Process for the energy-efficient preparation of alkali metal alcoholates

A process for producing at least one alkali metal alkoxide of the formula MAOR, wherein R is a C1-C6 hydrocarbon radical and MA is sodium or potassium, comprising:

• (a1) reacting a feed stream SAE1 comprising ROH with a feed stream SAE2 comprising MAOH in countercurrent in a reactive rectification column RRA to give a crude product mixture RPA comprising MAOR, water, ROH, and MAOH,
• wherein a bottom product stream SAS comprising ROH and MAOR is taken off at the lower end of RRA and a vapour stream SAB comprising water and ROH is taken off at the upper end of RRA,
• (a2) optionally, simultaneously with, and spatially separately from step (a1), a feed stream SBE1 comprising ROH is reacted with a feed stream SBE2 comprising MBOH in countercurrent in a reactive rectification column RRB to give a crude product mixture RPB comprising MBOR, water, ROH, MBOH, where MB is selected from sodium or potassium,
• wherein a bottom product stream SBS comprising ROH and MBOR is taken off at the lower end of RRB and a vapour stream SBB comprising water and ROH is taken off at the upper end of RRB,
• (b) the vapour stream SAB, and, when step (a2) is carried out, the vapour stream SBB, is/are mixed with SAB or, separately from SAB, fed into a rectification column RDA so that a mixture GA comprising water and ROH is present in RDA,
• (c) GA is separated in RDA into a vapour stream SDAB comprising ROH at the upper end of RDA and a bottom stream SDAS comprising water and ROH at the lower end of RDA,
• wherein the bottom stream SDAS is discharged from RDA at an offtake point EAS at the lower end of RDA and the vapour stream SDAB is discharged from RDA at an offtake point EAK at the upper end of RDA,
• (d) optionally, SDAS is, in its entirety or partly, separated in at least one rectification column RDX which is different from RDA, and in which a mixture GX comprising water and ROH is present, into a vapour stream SXB comprising ROH at the upper end of RDX and a bottom stream SXS comprising water and optionally ROH at the lower end of RDX,
• wherein the bottom stream SXS is discharged from the at least one rectification column RDX at an offtake point EXS at the lower end of this column and the vapour stream SXB is discharged from the at least one rectification column RDX at an offtake point EXK at the upper end of this column,
• (e) energy is transferred from a heating vapour H1 having a pressure p1 to at least one component Q1, as a result of which the heating vapour H1 condenses at least partially and a condensate K1 is thus obtained,
• wherein:
• (f) K1 is at least partially depressurized to give a heating vapour H2 having a pressure p2, where p2<p1,
• (g) H2 is mixed with further heating vapour H3 having a pressure p3 so as to give a heating vapour H4 having a pressure p4, where p2<p4<p3,
• (h) energy is transferred from H4 to at least one component Q2,
• wherein:
• i) Q1 and Q2 are identical or different from one another,
• ii) Q1 and Q2 are selected from the group consisting of SAE1, SAE2, RPA, SAS, SAB, GA, SDAS, SDAB,
• iii) Q1 and Q2 can, when step (a2) is carried out, alternatively or additionally be selected from the group consisting of SBE1, SBE2, RPB, SBS, SBB,
• iv) Q1 and Q2 can, when step (d) is carried out, alternatively or additionally be selected from the group consisting of GX, SXB, SXS.