OPERATING MANUAL VOLUME 13 LIGHT NAPHTA ISOMERIZATION UNIT

The major elements of the Penex / DIH Unit are the liquid feed and make-up gas driers, the methanator, the feed surge drum, the reactors and associated heater and exchangers, the product

A

PENEX UNIT (023) OPERATING MANUAL

DUNG QUAT REFINERY

OPERATING MANUAL

LIGHT NAPHTA ISOMERIZATION UNIT

UNIT 023

BOOK 1/2

Rev 0

CONTENTS

1 DUTY OF THE PLANT

2 ENVIRONMENTAL CONDITIONS

3 FEEDSTOCKS AND PRODUCTS SPECIFICATIONS

4 OVERALL MATERIAL BALANCE OF THE UNIT

5 BATTERY LIMIT CONDITIONS

6 DESIGN FEATURES

7 GAS AND LIQUID EFFLUENTS

1 PROCESS THEORY

2 DESCRIPTION OF FLOW

1 DESCRIPTION OF FLOW WITH CONTROLS

2 OPERATING CONDITIONS

3 PROCESS VARIABLES

4 INTER-UNIT CONTROL SCHEME

5 UNINTERRUPTIBLE POWER SUPPLY (UPS)

6 COMPLEX CONTROL DESCRIPTION

4 HYDROCARBON CIRCULATION AND INITIAL DRYDOWN

5 ACIDIZING AND FINAL DRYDOWN

1 NORMAL SHUTDOWN PROCEDURES

2 CATALYST UNLOADING AND HANDLING PROCEDURES

1 PRESSURE SAFETY DEVICES

2 ALARM SETTINGS

3 TRIP SETTINGS

4 TRIP SYSTEM CHART

5 CAUSE AND EFFECT DIAGRAM

6 MATERIAL HAZARD DATA SHEETS

7 SAFEGUARDING MEMORANDUM

1 CONTROL VALVES AND INSTRUMENTS

1 DISTRIBUTED SYSTEM CONTROL (DCS)

1 PLOT PLAN AND HAZARDOUS CLASSIFICATION

2 PROCESS FLOW DIAGRAMS AND MATERIAL SELECTION DIAGRAMS

3 PIPING AND INSTRUENTATION DIAGRAMS

4 OTHER DRAWINGS

4.2 PROCESS OUTLET

5 BATTERY LIMIT CONDITIONS

5.1 FEEDSTOCKS BATTERY LIMIT CONDITIONS

5.2 PRODUCTS BATTERY LIMIT CONDITIONS

5.3 UTILITIES BATTERY LIMIT CONDITIONS

6 DESIGN FEATURES

6.1 EQUIPMENT OUTSIDE LICENSOR SCOPE

6.2 MANDATORY SUPPLY

6.2.1 SULFUR ABSORPTION AND METHANATION CATALYSTS

6.2.2 ISOMERIZATION REACTOR CATALYST

6.2.3 MOLECULAR SIEVES

6.2.4 DRCS

7 GAS AND LIQUID EFFLUENTS

1 DUTY OF THE PLANT

1.1 LICENSOR

The Penex / DIH Process (Unit 023) is based on the UOP (Universal Oil Products) process The Licensor has issued the following documents:

♦ UOP Project Specification (Project 928504)

♦ UOP Penex Process Hydrogen Once Through: General Operating Manual

♦ UOP Deisohexanizer: General Operating Manual

♦ UOP Methanator Information (Additional section of the Penex Process Hydrogen Once Through General Operating Manual)

1.2 FUNCTION OF THE UNIT

The function of the Penex / DIH Unit is to process straight run light naphtha from the overhead of the Naphtha Splitter column T-1202 (Unit 012) to produce a high octane isomerate naphtha product The light straight run naphtha is derived from either 100% Bach Ho Crude or Mixed Crude (85% Bach Ho / 15% Arabian Light) The Penex unit is designed for a capacity of 231 613 metric tonnes per year (equivalent to 6500 BPSD) The UOP Penex Process is a continuous catalytic isomerization of pentanes, hexanes and mixtures thereof, based on an equilibrium reaction The reactions take place in a hydrogen atmosphere, over a fixed bed of catalyst and at operating conditions, which promote isomerization and minimize hydrocracking This product is a mixture of iso-paraffins with a high octane number

The process is simple and straightforward in design and operation and trouble-free in performance permitting a minimum of staffing and supervision Operating conditions are not severe as reflected by moderate operating pressure, low temperature, high catalyst space velocity and low hydrogen partial pressure requirements

Except for normal hydrotreating, the PENEX Process requires neither special feed pretreatment nor especially sharp prefractionation for removal of C6 cyclics or C7+ Penex affords the refiner considerable flexibility in the choice of feedstocks both at the time of design or after the unit is constructed

The major elements of the Penex / DIH Unit are the liquid feed and make-up gas driers, the methanator, the feed surge drum, the reactors and associated heater and exchangers, the product stabilizer, the net gas scrubber and the deisohexanizer

Although not essential to the success of the process, the Penex system will normally employ two reactors in a series flow configuration with the total required catalyst loading being equally distributed between the vessels Valving and piping are provided which permit reversal of the processing positions of the vessels and the isolation of either for partial catalyst replacement With time, the Penex catalyst will become deactivated by water, not hydrocarbon Because the water deactivation proceeds as a sharp front, which moves down the bed in a piston-like fashion, catalyst downstream of the front remains unaffected When catalyst in the lead reactor is spent, the reactor is taken off line for reloading During the short period of time the reactor is out of service, the second reactor is capable of maintaining continuous operation at design throughput and yield; conversion is moderately lower After catalyst reloading is completed, the processing positions of the two reactors may be reversed

The two reactor design permits essentially 100% unit onstream efficiency and reduces catalyst consumption costs by making partial catalyst replacements practical It also permits the unit to be designed for a smaller catalyst inventory (higher space velocity) thus reducing catalyst capital requirements Isomerization and benzene hydrogenation reactions are both exothermic and the temperature increases across the reactor Equilibrium requires that the outlet temperature be as low as the activity of the catalyst

permits With a single reactor, this would lead to a low inlet temperature and low isomerization rates in part of the catalyst bed The two reactor system permits the imposition of an inverse temperature gradient by cooling between reactors through exchange against cold feed The first reactor may, therefore, be operated at a higher temperature and achieve a higher reaction rate This reduces the inventory of catalyst and the reactor size required Most of the isomerization is thus accomplished at high rate

in the first reactor and the final portion is performed at a lower temperature to take advantage of the more favorable equilibrium

Not all catalysts are suitable for application of the inverse temperature gradient principle Some might coke or sludge if operated at a higher inlet temperature, or else they might promote excessive hydrocracking and yield loss Since the Penex catalyst does neither

of these, the inverse gradient can be applied to economic advantage

Chloride promoter (perchloroethylene) is added continuously with the feed and is converted to hydrogen chloride in the reactor Since the catalyst functions with very small amounts of promoter (measured in parts per million), it is not necessary to provide separate equipment for recovery and re-use of hydrogen chloride It is permitted to leave the unit by way of the stabilizer gas The quantity of stabilizer gas is small, due to the selective nature of the catalyst, which permits very little hydrocracking of the pentane/hexane charge to take place

To protect the catalyst, the liquid feed is first charged to the feed dryers and then to the charge surge drum Hydrogen make-up gas is sent to a methanator to remove trace levels of CO, CO2 and H2S and then onto the make-up gas dryers prior to be mixed with the combined feed from the charge surge drum and sent to the reactors

The effluent from the reactor is charged to a stabilizer to remove the residual hydrogen from the reaction and the light gases (C1 through C4) introduced with the make-up gas and produced in the reactor as a result of cracking The stabilizer gas is scrubbed for hydrogen chloride removal before entering the refinery fuel gas system (Unit 037)

The catalyst itself is non-corrosive in the plant and, despite the presence of small amounts of hydrogen chloride during operation, the dryness of the system permits construction of carbon steel

Bottom stream from the stabilizer is sent to the deisohexanizer (DIH) column The DIH primarily separates C5, 2,2-dimethylbutane and 2,3-dimethylbutane from the other C6

isomers and heavier components of the isomerate The benefit of the addition of a DIH column is to upgrade to a product with an octane value of 88.0 - 90.0 RONC Compared

to a maximum research octane number of approximately 84.0 RONC for a hydrocarbon once-through operation, this is a significant increase

More benefits from a DIH column are derived as the C5/C6 ratio of the fresh charge decreases since the nC5 is not recycled back to the reactor section for further isomerization

The DIH overhead product, composed primarily of C5's and dimethylbutanes, is sent to storage for gasoline blending The bottoms, flow-controlled at a small rate, are also typically sent to storage with the DIH overhead product; however, the bottoms should be evaluated as potential reformer feedstock as well The bottoms draw is necessary to avoid a build-up of heavies in the reactor section charge

The DIH side draw, composed primarily of methylpentanes, some dimethylbutanes and

nC6, is recycled back on flow control to the isomerization unit upstream of the reactors Hereafter are supplied the following documents:

Diagrams showing all process and utilities connections with other units Overall block flow diagram of the Refinery

PENEX / DIH PROCESS (UNIT 023)

Isomerate to TK-5106 A/B

Net gas to FG (unit 037)

Light naphtha from unit 012

Make-up gas from unit 012

Potable water Plant Air Instrument air Refinery Nitrogen Cold BFW Service water

CW supply

LP steam

MP steam 20°Be Caustic from unit 039

2 ENVIRONMENTAL CONDITIONS

2.1 AIR TEMPERATURE

2.2 RELATIVE HUMIDITY

2.3 RAINFALL

e Maximum rainfall intensity 40 mm for 10 min period

60 mm for 30 min period 108.1mm for 60 min period

N/NE 9.7/6.2 W/NW 4.1/14.3 E/SE 12.8/6.7 S/SW 1.1/1.0 The maximum velocity over a 2 minutes is 41.6 m/s for a return period of 50 years

The maximum velocity over a 2 minutes is 32.7 m/s for a return period of 20 years

2.7 ATMOSPHERE

a Extreme moisture - tropical climate

b Marine exposure - salt spray

c Sand storms - not applicable

d Copper-attacking fumes - sulphur

e Exposure to conductive or corrosive dusts (carbon, iron oxide, ammonium nitrates or phosphates, etc): NO

f Exposure to corrosive agents (nitric or sulphuric acids, chlorine, caustic, etc): NO

g Exposure to other pollutants originating from surrounding industrial plant: YES

2.8 MISCELLANEOUS DATA

b Typhoon frequency 2 to 3 per year

c Thunderstorm frequency 102 storm days per year

d Temperature inversion occurrence Not applicable

e Earthquakes to be taken into account and design shall be as per code UBC, zone

2

f The site is subjected to possible flood condition

3 FEEDSTOCKS AND PRODUCTS SPECIFICATIONS

3.1 FEEDS CHARACTERISTICS

3.1.1 HYDROTREATED LIGHT NAPHTHA

The Penex / DIH unit is designed to process straight run hydrotreated light naphtha, coming from Naphtha hydrotreating unit (Unit 012), derived from 100% Bach Ho or Mixed crude oils (85% Bach Ho and 15% Dubai crude) at a design capacity of 6500 BPSD

Following UOP’s evaluation of the full range naphtha for the 100% Bach Ho case and the Mixed case, the naphtha composition has been determined to be identical for both cases except for the higher sulfur in the Mixed case Accordingly only a single design case based on 100% Bach Ho with a maximum sulfur level content of 100 ppm wt shall

be used as the basis of design for the NHT/Penex-DIH and the CCR Paltformer Complex The NHT/Penex-DIH and the CCR Paltformer shall be capable of processing both cases

The feed definition for the Penex / DIH unit has the following properties:

Water Saturated at design temperature UOP 481

Mol Weight, kg/kg mole 80.48

Total Oxygenates (excluding

Method based on suspected compound

3.1.2 MAKEUP GAS

Make-up gas for the Penex / DIH Unit is delivered from the 3rd stage discharge of the make-up gas multi-stage compressors C-1202A/B/C (Unit 012) at a pressure of 42.3 kg/cm2 (g) It is a product of CCR platforming unit (Unit 013)

The composition of hydrogen is the following in normal operation:

Compound Make-up Hydrogen

mole %

H2 93.3 Methane 2.5 Ethane 2.4 Propane 1.4

For the total refinery, two design cases are specified: a Design case corresponding to

6500 BPSD (Light Naphtha with cut points C5 - 82°C / high benzene feed) and an Alternate case corresponding to 5336 BPSD (Light Naphtha with cut points C5 - 70°C / low benzene feed) The isomerate properties depend on the operating case and on the reactors catalyst level of activation

Hereafter are given the composition of the isomerate obtained for each case at Start Of Run (fresh catalyst) and End Of Run (spent catalyst)

Property Value

C5 +

Product Yield at Start-of-Run, 95.2

(wt % Fresh Feed, minimum)

C5 +

Design Case A l t e r n a t e C a s e PROPERTY

3.2.2 NET GAS

A net gas stream will be produced from the overhead of the Stabilizer and will be routed via

a caustic scrubber for hydrogen chloride removal before being sent to Fuel Gas Unit (Unit 037)

The composition of this gas is given hereafter for the different cases:

4 OVERALL MATERIAL BALANCE OF THE UNIT

5 BATTERY LIMIT CONDITIONS

The total refinery site is divided in blocks Every block contains one or more units The isomerization unit is situated together with NHT and CCR units (012 and 013) Because

of this construction there are two types of battery limits: battery limits for units and battery limits for blocks For feedstocks and products the unit battery limit conditions for the process streams are given For utilities the block battery limits are given

All the process lines entering/leaving the considered block are represented on PID 8474L-012-PID-0021-001 whereas the process lines leaving NHT/CCR or PENEX units but not leaving the block are represented on PID 8474L-012-PID-0021-002 Utility lines are represented on utility PIDs

5.1 FEEDSTOCKS BATTERY LIMIT CONDITIONS

DESIGN CONDITIONS AT

B/L

OPERATING CONDITIONS

AT B/L ORIGIN

light naphtha

5.2 PRODUCTS BATTERY LIMIT CONDITIONS

DESIGN CONDITIONS AT

B/L

OPERATING CONDITIONS

AT B/L DESTINATION

Note: (1) At grade – Unit 023 Battery Limit elevation is 6 m

5.3 UTILITIES BATTERY LIMIT CONDITIONS

DESIGN CONDITIONS AT

B/L

OPERATING CONDITIONS

AT B/L DESTINATION /

UTILITIES RETURN

Notes: (1) At grade – Units 012/013/023 Battery Limit elevation is 15 m

(2) At grade – Units 012/013/023 Battery Limit elevation is 12 m

(3) At grade – Units 012/013/023 Battery Limit elevation is 9 m

(4) At grade – Units 012/013/023 Battery Limit elevation is 6 m

6 DESIGN FEATURES

6.1 EQUIPMENT OUTSIDE LICENSOR SCOPE

Neutralization of spent caustic The net gas stream produced from the overhead of the stabilizer is routed to the net gas scrubber (T-2302) for hydrogen chloride removal before being sent to Fuel Gas (Unit 037) This is accomplished by contacting the rising acidic gases with a 10 wt% caustic solution The caustic is to be changed out before it falls below 2 wt%, therefore, periodically (once a week), a portion of caustic is withdrawn to a degassing drum (D-2305) and sent by gravity to

a Neutralization Pit TK-2399 This stream contains NaClO which needs to be neutralized This is done with sulfuric acid on pH control, which acts as an oxygen scavenger The neutralized spent caustic is then routed to the oily water sewer by means of the Neutralization Pit Eductor (J-2399)

The Neutralization Pit Eductor (J-2399) and the Neutralization Pit (TK-2399) are part of the Isomerization Unit but are outside Licensor scope

6.2 MANDATORY SUPPLY

6.2.1 SULFUR ABSORPTION AND METHANATION CATALYSTS

Catalyst type required for sulphur absorption in Methanator vessel (R-2301) is Puraspec

2010 from Johnson Matthey This catalyst has a density of 1155 kg/m3 and the installed volume is of 0.43 m3 It shall be replaced approximately every 3 years

Catalyst type required for methanation reaction in Methanator vessel (R-2301) is Puraspec 2443 from Johnson Matthey This catalyst has a density of 1105 kg/m3 and the installed volume is of 2.21 m3 It shall be replaced approximately every 3 years

Sulfur absorption and methanation catalysts are sock-loaded into the methanator

MSDS will be in the attachments

6.2.2 ISOMERIZATION REACTOR CATALYST

Isomerization catalysts required are I-8 Plus and I-82 Penex Catalysts from UOP They are amorphous, chlorided alumina, light paraffin isomerisation catalysts containing platinum, optimized for use in Penex units They selectively convert normal butane, pentane and hexane to high octane branched hydrocarbons In addition to isomerisation

of paraffins, they also saturate benzene

Initially lead reactor is loaded with I-8 Plus catalyst and lag reactor with I-82 catalyst These catalysts have a density of 885 kg/m3 and the installed volume is of 24.7 m3 per reactor They shall be replaced approximately every 6 years

The I-8 Plus/I-82 Penex catalysts are dense loaded into the reactors

MSDS will be in the attachments

6.2.3 MOLECULAR SIEVES

Molecular sieves required for Makeup Gas Driers (DR-2301/2302) shall be Molsiv Adsorbent type PDG-418 from UOP Sieves density is of 660 kg/m3 and the installed volume is of 1.97 m3 per drier Molecular sieves shall be replaced approximately every 3 years

Molecular sieves required for Feed Driers (DR-2303/2304) shall be Molsiv Adsorbent type HPG-250 from UOP Sieves density is 640 kg/m3 and the installed volume is of 5.90 m3 per drier Molecular sieves shall be replaced approximately every 3 years

Molecular sieves are normally sock-loaded into the driers

MSDS will be in the attachments

7 GAS AND LIQUID EFFLUENTS

Refer to attached document: “Effluent Summary Table” – 8474L-200-NM-6200-002

1.3.1 FRIEDEL-CRAFTS TYPE CATALYST

1.3.2 HYDRO-ISOMERIZATION CATALYSTS ABOVE 200°C

1.3.3 HYDRO-ISOMERIZATION CATALYSTS BELOW 200°C

2.1 FEED DRIERS (DR-2303/2304) (P&ID 023-PID-0021-013)

2.2 METHANATOR (R-2301) (P&ID 023-PID-0021-010)

2.3 MAKE-UP GAS DRIERS (DR-2301/2302) (P&ID 023-PID-0021-011)

2.4 REGENERANT VAPORIZER (E-2305) (P&ID 023-PID-0021-012)

2.5 REGENERANT SUPERHEATER (A-2301) (P&ID 023-PID-0021-012)

2.6 FEED SURGE DRUM (D-2301) (P&ID 023-PID-0021-015)

2.7 REACTOR EXCHANGER CIRCUIT (P&IDs 023-PID-0021-015 to 018)

2.8 ISOMERIZATION REACTORS (R-2302/2303) (P&ID 023-PID-0021-019)

2.9 STABILIZER (T-2301) (P&IDs 023-PID-0021-020/021)

2.10 NET GAS SCRUBBER (T-2302) (P&IDs 023-PID-0021-022 to 026)

2.11 DE-ISOHEXANIZER (T-2303) (P&IDs 023-PID-0021-026 to 030)

1 PROCESS THEORY

1.1 PROCESS PRINCIPLES

The principle of the process is the isomerization reaction, which takes place in the reactors It is an equilibrium reaction and converts normal paraffins to isoparaffins, which have a higher octane number

Reaction takes place on a fixed bed catalyst, containing a supported noble metal and a component to provide acidity The reaction is operated in a hydrogen atmosphere and employs perchloroethylene as a catalyst promoter, which is injected with the feed in the range of concentration of 150 parts per million weight The catalyst requires a dry, low sulfur feedstock Hydrocracking to light gases is generally slight

The C5/C6 paraffin isomerization reactions, which occur in the Unit 023, are shown below The octane numbers presented in this section are for pure components:

1.2 REACTION MECHANISMS

Paraffin isomerization catalysts fall mainly into either of two principal categories:

1 Those based on Friedel-Crafts catalysts as classically typified by aluminum chloride/hydrogen chloride

2 Dual-function hydro-isomerization catalysts

The catalyst used in this isomerization unit is of the second category For completeness both mechanisms will be discussed

1.2.1 FRIEDEL-CRAFTS CATALYST

No attempt is made to present a discussion of mechanisms of a degree of sophistication acceptable to a chemist specializing in the area The intention is simply to provide those practicing engineers who have not previously had reason to consider isomerization with

a basic introduction to the subject

Isomerization by either Friedel-Crafts or dual-function catalysts is generally thought to entail intramolecular re-arrangements of carbonium ions as illustrated for pentane:

Friedel-Crafts isomerization is believed by some to require the presence of traces of olefins or alkyl halides as carbonic ion initiators, with the reaction thereafter proceeding through chain propagation The initiator ion, which needs to be present in small amounts only, may be formed by the addition of HCl or HAICI4 to an olefin, which is present in the paraffin as an impurity or which is formed by cracking of the paraffin:

2 RCH = CH2 + HAICI4 → RCHCH3 + AICI4-

⊕ The initiator then forms a carbonic ion from the paraffin to be isomerized:

3 RCHCH3 + CH3-CH2-CH2-CH2-CH3 ⇔ RCH2CH3 + CH3-CH-CH2-CH2-CH3

Skeletal re-arrangements then occur:

of the final mixture is, of course that set by thermo-dynamic equilibrium assuming that sufficient reaction time has been provided

Another Friedel-Crafts route, which has been suggested, is direct hydride ion abstraction:

6 CH3 - CH2 - CH2 - CH2 - CH3 + AICI3 ⇔ CH3 - CH - CH2 - CH2 - CH3 + HAICI3-

⊕ The carbonic ion, as before, re-arranges:

9 CH3 - CH2 - CH2 - CH2 - CH3 + H+(AICI4)- ⇔ CH3 - CH - CH2 - CH2 - CH3 + (AICI4)- +

⊕ H2

Some chemists feel uncomfortable with the above because of the required postulation of hydrogen formation

1.2.2 DUAL-FUNCTION HYDRO-ISOMERIZATION CATALYST

The dual-function hydro-isomerization catalysts are thought by some to operate through

an olefin intermediate whose formation is catalyzed by the metallic component, assumed for illustration purposes to be platinum:

Pt

10 CH3 - CH2 - CH2 - CH2 - CH3 ⇔ CH3 - CH2 - CH2 - CH = CH2 + H2

This reaction is, of course, reversible and, since these catalysts are employed under substantial hydrogen pressure, the equilibrium is far to the left However, the acid function of the catalyst consumes the olefin by formation of a carbonic ion and thus permits more olefin to form despite the unfavorable equilibrium This step is entirely analogous to Reaction (2) shown for Friedel-Crafts, except that it is better to denote the acid function by a more general "H+A-"

11 CH3 - CH2 - CH2 - CH = CH2 + H+A- ⇔ CH3 - CH2 - CH2 - CH - CH3 + A-

⊕ The usual re-arrangements ensues:

CH3

12 CH3 - CH2 - CH2 - CH - CH3 ⇔ CH3 - CH2 - C - CH3

⊕ ⊕ The iso-olefin is then formed by the reverse analog of (11):

13 CH3 - CH2 - C - CH3 + A- ⇔ CH3 - CH2 - C = CH2 + H+A

⊕ The iso-paraffin is finally created by hydrogenation:

15 CH3 - CH2 - CH2 - CH2 - CH3 + H+A- ⇔ CH3 - CH - CH2 - CH2 - CH3 + A- + H2

⊕

1.3 HISTORY OF CATALYST

1.3.1 FRIEDEL-CRAFTS TYPE CATALYST

The isomerization catalysts employed during World War II were all of the Friedel-Crafts type Those, which contained aluminum chloride only, were either a hydrocarbon/aluminum chloride complex (the so-called sludge process) or they were manufactured in-situ by deposition onto a support such as alumina or bauxite They were intended to operate at very low temperatures (49°-129°C) and to approach the very favorable equilibrium composition characteristics of these temperatures

The catalyst tended to consume itself by reaction with the feedstock and/or product When temperature was raised a little in an effort to compensate for loss of catalyst and to speed the reaction to effect more isomerization, light fragments were formed by cracking and these, when vented, caused an excessive loss of the HCl promoter

Corrosion of downstream equipment was also commonplace, due to the solubility of aluminum chloride in hydrocarbon, to its relatively high volatility and to the difficulty of removing it from the product by caustic washing Aluminum chloride deposition in and plugging of reboiler tubes was not uncommon

The process faced problems in sludge disposal, which were considered onerous even before the present acute awareness of environmental factors developed The fixed bed process sometimes experienced unpredictable amounts of isomerization

1.3.2 HYDRO-ISOMERIZATION CATALYSTS ABOVE 200°C

The operational problems which had characterized the wartime Friedel-Crafts type isomerization plants, the advent of catalytic reforming which not only made hydrogen generally available in refineries but also demonstrated the practicality of using noble metal containing catalysts on a large scale, and the octane number race which postwar high compression engines initiated all combined in the 1950's to spawn a spate of hydro-isomerization processes These catalysts generally contained a noble metal and some halide, operated at temperatures between about 299°C and temperatures approaching those characteristics of catalytic reforming, employed recycle hydrogen to prevent catalyst carbonization and utilized either no promoter or traces at most In general, they did not require an especially dry feedstock but did benefit from a low sulfur content feedstock Most achieved a close approach to the equilibrium characteristic of their particular operating temperature

Because of their high operating temperatures and their necessarily low conversions to iso-paraffins, these high temperature catalysts were quickly replaced with the advent of the "third generation" low temperature catalysts

1.3.3 HYDRO-ISOMERIZATION CATALYSTS BELOW 200°C

"Low temperature" is considered rather arbitrarily for catalyst classification purposes as anything below 200°C operating temperature Typically these are fixed bed catalysts containing a supported noble metal and a component to provide acidity in the catalytic sense They operate in a hydrogen atmosphere and may employ a catalyst promoter whose concentration in the reactor may range from parts per million to substantially higher levels They generally all require a dry, low sulfur feedstock; however, they may differ importantly in their tolerance of certain types and molecular weights of hydrocarbons Hydrocracking to light gases is generally slight, so liquid product yields are high As stated before, it is this type of catalyst that is used in the Isomerization Unit

1.4.1 NAPHTENE RING OPENING

The three naphthenes, which are present in the feed of the isomerization unit, are cyclopentane (CP), methyl cyclopentane (MCP) and cyclohexane (CH) The naphthene rings will hydrogenate to form paraffins This ring opening reaction increases with increasing reactor temperature At typical isomerization reactor conditions, the conversion of naphthene rings to paraffins will be on the order of 20-40 percent

1.4.3 BENZENE SATURATION

The isomerization section is generally designed for 2 LV% benzene The 8 Plus and

I-82 catalysts will saturate benzene to cyclohexane This reaction proceeds very quickly and is achieved at very low temperatures Saturation of benzene is not equilibrium limited at the isomerization reactor conditions and conversion should be 100% The amount of heat generated by the saturation of benzene limits the amount of benzene, which can be tolerated in the Penex, feed The isomerization section feed can contain up

to 5% benzene The platinum function on the isomerization catalyst is responsible for benzene saturation

1.4.4 HYDROCRACKING

Hydrocracking occurs in the Penex reactors to a degree, which depends on the feed quality and severity of operation Large molecules such as C7's tend to hydrocrack more easily than smaller molecules C5 and C6 paraffins will also hydrocrack to a certain extent As

C5/C6 paraffin isomerization approaches equilibrium, the extent of hydrocracking increases If isomerization is pushed too hard, hydrocracking will reduce the liquid yield and increase heat production Methane, ethane, propane and butane are produced as a result of hydrocracking

Moderately high levels of CO/CO2 can be produced in the continuous catalytic reformer unit (U013) Even concentrations of 5-10 ppm CO/CO2 may be sufficient for justifying the necessity of a methanator upstream of the reactors Level traces of CO/CO2 will be removed

in the methanator through a nickel catalyst bed (PURASPEC 2443) The methanation of CO occurs readily at 204°C, but the methanation of CO2 requires 316°C

CO + 3H2 → CH4 + H2O + heat

CO2 + 4H2 → CH4 + 2H2O + heat The methanation catalyst will also hydrogenate olefins and crack C2+ hydrocarbons But it can be permanently deactivated by sulfur So, a preliminary catalyst bed (PURASPEC 2010) will be used for H2S traces removal

+ 3H2

>100 RON-O 84.0 RON-O

The water produced by the reactions will be removed in the makeup gas driers 2301/2302.The methanation reaction is exothermic as are the side reactions, hydrogenation and cracking The methanation of feedstream with 1 mole percent of CO or 1 mole percent

DR-CO2 can generate a delta T of hundreds of degrees There is a danger of a temperature excursion in circumstances where a sudden increase in CO/CO2 concentration can occur, or where C2+ hydrocarbons, benzene or olefins can enter the methanator

1.6 ACIDIZING

During the initial commissioning period, hydrogen chloride (HCl) is injected into the process stream where it reacts with iron oxide (Fe2O3) to form iron chloride (FeCI3) and water This reaction will continue to take place until the rust present in the unit is depleted The absence of H2O in the unit, as detected by the moisture analyzers, will signify that the reaction has gone to completion

Hydrogen chloride + iron oxide → Iron chloride + water 6HCl + Fe2O3 → 2FeCI3 + 3H2O

1.7 CHLORIDE PROMOTER

The addition of the chloride promoter (perchloroethylene C2Cl4) to the process stream is intended to maintain the acid function of the catalyst with chloride atoms (Cl) At a reactor temperature of 105°C or higher, the organic chloride will decompose to HCl in the presence of the I-8 Plus and I-82 catalysts

Perchloroethylene + hydrogen → Hydrogen chloride + ethane

If a hydrogen stripping operation is performed, hydrogen sulfide (H2S) will be present in the stabilizer off gas and will react with sodium hydroxide to form sodium sulfide (Na2S), sodium bisulfide (NaHS) and water During the sulfur stripping procedure it is important

to monitor the total alkalinity and the percent spent (the difference between the total alkalinity and the strong base) as shown in Figure 2.1.2 and Figure 2.1.3 Report the concentration of strong base as wt% NaOH

HCl + NaOH → NaCl + H2O

H2S + 2NaOH → Na2S + 2H2O

H2S + Na2S → 2NaHS HCl + Na2S → NaCl + NaHS HCl + NaHS → NaCl + H2S

1.9 DE-ISOHEXANIZER (DIH): THEORY OF FRACTIONATION

At this point we will try to give the reader an understanding of how the various fractions are separated in the DIH (T-2303)

It is well known that if water is heated to 100°C at atmospheric pressure, the water will boil and steam vapors will rise from the surface of the liquid It is equally well known that

if steam vapors are cooled they will condense to liquid water The evaporation and condensation of water are the fundamental principles underlying the production of distilled water

Now let us examine a mixture of alcohol and water and see how we can produce essentially pure water and pure alcohol

The alcohol will boil at approximately 60°C at atmospheric pressure; therefore, the mixture of the two liquids will boil somewhere between 60°C and 100°C The actual boiling point will depend upon the composition of the mixture The more alcohol that is present, the lower will be the boiling point

If this mixture is boiled, vapors made up of alcohol and water will be given off Since alcohol is the lighter compound in the mixture, there will be more alcohol, as a percentage, in the vapors than in the liquid

Let us now consider a mixture composed of 50% alcohol and 50% water This mixture will boil at about 79°C and will give off vapors consisting of, say 60% alcohol and 40% water If these vapors were condensed, and reboiled, the 60/40 mixture would boil at about 77°C and give off vapors consisting of about 70% alcohol and 30% water In this manner, by successive vaporization and condensation, we would eventually obtain almost pure alcohol boiling at about 60°C

Likewise, the liquid remaining after the first vaporization would consist of only 40% alcohol plus 60% water This mixture would require a higher temperature of about 82°C

to produce vaporization The vapors boiling from this mixture would consist of about 50% alcohol and 50% water, leaving a liquid containing 30% alcohol and 70% water Thus, by successive reboiling and vaporizing off the lower-boiling alcohol, we would eventually obtain substantially pure water boiling at 100°C

It would require about six successive vaporizations and condensations between 79°C and 60°C to produce almost pure alcohol A further five reboilings of the liquid left after the first vaporization, at temperatures between 79°C and 100°C, would result in the production of almost pure water

If all these steps were carried out separately, we would require 11 vessels, which would make for a very uneconomical process In practice, however, only one vessel would be used and the 11 steps would be conducted on what are called "Fractionating trays" These are just trays constructed in such a manner that a level of boiling liquid is maintained on the tray while vapors from the tray below are bubbled through the liquid One type of fractionating tray used extensively in the past is one that is commonly called

a "bubble deck"

The vapors rise from the tray below and flow up through a number of risers in the tray above The bubble caps over each riser force the vapors into the liquid The vapors then flow through a number of slots on the side of the bubble cap and finally escape from the liquid to rise to the next tray to repeat the process The vapors coming from the tray below will be cooled to the temperature of the liquid through which it bubbles The vapors that then rise from this tray will have a new composition, the actual composition depending upon the temperature of the boiling liquid from which it leaves

In the DIH of this isomerization unit sieve trays are used The sieve tray is a flat perforated plate Vapor issues from the holes to give a multi orifice effect The vapor velocity keeps the liquid from flowing down through the holes Sieve trays are simple and therefore relatively inexpensive, but have a relatively poor turndown

Now, if 11 of these fractionating trays were placed into one vessel, a "fractionating tower"

is produced that would fractionate or separate the alcohol and water A sketch of the fractionating tower for the alcohol/water separation is included to simplify the explanation

of the working of the tower Some of the trays have been omitted to simplify the sketch (Figure 2.1.4)

In order to have the column operate at its best, the 50/50 alcohol/water mixture is first heated to its boiling point of 79°C and fed to the tower on the tray that is also operating at 79°C If the alcohol/water mixture was fed in cold, it would upset the temperature gradient through the tower by chilling the feed tray

At the temperature of 79°C the vapors rising from the feed trays consist of 60% alcohol and 40% water The excess liquid from this tray flows down the downcomer to the trays below and is composed of 40% alcohol and 60% water

As the vapors from the feed tray rise through the liquid on the tray above they would condense to form a liquid with a higher percentage water and a vapor containing a higher percentage alcohol than the original vapor The temperature of this tray is at the boiling point of the liquid on the tray, so the vapors from this tray will consist of 70% alcohol and 30% water The excess liquid from this trays will flow down the downcomer to the feed tray The vaporization and condensation will continue on up the column until we have almost pure alcohol vapors leaving the top of the column at a temperature of 60°C This

is referred to as "tower top temperature" The cooling of the tower from the 79°C feed tray temperature to the 60°C top temperature is obtained by pumping back a portion of the cooled and condensed overhead product to the top of the column This stream is called "reflux"

Meanwhile, the excess liquid from the feed tray is reboiled at a temperature of 82°C and the vapors from this reboiling will consist of 50% alcohol and 50% water The excess liquid, 30% alcohol and 70% water, will flow to the tray below and will be reboiled at a higher temperature This will continue until the liquid is essentially pure water at the bottom of the column This is the "bottoms" and the temperature at which it leaves the tower is the "bottoms temperature" The temperature rise between the feed tray at 79°C and the bottoms temperature at 100°C is obtained by reboiling the bottoms product with some outside source of heat This source can be a circulating stream of hot oil (reboiler oil), steam, or a gas or oil fired heater By using 11 fractionating trays, a top reflux and a bottom reboiler heat, we have separated the original 50/50 alcohol/water mixture into alcohol and water The whole process is referred to as "fractionation", "distillation" and even "fractional distillation"

There are a few more points regarding fractionation that can be explained using the foregoing illustration as an example

The above discussion is mainly about the top reflux, but there is also an "internal reflux" This is the excess liquid that flows from one tray down to the next Using the feed tray as

an example and assuming some of the excess liquid can be removed as it flows to the tray below and that the same quantity of reboiler heat is being added to the bottom of the tower, there would be less liquid reaching the tray below the feed tray if some of the internal reflux is removed With less liquid flowing across this tray and the same amount

of heated vapors coming from the tray below, this tray temperature would increase and can become 85°C instead of 82°C and less vapors would condense and more liquid would vaporize, thus changing the equilibrium The vapors leaving this tray now would contain about 40% alcohol and 60% water instead of the previous 50/50 mixture This would change the liquid composition on the feed trays giving it a higher water content than before and would require a higher tray temperature to boil this mixture This would also mean that the internal reflux leaving this tray would now have 65% water instead of the 60% water it had before Some of the internal reflux has been removed as a "side cut" If we now increase this side cut, we will end up with a side cut having a water content something greater than 65%

If the rate at which the side cut product is withdrawn from the column is increased, there will be less internal reflux available for the trays below The tray temperature will increase and a liquid of a heavier composition will be present on each of the trays and the side cut product, still being taken from the same tray, will also be heavier

The most important reflux stream, however, is still the top reflux The amount of this reflux will determine how good the fractionation will be between two compounds or two fractions If there is too much top reflux, there will be too much internal reflux Each tray will have a greater flow of liquid across it and the turbulence of the liquid on the tray will increase This will result in greater and greater liquid entrainment in the vapor as it passes from one tray to the next This liquid composition on each tray will change because of this entrainment and the fractionation will no longer be a precise one On the other hand, too low a reflux will result in too little internal reflux resulting in a very low flow of liquid across each tray The contact between the rising vapors and the liquid on each tray will not be as good The vapors may not even have time enough to establish

an equilibrium with the liquid and less vapors will condense The liquid composition on each tray will change and again the fractionation will be a sloppy one

The amount of reflux required to the top of a fractionating tower will depend upon the quantity of the overhead vapors plus the quantity of heat to be removed from the top portion of the tower In order to increase the top reflux for better fractionation, it is usually only necessary to increase the amount of heat that needs to be removed This can normally be done by increasing the quantity of reboiler heat applied to the bottom of the column

It would also be pertinent at this time to discuss the boiling point of a compound or of a mixture Each compound has its own vapor pressure, which is a measure of the tendency of a molecule of the compound to escape from the liquid as a vapor The vapor pressure of a mixture is the sum of all the partial pressures of each compound in the mixture For example, in our 50/50 alcohol/water mixture, we could determine the vapor pressure of the mixture by adding together 1/2 the vapor pressure of the alcohol plus 1/2 the vapor pressure of the water The vapor pressure of this mixture would be midway between the vapor pressure of the two compounds; hence, the boiling point will be between the boiling points of the two compounds

Analog to the alcohol/water example, the DIH fractionates the C5/C6 naphtha mixture that

is fed to the column

The overhead consists of C5's and dimethyl butanes, the side draw is primarily composed of methylpentane, some dimethyl butanes and nC6 The bottom stream is a small flow, composed of the heavier boiling components, like cyclohexane and C7+

Figure 2.1.1

Figure 2.1.2

Figure 2.1.3

Figure 2.1.4

2 DESCRIPTION OF FLOW

This section will present a description of the flow through the isomerization unit, as well

as each major piece of equipment with its function and place in the process Details relating to operation will be discussed in Chapters 5 to 8

For reference, Process Flow Diagrams of the Penex/DIH process unit are included in § 2

of Chapter 14 Further reference is made to the P&ID's of this unit: 010/032

023-PID-0021-2.1 FEED DRIERS (DR-2303/2304) (P&ID 023-PID-0021-013)

Hydrotreated light naphtha enters straightly the PENEX unit, and is first dried in the feed driers DR-2303/2304

The purpose of these driers is to ensure that the hydrotreated naphtha is dry before entering the Reactors (R-2302/2303)

Indeed, due to the sensitivity of the I-8 Plus and I-82 reactors catalysts to water, the feedstock must be routed through these molecular sieve driers The driers are loaded with UOP Molsiv Adsorbent HPG-250 for the removal of water and trace levels of oxygenates or sulfur compounds

The driers are operated in series except when they are in the regeneration mode At that time only one will be in service

The hydrotreated C5/C6 stream is mixed with the recycle DIH side draw before being introduced to the Feed Drier (DR-2303 or 2304) at the bottom and passes upflow through the molecular sieve desiccant and exits at the top The flow is then routed through one of the drier crossovers to the other feed drier The flow through the second feed drier is also in the upflow pattern The dried hydrocarbon is then routed to Feed Surge Drum (D-2301) Over a period of time, the drier in the lead position will become spent as indicated by the Moisture Analyzer (023-AT-001B) located between the two driers At this time, it will become necessary to regenerate this drier The driers should be regenerated on a schedule frequent enough to avoid moisture breakthrough The spent drier is taken out of service by closing the appropriate block valves The second drier is now alone in service as the only drier drying the feed The moisture analyzer tap is switched to monitor this in-service drier After the drier regeneration has been completed,

it is now ready for service A switch is made such that the regenerated drier takes the lag position with the in-service drier remaining as the lead drier Over a period of time the lead drier will become spent and is now set up for regeneration with the tail drier now being the only one in service This will be the manner in which these driers will be lined

up for process flow The regeneration procedure for the liquid driers is detailed in Chapter 6

The liquid feed driers are constructed from carbon steel and the hydrogen driers are made from killed carbon steel The bottom of the vessel is equipped with a carbon steel outlet basket, covered with a steel mesh screen, to prevent loss of sieve or support material The molecular sieve and alumina are loaded between several layers of support material A holddown grating or screen is used on top of the sieve and the support material to provide bed stability

2.2 METHANATOR (R-2301) (P&ID 023-PID-0021-010)

Make-up gas is imported from the Make-Up Gas Knock-Out Drum / Lube Oil Mist Eliminator (D-1208), downstream of the CCR Platforming Unit and Make-Up Gas Compressor Section It enters the Penex Process Unit at 42.3 kg/cm² (g) and 38 °C It is

heated to 231 °C through the Methanator Feed / Effluent Exchanger (E-2301) and the Methanator Heater (A-2302), then routed to the Methanator (R-2301)

The Methanator purpose is to protect the catalysts of the Reactors (R-2302/2303) from trace levels of sulphur, CO or CO2 that could remain in the feed stream

The Methanator is loaded with two catalysts dispatched on two superposed beds with the feed passing down flow:

Puraspec 2010 for sulphur absorption (upper bed) Puraspec 2443 for methanation (lower bed) The catalysts are loaded between a graduated system of inert ceramic balls

The water produced during the methanation reaction and any CO2 not methanated will

be removed in the Make-up Gas Driers DR-2301/2302

The treated gas is cooled through the Methanator Feed / Effluent Exchanger E-2301 and the Methanator Cooler E-2303 It enters the Make-Up Gas Driers at 38°C and 37.4 kg/cm² (g)

2.3 MAKE-UP GAS DRIERS (DR-2301/2302) (P&ID 023-PID-0021-011)

Make-up gas must be dried in order to protect the I-8 Plus and I-82 catalysts for the same reason as described at the feed drier section The make-up gas driers are loaded with UOP Molsiv Adsorbent PDG-418, a molecular sieve for the removal of water

The two gas driers operate in the same manner as the feed driers The driers operate upflow, in series The dried hydrogen is then sent to the reactor circuit on Flow Control (023-FIC-013) The hydrogen is also used for pressure control (023-PIC-090) in the Feed Surge Drum (D-2301) and, for start-up, in the Stabilizer (T-2301) The regeneration procedure for the gas driers is detailed in Chapter 6

The make-up gas driers are made from killed carbon steel The design of the drums is similar to the feed driers one

2.4 REGENERANT VAPORIZER (E-2305) (P&ID 023-PID-0021-012)

The regenerant vaporizer uses low pressure steam to heat the regenerant stream before

it reaches the electric superheater The vaporizer, shown in Figure 2.2.2, is an upright heat exchanger which uses bayonet type tubes that have been strength welded and fully rolled This heater is equipped with a level indicator and a high level alarm, and is designed to operate with the top portion of the tubes uncovered Low pressure steam on the inside of the bayonet tubes transfers heat to the regenerant on the outside of the bayonet tubes This arrangement allows hot steam in the tip of the bayonet tube to transfer heat to the vaporized regenerant stream to 119-120°C, giving it several degrees

of superheat This prevents the regenerant from condensing which could damage the electric bundles in the regenerant superheater (A-2301) when operating The liquid level

in the vaporizer is available from 023–LI-003 023-LXAHH-004 in E-2305 will trip the regenerant superheater A-2301

2.5 REGENERANT SUPERHEATER (A-2301) (P&ID 023-PID-0021-012)

The regenerant superheater, shown in Figure 2.2.3, raises the temperature of the vaporized regenerant to a temperature of 316°C The regenerant stream is heated by Inconel electric elements, which are capable of reaching temperatures of over 600°C