PROCESS FOR HETEROGENEOUSLY CATALYZED PARTIAL GAS PHASE OXIDATION OF PROPYLENE TO ACRYLIC ACID

Abstract

A process for heterogeneously catalyzed partial gas phase oxidation of propylene to acrylic acid in the absence of propane as an inert diluent gas, in which, in the starting reaction gas mixture, cyclopropane is substantially avoided as an impurity and crude propylene is used additionally as a propylene source.

Description

Claims

1. A process for heterogeneously catalyzed partial gas phase oxidation of propylene to acrylic acid, in which, in a first reaction zone, a starting reaction gas mixture 1 which comprises propylene and molecular oxygen as reactants and at least propane as an inert diluent gas and comprises the molecular oxygen and the propylene in a molar O2:C3H6 ratio of ≧1 is first, in a first reaction stage at elevated temperature, conducted through at least one first catalyst bed whose catalysts have at least one multimetal oxide comprising Mo, Fe and Bi as the active composition in such a way that the propylene conversion in single pass through the catalyst bed is ≧90 mol % and the accompanying selectivity SAC of acrolein formation and of acrylic acid by-product formation together is ≧80 mol %, the temperature of the product gas mixture 1 leaving the first reaction stage is reduced if appropriate by direct cooling or by indirect cooling or by direct and indirect cooling, and, if appropriate, secondary gas in the form of molecular oxygen or inert gas or molecular oxygen and inert gas is added to product gas mixture 1, and then product gas mixture 1, as a starting reaction gas mixture 2 which comprises acrolein and molecular oxygen as reactants and at least propane as an inert diluent gas and comprises the molecular oxygen and the acrolein in a molar O2:C3H4O ratio of ≧0.5, in a second reaction stage at elevated temperature and with formation of a product gas mixture 2, is conducted through at least one second catalyst bed whose catalysts have at least one multimetal oxide comprising Mo and V as the active composition in such a way that the acrolein conversion in single pass through the catalyst bed is ≧95 mol % and the selectivity SAA of acrylic acid formation assessed over both reaction stages, based on propylene converted, is ≧70 mol %, wherein starting reaction gas mixture 1, based on the molar amount of propane present therein, comprises ≦3 mol % of cyclopropane and has been obtained with additional use of crude propylene.

2. The process according to claim 1, wherein the acrolein conversion in single pass through the catalyst bed is ≧96 mol %.

3. The process according to claim 1, wherein the acrolein conversion in single pass through the catalyst bed is ≧97 mol %.

4. The process according to claim 1, wherein the acrolein conversion in single pass through the catalyst bed is ≧98 mol %.

5. The process according to claim 1, wherein the acrolein conversion in single pass through the catalyst bed is ≧99 mol %.

6. The process according to any of claims 1 to 5, wherein starting reaction gas mixture 1, based on the amount of propane present therein, comprises ≦2 mol % of cyclopropane.

7. The process according to any of claims 1 to 5, wherein starting reaction gas mixture 1, based on the amount of propane present therein, comprises ≦1 mol % of cyclopropane.

8. The process according to any of claims 1 to 5, wherein starting reaction gas mixture 1, based on the amount of propane present therein, comprises ≦0.2 mol % of cyclopropane.

9. The process according to any of claims 1 to 5, wherein starting reaction gas mixture 1, based on the amount of propane present therein, comprises ≦0.15 mol % of cyclopropane.

10. The process according to any of claims 1 to 9, wherein the propylene conversion in single pass through the catalyst bed is ≧92 mol %.

11. The process according to any of claims 1 to 9, wherein the propylene conversion in single pass through the catalyst bed is ≧94 mol %.

12. The process according to any of claims 1 to 11, wherein starting reaction gas mixture 1, based on the amount of propane present therein, comprises ≧10 molppb of cyclopropane.

13. The process according to any of claims 1 to 11, wherein starting reaction gas mixture 1, based on the amount of propane present therein, comprises ≧50 molppb of cyclopropane.

14. The process according to any of claims 1 to 11, wherein starting reaction gas mixture 1, based on the amount of propane present therein, comprises ≧1 molppm of cyclopropane.

15. The process according to any of claims 1 to 14, wherein the at least one multimetal oxide comprising Mo, Fe and Bi is one of the general formula IV Mo12BiaFebXc1Xd2Xe3Xf4On   (IV)whereX1=nickel and/or cobalt,X2=thallium, an alkali metal and/or an alkaline earth metal,X3=zinc, phosphorus, arsenic, boron, antimony, tin, cerium, lead and/or tungsten,X4=silicon, aluminum, titanium and/or zirconium,a=from 0.5 to 5,b=from 0.01 to 5,c=from 0 to 10,d=from 0 to 2,e=from 0 to 8,f=from 0 to 10 andn=a number which is determined by the valency and frequency of the elements in IV other than oxygen.

16. The process according to any of claims 1 to 15, wherein the at least one multimetal oxide comprising Mo and V is one of the general formula VII Mo12VaXb1Xc2Xd3Xe4Xf5Xg6On   (VII)whereX1=W, Nb, Ta, Cr and/or Ce,X2=Cu, Ni, Co, Fe, Mn and/or Zn,X3=Sb and/or Bi,X4=one or more alkali metals,X5=one or more alkaline earth metals,X6=Si, Al, Ti and/or Zr,a=from 1 to 6,b=from 0.2 to 4,c=from 0.5 to 18,d=from 0 to 40,e=from 0 to 2,f=from 0 to 4,g=from 0 to 40 andn=a number which is determined by the valency and frequency of the elements in VII other than oxygen.

17. The process according to any of claims 1 to 16, wherein the volume-specific activity of the at least one first catalyst bed increases at least once over the length of the flow path in flow direction of starting reaction gas mixture 1.

18. The process according to any of claims 1 to 17, wherein the volume-specific activity of the at least one second catalyst bed increases at least once over the length of the flow path in flow direction of starting reaction gas mixture 2.

19. The process according to any of claims 1 to 18, wherein the at least one first catalyst bed is a fixed bed and its propene loading is ≧120 I (STP)/I·h and ≦250 I (STP)/I·h.

20. The process according to any of claims 1 to 19, wherein starting reaction gas mixture 1 comprises from 6 to 13% by volume of propylene.

21. The process according to any of claims 1 to 20, wherein starting reaction gas mixture 1 comprises from ≧0 to 35% by volume of H2O.

22. The process according to any of claims 1 to 21, wherein starting reaction gas mixture 1 comprises from ≧0.01% by volume of propane.

23. The process according to any of claims 1 to 21, wherein starting reaction gas mixture 1 comprises from ≧1% by volume of propane.

24. The process according to any of claims 1 to 21, wherein starting reaction gas mixture I comprises from ≧5 to ≦70% by volume of propane.

25. The process according to any of claims 1 to 24, wherein starting reaction gas mixture 1 comprises from ≧0.01% by volume of CO2.

26. The process according to any of claims 1 to 25, wherein starting reaction gas mixture 1 comprises from ≧1% by volume of N2.

27. The process according to any of claims 1 to 26, wherein the acrylic acid is removed in a separation zone 1 from product gas mixture 2 by conversion to the condensed phase.

28. The process according to claim 27, wherein the acrylic acid is converted from product gas mixture 2 into the condensed phase by absorptive measures.

29. The process according to claim 27, wherein the acrylic acid is converted from product gas mixture 2 into the condensed phase by condensative measures.

30. The process according to claim 27, wherein the acrylic acid is converted from product gas mixture 2 into the condensed phase by absorptive and condensative measures.

31. The process according to claim 28 or 30, wherein the absorbent used is water or an aqueous solution.

32. The process according to any of claims 27 to 31, wherein the acrylic acid is removed in a separation zone 2 using at least one thermal separation process from the condensed phase obtained in separation zone 1.

33. The process according to any of claims 27 to 32, wherein at least a portion of the residual gas remaining in the conversion of the acrylic acid from product gas mixture 2 into the condensed phase is recycled into the first reaction stage and/or into the second reaction stage.

34. The process according to any of claims 1 to 33, wherein the propylene present in starting reaction gas mixture 1 is fed to starting reaction gas mixture 1 at least partly from a partial dehydrogenation of propane.

35. The process according to claim 34, wherein at least a portion of the residual gas remaining in the conversion of the acrylic acid from product gas mixture 2 into the condensed phase is recycled into the partial dehydrogenation of propane.

36. The process according to any of claims 1 to 35, which is followed by a process for preparing polymers in which acrylic acid prepared by a process according to claims 1 to 35 is polymerized.

37. The process according to any of claims 1 to 35, which is followed by a process for preparing acrylic esters in which acrylic acid prepared by a process according to claims 1 to 35 is esterified with an alcohol.

38. The process according to claim 37, which is followed by a process for preparing polymers in which acrylic ester prepared by a process according to claim 37 is polymerized.