Para-xylene process modelling

Para-xylene plants are loops, not lines. Only about a quarter of the circulating xylenes are para-xylene at any moment, so material goes round several times before it leaves as product, and almost every cost in the plant is charged on that circulation rather than on production. Changing one parameter moves everything downstream of it — usually by more than expected, and occasionally in the opposite direction to intuition.

This site exists to make that behaviour visible. It has two halves: a technical reference that explains how para-xylene is produced, and a calculator that solves the balance with your own numbers.

Start with the process

If you want to understand how para-xylene is produced — or refresh a particular corner of it — begin with the main article and follow it into the detail:

• How para-xylene is produced — the whole chain, from mixed xylenes to product, and why everything is recycled.
• Crystallization vs adsorption — the two separation routes compared, and which feed makes each the cheaper choice.
• Xylene isomerization and the recycle loop — approach to equilibrium, the ethylbenzene fork, and why small per-pass losses are not small.
• Purity and specifications — what fibre grade means and which impurities matter downstream.
• Process economics — where the cost actually sits, and the recycle multiplier that governs it.
• Glossary — the vocabulary, defined plainly.

Then run the numbers

The calculator is a process model, not a spreadsheet of correlations. It closes the material balance around the recycle loop, tracks each stream through the crystallization cascade, computes the refrigeration and reboiler duties that follow, and attaches costs and revenues to the result.

• Reaction yield search — the inverse problem: find the yields that reproduce a set of measured stream compositions.
• Material balance with given yields — feed rates and reaction yields in, every stream, utility, cost and revenue out.
• Sensitivity analysis — sweep any input across a range and plot how the outputs respond.

Who it is for

• Process engineers sizing, debottlenecking or troubleshooting an aromatics complex.
• Technology evaluators comparing crystallization against adsorption for a specific feed.
• Planners and economists who need the utility and by-product consequences of a change, not just the headline spread.
• Engineers learning the process who want to see cause and effect rather than read about it.

Engineering support

Beyond the tool, we take on process studies that use it: technology comparison, debottlenecking assessment, yield reconciliation against plant data, and economic evaluation of design changes. What we do.