Thionyl chloride from sulfur, chlorine and SO2 over activated carbon (3.75 t/h)

Sulfur is chlorinated to sulfur chlorides, whose SCl2 reacts with sulfur dioxide and chlorine over activated carbon at about 200 C; the crude is condensed, degassed (SO2 and Cl2 recycled) and distilled with sulfur to 99.7 wt% thionyl chloride. Concept stage, assumed basis, preliminary gate-to-gate LCI.

Calculation maturity: not assessedDesign maturity: Concept (research)Not independently reviewedSulfuric acidInorganic 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

Molten sulfur and chlorine (from chlor-alkali-1) form S2Cl2 in a pool of sulfur chlorides and are chlorinated on to SCl2 inside the boundary, together with the still bottoms of the purification. The SCl2 vapour is mixed with liquid SO2 (bought, vaporised), chlorine make-up and the recycle gas (SO2 2.0 x, Cl2 1.05 x stoichiometric, after US2431823A) and converted over activated carbon in a cooled multitubular reactor (398 K in, 473 K out; 75 % of the SCl2 per pass, the range of DE2430631A1). The reactor gas is condensed against cooling water and brine, the crude degassed, and the SO2/Cl2 gas recompressed to the reactor; 1 % is purged to a caustic scrubber to carry out the O2 of the chlorine. The degassed crude (84 wt% SOCl2, 16 wt% SCl2) is distilled with sulfur, which turns the SCl2 into high-boiling S2Cl2 (US4759826A, EP0042530B1); the S2Cl2-rich bottoms return to the chlorination, so the only sulfur-chloride exit is the product.

Every stream value and duty comes from an independent script (Raoult's law, ideal gas, conversion reactors; scripts/balance.py) because no property package of core is qualified for the sulfur chlorides, thionyl chloride or the caustic liquor. cheme closes the mass, component and element balances and reproduces the reactor duty. See DESIGN.md for every assumption and gated step.

Capacity
3750 kg/h thionyl chloride (30 kt/a at 8000 h), 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 (8)
  • ASSUMED sulfur chlorides made inside the boundary from sulfur and chlorine (D-001, D-004): the still bottoms (S2Cl2 with sulfur) are rechlorinated there, as US2431823A describes.
  • ASSUMED reactor feed SO2 2.0 x and Cl2 1.05 x stoichiometric, after US2431823A (about 100 % SO2 and 0-10 % Cl2 excess) (D-005).
  • Per-pass conversion of SCl2 0.75 from DE2430631A1 (70-75 % in its examples); S2Cl2 0.95 ASSUMED (D-005). A conversion model, not kinetics; the ideal-gas equilibrium lies much further on (ln(Q/K) = -8.6, cheme process reactors).
  • ASSUMED reactor 398 K in, 473 K out, 170 -> 140 kPa(a), cooled by a tempered-water circuit to cooling water (D-005).
  • ASSUMED condensation at 308 K (cooling water) and 263 K (brine), Raoult's law, O2 insoluble; degasser strips SO2 and Cl2 completely (D-006, D-007).
  • ASSUMED purge 1 % of the recycle gas (O2 7 mol% in the loop) to a caustic scrubber, 99.9 % absorption (D-007, D-009).
  • ASSUMED distillation with sulfur 1.10 x the SCl2 converted, 20 wt% SOCl2 left in the bottoms, reflux ratio 2 (D-008).
  • All flows, temperatures and duties are concept estimates (scripts/balance.py, D-006); accuracy +/-30 % not demonstrated.

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

  • SulfurFeedstockfeed:SULFUR: molten merchant sulfur (refinery or gas-plant sulfur recovery), 0.136 kg/kg
  • ChlorineFeedstockfeed:CL2: chlorine gas (chlor-alkali-1), 0.598 kg/kg
  • Sulfur dioxideFeedstockfeed:SO2: liquid sulfur dioxide (merchant; sulfur burning), 0.274 kg/kg
  • Sodium hydroxideFeedstockfeed:NAOH: caustic soda 50 wt% (chlor-alkali-1), counted by mass of the solution
  • WaterFeedstockDilution water of the scrubber caustic, 84 g/kg SOCl2

Out

  • Thionyl chlorideMain productLiquid thionyl chloride (99.7 wt%) to storage
  • WastewaterWasteSpent scrubber liquor, 113 g/kg SOCl2: Na2SO3, Na2SO4, NaCl and excess NaOH in water, to treatment
  • OxygenEmission0.27 g/kg SOCl2: the O2 impurity of the chlorine, vented after the scrubber with traces of SO2 (5.3 mg/kg) and Cl2 (1.7 mg/kg)

Utilities: Electricity (4.7 Wh/kg SOCl2: recycle gas compressor and pumps (ASSUMED efficiencies); the brine refrigeration's power is in its own exchange), Steam (0.422 kWh (1.52 MJ)/kg SOCl2 of LP steam at 500 kPa(a): vaporisers, feed preheater, degasser and column reboilers), Cooling water (0.501 kWh/kg SOCl2: chlorinators, reactor, crude and column condensers, 25/35 C (ASSUMED))

Show in the process graph

Reactions

IdAs writtenReactionOther processes
CL2_SULFITECl2 + Na2SO3 + 2 NaOH → Na2SO4 + 2 NaCl + H2ONa2SO3+Cl2+2NaOHNa2SO4+2NaCl+H2O1 other process
S2CL2_FORM2 S + Cl2 → S2Cl22S+Cl2Cl2S2
S2CL2_NAOH2 S2Cl2 + 6 NaOH → Na2S2O3 + 2 S + 4 NaCl + 3 H2O2Cl2S2+6NaOHNa2S2O3+2S+4NaCl+3H2O
SCL2_FORMS2Cl2 + Cl2 ⇌ 2 SCl2Cl2S2+Cl22Cl2S
SCL2_FORM_R201S2Cl2 + Cl2 ⇌ 2 SCl2Cl2S2+Cl22Cl2S
SCL2_NAOH2 SCl2 + 6 NaOH → Na2S2O3 + 4 NaCl + 3 H2O2Cl2S+6NaOHNa2S2O3+4NaCl+3H2O
SCL2_SULFURSCl2 + S → S2Cl2Cl2S+SCl2S2
SO2_NAOHSO2 + 2 NaOH → Na2SO3 + H2OSO2+2NaOHNa2SO3+H2O
SOCL2_NAOHSOCl2 + 4 NaOH → Na2SO3 + 2 NaCl + 2 H2OSOCl2+4NaOHNa2SO3+2NaCl+2H2O
SOCL2_SYNSCl2 + SO2 + Cl2 → 2 SOCl2Cl2S+SO2+Cl22SOCl2

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

Footprint not publishedThe process changed since the LCA was last run; its values return once it is run again. Method, functional unit and inventory are below.
Method and data
Goal
Preliminary gate-to-gate life cycle inventory of technical-grade thionyl chloride made from sulfur, chlorine and sulfur dioxide over activated carbon at the concept stage: which raw materials, utilities, wastes and emissions the plant exchanges per kg of thionyl chloride, as the foreground for a later cradle-to-gate study. No impact results: the backgrounds are not mapped yet (D-012).
Functional unit
1 kg Thionyl chloride (1 kg thionyl chloride)
Boundary
cradle-to-gate
Characterisation
Factors kept with the process · GWP100
Data quality
No factors
Result
partial screening carbon footprint · 10 data gaps

Inventory per 1 kg Thionyl chloride (19 flows)

FlowPhaseDirectionQuantityUnitProvenance
Molten sulfur (merchant sulfur from refinery or gas-plant sulfur recovery)operationinput0.1357kgassumed
Chlorine gas (chlor-alkali-1)operationinput0.598kgassumed
Liquid sulfur dioxide (merchant; sulfur burning)operationinput0.2738kgassumed
Caustic soda 50 wt% (chlor-alkali-1)operationinput0.02111kgassumed
Process water (scrubber dilution)operationinput0.08443kgassumed
Electric poweroperationinput0.004715kWhassumed
LP steam 500 kPa(a)operationinput0.4219kWhassumed
Thionyl chloride to storageoperationoutput1kgassumed
Spent scrubber liquor to wastewater treatmentoperationoutput0.1127kgassumed
Scrubbed vent to atmosphereoperationoutput0.0002837kgassumed
Cooling water returnoperationoutput0.5015kWhassumed
Refrigerated brine return (253 K)operationoutput0.1186kWhassumed
CL2 to the environmentoperationoutput0.000001671kgassumed
H2O to the environmentoperationoutput0.000006491kgassumed
O2 to the environmentoperationoutput0.00027kgassumed
S2CL2 to the environmentoperationoutput0.00000000001739kgassumed
SCL2 to the environmentoperationoutput0.00000002721kgassumed
SO2 to the environmentoperationoutput0.000005267kgassumed
SOCL2 to the environmentoperationoutput0.0000002306kgassumed

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-c3ab348) as Thionyl chloride to 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 5 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:SOCL2 100 %
Allocation findings
none
Change report
Not available: this build has no change report against an earlier release.
Dataset pages
Thionyl chloride to storage 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: all 5 blocks and 20 steps within tolerance; cheme process propagate --check agrees). The reactor R201 is a conversion model; core reproduces its duty from the ideal-gas data (-386.6 kW). The condensers, degasser, column and scrubber are specified values from scripts/balance.py: no property package of core covers the sulfur chlorides, thionyl chloride or the caustic liquor, so their energy balance is not evaluable in core. The ideal-gas equilibrium of SCl2 + SO2 + Cl2 lies far beyond the published 50-80 % per-pass conversion (ln(Q/K) = -8.6): the conversion is taken from the patent, not predicted. Preliminary gate-to-gate LCI with every background unmapped (gaps). cheme maturity reaches no level (assumed feeds, conversions and separations, DESIGN.md); the claim `maturity: concept` is the lowest value of the schema, not an evidenced level, and cheme maturity reports it as cheme.maturity-claim-exceeds (accepted, review R-04). 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/thionyl-chloride-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
Thionyl chloride · 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: "Thionyl chloride from sulfur, chlorine and SO2 over activated carbon (3.75 t/h)", 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}
}