Hydrogenation of substrate and products manufactured according t

Details Hydrogenation of substrate and products manufactured according t Hydrogenation of substrate and products manufactured according t

1996-12-27

1999-10-05

Geist, Gary

Organic compounds -- part of the class 532-570 series

Organic compounds

Fatty compounds having an acid moiety which contains the...

554141, 554143, 554144, 568876, 568880, 423587, C07C 5136

Patent

active

059627115

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION

The present invention relates to a process for the hydro-genation of a substrate, where hydrogen gas is mixed with the substrate in the presence of a catalyst and the reaction is carried out at certain reaction conditions of pressure, time and temperature. The hydrogenation reactions are mainly related to the hydrogenation of carbon-carbon double bonds (C.dbd.C) in lipids; alcohols; and the direct hydrogenation of oxygen to hydrogen peroxide.


BACKGROUND OF INVENTION

C.dbd.C in lipids.
The annual production of vegetable oils is about 90.million tons (Mielke 1992), of which about 20% are hardened (hydrogenated). Furthermore, about 2 million tons of marine oils are hydrogenated yearly. The production is spread over the whole industrialized world. Through the hydrogenation, hydrogen is added to the double bonds of the unsaturated fatty acids. The largest part of the oils is only partly hydrogenated. The desired conditions of melting and the desired consistency of the fats are thereby obtained, which are of importance for the production of margarine and shortening. The tendency to oxidation is reduced by the hydrogenation, and the stability of the fats is increased at the same time (Swern 1982).
In the future, the lipids may be modified by methods belonging to bio technology, especially gene technology, but hydrogenation will certainly remain.
A problem with the hydrogenation processes of today is, that new fatty acids are produced which to a great extent do not exist in the nature. They are often called trans fatty acids, but the double bonds change position as well as form (cis-trans) during the hydrogenation (Allen 1956, Allen 1986).
As a rule, trans fatty acids are desired from a technical and functional point of view (Swern 1982), but regarding health, their role is becoming more and more questionable (Wahle & James 1993).
A typical state of the art reactor for hydrogenation is a large tank (5 to 20 m.sup.3) filled with oil and hydrogen gas plus a catalyst in the form of fine particles (nickel in powdery form). The reaction is carried out at a low pressure, just above atmospheric (0.5 to 5 bar), and high temperatures (130 to 210.degree. C.). The hydrogen gas is thoroughly mixed into the oil, as this step restricts the reaction rate (Grau et al., 1988).
If the pressure of hydrogen gas is increased from 3 to 50 bar when soya oil is partially hydrogenated (iodine number at the start=135, at the end=70), the content of trans is reduced from 40 to 15%. The position isomerization is also reduced to a corresponding level (Hsu et al., 1989). These results are of no commercial interest, as these conditions enforce a replacement of the low pressure autoclaves by high pressure autoclaves.
According to the "half hydrogenation" theory, the concentration of activated H-atoms on the catalyst surface determines the number of double bonds being hydrogenated and deactivated without being hydrogenated respectively. A lack of activated H-atoms causes a trans- and position-isomerization (Allen 1956, Allen 1986). A lack of activated
H-atoms can be the consequence of low solubility of H.sub.2 in the oil, or of a bad catalyst (poisoned or inadequately produced). Thus, the "half hydrogenation" theory corresponds very well to the empirical results (Allen 1956; Allen 1986; Hsu et al., 1989).
It is possible to deodorize and hydrogenate an oil in the presence of CO.sub.2 and hydrogen (Zosel 1976). Zosel describes in detail how to use CO.sub.2 in order to deodorize the oil. However, it must be emphasized that Zosel does not give any hint, that CO.sub.2 should have an influence on the hydrogenation process. Furthermore, Zosel does not touch on the cis/trans problem.
In the experiments of Zosel, the catalyst is surrounded by a liquid phase during the entire process. Zosel does not disclose the composition, but in the light of the other data, we estimate that the liquid phase consists of oil (about 95%), CO.sub.2 (about 5%) and hydrogen (about 0.03%). This phase is far away from a supercritical conditi

REFERENCES:
patent: 3969382 (1976-07-01), Zosel
Pickel et al. "Supercritical Fluid Sovents for Reactions", Proc. 3.sup.rd Int'l Symp. on Supercitical Fluids pp. 25-29 (1994).

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