MA conversion (liq., up ow)
EA conversion (liq., up ow)
VA conversion (liq., up ow)
40
20
0
MA conversion (gas)
EA conversion (gas)
VA conversion (gas)
40
20
0
50
100
50
100
50
100
Conversion of acetylenes (wt. %)
H /VA ratio (liq.) = 0.99 H /VA ratio (liq.) = 2.03
H /VA ratio (liq.) = 4.12 H /VA ratio (liq.) = 7.2
H /VA ratio (liq.) = 0.29 H /VA ratio (liq.) = 2.03
H /VA ratio (liq.) = 0.47 H /VA ratio (liq.) = 1.44
H /VA ratio (liq.) = 6.91
Figure 5 1,3-butadiene loss vs acetylene conversion, liquid phase upflow (24 barg, 35°C, LHSV =22 h -1 ) vs gas phase (0.6 barg, 35°C, LHSV =22 h -1 )
Carbon monoxide (CO) dosage As for MAPD selective hydrogenation, front-end and tail-end configurations are possible in acetylene selective hydrogenation in an ethylene matrix. In the case of front- end hydrogenation, an excess of H 2 is present in the feed gas, plus low levels of CO, which moderate the activity of the hydrogenation catalyst towards acetylene. In tail-end configuration, the H2 content can be controlled at stoichio - metric levels, so it is therefore desirable to operate with an intrinsically selective catalyst system. 6 To simulate a CO impurity in the feedstock, typical for front-end hydrogenation, a capillary for dosing CO, designed to dose 100 ppm CO in H2 at standard conditions, was installed. The CO could not be detected by online GC, as the H 2 itself became heavily diluted by excess hydrocarbon
feed and further downstream nitrogen (N2) dilution. Figure 6 shows a significant drop in all acetylene conversions at the onset of the CO dosage. Also, H2 was no longer quanti - tatively consumed, with H2 consumption instead dropping to about 75 mol%. A marginal temperature drop could be observed in the catalyst zone. A shift of conversion levels toward triple bond hydrogenation was not observed, with the BD conversion staying virtually stable. Greenoil formation and handling When running selective hydrogenation reactions in an olefinic matrix, the control and handling of greenoil are important aspects. During the operations, it was crucial to separate greenoil from the C1-C8 product fraction before online GC analysis. This could be achieved by downstream
90
Onset of CO dosage
35.9
VA conversion BD conversion Temperature
80
30 20 40 50 60 70
35.85
35.8
35.75
35.7
35.65
10
35.6
0
580
585
590
595
600
605
610
615
620
625
630
635
TOS (h)
Figure 6 Effect of a 100 ppm level CO dosage on VA and BD conversion at standard conditions, 24 barg, 35 °C, H 2 :VA = 2, mol/mol, LHSV = 22 h -1 .
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