hans Hasse at RPTU Kaiserslautern (published in Chemical Science), which reads each component's molecular structure directly — no group assignment and no σ-profile needed. It runs on the lab's own server, so no structure of yours ever leaves the lab, and the published model is used unchanged. HANNA is offered in the predicted-model list on the binary, mixture and ternary pages for neutral, single-fragment molecules; it is not offered for salts or multi-fragment SMILES, and the option is greyed out with the reason when the lab endpoint is unavailable. Because every evaluation is a call to the network model, Rareytec Thermo evaluates it once on a composition grid per isotherm — a fine grid on the binary line, a triangular grid over the whole composition simplex on the ternary page — and interpolates ln γ between the grid points, so a whole bubble curve or a complete liquid-liquid diagram is drawn from a single batched evaluation. The pure-component corners and the infinite-dilution limits are grid points themselves, so those are exact rather than interpolated.
• Parameter corrections — Modified UNIFAC (Dortmund) — validation against independent parameter sets and experimental data uncovered two defects in the published Revision 6 table (Constantinescu & Gmehling, J. Chem. Eng. Data 2016, 61, 2738), corrected in Rareytec Thermo:
  • Main-group pair 18 ↔ 42 (pyridines ↔ cyclic CH₂): the Revision 6 entry (a_42,18 = −5894.1 + 13.088·T) predicts γ^∞(cyclohexane in pyridine) ≈ 3·10⁻⁷; original and NIST-modified UNIFAC agree on ln γ^∞ ≈ +0.6…+1.0. Replaced by the earlier published 2006/2012 values, which behave correctly.
  • Main-group pairs 93 ↔ 7 and 93 ↔ 3 (disulfide ↔ water / aromatic CH): the Revision 6 values give dimethyl disulfide γ^∞ in water ≈ 0.02, while its measured water solubility implies ≈ 2·10³ — five orders of magnitude off. Group 93 is new in Revision 6, so no earlier values exist; predictions for these pairs are withheld rather than reported wrong.
  The full details are recorded in the parameter file's provenance note.
• Literature for each parameter — Modified UNIFAC (Dortmund) — when a binary is estimated with Modified UNIFAC (Dortmund), the estimate's note names the original paper in which each of the pair's group-interaction parameters was published (Weidlich & Gmehling 1987, Gmehling et al. 1993, 1998, 2002, … Constantinescu & Gmehling 2016). It also lists the group pairs the UNIFAC Consortium has revised since; for those, Rareytec Thermo uses the published values, and the consortium's current values may differ.

Derived properties inherit whatever you chose for their inputs (e.g. a chosen Tc feeds the ω and Z_RA estimates).

4.1 Range of validity

A group-contribution method returns a number for any structure you give it, whether or not the number means anything. Rareytec Thermo therefore limits each method to the range in which it was shown to work: outside it a value is either flagged with a warning or withheld altogether. The limits below are not conventions — they were measured against the NIST/TRC ThermoML archive, using each component's experimental normal boiling point so that the method's own error is not confused with the error of an estimated T_b.

Temperature

The temperature-dependent methods are simple functions of the reduced temperature and cannot follow a liquid property into the critical region — or, for viscosity, far below its reference temperature T_v. The figure gives the measured mean deviation against T/T_c; the shaded band is where all three methods are inside their accepted window, and the dashed lines are the points beyond which a value is refused.

Viscosity fails in the opposite direction to the other two: it is extrapolated downwards, below T_v, where the exponential form runs away — the classic symptom is a glycerol-like value of 10⁶ mPa·s at room temperature. Its deviations are larger throughout because viscosity spans orders of magnitude, so a relative measure is harsher on it than on the others. T_c is itself estimated unless you supply one, which is why the inner limit warns rather than withholds.

Molecule size

Group contribution assumes a molecule is the sum of its parts. That assumption is weakest at both ends of the size range: in a very small molecule almost every atom is a neighbour of every other, so the groups interact rather than add; in a very large one the accumulated group count amplifies any single bad contribution, and such molecules tend to be the exotic, poorly represented ones.

The same shape appears in thermal conductivity (22.6 % at n = 3, 4–6 % from n = 5) and surface tension (16.7 % → 4–6 %). For the smallest molecules an experimental value is almost always available and should be preferred over any estimate.

Structure

Independently of temperature and size, a method is applicable only if every group in the molecule carries a fitted contribution. Where a structure needs a group the method never regressed, no value is produced — Rareytec Thermo says so rather than dropping the group silently, which would return a plausible but meaningless number. Fragmentation that cannot cover the whole molecule is reported the same way.

5. Temperature-dependent correlations & regression

Each T-dependent property (vapour pressure, density, ΔH_vap, heat capacities, viscosities, thermal conductivities, surface tension) is carried as a correlation in a DIPPR / Antoine form. You can adopt an imported/bank correlation, enter coefficients by hand, or regress the curve to the component's experimental points.

Regression modes

• Direct — least-squares fit of the chosen form to the points, in ln (relative) space so low-magnitude points are not drowned out.
• Anchored — for sparse data (or a single Tb-style value): take the temperature dependence of the Rarey-Nannoolal P_s(T) method and shift it by a constant to pass through the data, then express it in the chosen form.

Degrees of freedom

Never more than n − 1 constants are fit for n data points; the remaining constants are held at zero. In particular, an Antoine fit to exactly 3 points fixes C = −Tb/8 — the denominator of the Rarey-Nannoolal P_s(T) method, log₁₀P = (ΔB₀+ΔB)·(T_rb−1)/(T_rb−⅛) — and fits only A and B.

Fit objective & experimental error

The final fit minimises the deviation weighted by the probable experimental error of each point, σ, rather than a plain least-squares:

σ = max( ThermoML reported uncertainty , σfloor + Y·0.1% + |dY/dT|·0.01 K )

σ_floor is a typical absolute measurement error for the property (e.g. 1 mbar for vapour pressure); the 0.1 % relative and 0.01 K temperature-uncertainty terms (the latter propagated through the local slope dY/dT) apply to all properties. An author's reported uncertainty is used only where it is larger than this model — it can down-weight a point flagged as poor, but a small (often over-optimistic) stated uncertainty is never allowed to make one point dominate the fit.

Exponential properties

Vapour pressure and liquid viscosity vary exponentially with temperature (ln Y ≈ linear in 1/T). Their plots offer a log Y vs 1/T view, on which a good correlation is a straight line — the quickest way to spot a bad point or an over-extrapolated curve. (ΔH_vap, density, vapour viscosity, heat capacities, vapour thermal conductivity and surface tension are not exponential.)

The “CHEMCAD (simulator)” curve

When a project is linked to a CHEMCAD simulation in COM (live) mode, every T-dependent property page offers a CHEMCAD curve (simulator) overlay. It computes the property inside CHEMCAD over COM and draws what the simulator actually calculates with its selected models. This is deliberately separate from the stored correlation: with a special enthalpy / K-value / property model (for example an equation of state such as SRK), the vapour pressure, ΔH_vap, heat capacity, etc. no longer come from the DIPPR / Antoine coefficients stored in the file — so the page lets you compare three things at once: the correlation stored in the .ccsim (our evaluation of it), the simulator's live calculation, and the experimental data. Any disagreement between the first two is exactly what you want to see before trusting a unit-op result.

Each point is obtained from the simulator's own engine: a pure bubble flash gives P_s(T); liquid properties (density, viscosity, thermal conductivity, surface tension, C_p, ΔH_vap) are read from a slightly sub-cooled stream (liquid properties are essentially pressure-independent, so this equals the saturated-liquid value); vapour properties (vapour viscosity and thermal conductivity) are read at the vapour pressure but capped at 6 bar, and above T_r = 0.9 a flat 6 bar is used instead of P_s (near the critical point the saturation pressure is high and unreliable, and the saturated vapour is far from ideal). The ideal-gas heat capacity is the vapour C_p evaluated at a very low pressure, where the real-gas departure vanishes. Values are returned in SI and shown in the property's own units. A computed curve is cached per component, so re-opening the page is instant.

Requires the linked simulation to be reachable over COM (the CHEMCAD host) and its property set to have been read in (Read sim properties after linking).

6. Binary interaction parameters

For each component pair you can regress an NRTL (or other g^E-model) parameter set to VLE/LLE/h^E/azeotrope data, review it against the CHEMCAD databank BIPs harvested from an attached simulation, and select the set the project should use. Chosen BIP sets ride along in both exports.

6.1 Vapour-phase treatment (γ-φ)

Bubble pressures and vapour compositions use the γ-φ formulation y_i φ_i^V P = x_i γ_i P_i^sat. The activity coefficient γ_i comes from the chosen g^E model; the vapour-phase reality is handled as follows:

• Carboxylic acids — the vapour does not behave as free monomers: two acid molecules form a hydrogen-bonded dimer, and near saturation most of the vapour is dimer (acetic acid at 373 K has an apparent molar mass near 100 instead of 60). Rareytec Thermo models this with the Marek-Standart chemical theory — the vapour is an ideal mixture of reacting monomers and self-/cross-dimers in chemical equilibrium — using the DDB dimerisation constants for the 17 parameterised acids. It is enforced (not optional) for those acids: it is applied when a curve is drawn and inverted when experimental points are reduced to activity coefficients, so γ stays a true liquid-phase quantity. When it is in effect it is named on the plot and in the regressed parameter set's description; an associating species with no dimerisation data (HF, acids outside the set) is reported and its estimated curve withheld rather than shown wrong.
• All other components — the physical vapour non-ideality (fugacity coefficient φ_i^V) is presently taken as ideal (φ = 1, i.e. modified Raoult), which is accurate at the low-to-moderate pressures where these correlations are used. A physical correction (Redlich-Kwong, the usual simulator convention) is planned; PSRK / VTPR predictive models are a separate later addition.

6.2 Electrolyte mixture properties

A salt–solvent pair of an electrolyte project opens on a hub: the pair's parameter card, model-only γ_± estimates, and a table of all measured data the banks hold for the pair. Each mixture property (density, viscosity, electric conductivity, refractive index, surface tension, speed of sound, diffusion coefficient) has its own page showing its data sets. Where a model is built, that page also shows the model's value at every data point, per-set deviations (calc/exp − 1) and the parameters. Activity, VLE, heat-capacity and enthalpy data stay on the γ-φ model-fit page.

The model for each property is chosen once for the whole project in the Property models row of the project page. Aspen Plus and CHEMCAD both choose these models globally, so every pair of the mixture has to use the same one. Models the simulators offer that are not built yet appear as planned. Every fit reads its solvent values (density, viscosity, permittivity) from the solvent's own component page (section 3.1), pressure included. A point that gets no model value is counted and the reason is given; it is never dropped silently. Right-click and per-set exclusions apply on every page.

• Density — Clarke (Aspen VAQCLK, CHEMCAD “Clark correction”). This model uses the apparent basis: the salt counts as one species with mole fraction x_s. V_m(298 K) = x_wV_w + x_s(V^∞ + A √x_s/(1+√x_s)). The temperature and pressure dependence follows the solvent: V_m(T,P) = V_m(298 K)·V_w(T,P)/V_w(298 K). V^∞ and A are fitted per salt in one linear least-squares fit over every salt–solvent page of the project containing that salt. Densities and apparent molar volumes both enter the fit. The parameters are stored at project level.
• Density — Debye-Hückel volume (Aspen VAQDH; aqueous only). Same apparent basis as Clarke: V_m = x_wV_w(T,P) + x_sV_φ, with V_φ = V^∞ + S₂A_V/(2b)·ln(1 + b√I), S₂ = Σν_kz_k², I = ½S₂m (molality m), b = 1.2. The Debye-Hückel slope A_V = 2A_φRT(3∂lnε/∂P − κ_T) comes from water's density and compressibility (IAPWS-IF97) and its permittivity (Bradley-Pitzer, which also gives ∂ε/∂P; the CRC form used by eNRTL has no pressure term). A_V(25 °C) = 1.876 cm³ kg^½ mol^−3/2; the range is 273–623 K. The only parameter is V^∞, the salt sum of Aspen's per-ion VLBROC, fitted linearly over every water page of the project with that salt. Aspen's V^∞ has no temperature term; ticking V^∞(T) adds its own dV^∞/dT. Two deviations from the manual's printed form: the Debye-Hückel term is Pitzer's consistent one, because Aspen's printed |z_k|·A_V/(3b) gives only ⅔ of the limiting law for a 1:1 salt and its A_V lacks the factor T; and the manual's ion “molarity” is read as molality, the Debye-Hückel variable.
• Viscosity — Jones-Dole (Aspen MUL2JONS). η = η_solv(1 + A√c + B·c), where the molarity c = x_s/V_m comes from the project's density model (Clarke or Debye-Hückel volume) and B = B₁ + B₂T. A is fitted, fixed at a value you enter, or Falkenhagen. Falkenhagen computes A from the limiting law using the ions' IONMOB, the solvent viscosity and the solvent permittivity; it is available for 1:1 salts. Aspen builds B from per-ion IONMUB. One salt's data fix only the sum, so B is stored at salt level. η_solv for water is IAPWS 2008. A stored fit records the inputs it used and is flagged stale when one of them changes, for example the solvent density or an ion's IONMOB.
• Ion mobilities (IONMOB) — the limiting molar conductivity λ^∞_i = l₁ + l₂T per mole of ion. A doubly charged ion therefore carries twice the value tabled per equivalent (½ Ca²⁺). Enter λ^∞(25 °C) in S·cm²/mol, its slope dλ^∞/dT and a source (required). The page shows the Aspen IONMOB/1, /2 values in S·m²/kmol next to your entry. The values are stored once per project and shared by the Jones-Dole and diffusion pages. Rareytec Thermo supplies no ion table.
• Diffusion — Nernst-Hartley (Aspen DL0NST/DL1NST, CHEMCAD). This model is predictive: nothing is fitted, and the page has no fit button. Each ion's effective diffusivity is D_i = RTλ_i/(z_i²F²)·Σx_mol, where Σx_mol is the true mole fraction of the molecular species (Aspen's factor; 1 at infinite dilution). Measured values are the salt's mutual diffusion coefficient, so the page compares them with the Nernst-Haskell combination D_salt = (|z₊|+|z₋|)D₊D₋ / (|z₋|D₊ + |z₊|D₋). This is exact at infinite dilution. The deviation at finite concentration is the thermodynamic factor and the relaxation effect, which the model does not contain. A point where an ion's λ^∞(T) line is no longer positive is counted as having no model value. The Aspen manual prints the denominator as z_iF² rather than z_i²F². That form holds for λ per equivalent; Rareytec Thermo's λ is per mole of ion and therefore uses z². Both give the same result for singly charged ions. Before you enter Aspen IONMOB values for a multiply charged ion, check which basis they are on.
• Thermal conductivity — Riedel (Aspen KL2RDL, CHEMCAD Riedel/Jamieson). λ = [λ_solv(293 K) + a·c]·λ_solv(T)/λ_solv(293 K), where the molarity c = x_s/V_m comes from the project's density model, so the salt's density must be fitted first. Aspen builds a from per-ion IONRDL (a = a_c + a_a). One salt's data fix only the sum, so a is fitted and stored at salt level, in W/(m·K)·L/mol; this is numerically the same as Aspen's W/(m·K)·m³/kmol. λ_solv comes from the solvent's page. For water without a chosen correlation, that is IAPWS 2011 including the critical enhancement; the enhancement is negligible below about 450 K and adds about 1 % on the saturated liquid at 573 K. λ_solv(293 K) is taken at 1 atm. The model has no pressure term of its own beyond λ_solv(T, P). The fit is flagged stale when the density parameters or the density model change.
• Surface tension — Onsager-Samaras (Aspen SIG2ONSG, CHEMCAD). This model is predictive: nothing is fitted. σ = σ_solv + x_s·Δσ, with Δσ = (80/ε)·c·log₁₀[1.13·10⁻¹³(εT)³/c] in mN/m. The molarity c = x_s/V_m comes from the project's density model, so the salt's density must be fitted first. σ_solv comes from the solvent's page; for water without a chosen correlation, that is IAPWS 1994. ε is the solvent's relative permittivity, which is built only for water (the CRC form used by eNRTL). The x_s weight on Δσ follows Aspen's documented equation; the Onsager-Samaras law itself adds Δσ unweighted. Either way this is a limiting law: Δσ peaks near 0.5 mol/L and turns negative above about 1.4 mol/L for water at 25 °C, so expect the model to fall short of measured data beyond dilute solutions.
• Planned — Breslau-Miller, Carbonell and the CHEMCAD log-mole / log-mass forms (viscosity).

7. Exports: .nf vs .ccsim

Two ways to hand the data to CHEMCAD — they differ in how the T-dependent correlations travel:

Modifying an uploaded simulation

A .ccsim you upload can be re-downloaded with your changed constants and BIPs written in. A CHEMCAD databank component can't be altered in place, so any component whose parameters you change is cloned into a user component: it keeps its slot in the simulation but is given its own identity, so CHEMCAD uses your values instead of its databank ones. When you open the file, CHEMCAD recognises it as a user component and offers to save it to a user database. Its binary interaction parameters travel with it, and the flowsheet is untouched — streams and units reference components by their position in the component list, not by name or id, so re-identifying one component never disturbs the flowsheet.

What gets exported

Exactly the values on each component page (section 3.1): your choices, core-DB values and the rulebook defaults, including the default vapour-pressure curve. Each value's source is written alongside it. A component whose parameter source is the CHEMCAD databank is not exported to .nf or Aspen Plus — a project export containing one stops as a whole and names the component, so no file ever mixes in values you did not see.

Neither export touches a CHEMCAD licence or dongle — the files are written directly.

8. Data sources

The clean core is the public NIST/TRC ThermoML archive plus our own estimations; the company and project layers hold your imported and measured data. External sources (Dortmund Data Bank availability, KDB, NIST WebBook, PubChem, …) are queried per project and not folded into the core. See Data Sources & Licensing for the full source tiers and the licensing posture. DDB licence holders import DDB data sets from their own installation — see section 10.

Ratios and differences are withheld. ThermoML can report a property as a ratio or a difference to a reference state (e.g. viscosity relative to pure water, density increment over the solvent) instead of an absolute value. The reference value is not part of the record, so such values cannot be converted back. They are kept in the bank but withheld from plots, fits and exports; data-set lists show them as withheld (not a direct value) with ThermoML's own wording. Enthalpies of solution reported as a difference to the pure solute stay readable — that difference is the property itself.

Which component a value belongs to. ThermoML names the component of every composition, activity coefficient and azeotropic composition. Rareytec Thermo keeps that reference and orients γ∞, azeotrope and vapour-composition data by it. A value without it is reported as skipped, not guessed. Some older core sets still hold two ThermoML columns of the same name (e.g. the mole fractions of two components) in one channel; they are kept as they are until a re-ingest of the core.

9. Claude assistant

The assistant (orange button, or the Claude operator mode) reads your projects and data, computes with Rareytec Thermo's own engine, and — inside your own project — acts directly: no confirmation clicks. Before the first change of a turn it takes a dated restore point of your project database, and every action is logged. Its chat is stored with the project and restored when you reopen it; the button starts a fresh session.

• Components — add single components by exact name or SMILES; add a whole homologous series (e.g. the first 100 oligomers of an acid + epoxide) in one request. Identification is exact-or-nothing: novel structures become honest custom components, never a "similar" database hit.
• Properties — pin Rarey-Nannoolal estimates into the parameter block for all components at once; your own chosen values and core-DB values are never overwritten, and out-of-range methods are reported, not silently filled.
• UNIFAC groups — list the group assignments (original UNIFAC, modified UNIFAC (Dortmund), PSRK) per component.
• Kinetic reactions — build a reaction ladder with one shared rate constant k(T) = k0·exp(−Ea/RT); k0 and Ea stay editable on the project page under Kinetic Reactions (deliberately separate from the electrolyte equilibrium block).

10. Your own Dortmund Data Bank

The DDB card on every component, binary and ternary page searches the Dortmund Data Bank (DDB) for the component or system of the page and imports the data sets you tick into the current project: pure-component data (vapour pressure, density, heat capacity, critical data, viscosity, …) and mixture data (VLE, h^E, γ^∞, LLE, SLE, azeotropes, …). Constants land in the parameter choosers, point data in the project's experimental store, each set with its DDB bank and set number as source; sets already in the project are marked and are not imported twice.

One copy of every data set. Point data from IK-CAPE files (including DDB IK-CAPE exports) and from DDB data list exports go into the same experimental store. Every figure and every fit reads that store, so each set is shown and fitted once. γ^∞ tables are stored as the activity coefficient of the first-listed component at infinite dilution. Azeotrope tables enter the binary fit with their composition, temperature and pressure. Importing the same file again keeps the unchanged sets, with their ids, so sets you excluded stay excluded, and replaces the rest. A set that another file already brought in is not stored a second time.

DDB is a licensed product installed on your PC, not on this server. The card therefore works through the DDB bridge: a small program you run on your PC next to DDB. Your browser talks to it locally, the bridge reads your DDB through its MixView interface with your licence, and the browser hands only the selected, parsed data sets to your project. The Rareytec Thermo server never connects to your computer and never runs MixView.

• Set-up (once) — open the DDB bridge page, download the zip (pre-configured for this site), unpack it and double-click ddb_bridge.bat. Leave the console window open while you work. Requirements: Windows with DDB 2026 including MixView, Python 3.8 or newer, Chrome, Edge or Firefox.
• Searching — the DDB component numbers are resolved automatically (InChIKey / CAS); type them into the number fields to override. For mixtures tick the banks to search (VLE, HE, ACT, LLE, SLE, AZD, …). Hidden or already imported sets are flagged in the list.
• Licence — the card shows the licence the bridge found (customer, expiry, educational version, banks not licensed). A bank you are not licensed for yields only DDB's demo sets.
• Security — the bridge listens on 127.0.0.1 only, answers only to the sites listed in its ddb_bridge.ini and only to requests from Rareytec Thermo's pages, reads DDB without writing to it, and is plain readable Python.

11. Moving CHEMCAD projects in and out

A project lives in Rareytec Thermo's sandbox; your CHEMCAD lives on your own PC. The CHEMCAD bridge — the same helper that runs VLE, h^E and flash calculations in your licensed CHEMCAD — also moves a whole project between the two, so its components, chosen parameters, fitted BIPs and library links travel together instead of only the computed numbers. See the CHEMCAD bridge page for the one-time set-up.

Two ways you drive Rareytec Thermo with CHEMCAD

• Client mode — you start from Rareytec Thermo and tick Use my own CHEMCAD on a project. Your .ccsim stays on your PC; the bridge opens it there.
• Live-link mode — you launch Rareytec Thermo from inside CHEMCAD with a simulation already open: a Visual Basic unit op in the flowsheet runs the platform_serve.bas macro, sends the simulation's components to a new project here and, with PlatformServe, computes the CHEMCAD curves you ask for on the binary pages in that running flowsheet.

Example simulation with the live link (.ccsim) IPA azeotropic distillation with cyclohexane as entrainer; the set-up steps are on the CHEMCAD bridge page.

In both modes the calculations run on your machine, with your licence. The Rareytec Thermo server never connects to your computer: in client mode your browser talks to the bridge over 127.0.0.1, in live-link mode the simulation itself calls Rareytec Thermo.

The lifecycle bar

When either mode is in play, a small bar appears at the top of the project page with up to three actions. They are deliberately explicit buttons rather than something that fires when you close the tab — a browser cannot reliably finish the multi-step round-trip to the local bridge while a tab is closing, and a project has many inner pages, so "navigated away" is not the same as "done".

• Return project to CHEMCAD (live-link) — packs the project into its portable container and drops it straight into your open CHEMCAD's working folder, so it rides home inside your .ccsim the next time you Save in CHEMCAD. Rareytec Thermo keeps nothing.
• Save simulation to Rareytec Thermo (client) — after you Save in your own CHEMCAD, stores a copy of that .ccsim here so the project's last-saved state is preserved on Rareytec Thermo.
• Load onto this PC — fetches the copy Rareytec Thermo is holding, places it on your machine and hands its path to the bridge so CHEMCAD can open it. Offered once a copy has been saved here.

The dashboard project list shows a Saved column with the name and time of the copy Rareytec Thermo currently holds, so you can see which projects have a simulation parked here and how fresh it is.

Your simulation is uploaded only when you press Save simulation to Rareytec Thermo yourself; the other two actions move the file the other way, onto your PC.

12. Outlook — planned

On the roadmap, not yet available:

• Uncertainty-weighted regression — use each experimental point's reported (ThermoML) uncertainty as the fit weight, falling back to the typical absolute-error model where a point carries none.
• Full custom-component export — write a complete property set into the .ccsim for components not found in the CHEMCAD bank (today those export with minimal data and may need completion in CHEMCAD).
• User-configurable units — choose your preferred units for every displayed variable (temperature, pressure, composition, energy, …) instead of the current fixed SI-based display.
• Entrainer / solvent selection — systematic screening and ranking of candidate entrainers for extractive and azeotropic distillation and of solvents for liquid-liquid extraction, built on the predictive models (selectivity, capacity, boiling-point and azeotrope/LLE constraints).
• More data-source connectors — extending the current Dortmund Data Bank / KDB / NIST WebBook / PubChem set.

Glossary

BIP

Binary interaction parameter: the pair-specific constants of an activity-coefficient model (NRTL, UNIQUAC, Wilson), fitted to mixture data.

NRTL / UNIQUAC / Wilson

Activity-coefficient models used by process simulators to describe how far a liquid mixture deviates from ideal behaviour. They need BIPs for every component pair.

γ, γ∞

Activity coefficient; γ∞ is its value at infinite dilution (one molecule of a solute surrounded by solvent). A sensitive measure of non-ideality, used for solvent screening.

UNIFAC

A group-contribution model that predicts activity coefficients from the functional groups of the molecules, with no mixture data needed.

COSMO-SAC, σ-profile

A predictive model that computes activity coefficients from the charge distribution on each molecule's surface (quantum chemistry); the σ-profile is that distribution, summarised as a histogram.

Group contribution

Estimating a property by adding up contributions of the structural groups in a molecule (e.g. normal boiling point, critical data, vapour pressure).

VLE / LLE / SLE

Vapour-liquid, liquid-liquid and solid-liquid equilibrium data.

Tb, Tc, Pc, ω

Normal boiling point, critical temperature, critical pressure, acentric factor.

.nf

CHEMCAD neutral file: a text file of component properties that CHEMCAD can import into its databank.

.ccsim

A CHEMCAD simulation file; Rareytec Thermo can read components from it and write parameters back into it.

.bkp

Aspen Plus backup file (a portable simulation file).

.rtp

Rareytec Thermo project file (encrypted) for keeping a project on your own PC.

InChIKey

A standard fingerprint of a chemical structure; used to recognise the same substance across sources.

ThermoML

The open XML standard (IUPAC/NIST) for exchanging measured thermophysical data.

DDB

Dortmund Data Bank, a commercial collection of measured property data. Rareytec Thermo can use your own DDB licence.