Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – From nonhydrocarbon feed
Reexamination Certificate
2002-02-08
2003-09-30
Richter, Johann (Department: 1621)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
From nonhydrocarbon feed
C585S640000, C568S880000, C568S881000
Reexamination Certificate
active
06627782
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the preparation of 1-olefins from aldehydes by means of a three-stage synthesis.
2. Discussion of the Background
Owing to their reactivity, olefins are among the most important synthetic building blocks in organic chemistry. They are precursors for many compounds, for example aldehydes, ketones, alcohols, carboxylic acids and halogen compounds. They are used in large quantities for the preparation of homo-oligomers or co-oligomers and homopolymers and copolymers, for example polyethylene or polypropylene.
Ethylene and propylene are prepared in large quantities throughout the world by steam cracking or by catalytic cracking of hydrocarbons. These processes also produce considerable amounts of C
4
-olefins (isobutene, 1-butene, 2-butenes) and to a lesser extent C
51
-olefins. Higher 1-olefins are mostly produced by chain buildup reactions.
Ethylene can be oligomerized with the aid of Ziegler catalysts to give a mixture of unbranched 1-olefins having an even number of carbon atoms.
In a variant of the SHOP process, unbranched 1-olefins having an even or odd number of carbon atoms can be prepared from ethylene. This process comprises three reaction steps, namely ethylene oligomerization, isomerization, i.e., a shift of the double bonds, and cross-metathesis of the olefin mixture having internal double bonds with ethylene.
Dehydrogenation of straight-chain paraffins, for example by chlorination and dehydrochlorination, forms olefins having predominantly internal double bonds which can be converted by cross-metathesis into 1-olefins. The above-mentioned processes all have the disadvantage that a large number of 1-olefins is always produced.
Straight chain 1-olefins having an even number of carbon atoms can be obtained from fatty alcohols by elimination of water. Disadvantages of this method are the high price of the starting materials and the fact that essentially only fatty alcohols having from 12 to 18 carbon atoms are available in sufficient quantities.
Since the known methods do not give all desired 1-olefins in a sufficiently large quantity and/or in a sufficiently high purity, there is a need for a method of preparing 1-olefins from readily available starting materials.
It has now been found that 1-olefins can be prepared from aldehydes by aldol condensation with acetone, hydrogenation of the &agr;,&bgr;-unsaturated ketones to form the unsaturated alcohols and subsequent elimination of water from alcohols.
SUMMARY OF THE INVENTION
The invention accordingly provides a process for preparing 1-olefins having from 7 to 24 carbon atoms from aldehydes having from 4 to 21 carbon atoms, which comprises condensing an aldehyde with acetone to form an &agr;,&bgr;-unsaturated ketone, hydrogenating the unsaturated ketone obtained in this way to form the saturated alcohol and eliminating water from the saturated alcohol.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein: a schematic diagram of the reaction apparatus is presented.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.
In the process of this invention, it is possible to use aldehydes or aldehyde mixtures having from 4 to 21 carbon atoms. The aldehydes used can originate from various sources. It is possible to use aldehydes which have been obtained by dehydrogenation of alcohols, for example, fatty alcohols. Likewise, aldehydes from cleavage reactions, for example heptanal from methyl ricinoleate, can be used as starting materials. In particular, it is possible to use aldehydes which have been produced by hydroformylation of olefins.
Furthermore, unsaturated aldehydes formed by self-condensation of an aldehyde, e.g., 2-ethylhex-2-enal from n-butyraldehyde, can also be used.
For example, the aldehydes mentioned below can serve as starting material for the process of the invention:
n-butyraldehyde, isobutyraldehyde, crotonaldehyde, valeraldehyde, 2-methylbutanal, 3-methylbutanal, dimethylpropanol, tiglinaldehyde, 3,3-dimethylacrolein, n-hexanal, isohexanal, n-heptanal, citral, &agr;- and &bgr;-citral, benzaldehyde, cinnamaldehyde, phenylacetaldehyde, hydrocinnamaldehyde, 2-phenylpropionaldehyde, cyclohexyl carbaldehyde, anisaldehyde; aldehyde mixtures prepared by hydroformylation of dipropene, dibutene, tripropene, tetrapropene, tributene, pentapropene, tetrabutene.
A preferred starting material is n-pentanal.
The aldol condensation of aldehydes with acetone to form &agr;,&bgr;-unsaturated ketones is preferably carried out as a two-phase reaction. The reaction is, as described in DE 199 57 522, the disclosure of which is hereby expressly incorporated by reference, carried out in a tube reactor, with the catalyst being present in the continuous phase and the starting material being present in a disperse phase and the loading factor B of the reactor being equal to or greater than 0.8 and the mass ratio of the catalyst phase to organic phase being greater than 2. (The loading factor B is defined as follows: B=PD/PS. PD [Pa/m] is a pressure dropper unit length over the reactor under operating conditions and PS [Pa/m] is a mathematical parameter having the dimensions of pressure per unit length, defined as the ratio of mass flow M [kg/s] of all components under operating conditions multiplied by g=9/81 [m/s
2
], i.e., PS=(M/V)*g.)
As catalyst phases, preference is given to using aqueous solutions of hydroxides, hydrogen carbonates, carbonates and carboxylates in the form of their alkali metal or alkaline earth metal compounds, in particular sodium hydroxide and potassium hydroxide. The concentration of the catalyst in the catalyst solution is from 0.1 to 15% by mass, in particular from 0.1 to 5% by mass.
Aldehyde, acetone and optionally a solvent are introduced into the catalyst phase upstream of the reactor. The molar ratio of aldehyde to acetone is from 5/1 to 1/10, preferably from 1/1 to 1/5. The reaction is carried out in a temperature range from 40° C. to 150° C., preferably in the range from 50° C. to 120° C. The reaction time is from 0.1 to 20 minutes, preferably from 0.2 to 10 minutes.
The catalyst phase is separated off from the product mixture leaving the reactor and is recirculated to the reactor. Before the phase separation, unreacted starting materials, some product, water and optionally solvent are preferably distilled off. After condensation, the distillate separates into an aqueous phase and an organic phase which is returned to the reactor. Starting materials, in particular acetone, are distilled off from the aqueous phase and part of the aqueous phase is then discarded to discharge the water of reaction from the system and part of it is, after optional use as scrubbing liquid, returned to the process. The product phase which has been separated off from the catalyst can, if desired after scrubbing with water, be worked up by distillation to give the pure &agr;,&bgr;-unsaturated ketone. Another possibility is to use the crude product in the next stage. This procedure enables the desired &agr;,&bgr;-unsaturated ketone to be prepared highly selectively.
Any organic solvent added to the starting material or to the product mixture from the reaction has to have the following properties: it dissolves products and starting materials and is itself sparingly soluble in the catalyst phase. It is inert toward the aldol condensation and optionally in the hydrogenation. It can be separated by distillation from the intermediate, namely the &agr;,&bgr;-unsaturated ketone and/or the subsequent product, namely the saturated alcohol. Preferred solvents are those which form a minimum heteroazeotrope with water, so that water
Bueschken Wilfried
Kaizik Alfred
Protzmann Guido
Wiese Klaus-Diether
Oxeno Olefinchemie GmbH
Richter Johann
Zucker Paul A.
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