Uncertainty-Aware Techno-Economic Assessment of Calcium-Based Treatment and Caustic Recovery from Refinery Spent Caustic
- 1Independent researcher
Abstract
Refinery spent caustic is difficult to treat because of its high alkalinity, sulfur species and dissolved organics. Independent electrolyte-model calculations (PHREEQC; not experimental validation) show that lime treatment cannot both recover caustic and precipitate sulfate as gypsum: gypsum fell below 0.1% of the sulfate once the equilibrium hydroxide exceeded 0.08–0.23 mol/kg (25–90 °C; up to 0.31 with solubility-product shifts of ±0.5 log units), while carbonate causticization stayed favorable (97% conversion at 25 °C, 1 M initial NaOH). Sulfate removal as a solid therefore needs a separate environment from caustic recovery, which defines when neutralization, causticization with recycle or a staged hybrid applies. A Monte Carlo model (10,000 draws; 720 to 1,320 designs) carries this constraint into process design, a sulfate-limited recycle loop and an economic screen against third-party disposal. Oxygen supply is the physical limit: at 80 °C with atmospheric air the required oxygen-transfer rate exceeds the achievable one by a median factor of 23, so the kinetics-only optimum (median NPV $11.7M for Route B, $5.4M for neutralization) is an upper bound. The preferred design is conditional on oxygen enrichment: with 90% oxygen, 60 °C and 12 h, Route B has a median NPV of $6.4M (P10 −$1.3M; P(NPV>0) = 84%) against $0.2M for neutralization, but it meets the sulfide-removal requirement in only 39% of draws without chemical enhancement of transfer and 67% with half the assumed kLa; with air it is not viable. Results are conditional screening values, not forecasts; no experimental data are reported.
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BibTeX
@misc{sandler2026uncertaintyaware,
title = {{Uncertainty-Aware Techno-Economic Assessment of Calcium-Based Treatment and Caustic Recovery from Refinery Spent Caustic}},
author = {Leon Sandler},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010706/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010706/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Uncertainty-Aware Techno-Economic Assessment of Calcium-Based Treatment and Caustic Recovery from Refinery Spent Caustic
AU - Leon Sandler
PY - 2026
DA - 2026/10/20
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010706/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010706/v1
AB - Refinery spent caustic is difficult to treat because of its high alkalinity, sulfur species and dissolved organics. Independent electrolyte-model calculations (PHREEQC; not experimental validation) show that lime treatment cannot both recover caustic and precipitate sulfate as gypsum: gypsum fell below 0.1% of the sulfate once the equilibrium hydroxide exceeded 0.08–0.23 mol/kg (25–90 °C; up to 0.31 with solubility-product shifts of ±0.5 log units), while carbonate causticization stayed favorable (97% conversion at 25 °C, 1 M initial NaOH). Sulfate removal as a solid therefore needs a separate environment from caustic recovery, which defines when neutralization, causticization with recycle or a staged hybrid applies. A Monte Carlo model (10,000 draws; 720 to 1,320 designs) carries this constraint into process design, a sulfate-limited recycle loop and an economic screen against third-party disposal. Oxygen supply is the physical limit: at 80 °C with atmospheric air the required oxygen-transfer rate exceeds the achievable one by a median factor of 23, so the kinetics-only optimum (median NPV $11.7M for Route B, $5.4M for neutralization) is an upper bound. The preferred design is conditional on oxygen enrichment: with 90% oxygen, 60 °C and 12 h, Route B has a median NPV of $6.4M (P10 −$1.3M; P(NPV>0) = 84%) against $0.2M for neutralization, but it meets the sulfide-removal requirement in only 39% of draws without chemical enhancement of transfer and 67% with half the assumed kLa; with air it is not viable. Results are conditional screening values, not forecasts; no experimental data are reported.
ER -