Di-tert-butyl dicarbonate by semi-batch carbonation and phosgenation of potassium tert-butoxide (500 t/a)

A batch plant: potassium tert-butoxide in recovered hexane takes up CO2 and then phosgene in one semi-batch at 278 K (CO2 vented to a caustic scrubber); the hexane is stripped and recycled, the Boc2O melt washed and distilled under vacuum from a paraffin heel. Concept stage, 655.71 kg per batch every 10.39 h, preliminary gate-to-gate LCI.

Calculation maturity: not assessedDesign maturity: Concept (research)Not independently reviewedOxygenatesReport 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

The route is the one-pot phosgene route of EP 0 256 559 A2 (Mitsubishi Kasei, 1986/1988): per mol of potassium tert-butoxide 1.3 mol of CO2 (US 5 151 542 A, Example 1: 4 mol on 3) and 0.49 mol of phosgene (EP Examples 6-7 use 0.54; a 2 % deficit on the net reaction's 0.5 is ASSUMED, so that no phosgene is left for the work-up), with 1.2 mol% DABCO (EP Example 1). The carbonate forms from the suspended alkoxide and the dissolved CO2 (85 % of the dose taken up, the rest vented); the phosgene and the amine give Boc2O, KCl and CO2 directly (the patent's point: no tricarbonate is isolated), 7 % of the phosgene going to a lumped side path to tert-butanol, isobutene and CO2 (ASSUMED). The patent's own example runs in THF; hexane, an aliphatic hydrocarbon within its claimed solvents and the Sumitomo patent's solvent, is ASSUMED here so that the KCl is washed out with water after the solvent strip and no THF must be swapped out. The slurry is degassed with a nitrogen sweep, the hexane stripped at 15 and then 1 kPa(a) at up to 313 K (both patents keep Boc2O below 50 C when the solvent is removed), the melt washed with warm water and split from the KCl brine, and the Boc2O distilled at 0.13 kPa(a) from a liquid paraffin, which EP 0 256 559 A2 adds to suppress decomposition; the heel returns to the next batch with a 10 % purge. The modelled yield is 89.4 % on the alkoxide and 91.2 % on phosgene: below the 91.0 % EP 0 256 559 A2's Example 1 gives by mass (149 g from 1.5 mol, its purity not stated in the text), so that source bounds it from above. The modelled product is 99.98 wt% Boc2O, an upper bound: di-tert-butyl carbonate, the tricarbonate and other by-products are not modelled (US 5 151 542 A reports 98.6 to 99.7 % for its route).

The batch is modelled with cheme-as-code 1.10.0: R101 is a semi-batch (reactor: semibatch) with two gas doses (dosing.absorbed, with their heats of solution, core ADR 0063) and a vent for the CO2 and isobutene (batch.vent, core ADR 0054) that carries the slurry's hexane and phosgene vapour through R-101's vent condenser (vent.vapour, vent.condenser, ADR 0062); the degassing and the three distillations are core's batch stills (ADR 0055), the first strip with its charge's heat-up; both recycles, the recovered hexane and the paraffin heel, are tear streams converged by propagate (ADR 0060); the semi-batch's, its vent condenser's and the stills' duties come from their models (ADR 0059). The recipe gives the cycle (10.39 h, R-101 the bottleneck, 762.5 batches a year), sizes R-101, V-201 (12.5 m3 each) and C-301 (1.6 m3) and checks R-101's jacket (98.4 kW against the model's 73.8 kW peak). Kinetics and heats of reaction are ASSUMED (no open data): the phosgene accumulates 2.7 % at the end of its dosing (36.1 % at k/100); the MTSR is 279.5 K against an MTT of 333.15 K, the decomposition limit (Boc2O's precursors gave vigorous gas at 60-70 C, US 5 151 542 A), and a cooling failure releases at most 24.5 m3/h of gas with its vapour against the vent's 50 m3/h (52.9 m3/h at k/100, 1.06 of it: a design finding). No TD24 is known: no class. See DESIGN.md for every assumption.

Capacity
500 t/a distilled Boc2O: 762.5 batches/a of 655.71 kg in 7920 h on a dedicated train (63.13 kg/h year average), ASSUMED (DESIGN.md D-002, D-003, D-013)
Operation
7,920 h/a
Location
generic fine-chemicals site with a captive phosgene unit and a thermal oxidiser (not chosen)
Engineering gates
Concept and feasibility (no results yet)
Maintainers
Artur Schweidtmann
Design basis and assumptions (4)
  • Route: the one-pot phosgene route of EP 0 256 559 A2 (alkoxide carbonated with CO2, then phosgene with DABCO, no tricarbonate isolated), in hexane instead of the example's THF (ASSUMED, within the claimed solvents; D-001).
  • ASSUMED effective rate laws: CARB k 0.05 m3/(kmol s), PHOS 0.05 and SIDE 0.0038 at 278 K (7 % of the phosgene to the side path); the 2.7 % phosgene accumulation follows from them (D-005, D-011).
  • Stills: Raoult's law with NIST Antoine constants (an ideal liquid, ASSUMED), Boc2O's vapour pressure ASSUMED from one open point; the degassing (a nitrogen sweep at 30 kPa(a)) at ASSUMED constant volatilities, its CO2 volatility set so that its gas carries the hexane that saturates R-101's vent-condenser gas over the batch (D-006, D-008).
  • The wash's split and the scrubber's CO2 uptake are specified (ASSUMED, D-007); all flows are year averages of the recipe (D-003); accuracy +/-30 % not demonstrated.

From process/design-basis.yaml.

Engineering model

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Snapshot of a3c52e4, cheme-as-code 1.6.0.

What goes in and out

In

  • Potassium tert-butoxideFeedstockPotassium tert-butoxide (technical solid), 1.150 kg/kg Boc2O; linked to potassium-tert-butoxide-1 kg for kg (its make-up tert-butanol from tert-butanol-1, its potassium metal a gap there, D-012)
  • PhosgeneFeedstockLiquid phosgene (phosgene-1), 0.497 kg/kg Boc2O, 0.49 mol per mol of the alkoxide, evaporated and dosed as gas
  • Carbon dioxideFeedstockCO2 gas (merchant), 0.587 kg/kg Boc2O, 1.3 mol per mol of the alkoxide; a gap
  • n-HexaneFeedstockn-Hexane make-up (merchant), 0.113 kg/kg Boc2O, most of it lost with R-101's vent-condenser gases (the dosing's vent and the degassing's nitrogen sweep, saturated at 263 K); the strips recover the rest of the 7.94 kg/kg the charge holds
  • Triethylenediamine (1,4-diazabicyclo[2.2.2]octane)FeedstockDABCO catalyst (merchant), 0.0138 kg/kg Boc2O, 1.2 mol% of the alkoxide (EP 0 256 559 A2, Example 1)
  • White mineral oil (liquid paraffin)FeedstockLiquid paraffin make-up for the still's heel, 0.030 kg/kg Boc2O (the heel's 10 % purge)
  • Sodium hydroxideFeedstockCaustic soda 50 wt% (chlor-alkali-1) to the scrubber, 0.164 kg/kg Boc2O, counted by mass of the solution
  • WaterFeedstockWash water and scrubber make-up, 4.18 kg/kg Boc2O
  • NitrogenFeedstockNitrogen (asu-1) for inerting, the degassing's sweep, purging and breaking the vacuums, 157.5 kg per batch, 0.240 kg/kg Boc2O (ASSUMED)

Out

  • Di-tert-butyl dicarbonateMain productDistilled Boc2O melt to heated storage; modelled 99.98 wt%, an upper bound: di-tert-butyl carbonate, the tricarbonate and other by-products are not modelled
  • WastewaterWasteWash brine, 4.35 kg/kg Boc2O: about 17 wt% KCl with tert-butanol, DABCO and the unreacted carbonate, to wastewater treatment
  • WastewaterWasteSpent scrubber liquor, 0.836 kg/kg Boc2O, sodium carbonate with excess NaOH, to wastewater treatment

Utilities: Electricity (0.424 kWh/kg Boc2O: agitators of R-101, V-201 and C-301, the three vacuum pumps, the scrubber's pump and fan (ASSUMED)), Steam (1.209 kWh (4.35 MJ)/kg Boc2O of LP steam through hot-water circuits: the hexane strips (0.970 kWh with the charge's heat-up and V-201's sensible heat), the still (0.107 kWh), the wash water, the phosgene evaporator and the degassing), Chilled water (0.925 kWh/kg Boc2O removed by chilled water at 278 K: the strips' and the forerun's condensers), Chilled water (0.524 kWh/kg Boc2O removed by brine at 258 K: R-101's charge cooling, the heats of carbonation and phosgenation with the gases' heats of solution, and R-101's vent condenser (R101's model) (the registry has chilled water, not brine: closest entry)), Cooling water (0.123 kWh/kg Boc2O removed by cooling water: the main-cut condenser and product cooler, and the scrubber)

Show in the process graph

Reactions

IdAs writtenReactionOther processes
CARB(CH3)3COK + CO2 → (CH3)3COC(O)OK · Carbonation of potassium tert-butoxideC4H9KO+CO2KTBC
NCOCO2 + 2 NaOH → Na2CO3 + H2O · CO2 taken up by the caustic in the scrubberCO2+2NaOHNa2CO3+H2O3 other processes
NPHCOCl2 + 4 NaOH → Na2CO3 + 2 NaCl + 2 H2O · Phosgene destroyed in the caustic scrubberCOCl2+4NaOHNa2CO3+2NaCl+2H2O2 other processes
PHOS2 (CH3)3COC(O)OK + COCl2 → [(CH3)3COC(O)]2O + CO2 + 2 KCl · Phosgenation of potassium tert-butyl carbonate to di-tert-butyl dicarbonate (amine-catalysed, net)2KTBC+COCl2C10H18O5+CO2+2ClK
SIDE2 (CH3)3COC(O)OK + COCl2 → (CH3)3COH + C4H8 + 3 CO2 + 2 KCl · Loss to tert-butanol and isobutene (lumped acidic by-product path)2KTBC+COCl2C4H10O+C4H8+3CO2+2ClK

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

–kg CO2-eqPreliminarypartial, 20 data gaps

Climate change per 1 kg Boc2O melt, cradle-to-gate

No factors. No contribution is characterised, so no factor stands behind any number.

Main contributors
    Method and data
    Goal
    Preliminary gate-to-gate life cycle inventory of di-tert-butyl dicarbonate (Boc2O) made by the one-pot phosgene route: potassium tert-butoxide carbonated with CO2 and phosgenated with a DABCO catalyst in hexane (one semi-batch), the hexane stripped and recycled, the melt washed with water and distilled under vacuum from a liquid-paraffin heel, the vents scrubbed with caustic, at the concept stage: which raw materials, utilities and wastes the batch plant exchanges per kg of distilled Boc2O, as the foreground for a later cradle-to-gate study. No impact results: most backgrounds are not mapped yet (D-012).
    Functional unit
    1 kg Boc2O melt (1 kg di-tert-butyl dicarbonate)
    Boundary
    cradle-to-gate
    Characterisation
    Factors kept with the process · GWP100
    Data quality
    No factors
    Result
    partial screening carbon footprint · 20 data gaps
    ScenarioClimate change (kg CO2-eq)
    baselineno total (data gaps)

    Inventory per 1 kg Boc2O melt (21 flows)

    FlowPhaseDirectionQuantityUnitProvenance
    Potassium tert-butoxide (merchant solid)operationinput1.15kgassumed
    n-Hexane make-up (merchant)operationinput0.1132kgassumed
    DABCO catalyst (merchant)operationinput0.0138kgassumed
    Carbon dioxide gas (merchant)operationinput0.5866kgassumed
    Liquid phosgene (phosgene-1)operationinput0.4969kgassumed
    Liquid paraffin make-up (merchant white oil)operationinput0.0303kgassumed
    Process water (wash, scrubber make-up)operationinput4.176kgassumed
    Caustic soda 50 wt% (chlor-alkali-1)operationinput0.164kgassumed
    Electric poweroperationinput0.4237kWhassumed
    LP steam 350 kPa(a) (the tempered and hot-water circuits)operationinput1.209kWhassumed
    Boc2O melt to heated storageoperationoutput1kgcalculated
    Wash brine (KCl) to wastewater treatmentoperationoutput4.352kgassumed
    Forerun (hexane, water, tert-butanol) to solvent incinerationoperationoutput0.05382kgcalculated
    Paraffin heel purge to incinerationoperationoutput0.03875kgcalculated
    Spent scrubber liquor to wastewater treatmentoperationoutput0.8356kgassumed
    Scrubbed vent (CO2, isobutene, hexane) to the thermal oxidiseroperationoutput0.451kgassumed
    Cooling water returnoperationoutput0.1234kWhassumed
    Chilled brine return (263 K)operationoutput0.5243kWhassumed
    Chilled water return (283 K)operationoutput0.9248kWhassumed
    Nitrogen for inerting R-101, sweeping the degassing, purging the phosgene line, breaking the vacuums and blanketing the tanksoperationinput0.2402kgassumed
    Disposal: Nitrogen for inerting R-101, sweeping the degassing, purging the phosgene line, breaking the vacuums and blanketing the tanks (through the vent header, the scrubber and the site's thermal oxidiser to air, unchanged (D-012))operationoutput0.2402kgassumed

    Computed by ChemE-as-Code from lca/README.md, lca/dataset.yaml, lca/factors.yaml, lca/gaps.csv, lca/inventory.csv, lca/lca.yaml, lca/mappings.yaml, lca/results.csv, lca/results.md.

    In the open LCI database (cheme-as-code-atlas-preview-a3c52e4) as Di-tert-butyl dicarbonate, Boc2O melt to heated storage 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 10 unmapped exchanges. 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 (single-output, from default) · product:BOC 100 %
    Allocation findings
    none
    Change report
    Not available: this build has no change report against an earlier release.
    Dataset pages
    Di-tert-butyl dicarbonate, Boc2O melt to heated storage Preliminary

    KPI benchmark positions

    KPIValueReference rangePosition
    Phosgene consumption per kg of di-tert-butyl dicarbonate
    No open source with a plant's phosgene use per kg of Boc2O found (searched 2026-11-06 as for boc2o-specific-potassium-tert-butoxide); EP 0 256 559 A2 uses 0.54 to 1.5 mol per mol of the alkoxide in its examples (1.5 in Example 1, 1.50 kg/kg on its 149 g), laboratory ratios. Only the stoichiometric floor, 0.453 kg/kg, is known.
    		– kg/kgnot availablenot evaluated
    Potassium tert-butoxide consumption per kg of di-tert-butyl dicarbonate
    No open source with a plant's or a pilot's alkoxide use per kg of Boc2O found (searched 2026-11-06: Google Patents EP 0 256 559 A2 and US 5 151 542 A read, laboratory examples only; Wikipedia, Di-tert-butyl dicarbonate, routes without figures; web search for Boc2O production consumption figures, none found). EP 0 256 559 A2 Example 1 implies 1.13 kg/kg (168 g for 149 g, its purity not stated), US 5 151 542 A Example 1 about 1.18 kg/kg on its methanesulfonyl chloride route (3 mol for 285.8 g at 87 %), single values; the stoichiometric floor is 1.028 kg/kg.
    		– kg/kgnot availablenot evaluated

    Maturity and review

    Design maturity Concept (claimed): An idea or first flowsheet; numbers are rough. Concept batch PFD with closed mass, component and element balances (cheme validate: 5 blocks, 18 steps). The streams are calculated by cheme process propagate from the feeds: the semi-batch R101 from its ASSUMED rate laws with the CO2 and isobutene vented and both gas doses partly or wholly taken up with their ASSUMED heats of solution (core ADRs 0054, 0063), its vent saturated with the slurry's hexane and phosgene and passing R-101's vent condenser at 263 K (core ADR 0062), the degassing DG101 (a nitrogen sweep at 30 kPa(a)) at ASSUMED constant volatilities, its gas carrying the hexane that saturates the sweep past the vent condenser (core's vent and still carry no sweep gas), the strips ST101, ST102 and the vacuum still ST301 on Raoult's law with NIST Antoine constants and an ASSUMED line for Boc2O (core ADR 0055), ST101 with its charge's heat-up (ADR 0063), the scrubber S101 a conversion step; the recovered hexane S30 and the paraffin heel S22 are tears converged by propagate (core ADR 0060). The wash DC201 and the vent split X401 are specified splits from scripts/balance.py (no liquid-liquid or gas-liquid separator in core's propagate), outside any recycle, as are the duties the models leave out (the stills' sensible rise and vessel steel, condensers, the evaporator, the scrubber). The feeds are sized for 500 t/a (scaled to the product). The recipe takes the dosing, post-reaction, degassing, strip and distillation times from the models and the cool-down from the jacket, and sizes R-101, V-201 and C-301 (cheme process recipe, no cheme.recipe-basis finding). Thermal screening (cheme process reactor-hazards): R101 dT_ad 40.5 K (with the doses' heats of solution), accumulation 10.1 % (the deliberate CO2 excess; the phosgene's 2.7 % at the end of its dosing), MTSR 279.5 K against an MTT of 333.15 K (hazard.mtt, Boc2O's decomposition limit); the largest cooling-failure gas over the batch 24.5 m3/h with its vapour against an ASSUMED vent capacity of 50 m3/h; no criticality class without a TD24 (never estimated). The kinetics are assumed: at k/10 the MTSR is 282.5 K and the gas 26.6 m3/h, at k/100 292.0 K and 52.9 m3/h, 1.06 times the vent, with 36.1 % of the phosgene accumulated and stripped into that gas at up to 5.5 kg/h (y = x p*(T)/P over the cooling profile; 0.11 kg/h at the design rate) (a design finding: dosing interlocks, the scrubber's caustic inventory, relief from calorimetry, DESIGN.md D-014). Preliminary gate-to-gate LCI with nitrogen as a per-batch consumable; potassium tert-butoxide, phosgene, caustic soda and nitrogen linked to potassium-tert-butoxide-1, phosgene-1, chlor-alkali-1 and asu-1, hexane, DABCO, CO2 and the paraffin gaps. Not reviewed. Needs cheme-as-code 1.10.0 (DESIGN.md D-015).

    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/di-tert-butyl-dicarbonate-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
    Di-tert-butyl dicarbonate · cheme-as-code>=1.10
    Library version
    a3c52e4 (process last changed in a3c52e4)
    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: "Di-tert-butyl dicarbonate by semi-batch carbonation and phosgenation of potassium tert-butoxide (500 t/a)", ChemE-as-Code process library, version a3c52e4.

    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). ChemE-as-Code: An Open-Source Platform for Agentic AI in Chemical Engineering. arXiv:2611.07947. https://doi.org/10.48550/arXiv.2611.07947

    BibTeX
    @misc{schweidtmann_cheme_as_code,
  author = {Schweidtmann, Artur M.},
  title = {{ChemE-as-Code: An Open-Source Platform for Agentic AI in Chemical Engineering}},
  year = {2026},
  eprint = {2611.07947},
  archivePrefix = {arXiv},
  doi = {10.48550/arXiv.2611.07947},
  url = {https://arxiv.org/abs/2611.07947}
}