Method for obtaining alcohols from aldehydes II

1. A method for preparing saturated C n - and C 2n -alcohols, where n=4, 5 and 6, comprising the method steps of

a) providing a mixture of isomeric C n -aldehydes where n=4, 5 and 6 comprising unbranched aldehydes, wherein the proportion of unbranched aldehydes is at least 20% by weight, based on the C n -aldehydes where n=4, 5 and 6, and dividing the mixture into a first substream ( 1 a ) and a second substream ( 1 b ),

b) carrying out an aldol condensation in a tubular reactor of the aldehydes present in the first substream to obtain a mixture of C n - and α,β-unsaturated C 2n -aldehydes wherein the tubular reactor comprises a mixing module which disperses the reactant aldehyde into droplets having an average diameter (Sauter diameter) of 0.2 mm to 2 mm in a process liquor comprising aqueous sodium hydroxide solution and sodium salts of carboxylic acids and has a sodium content of 0.6 to 1.75%,

c) mixing the mixture of C n - and α,β-unsaturated C 2n -aldehydes obtained in b) with the second substream provided in a),

d) hydrogenating the mixture of C n - and α,β-unsaturated C 2n -aldehydes and isomeric C n -aldehydes where n=4, 5 and 6 obtained in c) with hydrogen to obtain a mixture of saturated C n and C 2n -alcohols, and

e) separating the mixture of C n and C 2n -alcohols,

wherein the isomer ratio of the C n -alcohol obtained is adjusted by the ratio of the first and second substream produced in step a) and by the aldol condensation carried out in step b).

2. The method according to claim 1 , wherein the C n -aldehydes where n=4, 5 and 6 used in step a) were prepared by hydroformylation of isomeric olefins having 3 to 5 carbon atoms with synthesis gas in the presence of a hydroformylation catalyst to form the aldehydes specified, and wherein the proportion of unbranched aldehydes is from 40 to 99.5% by weight, based on the C n -aldehydes where n=4, 5 and 6.

3. The method according to claim 2 , wherein in the hydroformylation a catalyst system is used which comprises rhodium as central atom and is complexed with the ligand (1):

4. The method according to claim 1 , wherein the aldol condensation in step a) is carried out in the presence of aqueous sodium hydroxide solution, and wherein the proportion of unbranched aldehydes is from 95 to 99.5% by weight, based on the C n -aldehydes where n=4, 5 and 6.

5. The method according to claim 1 , wherein the process liquor has a pH in the range from 12.5 to 13.5.

6. The method according to claim 1 , wherein the aldol condensation of the C n -aldehydes according to step a) is carried out in a temperature range from 100 to 150° C.

7. The method according to claim 1 , wherein a reaction pressure in the tubular reactor during the aldol condensation of the C n -aldehydes according to step a) is in a range from 0.2 to 1.0 MPa.

8. The method according to claim 1 , wherein the hydrogenation according to step b) is carried out in a temperature range from 170° C. to 200° C. at a pressure of 15*10 5 Pa to 30*10 5 Pa over a supported catalyst which contains at least nickel and copper as active components.

9. The method according to claim 1 , wherein the hydrogenation according to step b) is carried out with hydrogen in a pressure range from 5 to 100 bar and the hydrogenation temperatures are between 120 and 220° C.

10. The method according to claim 1 , wherein n=5.

11. The method according to claim 2 , wherein the aldol condensation in step a) is carried out in the presence of aqueous sodium hydroxide solution.

12. The method according to claim 3 , wherein the aldol condensation in step a) is carried out in the presence of aqueous sodium hydroxide solution.

13. The method according to claim 2 , wherein the process liquor has a sodium content of 1.1 to 1.20% by mass and a pH in a range from 12.5 to 13.5.

14. The method according to claim 3 , wherein the process liquor has a sodium content of 1.1 to 1.20% by mass and a pH in a range from 12.5 to 13.5.

15. The method according to claim 2 , wherein the aldol condensation of the C n -aldehydes according to step a) is carried out in a temperature range from 100 to 150° C.

16. The method according to claim 3 , wherein the aldol condensation of the C n -aldehydes according to step a) is carried out in a temperature range from 100 to 150° C.

17. The method according to claim 2 , wherein a reaction pressure in the reactor during the aldol condensation of the C n -aldehydes according to step a) is in the range from 0.2 to 1.0 MPa.

18. The method according to claim 2 , wherein the hydrogenation according to step b) is carried out in a temperature range from 170° C. to 200° C. at a pressure of 15*10 5 Pa to 30*10 5 Pa over a supported catalyst which contains at least nickel and copper as active components.

19. The method according to claim 1 , wherein the hydrogenation according to step b) is carried out with hydrogen in a pressure range from 5 to 100 bar and the hydrogenation temperatures are between 120 and 220° C.

20. The method according to claim 1 , wherein

the ratio between the first substream ( 1 a ) and the second substream ( 1 b ) are set such that the desired amount of the C 2n alcohol and the C n alcohol of the desired isomer distribution are formed according to the following approach:

Mass stream C 2 n alcohol(5)=Feed*Split*( Xn _Aldol*Feed_ w _ n+Xi _Aldol*Feed_ w _ i )*(2* M _ Cn _ al− 18)/(2* M _ Cn _ al+ 2)* X _Hydr* X _Dist

Mass stream Cn alcohol(4)=Feed*Split*((1- Xn _Aldol)*Feed_ w _ n )+Feed*(1-Split)*Feed_ w _ n/M _ Cn _ al*M _ Cn _ ol*X _ n _Hydr* X _ n _Dist+Feed*Split*((1- Xi _Aldol)*Feed_ w _ i )+Feed*(1-Split)*Feed_ w _ i/M _ Cn _ al*M _ Cn _ ol*X _ i _Hydr* X _ i _Dist

Mass stream handling(1 b )=Feed*(1-Split)

Proportion of linear alcohols(4)=Feed*Split*((1- Xn _Aldol)*Feed_ w _ n )+Feed*(1-Split)*Feed_ w _ n/M _ Cn _ al*M _ Cn _ ol*X _ n _Hydr* X _ n _Dist/(Feed*Split*((1- Xn _Aldol)*Feed_ w _ n )+Feed*(1-Split)*Feed_ w _ n/M _ Cn _ al*M _ Cn _ ol*X _ n _Hydr* X _ n _Dist+Feed*Split*((1- Xi _Aldol)*Feed_ w _ i )+Feed*(1-Split)*Feed_ w _ i/M _ Cn _ al*M _ Cn _ ol*X _ i _Hydr* X _ i _Dist)

wherein

Feed=feed ( 1 )

Split=percentage proportion the first substream ( 1 a ) based on feed ( 1 )

Feed_w_n=percentage concentration of linear aldehydes Cn in feed ( 1 )

Feed_w_i=percentage concentration of branched aldehydes Cn in feed ( 1 )

Xn_Aldol=yield of C2n aldolization product based on the linear aldehydes Cn in the aldolization (B)

Xi_Aldol=yield of C2n aldolization product based on the branched aldehydes Cn of the aldolization (B)

M_Cn_al=molar mass of the aldehydes Cn

X_Hydr=yield of C2n aldolization products hydrogenated to the corresponding alcohols

X_Dist=yield of C2n alcohols in the distillation

X_n_Hydr=yield of linear Cn aldehydes hydrogenated to the corresponding alcohols

X_i_Hydr=yield of branched Cn aldehydes hydrogenated to the corresponding alcohols

X_n_Dist=yield of linear Cn alcohols in the distillation

X_i_Dist=yield of branched Cn alcohols in the distillation.