Product

Raffinate-2 is the residual C₄ stream obtained after extraction or selective hydrogenation of 1,3-butadiene from steam-cracker or FCC-derived crude C₄ (yielding raffinate-1) followed by removal of isobutylene via MTBE/ETBE etherification, hydration into TBA, or an equivalent conversion route. RAF-2 typically emerges as the unreacted C₄ side-stream from a tert-Butyl Alcohol (TBA) unit or an MTBE/ETBE unit processing raffinate-1.  It is a mixed olefin/paraffin liquefied gas consists mainly of cis- and trans-2-butene (50–60 wt%), 1-butene (10–15 wt%), n-butane (~20 wt%), and minor isobutane. When raffinate-1 is fed to a tert-Butyl Alcohol unit, RAF-2 is produced as the unreacted C₄ side-stream.

Typical Composition (wt%)

Composition varies with C₄ origin (steam cracker vs. FCC), cracking severity, and the extraction/conversion technology applied.

Physical Properties

• Appearance: colorless liquefied petroleum gas, faint hydrocarbon odor
• Mean molecular weight: ~56–57 g/mol
• Boiling range (1 atm): approx. −12 °C to +4 °C
• Liquid density: ~0.57–0.60 g/cm³ (saturated)
• Flammable limits in air: ~1.6–10 vol%
• Storage/transport: pressurized spheres/bullets or refrigerated, LPG-type handling; commonly shipped under UN 1010 (butylene) or per the mixture SDS

Applications & End Uses

1. Metathesis feed (largest modern outlet): 2-butene + ethylene → 2 propylene (Olefin Conversion Technology / triolefin-type units); requires hydrogenated RAF-2 with butadiene reduced to ppm levels
2. 1-Butene recovery: polymer-grade 1-butene for LLDPE/HDPE co-monomer, polybutene-1, and oxo-derived plasticizer alcohols (valeraldehyde → 2-propylheptanol/DPHP)
3. Alkylation feed: high-value C₄ olefin source for H₂SO₄/HF alkylate; 2-butene is a preferred feed
4. MEK precursor: n-butenes via sec-butanol hydration/dehydrogenation to methyl ethyl ketone
5. Skeletal isomerization: n-butenes → isobutylene for MTBE/ETBE or downstream C₄ derivatives
6. Recycle/energy uses: steam-cracker feed recycle, hydrogenation to butane, LPG or fuel-gas blending

Quality Considerations

Typical sales/intermediate specs: butadiene < 0.1 wt% (ppm for metathesis feed), isobutylene < 0.5–1 wt%, acetylenes at ppm, low sulfur, and minimal oxygenate carryover (methanol/MTBE/TBA) from the upstream conversion unit.

Market Notes

Availability is structurally tied to butadiene extraction capacity plus MTBE/TBA operations. RAF-2 is traded mainly in Asia-Pacific and NW Europe, with prices assessed by agencies such as ICIS and Argus, typically referenced against naphtha, butadiene, and LPG values. Growth in on-purpose propylene via metathesis has strengthened demand for hydrogenated raffinate-2.