The para-xylene process calculator

What it calculates

1. 1
   Reaction yield search

   The inverse problem. Give it target stream compositions — from plant data or a technology guarantee — and it searches iteratively for the set of reaction yields that reproduces them.

2. 2
   Material balance with given yields

   Give it the feed rates, the feed composition and the reaction yields. It closes the balance around the full recycle loop and returns every intermediate stream, the utility consumption that follows, and the resulting costs and revenues.

3. 3
   Sensitivity analysis

   Sweep any input across a range and plot how any output responds. This is how the counter-intuitive couplings in the loop become visible.

What it models

• The multi-stage crystallization cascade, with filtrate recycles between stages and the purity achieved at each one.
• The isomerization loop, iterated to convergence — approach to equilibrium, ethylbenzene conversion, ring losses, non-aromatics purge.
• Ring and hydrogen balances across the loop.
• Refrigeration duty through the cascade, and column reboiler duties.
• By-product recovery — benzene, toluene, ortho-xylene, C9 aromatics.
• Fixed and variable costs, product revenues, and the resulting margin.

Why it can be trusted

The model did not start as a clean sheet. It is a re-implementation of a process simulator that had been developed and used over many years, and the re-implementation was held to an unusually strict standard: bit-for-bit identity with the original.

1. The original program is compiled and run to produce reference results — both its published outputs and a dump of its complete internal state, several thousand values per case.
2. The re-implementation is run on the same inputs and compared against that reference. Not "close enough" — every value identical to the last bit, which for floating-point arithmetic means the order of operations was preserved exactly.
3. The readable version of each model is then checked the same way against the verified implementation, so clarity was gained without changing a single number.
4. Physical invariants — mass balance, ring balance, hydrogen balance — are checked independently as unit tests.

Access

A public demo runs the real model on a reduced set of inputs, with no account required. Full access — every input, every output, saved scenarios and sensitivity analysis — is by request.

The calculation runs entirely on the server. The model itself is never sent to the browser.