Commercial 2-propanol, CAS 67-63-0, is a water-white liquid with normal boiling point 82.5 °C, closed-cup flash point 12 °C, and density 0.785 g/cm³ at 20 °C determined by ASTM D4052-22. Technical-grade material is supplied under ASTM D770-11, with water mass fraction controlled to 0.1–0.5% depending on downstream catalyst tolerance; the lower end is specified for aluminium-metal and alkoxide reactions, while the upper end may be tolerated in esterification if water is removed continuously. The four primary intermediate derivatives considered here—acetone, isopropyl acetate, isopropylamine, and aluminium isopropoxide—differ in their sensitivity to water, hydrogen partial pressure, and acid gases. The process windows described below reflect the reactor and separation boundaries that govern each route.

2-Propanol itself is produced from propylene by direct hydration over phosphoric acid on silica at 180–260 °C and 3.0–10.0 MPa, or by indirect hydration via isopropyl hydrogen sulfate hydrolysis. Directly hydrated material contains water and requires distillation to anhydrous or near-anhydrous grades before alkoxide or amination service. The vapour pressure at 20 °C is 4.4 kPa, and the closed-cup flash point is 12 °C; therefore, storage and transfer systems for intermediate use are nitrogen-blanketed and grounded.

Why Is Hydrogen Partial Pressure Managed So Tightly in Acetone Dehydrogenation?

In acetone service, 2-propanol is dehydrogenated in a fixed-bed tubular reactor. The catalyst is a copper-zinc oxide or copper chromite pellet of 3–5 mm diameter and bulk density 1.0–1.3 g/cm³; tube diameter is 25–40 mm inside diameter and length 3–6 m. The tubes are heated by circulating hot oil at 320–360 °C. Vaporised 2-propanol is superheated to 300–350 °C and fed at a liquid hourly space velocity of 0.5–1.0 h⁻¹. Reactor inlet pressure is 0.1–0.2 MPa.

The dehydrogenation reactor is endothermic, and the catalyst bed temperature can drop by 20–40 °C if hot-oil flow is interrupted or if throughput is increased beyond design. Hydrogen co-product is separated from the crude condensate and recycled to the reactor inlet to maintain a hydrogen-to-2-propanol molar ratio of 0.3–1.0. Below 0.3, carbon deposition on the copper surface increases and is observed as a rise in tube pressure drop at constant throughput; above 1.0, per-pass conversion is suppressed and the hydrogen recovery compressor becomes the process bottleneck. Per-pass conversion is normally 85–90%, with acetone selectivity above 99%; unconverted 2-propanol is recovered in the distillation train and returned to the reactor.

Equilibrium conversion at 350 °C and 0.1 MPa is above 95%; the process is kinetically limited, so catalyst activity and liquid hourly space velocity are the main conversion variables. The reactor volume is determined primarily by the heat-transfer area required to supply the endothermic heat of reaction. Side reactions include dehydration of 2-propanol to propylene over acidic sites and base-catalysed aldol condensation of the acetone product to diacetone alcohol and mesityl oxide. Copper-zinc oxide formulations are promoted with alkali or alkaline-earth oxides to neutralise surface acidity; feed acidity is controlled because organic acids increase dehydration and carbon formation. In commercial operation, the feed water content is held below 0.5%; water above this level accelerates copper crystallite sintering and reduces acetone yield over a campaign.

Crude acetone is distilled in a two-column or three-column train. The first column removes light impurities; the second column produces acetone meeting 99.5% minimum assay by ASTM D329-20. A third recovery column separates water and unreacted 2-propanol from heavy by-products. The main production-scale failure mode is hot-spot formation when the hot-oil temperature exceeds 360 °C; this causes thermal cracking to C3 hydrocarbons and shortens catalyst life. Regeneration with steam-hydrogen mixtures is applied after carbon laydown. Published data for the exact regeneration interval is limited; plants monitor tube pressure drop and acetone selectivity rather than following a fixed calendar cycle.

When acetic acid is fed to a reactive distillation column with 2-propanol, the equilibrium-limited esterification is driven by continuous water removal. The catalyst is a macroporous sulfonic acid ion-exchange resin charged as 0.5–1.5 mm beads between corrugated structured packing elements. The reaction zone operates at 80–110 °C and 0.1 MPa top pressure. Acetic acid is fed at a molar ratio of 1.1–1.5 relative to 2-propanol to compensate for vapour-phase acid losses in the overhead. The equilibrium constant is low, typically in the range 4–8, so water must be removed to shift the ester concentration toward completion.

In the reactive distillation column, water is taken overhead as a ternary overhead stream with unreacted 2-propanol and ester; after condensation, the decanter separates an aqueous phase that is withdrawn and an organic phase that is refluxed. The reaction zone typically contains 10–20 theoretical stages, with a reboiler temperature below 120 °C to avoid thermal desulfonation of the resin. The column is operated at a reflux ratio that keeps water concentration in the reaction zone low while preventing loss of acetic acid overhead. Because the resin swells in polar media, catalyst bed voidage changes with water and acid concentration; pressure drop and liquid holdup are monitored to avoid flooding. The main production bottleneck is the decanter capacity when water load is high; if the aqueous phase is not removed rapidly, the organic reflux becomes water-rich and column efficiency declines.

Crude isopropyl acetate is cooled, washed with 5–10% aqueous sodium carbonate to neutralise residual acetic acid, decanted, and distilled. The finished product is specified by ASTM D3131-10, with minimum ester assay 99.5%, water content below 0.05%, and acidity below 0.01% as acetic acid for urethane-grade service. A side draw in the purification column removes the isopropyl acetate-water-2-propanol ternary azeotrope for return to the reaction zone. Published data for exact resin lifetime in continuous reactive distillation is limited; replacement frequency depends on sulfonic acid site loss, bead attrition, and pressure drop increase.

When Ammonia-to-2-Propanol Ratio Falls Below 3:1, Secondary and Tertiary Amine Formation Becomes Significant

Catalytic ammonolysis of 2-propanol is conducted in an adiabatic fixed-bed reactor charged with nickel-on-alumina extrudate. The catalyst contains 15–40% nickel by mass and pellet diameter 3–6 mm. Ammonia and vaporised 2-propanol are preheated and fed at a total pressure of 1.0–5.0 MPa and a bed temperature of 160–220 °C. The ammonia-to-2-propanol molar ratio is maintained at 3:1–8:1 to favour mono-isopropylamine. At ratios below 3:1, the primary amine product competes with ammonia for nickel sites, and the product mixture shifts toward diisopropylamine and triisopropylamine.

Temperature above 220 °C increases 2-propanol dehydrogenation to acetone; the acetone can condense with isopropylamine to form imine intermediates that are hydrogenated to secondary amines. Conversely, temperature below 160 °C lowers reaction rate and requires a larger catalyst bed. A small hydrogen co-feed of 0.1–0.5 mol per mole of 2-propanol is sometimes used to maintain the nickel surface in the reduced state; without hydrogen, the catalyst slowly oxidizes or cokes, and pressure drop across the bed increases. The reaction proceeds through a dehydrogenation-amination-hydrogenation sequence: 2-propanol is first dehydrogenated to acetone on nickel, the acetone reacts with ammonia to form an imine, and the imine is hydrogenated to isopropylamine. Published data for exact mono-isopropylamine selectivity across all catalyst formulations is limited; the primary amine fraction is improved by operating above 3:1 ammonia ratio and below 200 °C.

Reactor effluent is cooled and depressurized. Ammonia is recovered in a distillation column and recycled to the reactor; the organic phase is dried with sodium hydroxide to below 0.1% water and then fractionated. Isopropylamine is withdrawn as distillate at normal boiling point 32.4 °C; diisopropylamine is taken as a side stream at 84 °C. Product isopropylamine is assayed at 99.0% minimum by gas chromatography, with ammonia below 0.01% and water below 0.1% for agrochemical and pharmaceutical use. Sulfur compounds in the 2-propanol feed are controlled below 1 mg/kg to prevent irreversible nickel deactivation; even trace thiophenes or mercaptans accumulate on the catalyst surface and reduce conversion.

The main production-scale failure mode is ammonia slip to the amine fractionation section. If the ammonia recovery column is overloaded, residual ammonia contaminates the isopropylamine distillate and can promote corrosion in carbon steel equipment. Caustic drying beds upstream of the fractionation column mitigate this by removing carbon dioxide and residual water; the drying bed inlet temperature is held below 40 °C to avoid amine-carbamate fouling.

For aluminium alkoxide production, the reactor is charged with aluminium metal and anhydrous 2-propanol in a glass-lined or stainless steel vessel equipped with a reflux condenser, a hydrogen vent with flame arrester, and a cooling jacket. Aluminium is charged as atomised powder or foil of 0.1–1.0 mm thickness. A halogenated initiator—typically iodine at 0.05–0.2% by mass relative to aluminium or aluminium trichloride at similar loading—is used to disrupt the oxide layer. The reaction starts after an induction period; once hydrogen evolution begins, the mass is maintained at 82–83 °C by jacket cooling. The reaction is sufficiently exothermic that loss of cooling can raise the temperature above the boiling point and flood the reflux condenser.

Water in the 2-propanol must be below 500 mg/kg. Water hydrolyses aluminium isopropoxide to aluminium hydroxide and isopropanol, reducing the final aluminium content and forming gelatinous solids that block downstream filters. The 2-propanol is therefore dried with molecular sieves or distilled from magnesium before charging. A slight excess of 2-propanol is maintained to keep the mixture stirrable; after all aluminium has dissolved, the solution is filtered, and excess alcohol is removed under vacuum at 60–80 °C. The residue is a white to pale-yellow solid with aluminium content 12.5–13.0% by mass and molar mass 204.24 g/mol. The product can also be retained as a concentrated solution in 2-propanol for downstream use.

Hydrogen generation is stoichiometric at 1.5 mol of hydrogen per mole of aluminium. The vent line is sized for peak hydrogen evolution, and the reactor is inerted with nitrogen before charging because hydrogen-air mixtures are flammable over a wide range. Mercury chloride is historically known as an initiator but is generally avoided in modern production because of waste-water limits; iodine and aluminium trichloride leave halogen residues that can be reduced by using a heel of previous aluminium isopropoxide. Aluminium isopropoxide is used as a catalyst in Meerwein-Ponndorf-Verley reductions and as a sol-gel precursor for high-purity alumina. Published data for exact batch yield under iodine catalysis is limited; yields above 90% are reported when the aluminium surface is freshly abraded and moisture is excluded.