N-Propanol Bulk Supplier: Industrial-Grade N-Propanol
Industrial-grade n-propanol is supplied as a clear, water-miscible oxygenated solvent with CAS registry number 71-23-8 and EINECS notification 200-746-9. The product typically carries a minimum purity of 99.5 wt% by GC-FID internal normalization, with the residual mass consisting of water, propionaldehyde, and trace branched or secondary alcohols. A representative bulk certificate of analysis includes density in the range 0.803–0.805 g/cm³ at 20 °C measured by ASTM D4052, distillation range 96.5–98.0 °C by ASTM D1078, water below 0.10 wt% by ASTM E203, acidity below 0.003 wt% as acetic acid by ASTM D1613, colour below 10 Pt-Co by ASTM D1209, and non-volatile residue below 0.002 wt% by ASTM D1353. The closed-cup flash point of 22 °C measured by ASTM D56 and the vapour pressure of 2.0 kPa at 20 °C place the liquid in UN 1274, Class 3, Packing Group II for land and sea transport. Bulk supply modes include dedicated stainless steel tank trucks with 25,000 L capacity, railcars, ISO tank containers, and 1,000 L intermediate bulk containers; each mode requires vapour recovery or nitrogen blanketing during transfer because the lower explosion limit is 2.2 vol% and the upper explosion limit is 13.7 vol% in air.
| Parameter | Typical range | Unit | Test method |
| Purity by GC-FID internal normalization | ≥99.5 | wt% | GC-FID internal normalization |
| Water | ≤0.10 | wt% | ASTM E203 |
| Acidity as acetic acid | ≤0.003 | wt% | ASTM D1613 |
| Distillation range | 96.5–98.0 | °C | ASTM D1078 |
| Density at 20 °C | 0.803–0.805 | g/cm³ | ASTM D4052 |
| Colour | ≤10 | Pt-Co | ASTM D1209 |
| Non-volatile residue | ≤0.002 | wt% | ASTM D1353 |
What Limits Water Tolerance in Flexographic Ink Solvent Blends?
The water tolerance of flexographic solvent blends is determined less by the absolute water content of n-propanol than by the Hansen solubility parameter mismatch between the solvent blend and the resin backbone. n-Propanol exhibits a hydrogen-bonding Hansen parameter of approximately 17.4 MPa^0.5, compared with 7.2 MPa^0.5 for ethyl acetate and 19.4 MPa^0.5 for ethanol; this places n-propanol between fast evaporating esters and strongly associated alcohols in terms of resin solvency. For a common nitrocellulose-polyamide laminating ink system, the solvent blend 70:20:10 n-propanol:n-propyl acetate:water maintains clear solution stability up to a water content of 6–8 wt% at 25 °C, but the same resin system can oil out or precipitate at water contents above 9 wt% when the pressroom relative humidity exceeds 65%. The threshold is not a fixed material constant; it shifts with resin acid number, co-solvent ketone or acetate concentration, and the presence of nitrocellulose wetting agents. On a 10-colour central impression flexographic press running at 300 m/min, the ink temperature is controlled to 25 ± 2 °C and the flow viscosity is maintained between 13 s and 18 s in a 4 mm ISO 2431 cup. The chambered doctor blade system on such a press recirculates ink through 40 μm channel filters; when a water-based ink changeover is performed and the solvent blend is returned to service, residual water in the chamber and supply lines can raise the blend water content overnight from 1 wt% to 9 wt% if the lines are not flushed with anhydrous n-propanol. The resulting resin precipitation causes filter blockage and print run interruptions, and the failure mode is frequently misread as a viscosity control error rather than a water tolerance excursion. A water tolerance test is therefore performed by titrating water into the blend until permanent clouding at 25 °C; a value below 8 wt% is considered unsuitable for humid pressroom environments unless the drying air dew point is controlled below 10 °C. ASTM D1720 can be used to determine the dilution ratio of cellulose nitrate solutions, but the water tolerance determination itself is commonly an internal ink laboratory method.
Bulk n-propanol delivered at 0.10 wt% water does not by itself exceed the water tolerance of a flexographic ink, but repeated exposure of partially filled drums to 60% relative humidity raises the water content by measurable increments depending on the ratio of headspace volume to liquid volume and the number of drum openings. For a 200 L drum stored in a non-air-conditioned ink compounding room, this moisture gain can move a production batch from an initial water content of 0.10 wt% to 0.20 wt% before the batch is pumped into the day tank; the shift is small in absolute terms but large enough to alter the water tolerance margin when the blend is cut with n-propyl acetate and polyurethane resin. The processing conflict arises when the ink formulator compensates for summer humidity by increasing n-propanol content to maintain solubility; this raises the VOC content of the final ink per ASTM D2369 and may exceed the volatile organic compound limit set by the local air quality district or the EU Solvent Emissions Directive 2004/42/CE. Consequently, bulk n-propanol tanks serving flexographic ink operations are often fitted with desiccant breathers on day tanks, and the transfer pumps are specified as positive displacement or small centrifugal units with total dynamic head below 30 m to avoid excessive shear heating because prolonged pumping at high differential pressure can raise the solvent temperature and accelerate evaporative loss.
Continuous production of propyl acetate from n-propanol and acetic acid in fixed-bed sulfonic acid resin reactors encounters a process conflict at water mass fractions above 0.2 wt% in the mixed feed. The esterification equilibrium for acetic acid with C₁–C₄ alcohols at 25 °C has an equilibrium constant in the approximate range 4.0–5.0, but the value declines with rising temperature; at the usual reactor jacket temperature of 110–120 °C, single-pass conversion through a macroporous sulfonic acid resin bed with a liquid hourly space velocity of 0.8–1.5 h⁻¹ is typically limited to 65–80% unless water is removed. A 316L stainless steel reactive distillation column with 10–14 theoretical stages and a reflux ratio of 2:1–4:1 can drive conversion above 98% by stripping the n-propyl acetate/water azeotrope overhead; the decanted organic phase returns as reflux while the aqueous phase is discharged to a wastewater stripper. Feed water above 0.2 wt% displaces acetic acid from the sulfonic acid active sites and increases the acid concentration in the overhead decanter, lowering the pH below 3.5 and accelerating stress corrosion cracking in unlined carbon steel unless 316L or PTFE-lined components are installed downstream. The side reaction dehydration of n-propanol to propylene and subsequent etherification to di-n-propyl ether is favoured by low water activity and high alcohol-to-acid feed ratios above 1.5:1; di-n-propyl ether above 0.5 wt% in the final propyl acetate reduces nitrocellulose solvency and can fail a customer ester purity specification of ≥99.0 wt%. A continuous gas chromatograph sampling the reactor effluent every 15 minutes is specified to monitor water, di-n-propyl ether, and unreacted acetic acid because a batch-to-batch shift in bulk n-propanol water concentration from 0.05 wt% to 0.15 wt% is sufficient to move the esterification reactor out of the 85–95% first-pass conversion window. Published data for this specific fixed-bed configuration are limited, but the water sensitivity of sulfonic acid resin catalysts is broadly documented in industrial esterification literature.
Amination Selectivity Collapses Below 1.2 MPa(g) at 180 °C
Gas-phase amination of n-propanol over nickel- or cobalt-based catalysts at 150–200 °C and 1.0–2.5 MPa(g) produces mono-n-propylamine, di-n-propylamine, and tri-n-propylamine in a multi-tubular reactor with a molten salt heat-transfer jacket. The exothermic disproportionation of mono-n-propylamine over acidic sites on the alumina support can raise local bed temperatures by 10–20 °C above the reactor set point; this temperature excursion is controlled by maintaining the ammonia-to-n-propanol molar feed ratio at 2.5:1–4:1 and by distributing the feed into the tube sheet through multi-point gas-liquid distributors. The pressure dependency is a critical process boundary: at 180 °C, a reduction in reactor pressure below 1.2 MPa(g) increases the di-n-propylamine molar fraction by 10–15 percentage points and decreases mono-n-propylamine selectivity below the 80% target typical of continuous amination units. Water produced in the condensation reaction is removed in a downstream separation train; if water is allowed to accumulate above 0.5 wt% in the recycle feed, hydration of the gamma-alumina support accelerates catalyst deactivation and shortens the 1,000 h time-on-stream interval between regenerations. The product mixture is purified by extractive distillation with sodium hydroxide solution; because n-propylamine forms an azeotrope with water at atmospheric pressure, the distillation column overhead must be controlled below 80 °C and the reflux ratio adjusted to keep the water content in the distillate below 0.2 wt% before dehydration over molecular sieves. A bulk n-propanol feed containing 0.15 wt% water is generally acceptable for the amination reactor; however, the storage tank must be nitrogen-blanketed to avoid dissolved carbon dioxide, which can form propylammonium bicarbonate salts and plug the feed preheater tube side.
In coil coating primers and thermosetting acrylic topcoats, n-propanol is used as a tail solvent with a relative evaporation rate of 1.0–1.4 relative to n-butyl acetate by ASTM D3539. The slower evaporation compared with isopropanol extends the wet edge time during curtain coating on high-speed flat lines; a 5 wt% substitution of n-propanol for isopropanol in a polyester-melamine formula can raise the flow time by 3–5 s in a 4 mm ISO 2431 cup at 25 °C without changing the volatile organic compound content measured by ASTM D2369. This viscosity shift is most pronounced when the water content is below 0.3 wt% because n-propanol associates with hydroxyl groups on the melamine resin and delays the onset of shear thickening under high-shear application. A limitation is the closed-cup flash point of 22 °C: the material remains classified as H225 and requires the same explosion-zone ventilation as isopropanol, with electrostatic grounding of piping, bulk storage tanks, and mixers according to IEC 60079-10-1 and EN 1127-1. Moreover, n-propanol is miscible with water and can draw moisture into open mixers above 60% relative humidity; in high-humidity coastal facilities, drum pumps are fitted with desiccant vents on the drum adapters to keep the solvent water content below 0.10 wt% and avoid amine blush in two-component epoxy topcoats. Solvent-borne coating formulations using n-propanol above 10 wt% of total solvent must also consider the moderate surface tension of approximately 23.8 mN/m at 20 °C, which can influence cratering and flow levelling on corona-treated polypropylene substrates.
When n-Propanol Replaces Isopropanol in Gravure Cylinder Cleaning
When n-propanol replaces isopropanol in gravure cylinder cleaning, the lower evaporation rate increases residence time on the engraved cell walls. A 200 L closed-loop cylinder wash unit operating at 40–50 °C and 0.3–0.5 MPa(g) spray pressure removes dried nitrocellulose-based ink more completely at a 3:1 n-propanol:n-propyl acetate ratio than an equivalent isopropanol blend because the longer dwell time softens the resin binder and lowers the mechanical load on the rotating brushes. The flash point of the blend remains below 23 °C unless water is added above 10 wt%, so the wash unit must be nitrogen-inerted and interlocked with the extraction airflow according to EN 1539 and NFPA 30. Elastomer seals in the pump and nozzle manifold require compatibility review because n-propanol can swell nitrile rubber by more than 8% volume after 168 h immersion at 25 °C in supplier immersion tests; EPDM or PTFE-encapsulated gaskets are substituted when the unit is converted. The cleaned cylinder must be dried at 80 °C for 10–15 s in an air knife before re-engraving or proofing because residual n-propanol at 0.05 mL/m² can interfere with water-based ink wetting and produce dot skipping on the next job. Conductivity probes used for water detection in isopropanol wash baths must be recalibrated because n-propanol-water mixtures exhibit different dielectric properties than isopropanol-water mixtures at water contents below 5 wt%; this can delay automatic phase separation and allow water accumulation in the solvent recovery loop. A distillation column in the recovery loop operated at 95–100 °C head temperature removes water overhead if the column is designed for the n-propanol/water azeotrope; otherwise, the recovered solvent may exceed 0.5 wt% water and fail the cleaning specification.
During API crystallizations where a Class 3 alcohol is required, n-propanol is used as an antisolvent or recrystallization solvent at addition levels determined by ICH Q3C residual solvent limits. The concentration limit for n-propanol in the drug substance is 0.5 wt% (5,000 ppm) based on the PDE of 50 mg/day under ICH Q3C Table 3; equipment trains with vacuum tray dryers at 60–80 °C and 10–20 kPa absolute pressure reduce residual n-propanol below 0.1 wt% within 4–8 h drying time depending on cake surface area and agitation speed. The high water miscibility of n-propanol compared with n-butyl acetate allows antisolvent crystallization in aqueous systems without two-phase splitting; however, this same miscibility can increase mother liquor viscosity and reduce crystal yield if the antisolvent is added faster than 0.5 mL/min per kg batch mass. A typical crystallization train charges n-propanol over 90–120 min to control supersaturation, with final n-propanol mass fractions of 10–15 wt%; the actual addition rate is determined by the metastable zone width measurement and seeded batch kinetics. The crystallizer jacket is often held at 5 °C during antisolvent addition, and seeding is required at a supersaturation ratio below 1.3 to prevent oiling out. The use of n-propanol in active pharmaceutical ingredient processing must be documented under EU GMP Part II Chapter 5 and USP 467 for solvent residues. Published data for a specific production-scale crystallization are limited, but the general antisolvent behaviour and Class 3 status are established in ICH guidance.
Bulk Tank Ullage and Vapour Recovery Requirements
Storage terminals handling industrial-grade n-propanol in 25,000–100,000 L above-ground tanks use internal floating roofs or nitrogen blanketing because the closed-cup flash point is 22 °C and the vapour pressure at 20 °C is 2.0 kPa. The flammability range of 2.2–13.7 vol% in air means the headspace of a conserved vent tank can cross the lower explosive limit at ambient temperatures if the blanket fails; therefore, oxygen analyzers set to alarm at 5.0 vol% oxygen are interlocked with transfer pumps. Unloading from a 25,000 L tank truck at 600–800 L/min through a 100 mm flexible hose requires a pump NPSH margin of at least 1.0 m above the liquid vapor pressure to avoid cavitation; centrifugal pumps with double mechanical seals and carbon versus silicon carbide faces are specified because single-seal leakage through the alcohol-wetted elastomer can create a pooled flammable layer in the containment dike. Thermal expansion in a full pipeline segment between closed block valves can raise pressure enough to exceed the 1.0 MPa(g) design pressure of common transfer piping if the segment is heated by only a few degrees; thermal relief valves must discharge to a closed drain or a flame arrestor. The material is not classified as a peroxide-forming solvent under standard laboratory storage categories, but prolonged exposure to air at temperatures above 35 °C can increase aldehyde content by autoxidation; therefore, bulk storage tanks are kept below 30 °C and sampled weekly for peroxide content using ASTM E298 or equivalent iodometric titration. Tank ullage calculations use a maximum filling ratio of 95% at 20 °C and a thermal expansion allowance based on the density difference between 5 °C and 30 °C; railcar loading charts from the bulk supplier should be consulted because the available outage varies with the tank design pressure and the pressure-relief valve setting.
Regulatory compliance for industrial-grade n-propanol requires simultaneous attention to transport classification, occupational exposure, and environmental emission obligations. The transport entry UN 1274 is used for bulk shipments with the proper shipping name “propanols” when the isomer content meets the class definition; the GHS classification under EC 1272/2008 includes Flam. Liq. 2 H225, Eye Dam. 1 H318, and STOT SE 3 H336. The EU workplace indicative occupational exposure limit value for n-propanol is not harmonized in all member states; several national lists use an 8-hour time-weighted average in the range 100–200 ppm, but site-level air monitoring must follow the supplier SDS and the applicable national standard. n-Propanol is not listed as a hazardous air pollutant under the US EPA 40 CFR 63 Subpart C list; however, it remains a volatile organic compound and is counted in emission inventories under the EU Solvent Emissions Directive 2004/42/CE and equivalent state implementation plans. For pharmaceutical applications, n-propanol is a Class 3 solvent under ICH Q3C with a PDE of 50 mg/day and a concentration limit of 0.5 wt%. In food-contact uses, n-propanol may be used as a solvent in adhesives and coatings under 21 CFR 175.105 and 21 CFR 175.300 only within the extraction and residual limits specified by those sections. The bulk supplier certificate of analysis should be issued under an ISO 9001 quality management system and include the batch number, analytical results, and the signature of the responsible quality officer.
| Factor | Classification or limit | Reference |
| CAS registry number | 71-23-8 | — |
| EINECS number | 200-746-9 | — |
| GHS classification | Flam. Liq. 2 H225; Eye Dam. 1 H318; STOT SE 3 H336 | EC 1272/2008 |
| UN transport | UN 1274, Class 3, Packing Group II | ADR/RID/IMDG |
| US HAP status | Not listed | 40 CFR 63 Subpart C |
| ICH Q3C residual solvent | Class 3, PDE 50 mg/day, limit 0.5 wt% | ICH Q3C Table 3 |
| FDA food-contact clearances | Adhesives and coatings sections | 21 CFR 175.105; 21 CFR 175.300 |
| Flash point method | 22 °C closed cup | ASTM D56 |
