Tetrahydrofuran (THF, CAS 109-99-9) is a saturated cyclic ether with molecular formula C₄H₈O and molar mass 72.11 g/mol. At 20 °C, density is 0.889 g/cm³, refractive index is 1.4073, and dynamic viscosity is 0.48 mPa·s. The atmospheric boiling point is 66 °C at 101.3 kPa, the closed-cup flash point is -14 °C, and the autoignition temperature is 321 °C. Lower and upper explosive limits in air are 2.0 vol% and 11.8 vol%, respectively. THF is fully miscible with water and many aliphatic or aromatic hydrocarbons, but this miscibility also means that water removal to anhydrous specification is a separate unit operation, not a simple settling process.

Because THF is an aliphatic ether, it undergoes slow autoxidation in contact with oxygen and light, forming tetrahydrofuranyl hydroperoxide and related species. Uninhibited material must not be stored in partially filled containers under air. Peroxide formation and stabilizer loading are therefore the first two physicochemical fields that constrain a supply specification.

Get a THF Quotation: The 9 Details That Speed Up Your Quote

Get a THF Quotation: The 9 Details That Speed Up Your Quote is a specification framework in which the following nine fields are supplied in the initial request.

A stabilizer-free anhydrous THF request without water content and packaging volume forces the supplier to clarify whether the application is organometallic chemistry or lyophilization, which can add multiple days. Conversely, a specification that includes all nine fields can be matched directly to an existing batch and dispatched under the correct transport class.

Polytetramethylene ether glycol (PTMEG) production is the largest monomer-consuming application for THF and is the most specification-sensitive with respect to water and inhibitor content. In continuous PTMEG synthesis, THF undergoes cationic ring-opening polymerization over fluorosulfonic acid or heteropolyacid catalysts to yield a linear polyether diol with terminal hydroxyl groups. The target number-average molecular weight is typically between 650 and 2,000 g/mol, determined by the ratio of molecular weight regulators such as water or 1,4-butanediol. Water in the feedstock is not a passive impurity; it participates in initiation and chain transfer, decreasing the degree of polymerization and broadening the molecular weight distribution. For this reason, THF feed for PTMEG plants is often dried to below 0.01 wt% water before entering the reactor. Published kinetic and thermodynamic data for this specific configuration are limited because reactor temperature, catalyst loading, and recovery loop design are licensor-controlled; however, industrial dryers frequently use molecular sieves or azeotropic distillation to reach the required water concentration. The recovery of unreacted THF downstream uses packed distillation columns under reduced pressure to limit reboiler temperature. Excessive dissolved oxygen in the recovered THF promotes color-body formation and shortens acid catalyst life. Inhibitor BHT is removed upstream by adsorption or distillation because it can act as a chain-transfer or catalyst-poisoning species depending on the catalyst system. The purchase specification for PTMEG-bound THF therefore must state stabilizer-free and include a maximum water concentration on the certificate of analysis; otherwise the supplier may default to BHT-stabilized industrial solvent that is incompatible without additional purification. Hydroxyl number of the resulting PTMEG is verified according to ASTM D4274, and the material is shipped as a viscous liquid or solid depending on molecular weight.

What Inhibitor Type and Loading Prevent Peroxide Accumulation in Storage?

Peroxide accumulation in THF is controlled primarily by the hindered phenol 2,6-di-tert-butyl-4-methylphenol, commonly abbreviated BHT. Industrial stabilized grades typically contain 50–250 ppm BHT; the exact loading is measured by gas chromatography or ultraviolet spectroscopy and reported on the certificate of analysis. BHT functions as a radical chain terminator, but it is not indefinitely effective. At temperatures above 25 °C and under prolonged ultraviolet exposure, inhibitor consumption accelerates. Storage in nitrogen-blanketed closed containers reduces the headspace oxygen concentration and extends shelf life. Peroxide value is normally controlled to ≤0.005 wt% as H₂O₂ by iodometric titration according to ASTM E298. Unstabilized THF should be consumed within 48 h after container opening unless kept under inert gas. Copper and copper alloys must be excluded from transfer lines because trace copper ions catalyze ether autoxidation. Distillation of aged THF is prohibited if peroxides are present except under controlled and continuously monitored conditions; the distillation residue can become shock-sensitive. A quotation must therefore identify whether standard BHT stabilization is acceptable or whether an inhibitor-free product with a shorter use window is required.

In organometallic routes, THF is used as a coordinating solvent for lithium and magnesium reagents. The production-scale requirement is not generic solvent cleanliness; it is the absence of proton-donating species that destroy the reagent. n-Butyllithium, for example, abstracts protons from water and from the hydroxyl group of BHT. For a pilot campaign operating at -78 °C in a glass-lined reactor, THF is transferred under a nitrogen purge from a day tank that has been dried to a dew point below -40 °C. Water content is confirmed by ASTM E203 Karl Fischer titration. A water concentration above 50 mg/kg can consume 1–2 mol% of the organolithium reagent before the intended reaction begins, generating lithium hydroxide solids and shifting stoichiometry. The same reaction system cannot accept stabilized THF unless a distillation or molecular-sieve drying step is installed. In large-scale campaigns, BHT-free THF is sometimes supplied in dedicated stainless steel isotanks with nitrogen padding and sealed return lines to prevent moisture ingress. This creates an operational boundary: once opened, a drum of BHT-free THF must be sampled and immediately resealed under dry nitrogen; repeated needle punctures through septa without inert gas are a documented source of water contamination in R&D and kilo-lab settings. The supplier should be informed of the intended organometallic application because residual inhibitor from a previous shipment can remain in the unloading manifold and contaminate a low-BHT batch.

PVC Solvent Cement Viscosity and Regional VOC Limits

THF solvates unplasticized PVC rapidly at room temperature, forming the base of solvent cements used for pipe jointing. In this application, the relevant technical specification is not trace purity but dissolution rate and final viscosity. Formulators control viscosity with ketonic co-solvents; a high THF fraction lowers viscosity and accelerates drying but increases volatile organic compound emissions. Viscosity of the cement is measured by ASTM D1084, and solvent cement bond strength is evaluated according to ASTM D2564. Regional VOC ceilings such as South Coast AQMD Rule 1168 for adhesives and sealants apply according to product category and application method. A formula containing more than 75 wt% THF may be outside the VOC limit in covered categories; the exact limit depends on the product subcategory. The low flash point of THF requires explosion-proof dispersion tanks, mechanical seals rated for Class I Division 1 or Zone 1 atmospheres, and grounded transfer piping. Water in the THF is normally kept below 0.05 wt% because higher water content slows PVC dissolution and can produce haze in the final cement film. The purchase specification for this sector typically accepts standard BHT-stabilized industrial THF, specifying only assay, water, and color because distillation to anhydrous grade is unnecessary and would not change joint performance.

For size-exclusion chromatography and gravimetric polymer analysis, THF must meet low non-volatile residue and low peroxide specifications because baseline noise and detector drift depend on solvent cleanliness. HPLC gradient grade THF is controlled for UV transmittance at 230 nm and 254 nm; assay is typically ≥99.7%. Nonvolatile residue is specified at ≤0.0005 wt% to avoid column fouling and weighing errors. The solvent is filtered through 0.2 µm membranes before packaging and is supplied in glass or fluorinated high-density polyethylene containers rather than standard steel drums because steel can introduce iron and rust fines. Water content may be below 0.02 wt% to protect water-sensitive sample matrices. This grade requires a lot-specific certificate of analysis with actual values for peroxide, water, and UV absorbance; published data for every packaging configuration are not standardized, so procurement groups must specify whether glass or fluoropolymer containers are required. Without this specification, the supplier may default to standard industrial packaging that is inappropriate for trace analysis.

Tank Padding and Transfer Connections Define Bulk Quote Terms

Bulk THF storage vessels are fabricated from 304L or 316L stainless steel, or from carbon steel with an internal phenolic or epoxy lining. The vessel is fitted with a nitrogen padding regulator, pressure/vacuum relief valves, and a desiccant filter on the vent to limit oxygen and moisture ingress. Transfer pumps for THF service are usually sealless canned-motor or magnetically coupled units to reduce mechanical seal leakage. Gaskets and hoses are specified as PTFE-lined or EPDM rubber; natural rubber and neoprene are incompatible with prolonged THF exposure. The unloading connection is commonly an 80 mm dry-disconnect coupling to limit vapour release. Because THF has a low flash point and wide flammability range, hazardous area classification is based on IEC 60079-10-1. For initial drum filling from bulk, the recommended linear velocity is below 1 m/s to prevent static charge accumulation. Grounding and bonding clamps are connected before decanting; nitrogen-blanketed drum transfer is standard when the material is stabilizer-free. These equipment interfaces affect quotation logistics: a standard industrial solvent quote may assume a single compartment truck with vapour return, while an anhydrous or BHT-free order may require a dedicated stainless steel tanker, a nitrogen purge during unloading, and tank cleaning documentation.