In f luence H O/ ethanol ratio on selectivity vs. Conversion (Cu catalysts) p = 8 barg
In flu ence H O/ ethanol ratio on selectivity vs. Conversion (Al O catalysts) p = 8 barg
Cu_1
Cu_2
Cu_3
Cu_4
Ratio H O/ ethanol = 1/10
Ratio H O/ ethanol = 0
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Ethylene
Diethyl ether
C Ole ns
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achieved only at high conversion levels. It was observed that a switch in the main products, diethyl ether as the intermediate product and ethylene as the target product, occurs at around 75% ethanol conversion in the case of the 1/10 H2 O/ethanol mixture. At a higher ethanol conversion, however, increased C 4 olefin formation is present, which is far more pronounced in the absence of steam (H2 O/ ethanol = 0). This is a particularly important aspect to consider when the ethylene product stream is intended for oligomerisation or polymerisation, as C 4 olefins represent a critical impurity. Consequently, the addition of steam to the ethanol feed significantly improves ethylene selectivity and, thus, process efficiency. Overall, hte’s extensive experience in ethanol conversion processes has resulted in a comprehensive library of more than 110 assigned (thereof 80 identified) components in the chromatograms separating paraffins, olefins, and oxygenates. This comprehensive database, combined with advanced analytical expertise, allows for closure of the carbon (C), hydrogen (H), and oxygen (O) balances, as well as overall mass balance across the full range of ethanol conversion (see Figure 5 ). These capabilities apply not only to the processes presented in this case study but also to a broad range of other Figure 4 Influence of feedstock composition on the product spectrum in ethanol conversion to ethylene over all tested Al 2 O 3 -based catalysts. Left: pure ethanol feed; right: 1/10 H2 O/ethanol feed mixture
Acetaldehyde (w/o H 2 O) Ethyl acetate (w/o H 2 O) Acetic acid (w/o H 2 O)
Acetaldehyde (w/ H O) Ethyl acetate (w/ H O) Acetic acid (w/ H O)
Figure 3 presents a selected dataset obtained from the Cu-based catalysts at 8 barg, focusing on the influence of H2 O in the feedstock on the product spectrum. It can clearly be observed that acetaldehyde selectivity is promoted in the presence of H2 O at comparable ethanol conversion levels, while the formation of a consecutive product such as ethyl acetate is significantly suppressed. However, the presence of H2 O in the feed generally reduces ethanol conversion and opens the reaction pathway toward acetic acid ( Santacesaria, et al., 2012 ). Meanwhile, only minor effects on, for example, C 4 oxygenates (mainly butanone) were present. During the same experiments, a strong influence of the feed composition on the product yields for the Al 2 O 3 -based catalysts was observed. The changes in the product spectrum of the main components with respect to ethanol conversion are shown in Figure 4 , demonstrating that high ethylene selectivity is Figure 3 Influence of feedstock composition on the product spectrum in ethanol conversion to acetaldehyde over four different Cu-based catalysts at 8 barg reactor pressure. Selected components: acetaldehyde, ethyl acetate, and acetic acid. Bright colours indicate a pure ethanol feed, while dark colours indicate a 1/10 H2 O/ethanol feed mixture
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