Isobutene by MTBE cracking (50 kt/a, gas-phase cleavage)

High-purity isobutene by gas-phase cracking of MTBE over an acidic catalyst, with MTBE recycle, a water wash for methanol, a drying/DME column and methanol recovery; methanol is a co-product. Concept stage, assumed basis, preliminary LCI (foreground inventory only).

Calculation maturity: not assessedDesign maturity: Concept (research)Not independently reviewedOlefinsReport a problem with this process
Research outputNot engineering advice and not an approved design: do not use it for construction, operation or safety decisions. What this means

Fresh MTBE (a boundary feed) and the MTBE/methanol recycle are freed of heavy ends in the MTBE column, whose vapour overhead is superheated against the reactor effluent and in a fired hot-oil heater and cracked at 553 K and about 0.9 MPa in a heated multitubular reactor over an acidic silica-alumina type catalyst (MTBE conversion 0.90 per pass, assumed inside the range of US 8,633,345 B2). Dimethyl ether and C8 dimers form as by-products. The condensed effluent is split in the isobutene column: crude isobutene overhead, methanol and unconverted MTBE as bottoms, from which the methanol column recycles the MTBE/methanol azeotrope and leaves methanol. Methanol is washed out of the crude isobutene with water; the drying column removes DME and water overhead and gives 99.97 wt% isobutene as bottoms (pure MTBE feed: the linear butenes and C5 that technical MTBE brings, which decide the polymer grade in a real plant, are not modelled; DESIGN.md D-003). The wash water is regenerated in a methanol/water column.

All values are concept estimates. The column, wash and duty values come from an independent script with specified component splits and shortcut duties from pure-component data; core cannot qualify the polar, azeotropic MTBE/methanol/water/C4 system yet. See DESIGN.md of the engineering files for every assumption and gated step. Designed independently from the open patent literature; no licensor data are used.

Capacity
50 kt/a isobutene (ASSUMED)
Operation
8,000 h/a
Location
generic (not chosen)
Engineering gates
Concept and feasibility (no results yet)
Maintainers
Artur Schweidtmann
Design basis and assumptions (6)
  • ASSUMED gas-phase cracking over an acidic silica-alumina type catalyst in a heated multitubular reactor at 553 K, 900 kPa(a) inlet (inside 150-500 C and 0.05-2 MPa of US 8,633,345 B2; D-004).
  • ASSUMED MTBE conversion 0.90 per pass (patent's preferred range 85-95 %); per kmol MTBE converted 0.010 kmol DME and 0.001 kmol C8 dimer: a conversion/selectivity model, not kinetics (D-005).
  • ASSUMED separations by component split specifications (D-007), shortcut duties from pure-component data (D-006); not a rigorous simulation.
  • ASSUMED pure MTBE feed: no MSBE (source of linear butenes), TBA, C5 or water in the feed (D-003).
  • ASSUMED pump efficiency 0.6; fans, the hot-oil circulation and instrument air not counted (D-009).
  • All flows, temperatures and duties are concept estimates; accuracy not stated.

From process/design-basis.yaml.

Engineering model

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Drawing of the process (preview)Open the engineering model

The interactive model (drawings, streams, 3D) is made for larger screens.

Snapshot of c3ab348, cheme-as-code 1.6.0.

What goes in and out

In

  • Methyl tert-butyl ether (MTBE)Feedstockfeed:MTBEF: fresh MTBE from an MTBE unit or terminal, 1.587 kg/kg isobutene before allocation
  • WaterFeedstockDemineralised wash-water make-up

Out

Utilities: Electricity (Pumps and the H-101 combustion-air fan and hot-oil pump (ASSUMED electric drives)), Steam (MP steam 1500 kPa(a), C-101 reboiler), Steam (LP steam 450 kPa(a), C-201, C-301, C-402 and C-403 reboilers), Cooling water (25/35 C (ASSUMED))

Show in the process graph

Reactions

IdAs writtenReactionOther processes
CRACKC5H12O ⇌ C4H8 + CH4OC5H12OC4H8+CH4O
DIM2 C4H8 → C8H162C4H8C8H16
DMEF2 CH4O → C2H6O + H2O2CH4OC2H6O+H2O2 other processes

Each reaction's page has the conversion, heat of reaction, catalyst and sources this process states, next to those of other processes with the same reaction. All reactions

Life cycle assessment

No footprint assessed yet; the process is part of the life-cycle inventory below.

In the open LCI database (cheme-as-code-atlas-preview-c3ab348) as Isobutene (2-methylpropene), High-purity isobutene to storage Preliminary; Recovered methanol (co-product, back to MTBE synthesis or sale) Preliminary; Heavy ends (C8 and MTBE) to the site fuel oil system Preliminary; DME-rich vents to the site fuel gas header Preliminary.

Download it for Brightway, openLCA and other tools.

In the LCI database: system model, datasets and KPIs against the benchmarks

In the LCI database

Status
Preliminary 1 unmapped exchange. Some exchanges have no background mapping yet: they are exported unlinked and count no burden, so the inventory is incomplete.
System model
attributional, cut-off (methodology 1.1.0)
Allocation
mass (deviation, from study) · product:FUELGAS 0.9 %, product:HEAVIES 0.32 %, product:IBP 63.1 %, product:MEOHP 35.7 %
Allocation findings
none
Change report
Not available: this build has no change report against an earlier release.
Dataset pages
DME-rich vents to the site fuel gas header Preliminary · Heavy ends (C8 and MTBE) to the site fuel oil system Preliminary · Isobutene (2-methylpropene), High-purity isobutene to storage Preliminary · Recovered methanol (co-product, back to MTBE synthesis or sale) Preliminary

KPI benchmark positions: not available (no benchmarked KPI for this process's datasets).

Maturity and review

Design maturity Concept (claimed): An idea or first flowsheet; numbers are rough. Concept PFD with closed mass, component and element balances (cheme validate, cheme process streams: every block and step ok) and a closed LCI mass and element balance (cheme assess lca --coverage). cheme maturity reaches no level: the MTBE feed and the capacity are assumed, and the columns and the wash are specified component splits from an independent script (scripts/ib_balance.py) whose shortcut duties rest on pure-component data and ideal Raoult bubble points; no qualified property package covers MTBE / methanol / water / C4. The reactor outlet is calculated by cheme (conversion reactor with assumed conversion and selectivities inside the patent ranges); cheme's ideal-gas reactor duty (1970.08 kW) reproduces the script's 1970.1 kW. The LCI is a foreground inventory with every background open (8 gaps): no impact result, and no LCA result passed to the catalog (lca.source none). Not reviewed. Main products and feeds are listed under chemistry with their chemicals registry entries (issue #251).

Calculation maturity, from the checked evidenceNot assessed

The process has no maturity report (cheme maturity, checks/maturity.json), so no calculation maturity is established.

No level shownThe design maturity (Concept) is the manifest's claim, not evidence. A level appears here once the process's repository holds a current report from cheme maturity --write.

Artifact completeness

Which deliverables exist. They never raise a calculation maturity level: a drawing from unchecked numbers is still unchecked.

Not reported without a maturity report.

Independent review

Not independently reviewed

No independent engineering review yet. Automated checks passing is not a review.

Set by people only. Reaching a calculation maturity level or passing automated checks is not an independent review or an approval.

Where the evidence comes from
Report
processes/isobutene-1/checks/maturity.json (not in the library)
Design basis
process/design-basis.yaml
Method
How ChemE-as-Code checks the levels (requirement by requirement)

Open items

0 open items · 0 closed

New action itemNew engineering holdNew technical queryNew design changeAll issues

Sources

Engineering project
Isobutene (MTBE cracking) · cheme-as-code>=0.8
Library version
c3ab348 (process last changed in c3ab348)
Drawings rendered by
cheme 1.6.0 (pyDEXPI 2.1.0)
Data
Catalog record (JSON) · CC-BY-4.0
Files
View the files on GitHub · change history and authors

References

How to cite

For the data, cite the Process Atlas paper; for the platform that builds and checks it, the ChemE-as-Code paper.

Schweidtmann, A. M. & Weber, J. M. (2026, in preparation). Process Atlas: an open, git-native, reproducible library and life cycle inventory of chemical processes (working title).

For this process: "Isobutene by MTBE cracking (50 kt/a, gas-phase cleavage)", ChemE-as-Code process library, version c3ab348.

BibTeX
@unpublished{schweidtmann_process_atlas,
  author = {Schweidtmann, Artur M. and Weber, Jana M.},
  title = {{Process Atlas: an open, git-native, reproducible library and life cycle inventory of chemical processes (working title)}},
  year = {2026},
  url = {https://atlas.cheme-as-code.org},
  note = {in preparation}
}

Schweidtmann, A. M. (2026, in preparation). ChemE-as-Code: An Open-Source Platform for AI-Accelerated Chemical Process Engineering (working title).

BibTeX
@unpublished{schweidtmann_cheme_as_code,
  author = {Schweidtmann, Artur M.},
  title = {{ChemE-as-Code: An Open-Source Platform for AI-Accelerated Chemical Process Engineering (working title)}},
  year = {2026},
  url = {https://cheme-as-code.org},
  note = {in preparation}
}