Uses and Core Differences of n-Butane, Isobutane, n-Butene and Isobutene

All four substances are C4 hydrocarbon components, divided into alkanes (saturated: n-butane, isobutane) and olefins (unsaturated: n-butene, isobutene). Their fundamental distinction lies in that olefins contain carbon-carbon double bonds and are mainly used for chemical synthesis, while alkanes have no double bonds and are primarily applied as fuels, refrigerants and foaming agents, leading to completely separate downstream industrial chains.

I. Basic Applications of the Four Monomers

1. n-Butane (n-C₄H₁₀, straight-chain saturated alkane)

Civil & industrial fuel: Blended into LPG and vehicle fuel gas

Chemical raw material

Dehydrogenation to produce n-butene and butadiene (raw material for cis-butadiene rubber)

Oxidation to maleic anhydride (raw material for unsaturated resins and coatings)

Foaming agent and refrigerant: For EPS foamed polystyrene and aerosol propellants

Refining: Blending component for gasoline

2. Isobutane (i-C₄H₁₀, branched saturated alkane)

Feedstock for alkylate oil (top application in oil refining): Reacts with olefins to manufacture high-octane gasoline, a core raw material for National VI standard gasoline

Refrigerant (R600a): Eco-friendly refrigerant for refrigerators and freezers (replaces CFCs, with huge market demand)

Dehydrogenation to isobutene (the most mainstream chemical production route)

Foaming agents, aerosols and portable fuel gas

✅ Common properties of alkanes: Saturated and chemically inert; unable to polymerize directly. Most undergo dehydrogenation to form olefins before further deep processing.

3. n-Butene (1-butene, 2-butene, straight-chain olefin)

Comonomer for LLDPE (largest consumption field): Modifies linear polyethylene plastics to enhance film toughness

Hydration to sec-butanol, then methyl ethyl ketone (MEK, high-end solvent for coatings and inks)

Oligomerization for lubricants and gasoline

Oxidation, epoxybutane production and fine chemical intermediates

4. Isobutene (2-methylpropene, branched olefin, highest value-added C4 product)

MTBE (gasoline antiknock agent): Synthesized with methanol, the world's top consumption application

Polyisobutene (PIB): Lubricant additives, hot melt adhesives and sealants

Raw material for butyl rubber: Copolymerized with isoprene for tire inner tubes and sealing gaskets

Methyl methacrylate (MMA, raw material for PMMA acrylic glass)

Tert-butanol, tert-butyl phenol and gasoline additives

✅ Common properties of olefins: Active carbon-carbon double bonds, easy to polymerize, add and esterify; core raw materials for high-end fine chemicals.

II. Summary Table of Four Core Differences

Category	Structural Property	Core Industry Track	Product Added Value	Representative Downstream Products
n-Butane	Straight-chain alkane	Fuels + Maleic anhydride + Butadiene	Medium-Low	Maleic anhydride, butadiene rubber, foaming agents
Isobutane	Branched alkane	Alkylate gasoline + Refrigerants + Dehydrogenation to isobutene	Medium	R600a refrigerant, alkylate gasoline
n-Butene	Straight-chain olefin	PE copolymerization + Methyl ethyl ketone	Medium-High	LLDPE plastic, MEK solvent
Isobutene	Branched olefin	MTBE + Rubber + PMMA + Polyisobutene	Highest	Acrylic glass, butyl rubber, lubricant additives

III. Fundamental Key Differences

1. Saturated vs Unsaturated (Primary Dividing Line)

n-Butane & isobutane: Saturated alkanes without double bonds, high reaction barriers. Mainly used as fuels and refrigerants; dehydrogenation is required for deep chemical processing.

n-Butene & isobutene: Unsaturated olefins with active carbon-carbon double bonds; no cracking needed, directly applied in various fine chemical productions.

2. Straight-chain vs Branched-chain (Secondary Dividing Line)

Branched structures (isobutane, isobutene): Compact molecular structure, high gasoline octane rating; suitable for synthesizing high-value branched chemicals such as MTBE, butyl rubber and R600a.

Straight-chain structures (n-butane, n-butene): Linear molecules, applicable to maleic anhydride, linear PE, MEK and other linear derivatives.

3. Market Volume & Price Variations

Isobutane: Dual rigid demand from oil refining and household appliance refrigerants, the highest consumption volume among the four products.

Isobutene: The ceiling of added value in C4 chemical industry, consistently maintaining the highest market price all year round.

n-Butene: Rigid demand from petrochemical plastic industry; consumption fluctuates with the operating rate of LLDPE plants.

n-Butane: Half of output is used as civil LPG; chemical demand is tied to the operation rates of maleic anhydride and butadiene units.

IV. Practical Distinction for Chemical Foreign Trade

Maleic anhydride for fiberglass-reinforced plastics, EPS foams, civil liquefied gas → n-butane

Refrigerants for refrigerators, alkylate gasoline for refineries → Isobutane

Raw materials for PE films, MEK ink solvents → n-Butene

Acrylic glass, butyl rubber, gasoline MTBE → Isobutene

V. Supplementary Physical & Hazardous Chemical Information (CAS / UN / Boiling Point / Hazard Classification, Required for Customs Declaration)

Category	CAS No.	UN No.	Hazard Class	State at Ambient Temp	Brief Key Physical Properties
n-Butane	106-97-8	UN1011	Class 2.1 Flammable Gas	Gaseous, liquefied under pressure	Boiling point: -0.5°C; straight-chain, exclusive raw material for maleic anhydride
Isobutane	75-28-5	UN1969	Class 2.1 Flammable Gas	Gaseous, liquefied under pressure	Boiling point: -11.7°C; branched chain, raw material for R600a
Mixed n-Butene (1-butene)	106-98-9	UN1012	Class 2.1 Flammable Gas	Liquefied under pressure	Boiling point: -6.3°C; comonomer for PE
Isobutene	115-11-7	UN1055	Class 2.1 Flammable Gas	Liquefied under pressure	Boiling point: -6.9°C; high-value C4 raw material

VI. Differences in Storage & Transportation (Key for Warehousing, Tank Trucks and Export Tank Containers)

n-Butane: Gaseous under normal temperature and pressure; transported via pressure storage tanks or LPG tank trucks. Moderate liquefaction pressure, commonly shipped in T50 tank containers for export. Prone to vaporization under high temperature; direct sunlight exposure is strictly prohibited.

Isobutane: Lower boiling point and stronger volatility; can be stored in refrigerated or pressure tanks. Refrigerant manufacturers purchase in bulk via pressure tankers and maintain permanent stock for R600a production.

n-Butene: Stored and transported in liquefied state with pressure tanks; spherical tanks are equipped in petrochemical plants for fixed storage in chemical parks. Mostly supplied to PE factories through dedicated pipelines.

Isobutene: Highest chemical activity and prone to self-polymerization. Requires temperature control and small amounts of polymerization inhibitors during storage and transportation in pressure tanks. Higher temperature control standards than the other three products; insulated T50 tanks are widely adopted for long-distance marine shipping.