Hydrocarbon Feed from Kwinana Refinery

In May 1996, BP Oil Australia agreed to supply hydrocarbon from the feed to the alkylation unit at Kwinana Refinery (immediately downstream of the catalytic cracking unit) for use in the pilot plant. The composition of the sample (approximately 80 L; taken on 2nd May, 1996) which was provided is shown in Table 11.2 and is considered typical for this source. However, the crude type, the processing conditions and the product slate will all affect the composition of this stream and key quantities (e.g. the isobutene concentration and the total C3 concentration, etc.) can be expected to vary somewhat if another sample is taken in the future.

Table 11.2 - Measured Composition of Hydrocarbon fromKwinand Refinery

Component

mol%

Isobutene

12.5

1 -Butene

11.5

trans-2-Butene

12.8

cis-2-Butene

7.9

Butadiene

0.3

Isobutane

30.4

n-Butane

23.4

Propane

0.8

Propene

0.4

Total

100.0

Two simulation cases were evaluated with the feed composition given above: (a) raw feed plus 5.0% excess ethanol at an overhead pressure of 950 kPag, reflux ratio of 5.0 and reboiler duty optimised with respect to isobutene conversion and the ETBE purity; and, (b) pre-reacted feed (80% isobutene conversion to ETBE) with the same conditions as used for case (a). The results are summarised in Table 11.3. The relatively low concentration of isobutene in the hydrocarbon from Kwinana Refinery (compared with the original design basis) generally reduced the attainable performance. Compared with the simulation data shown in Table 11.1, the maximum conversion is lower, the corresponding ETBE product purity is lower, and the volumetric yield of the ETBE product was substantially lower when the Kwinana Refinery sample was used.

The capacity of the pilot plant column was also reduced by the relatively higher energy requirement (since more inerts must be recovered overhead) and the design feed rate was reduced to 450-500 ml/min. The other operating conditions remain similar to the original design basis but a more extensive optimisation of operating pressure, reflux ratio and reboiler duty (to be undertaken during experimental testing) might result in some changes to the expected operating conditions which are indicated in Table 11.1. Interestingly, there is virtually no difference between cases (a) and (b). This indicates that, in an industrial application, a pre-reactor is essentially only required for convenience and could be eliminated if an appropriate means of regenerating the catalysts in situ was found.

Table 11.3- Predicted Pilot Plant Results with Kwinana Refinery Feed

Case (a)

Case (b)

Operating Conditions

Isobutene conversion (mol%)

93.4%

95.6%

Bottoms composition (wt%)

93.0% ETBE,

93.0% ETBE,

0.4% ethanol,

0.4% ethanol,

0.2% DIB,

0.2% DIB,

6.4% hydrocarbons

6.4% hydrocarbons

Distillate composition (wt%)

0.1% ETBE,

0.1% ETBE,

1.2% ethanol,

1 2% ethanol,

98.7% hydrocarbons

()8 7% hydrocarbons

Volumetric Yields

Bottoms product

17%

17%

Distillate product

82%

83%

Temperature Profile

Condenser outlet temperature (T1)

40°C

40°C

Overhead temperature (T2)

74°C

74° C

Temperature above reactive section (T3)

77°C

77°C

Temperature above stripping section (T4)

80°C

81°C

Temperature mid-stripping section (T5)

104°C

114°C

Bottoms temperature (T6)

155°C

160°C

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