Olefins Selective Hydrogenation

C₃ liquid-phase hydrogenation

Propylene cuts produced from steam cracker frequently contains from 2 to 8 wt% of methylacetylene and propadiene (MAPD).

These compounds are undesirable in both chemical - and polymer - grade propylene applications. Historically MAPD are converted into propylene via hydrogenation in vapor phase. Axens C₃ MAPD selective hydrogenation technology pioneered the MAPD hydrogenation in liquid phase in the 70’s, offering to the market liquid-phase hydrogenation technologies that require lower investment and lower operating costs as compared to gas-phase processing technologies.

Axens C₃ MAPD hydrogenation technology operates in the liquid phase under the mild conditions of ambient temperature and a pressure sufficient to maintain the liquid phase. This technology can be featured in different configuration with a single main reactor and/or with finishing reactor depending on the expected specification and/or feedstock quality, serving a large variety of applications.

C₄ Acetylene Hydrogenation

Existing solvent extraction technologies available on the market can separate butene from 1,3-butadiene successfully. Nevertheless, the high content of acetylenics vinylacetylene (VAC), 1-butyne (ethylacetylene, ETAC) and propyne (methylacetylene, MAC) in some purge of this process is often an issue in petrochemical sites for the following reasons:

• It contains BD that is therefore lost and takes down the overall butadiene yield of the complex,
• It is a hazardous cut, which is explosive when too highly concentrated in vinylacetylene,
• It is difficult to find a proper way to treat this stream due to the acetylenics that are unstable, and burning it as a way of disposal means higher environmental impact of the plant.

Axens Selective hydrogenation for VAC is a simple and reliable hydrogenation process that is industrially proven

C₄ Butadiene (BD) Rich Hydrogenation

Steam cracker C₄ cuts contain a butadiene content ranging generally within 40-70 wt%. Liquid Steam crackers produce typically large C₄ cuts to recover butadiene economically, but in some cases, the butadiene recovery might not meet economical profitability. This can happen when steam crackers do not produce sufficient C₄ or in situations where there is a low butadiene content in Steam cracker or FCC C4s cut. In all these instances, Axens Selective Butadiene (BD) Rich hydrogenation technology is the solution of choice to selectively hydrogenate butadiene into valuables n-butenes.

This technology provides an affordable opportunity to deliver flexibility to the Steam Cracker complex in case of Butadiene market fluctuation. This is achieved by by-passing part or the entire of the C₄ from the Butadiene extraction unit through the selective hydrogenation unit and making additional valuable n-butenes out of it.

This technology operates in liquid phase and can be featured with a single main reactor or in combination of a finishing reactor depending on the desired residual expected butadiene content.

Axens catalyst technology offer the possibility to operate in mild pressure and temperature conditions, which ultimately can save the related cost of feed vaporization and high alloy material selection.

C₄ BD Lean (Max B1/Max B2)

C₄ olefin cuts, sourced from FCC and/or from Butadiene extraction raffinate, contain butadiene with a concentration frequently higher than commercial specification.

Axens Selective Hydrogenation BD Lean is a reliable and industrially proven solution to polish the residual butadiene quantities down to ppm level.

Furthermore, this technology can be associated with different catalyst formulations:

• Either to preserve the Butene-1, the so-called BD Lean Max B1,
• Or to maximize the hydro-isomerization of the Butene-1 towards Butene-2, the so-called BD Lean Max B2.

Axens Hydrogenation BD Lean Max B1 or Max B2 technologies are the “jack-of-all-trades” of C₄’s olefin cut treatment scheme. Indeed, depending on the targeted butene yield, this technology can be used to isolate one of the butene compounds for further valorization.

C₅ Selective Hydrogenation

The steam cracker crude C₅ cut contains a significant amount of diolefins and olefins. For some downstream specific usages, there is an interest to significantly lower the amount of diolefins and maximize the olefins.

The selective hydrogenation of C₅ diolefins into the corresponding olefins is achieved with a very high selectivity, that is to say while minimizing the conversion of olefins into saturates, through Axens C₅ selective hydrogenation process.

The efficiency of the developed technology is based, among other elements, on a deep understanding of the reactivities of the various isomers, influence of contaminants, and importance of operating parameters including distribution.

1st Stage Gasoline Hydrogenation Unit, GHU-1

The first stage of the Gasoline Hydrogenation Unit (GHU-1) involves the selective hydrogenation of diolefins and styrenics. Efficiency of the conversion in this stage is essential for the downstream unit’s operation.

The first stage process aims to improve the stability of the raw pyrolysis gasoline by selectively hydrogenating the diolefins and alkenyl compounds, making it suitable for further processing in a second stage. The reaction is carried out mainly in the liquid phase, on a specific catalyst in a fixed bed reactor.

The operating conditions are selected to maximize the conversion of diolefins and alkenyl-aromatics, while minimizing the formation of heavy products by polymerization, preventing any aromatics loss.

In this stage, palladium or nickel-based catalysts are used depending on the site-specific constraints among which the feedstock characteristics, the product specifications, the unit characteristics and the operating conditions.

2nd Stage Gasoline Hydrogenation Unit, GHU-2

In the second stage of pygas hydrogenation (GHU-2) the C₆-C₈ heart cut is further processed to prepare a feedstock suitable for aromatics recovery, by selectively hydrogenating the olefins and hydrodesulfurization.

This process consists in olefins and sulfur removal from all or a specific fraction of the first stage effluent. The complete removal of olefins and sulfur has to be ensured while minimizing aromatics hydrogenation. The effluent is then routed to an aromatics recovery unit.