Sodium azide by the hydrazine / methyl nitrite route, batch, with precipitation from the reaction liquor (670 t/a)

A batch plant: methyl nitrite from sodium nitrite, methanol and sulfuric acid is absorbed into hydrazine and caustic soda; sodium azide precipitates from the concentrated liquor and is filtered, washed and dried in a filter-dryer, the mother liquor recycled. Concept stage, 1028 kg per batch every 12.1 h, thermal screening, preliminary LCI.

Calculation maturity: not assessedDesign maturity: Concept (research)Not independently reviewedInorganic chemicalsReport 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 of US 5 208 002 A (Nippon Carbide, 1993): in R-101, 98.5 % sulfuric acid is dosed over 10 h into aqueous sodium nitrite with an equimolar amount of methanol at 298 K, and the methyl nitrite gas formed passes straight into R-102. There it is absorbed (91.8 %, the share the patent's Example 1 balance accounts for) into hydrazine hydrate and caustic soda (1.20 mol NaOH per mol hydrazine) together with the mother liquor of the previous batch at 313 K, and gives sodium azide and methanol; about 5 % of the hydrazine consumed is lost to ammonia and nitrous oxide (95 % selectivity at the patent's 70 % conversion). The acid side and the azide side never share a vessel or a liquor, so the azide never meets acid; hydrazine carried in the recovered methanol would form HN3 in R-101, so that methanol has a hydrazine limit (D-015). The liquor is stripped of methanol and concentrated at 10 kPa(a) in the batch still C-101 (the methanol cut, 88 wt%, goes back to R-101 and to the cake wash; the residue ends at about 360 K, estimated with the caustic liquor's boiling-point elevation, an open reaction-hazard item), NaN3 precipitates at 303 K from the concentrated caustic liquor (39 wt% NaOH, 17 wt% hydrazine), and the agitated filter-dryer F-101 filters it, washes it with methanol (0.43 kg/kg) and dries it at 333 K under vacuum. The mother liquor, the wash filtrate and the dryer condensate go back to R-102, less a 5 % purge to azide destruction (the hydrazine oxidised first, then the azide with nitrite and acid). Product 99.6 wt% NaN3; yield 92.3 % on hydrazine. Per kg NaN3: sodium nitrite 1.222 kg, sulfuric acid 0.883 kg, hydrazine hydrate (64 %) 0.831 kg, caustic soda (50 %) 1.287 kg, methanol 0.074 kg; 0.036 kg N2O leaves in the off-gas to the thermal oxidiser.

It is the library's first entry on core's batch work-up models: R-101 and R-102 are semi-batches with their gas vents (batch.vent, dosing.absorbed; core ADR 0054), C-101 a batch Rayleigh still with two cuts (ADR 0055), the precipitation a crystallizer with spectator solutes and a solubility measured in the patent's mother liquor (ADR 0056), and F-101 a filter-dryer over four steps with its filtration and drying times (ADR 0057). R-102's jacket sets the 10 h dosing; R-102 is the bottleneck (cycle 12.14 h, 652.6 batches a year). The kinetics are ASSUMED (no open data): the dissolved methyl nitrite accumulates to 2.0 % and the cooling-failure temperature stays at 318.9 K, below the 337.6 K boiling point of methanol, but a ten times slower reaction would exceed it. The gas a cooling failure releases at the MTSR is within the vents (ASSUMED 50 and 60 m3/h), but a blocked vent pressurises R-101 or R-102: the acid dosing trips on pressure, and each reactor needs a relief device. See DESIGN.md for every assumption, the process safety notes (azide toxicity, hydrazoic acid from azide and from hydrazine, heavy-metal azides, methyl nitrite, the hot concentrated liquor) and the core limits met.

Capacity
670.6 t/a dried NaN3: 652.6 batches/a of 1027.6 kg in 7920 h on a dedicated train (84.68 kg/h year average), ASSUMED (DESIGN.md D-002, D-003, D-014)
Operation
7,920 h/a
Location
generic fine-chemicals site with a thermal oxidiser and an azide-capable wastewater treatment (not chosen)
Engineering gates
Concept and feasibility (no results yet)
Maintainers
Artur Schweidtmann
Design basis and assumptions (8)
  • Route: methyl nitrite generated from sodium nitrite, methanol and sulfuric acid in its own vessel and absorbed into aqueous hydrazine and caustic soda; NaN3 crystallised from the concentrated liquor, methanol recovered, the filtrate recycled (US 5 208 002 A, D-001).
  • Charge ratios from US 5 208 002 Example 1 (D-004): 1.20 mol NaOH, 0.769 mol NaNO2 and 6.63 mol water per mol hydrazine; 0.501 mol H2SO4 and 1.002 mol methanol per mol NaNO2; 91.8 % of the methyl nitrite absorbed; 95 % selectivity on hydrazine (D-005).
  • ASSUMED fast effective rate laws for both semi-batches (D-005): no open kinetics; the low accumulation follows from them (D-011).
  • Heats of reaction from pure-substance formation enthalpies (chemicals: CRC, ATcT, NIST WebBook), heats of solution not counted (D-005).
  • ASSUMED jackets: U 400 W/(m2 K) on chilled water at 278-283 K; R-102's jacket sets the 10 h dosing (D-010).
  • Effective relative volatility of methanol to water 150 in the one-stage still, calibrated to the patent's 90 wt% methanol cut (D-007); NaN3 solubility measured in the patent's mother liquor (D-008).
  • 5 % of the mother liquor purged per batch (D-016).
  • All flows are year averages of the recipe (D-003); duties from core's models, power ASSUMED (D-012); 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

  • Sodium nitriteFeedstockDried sodium nitrite (sodium-nitrite-1), dissolved in R-101's charge, 1.222 kg/kg NaN3
  • Sulfuric acidFeedstockSulfuric acid 98.5 wt% (sulfuric-acid-1), dosed into R-101, 0.883 kg/kg NaN3
  • HydrazineFeedstockHydrazine hydrate 64 wt% N2H4 (hydrazine-1), 0.831 kg/kg NaN3 as hydrate
  • Sodium hydroxideFeedstockCaustic soda 50 wt% (chlor-alkali-1), 1.287 kg/kg NaN3 as solution
  • MethanolFeedstockMethanol make-up (methanol-1) of the methanol loop, 0.074 kg/kg NaN3; the methanol itself is recovered and reused
  • WaterFeedstockProcess water to R-101's charge, 3.05 kg/kg NaN3
  • WaterFeedstockProcess water to R-102's charge, 1.38 kg/kg NaN3
  • NitrogenFeedstockNitrogen (asu-1) for inerting, vacuum breaks and pressure filtration, 50 kg per batch, 0.049 kg/kg NaN3 (ASSUMED)

Out

  • Sodium azideMain productDried sodium azide, 99.6 wt% NaN3, to packing
  • WastewaterWasteSodium sulfate liquor of the nitrite generator, 4.72 kg/kg NaN3, to wastewater treatment
  • WastewaterWasteEvaporator condensate (water, 0.12 wt% methanol), 2.78 kg/kg NaN3, to wastewater treatment
  • WastewaterWasteMother-liquor purge (product:PURGE: NaOH, hydrazine, 8 wt% NaN3), 0.086 kg/kg NaN3, to azide destruction (hydrazine oxidised first) and wastewater treatment; an LCI gap
  • Nitrous oxideEmissionR-102's off-gas (product:OFFGAS, 0.138 kg/kg NaN3) to the thermal oxidiser: methyl nitrite 64, N2O 26, NH3 10 wt%; 0.036 kg N2O per kg NaN3, whose fate in the oxidiser is open (DESIGN.md D-013)

Utilities: Electricity (0.154 kWh/kg NaN3: agitators, gas dispersion, vacuum pumps (ASSUMED)), Steam (2.30 kWh/kg NaN3 of LP steam 350 kPa(a), through tempered hot water: the still's boil-up and the filter-dryer), Chilled water (2.08 kWh/kg NaN3 removed by chilled water at 278-283 K: R-101, R-102 and the methanol condensers), Cooling water (1.98 kWh/kg NaN3: the still's water condenser and the crystallizer, 25/35 C (ASSUMED))

Show in the process graph

Reactions

IdAs writtenReactionOther processes
AZN2H4 + CH3ONO + NaOH → NaN3 + CH3OH + 2 H2O · Sodium azide from hydrazine, methyl nitrite and sodium hydroxideN2H4+CH3NO2+NaOHNaN3+CH4O+2H2O
NTG2 NaNO2 + H2SO4 + 2 CH3OH → 2 CH3ONO + Na2SO4 + 2 H2O · Methyl nitrite from sodium nitrite, methanol and sulfuric acid2NaNO2+H2SO4+2CH4O2CH3NO2+Na2SO4+2H2O
SIDEN2H4 + CH3ONO → N2O + NH3 + CH3OH · Hydrazine nitrosated to ammonia and nitrous oxide (selectivity loss)N2H4+CH3NO2N2O+NH3+CH4O

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, 16 data gaps

Climate change per 1 kg Dried sodium azide, 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 sodium azide made by the batch hydrazine / methyl nitrite route (methyl nitrite from sodium nitrite, methanol and sulfuric acid, absorbed into hydrazine and caustic soda; NaN3 precipitated from the concentrated liquor, filtered, washed with methanol and dried, the mother liquor recycled) at the concept stage: which raw materials, utilities and wastes the batch plant exchanges per kg of dried NaN3, as the foreground for a later cradle-to-gate study. No impact results: most utility and treatment backgrounds are not mapped yet (D-013).
    Functional unit
    1 kg Dried sodium azide (1 kg sodium azide)
    Boundary
    cradle-to-gate
    Characterisation
    Factors kept with the process · GWP100
    Data quality
    No factors
    Result
    partial screening carbon footprint · 16 data gaps
    ScenarioClimate change (kg CO2-eq)
    baselineno total (data gaps)

    Inventory per 1 kg Dried sodium azide (17 flows)

    FlowPhaseDirectionQuantityUnitProvenance
    Sodium nitrite (sodium-nitrite-1)operationinput1.222kgassumed
    Process water (nitrite generator)operationinput3.051kgassumed
    Sulfuric acid 98.5 wt% (sulfuric-acid-1)operationinput0.8834kgassumed
    Hydrazine hydrate 64 wt% N2H4 (hydrazine-1)operationinput0.8315kgassumed
    Caustic soda 50 wt% (chlor-alkali-1)operationinput1.287kgassumed
    Process water (azide reactor)operationinput1.377kgassumed
    Methanol make-up (methanol-1)operationinput0.07396kgassumed
    Electric poweroperationinput0.1535kWhassumed
    LP steam 350 kPa(a) (still and filter-dryer)operationinput2.297kWhassumed
    Dried sodium azide to packingoperationoutput1kgcalculated
    Sodium sulfate liquor to wastewater treatmentoperationoutput4.72kgcalculated
    Evaporator condensate to wastewater treatmentoperationoutput2.781kgcalculated
    Mother-liquor purge to azide destruction and wastewater treatmentoperationoutput0.08622kgcalculated
    Azide reactor off-gas to the thermal oxidiseroperationoutput0.1381kgcalculated
    Chilled water return (R-101, R-102 and the methanol condensers)operationoutput2.081kWhassumed
    Cooling water return (still's water condenser and crystallizer)operationoutput1.984kWhassumed
    Nitrogen for inerting R-101 and R-102, breaking C-101's vacuum and the pressure filtrations of F-101operationinput0.04865kgassumed

    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 Dried sodium azide to packing 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 3 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:NAN3P 100 %
    Allocation findings
    none
    Change report
    Not available: this build has no change report against an earlier release.
    Dataset pages
    Dried sodium azide to packing Preliminary

    KPI benchmark positions

    KPIValueReference rangePosition
    Hydrazine hydrate (64 wt% N2H4) per kg of sodium azide– kg/kg0.807 to 0.852 kg/kg
    Sasaki, M. et al. (Nippon Carbide Industries, 1993) US 5 208 002 A, Method of producing alkali metal azides (family EP 0 514 143 B1; priority 1991-05-17) (other)
    		not evaluated
    Azide reactor off-gas to treatment per kg of sodium azide
    No open source with the off-gas (unabsorbed methyl nitrite, N2O, NH3) of a sodium azide plant found (searched 2026-11-05: Google Patents US 5 208 002 A and US 5 098 597 A read, which name the nitrogen of side reactions but give no off-gas amounts; J. Studley, Scientific Update 2023, a secondary summary without figures). The dataset's off-gas follows from the methyl nitrite not absorbed in the patent's Example 1 balance and its ASSUMED side reaction (DESIGN.md D-004, D-005).
    		– 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: 4 blocks and 13 steps within tolerance). Calculated by cheme process propagate with core 1.9.0: the two vented semi-batches R101 and R102 from their ASSUMED rate laws, the batch still ST101 (constant relative volatility, ASSUMED), the precipitation CR101 from a solubility measured in the patent's mother liquor, the specified filters and the dryer; the two recycles (methanol to R-101, mother liquor to R-102) converged by propagate at the tear streams S3 and S11 (Wegstein, 32 iterations), the fresh feeds ASSUMED at the charge ratios; the duties of R101, R102, the still's boil-up and the crystallizer written by their models. The recipe's year-average product rate agrees with the flowsheet (no cheme.recipe-basis finding); the recipe sizes R-101 (6.3 m3), R-102 (8 m3) and F-101 (2 m3), both jacket checks pass. Thermal screening (cheme process reactor-hazards): R-102 dT_ad 307 K, accumulation 1.98 %, MTSR 318.9 K against an MTT of 337.63 K (core's default: methanol's boiling point); R-101 dT_ad 43 K, MTSR 298.6 K; the gas release at the MTSR 29.4 m3/h (R-101) and 6.3 m3/h (R-102) against ASSUMED vent capacities of 50 and 60 m3/h; the pressure of a blocked vent is estimated by hand (a design finding: pressure trip and relief); no criticality class without a TD24 from calorimetry (none estimated). Preliminary gate-to-gate LCI with the per-batch nitrogen; the purchased feeds linked to their library producers, utilities and treatments gaps. cheme maturity reaches no level (assumed feeds, kinetics and separations); the claim `maturity: concept` is the lowest value of the schema, not an evidenced level. Not reviewed. Needs cheme-as-code 1.9.

    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/sodium-azide-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
    Sodium azide · cheme-as-code>=1.9
    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: "Sodium azide by the hydrazine / methyl nitrite route, batch, with precipitation from the reaction liquor (670 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}
}