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Descripción: voda
6/22/2008
Wacker process
Acetaldehyde production
• Important intermediate (2 million t/a) for production of acetic acid (40%) and ethyl acetate (60 %) • Until the 1960: production from acetylene and water in diluted sulfuric acid (yield around 98 %) • Since the 1970ies: Wacker-Hoechst-process • Single or two-step process with oxygen or air as oxidant and Pd/Cu catalyst • Two-step process: higher investment and energy costs; more chlorinated chlorinated h drocarbons drocarbons in waste stream et still referred costs for air separation plant, as required for single step process, are even higher)
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Acetaldehyde from ethene
85% of world acetaldehyde production by Wacker process Exothermic catalytic direct oxidation with two component catalyst PdCl2 and CuCl2
Reactions in the Wacker process • Catalytic oxidation of ethene with H2O
• Pd regeneration with CuCl2
• Cu+ re-oxidation with oxygen and hcl
• Regeneration is rate determining
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Catalytic cycle
Catalytic cycle
2−
r CH CHO 3
=
k ⋅
[ PdCl4 ] ⋅ [C 2 H 4 ] −
+
[Cl ][ H ]
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Single stage process • Reaction of highly pure ethene and oxygen in a bubble column • 120 – 130 °C, 3 bar, conversion per pass: 35 - 45% • Effluent gas is cooled, separated from catalyst and scrubbed with water for acetaldehyde recovery • Excess ethene is recycled to the reactor. A small part is purged to prevent inert gas accumulation
Two stage process
Ethene reaction and Cu+ re-oxidation take place in different bubble columns. 105 – 110 °C, 10 bar, almost complete conversion of ethene No loop gas required Acetaldeh de recover b extractive distillation like in sin le sta e rocess
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Comparison of the processes • Acetaldehyde yield almost equal (about 95%) • Expensive construction materials required • Lower investment costs in the single stage process, because of the need of only one reactor • In two stage process air (less expensive) can be used for the reoxidation instead of pure oxygen • No explosive ethene/O2 mixtures in two stage process