Isomerization Process

Light naphtha feed is charged by charge pump P-101 to one of the two drier vessels, D-101 and 102, filled with molecular sieves, and designed to remove water to protect the catalyst (see Figure 4-7). The makeup hydrogen is compressed by makeup gas compressor C-101 to 500psig. The gas then flows to gas driers D103 and D104, similar to those for liquid feedstock before it is combined with fresh feed. The feed is mixed with makeup hydrogen, heated through heat exchange with reactor effluent in E-101 and E-102 and a steam heater E-103, heated with medium pressure steam, and sent to the reactors. In normal operation, two reactors in series are employed.

MAKEUP HYDROGEN Ofl IE HS D-101 D-1Û2

SURGE DRUM V-101

LIQUID FEED

MOLECULAR ShEVE DRIERS 0-103 D-1W

X.

\7

ADDITIVE IHJECTION PUMP P-102

MAKEUP HYDROGEN COMPRESSOR C-1C1

ISOMERIZATION REACTOR

R-101

ISOMERIZATION

REACTOR

STABILIZER CO NO ENS ER E-104

STABILIZER RE FLU*

DRJM

V-103

STABILIZER REFLUX PUMP

PRODUCT

COOLER

E-106

MAKEUP CAUSTIC SOLUTION

CAUSTIC

CIRCULATION PUMP P-1CQ

Figure 4-7. CVC6 paraffins isomerization process. M.P. = medium pressure; C.W. = cooling water.

Table 4-19

C5/C6 Isomerization Operating Conditions

Table 4-19

C5/C6 Isomerization Operating Conditions

VARIABLE

UNITS

REACTOR PRESSURE

psig

450

REACTOR INLET TEMP

°F

300-340

H2/HC MOLE RATIO

0.05

LHSV

hr-1

2

The reactor effluent is heat exchanged with fresh feed in E-101 and taken directly to product stabiliser column V-102. The column overhead vapor product flows to the off-gas caustic wash column. In this column, the off gas is washed with dilute caustic, circulated by a pump at the bottom of the column, to remove traces of chlorides before the gas flows to the fuel system. The stabilized, isomerized liquid product flows from the bottom of the column and is transferred to the gasoline blending system. Alternatively, the stabilizer bottom can be separated into normal and isoparaffin components to recycle low-octane normal paraffin. Product octanes in the range of 88-92 RON can be obtained by this method. Recycle of normal paraffins and, if possible, methyl pentanes is required to increase octane gain.

The efficiency of separation by distillation is limited, however, because normal C5 boils between i-C5 (isopentane) and C6 isomers, separation by a molecular sieve is more effective. The molecular sieve selectively adsorbs normal paraffins, due to their smaller pore diameter, while excluding the larger-branched molecules.

The operating conditions of an isomerization unit are shown in Table 4-19. The process yields, utility consumption, and feed and product properties are shown in Tables 4-20 to 4-22.

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Responses

  • nasih
    What factors affect an isomerization unit in a refinery?
    6 years ago
  • teodros
    How does isomerization affect the distillation?
    5 years ago

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