tratamento glp

8/19/2019 Tratamento GLP

1/30

White Products Refining by Sweetening

Claude Mar ty

Generally speaking, crude oils undergo basically two kinds of treatment inrefineries: physical separation processes and conversion processes (ther-mal/catalytic). The result is a range of intermediate or end products that then

need to have finishing operations called “chemical refining”. White productsweetening is among these operations whose aim is to partially or totallyremove or convert small percentages of unwanted substances found in theseproducts. The substances may be hydrocarbons (diolefins) or moleculescontaining heteroatoms (sulfur and nitrogen derivatives, phenols, etc.).Table 15.1 lists the main types of compounds tha t need t o be removed or con-verted.

Mercaptans, essentially present in white products (LPG, FCC and visbreak-ing gasolines, kerosene cuts), are eliminated by sweetening (see new tenden-cies elsewhere in th e text). Sweetening is necessary since mercaptans are cor-

rosive, detrimental and foul-smelling products (see the different families listedin Fig. 15.1). They result in engine fouling and have an unfavorable effect onoctane number when gasolines are leaded.

15.1 Mercaptan Distribution in Petroleum C u t s

Mercaptans are mainly present in light and middle fractions:

butane,gasolines (light and heavy),

solvent cut,

kerosene cu t (lamp oil),

gas oil, to a lesser degree.


2/30

504 Chapter 15 WHITE PRODUCTS REFINING Y SWEETENING

1. Hydrogen sulfide

2. Elementary sulfur

3. Mercaptans

4. Carbonyl sulfide

5. Neutral sulfurcompounds

6. Nitrogen bases

7. Organic peroxides

8. Naphthenic acids

9. Phenols

10. Ammonia

11. Hydrogen cyanide

12. Compounds alteringproduct color

13. Existent and

potential gums

Exists in some crudes, but is mostly formed from sulfurcompounds in the feed dur ing thermal and catalytic crack-ing operations, and obviously during hydrotreating opera-tions.

Is seldom present, but is usually formed by oxidation ofH,S, especially during product sto rage.

Have th e same origin as H,S.

Seldom present in crudes , COS is probably formed duringoperations such as thermal and also catalytic cracking.

The sulfur compounds present originally in the crudeundergo numerous transformations during operations,and th is explains the presence of sulfides, disulfides, thio-phenic and other similar derivatives.

Probably come from thermal or catalytic decomposition ofcomplex, nitrogen compounds existing previously in thecrude.

Are formed by oxidation of hydrocarbons and particularlyof olefins and diolefins. They are very troublesome as theydec rea se storage stability of gasolines and promote engine

fouling by forming carbon deposits.

Are present in some crudes called “naphthenic crudes”.Furthermore, they ar e also formed by thermal decomposi-tion of complex oxygenated compounds that are presentin the crude.

Have the sam e origin as naphthenic acids. High tempera-ture hydrolysis reactions have also been reported to occurduring catalytic cracking operations with formation ofphenols.

Is formed during thermal or catalytic cracking and obvi-ously during hydrotreating operations.

Is formed during catalytic cracking of petroleum cuts thatcome from crude s containing nitrogen compounds.

This group probably includes a very large number of com-plex molecules such as sulfur and nitrogen compounds,phenols, and even some hydrocarbons (fulvene series).These products are mainly formed during refinery opera-tions.

The compounds forming gums are probably cyclic conju-

gated diolefins. Other sulfide or acid compounds andmetallic contaminants formed during treatments canaccelerate gum formation.

List of main unwanted compoun ds with their probable origin.w


3/30

Chapter 15 WHITE PRODUCTS REFININGY SWEETENING 505

Lamp oil

-C-C-SH Primaryaliphatic

Solvent

SH

Lightgasoline

l l Secondary-c-c-c-aliphaticl l

Butane

Aryl. Example:thiophenol

302

0 34

8 9

@ S H Naphthenic

377

0 14

27

233

0 030

78

There are none in the fractions heavier than gas oil. Additionally their

concentration depends on th e type of crude, as indicated in Tables 15.2, 15.3and 15.4.Mercaptans account for 40 to 100 of total sulfur for light cuts of distilla-

tion (gasolines, butane). As an illustration, Table 15.5 gives a distillation bal-ance for an Iraqi crude along with th e “sulfur” and “mercaptan sulfur” distri-bution. When a catalytic cracking balance (see Table 15.6) is examined, thesignificance of mercaptans can be noted in th e butane, and the light and heavygasoline cuts.

From a more general standpoint, note that thermal conversion processeswithout hydrogen (e.g. FCC, coking, visbreaking) produce mercaptans in the

200

0 02

100

light fractions.

Gas oil

s@sH) 100 2 24S (total)

Heavygasoline

287

0 063

46

The propane cut contains H2S sulfur alone, but little or no rnercaptans.

0.015

p3Table IType of crude: Iraq-Kirkuk. Transfer temperature to atmospheric distillation:360°C. Total sulfur content: 2.05 .


4/30

506 Chapter 15 WHITE PRODUCTS REFINING BY SWEETENING

Gasoil Heavy LightLamp oil Solvent gasoline gasoline

RSH sulfur (g/t)Total sulfur ( wt)

x 100

_ _

I I I I

2.2 1.4 1.9 1.2 1.60.18 0.026 0.021 0.013 0.012

0.1 0.5 0.9 0.9 1.3

-

s RSH) 100 2.9 22.4 43 50 80

Table15.3 Type o f crude: Hassi-Messaoud. Transfer emperature to atmospheric distilla-

tion: 360°C. Total sulfur content: 0.14 .

RSH ulfur (g/t)Total sulfur ( wt

15.2 Background Data

The aim is t o eliminate mercaptans by conver ting them into disulfides by oxi-dation as follows:

1

22RSH 2 + R-S-S-R + H2O

For economic reasons, air is the mercaptan oxidation reactant, but mostmercaptans have a rather weak reducing activity with air. To make them morereactive, it is necessary to transform them into sal ts (called “mercaptides”) bytreating them with a base. This lowers the redox potential of the system,thereby favoring oxidation. To carry out a sweetening operation, two types ofoperat ion ar e required:

Transform mercaptans into mercaptides. For economic reasons aq ueous

Oxidize th e mercaptides to disulfides. During this operation t he caus tic

caustic sod a is used industrially.

soda is regenerated and can therefore be recycled.

240 246 256 250 4750.83 0.11 0.06 0.05 0.06

-~ -

Table15.4 Type o f crude: Qatar. Transfer emperature to atmospheric distillation: 36YC

Total sulfur content: 1.19 .


5/30

Chapter 15 WHITE PR ODUCTS REFINING BY SWEETENING 507

GasPropaneButaneLight gasolineHeavy gasoline

Solvent

Lamp oil

G a s oil

Distillate

Atmosphericresidue

Yield“A wt)

0.20.51.89.39.7

6

7.5

24

6

35

100

0.170.2710.162

0.5

1.2

14

5.7

75

100

Table

15.5 Atmospheric distillation. Example of sulfur balance.

Yield“A wt)

G a sc, cutc, cutLight gasolineHeavy gasoline

Fuel (slurry)

5.355.89

10.1735.12

5.25

18.63

12.42

7.17

100

SulfurS feed PA wt)

23.4422.56

0.441.921.15

20.37

14.24

15.88

100

- “A wt)5 total

00

1007846

27

9

2.2

-

-

-99.91025

0.3

I15.6 Catalytic cracking. Example of sulfur balance.


6/30


15.2.1 Recapitulation of Process History

The importance of chemical refining in petroleum product finishing operat ionshas led to research and development on a large number of sweetening pro-cesses in the past fifty years. Before discussing modern technologies in depth,a few of the older processes are presented briefly below. Since they are nowoutdated, the presen tation will be confined t o a description of th e principle ofeach one and it s major drawbacks, without going into detail about t he processitself.

15.2.1.1 Doctor Sweetening or “Plumbite Process**

The process includes thr ee reaction sequences:

(a) Plumbite treatment, PbOzNaz, with lead mercaptide formation:

2 RSH PbO HZO + Pb(RS), + 2 OH-(plumbite)

@) Oxidation of th e lead mercapt ide into disulfide by sulfur:

Pb(RS)2 + S + PbS + RSSR(disulfide)

(c) Regeneration of the plumbite by oxidation with air in an alkalinemedium (caustic soda):

PbS 2 0 2 4 OH- + SO,= PbOT 2 H20(regenerated)

The drawbacks a re a s follows:

dissolution of the sulfur in the reaction medium;

separation of aqueous and hydrocarbon phases;plumbite regeneration, causing the solution to age.

15.2.1.2 Sulfuric Acid Reatment

The process includes two sequences:

(a) Formation of a sulfuric diester a s illustrated below:

RSH HZSO, + SO, / H + H,OSR

/ S R +H,OOHRSH + SO, + SO, \ RSR(sulfuric acid diester)


7/30

Chapter 15 WHITE PRODUCTS REFININGY SWEETENING 509

@) Decomposition of the sulfuric diester, with formation of disulfide andso,:

SO,


8/30

51 0 Chapter 15 WHITE PRODUCTS REFININGY SWEETENING

15.2.1.4 Copper Sweetening

The feed is treated with a copper salt (CuCId. The process includes two stages:

4RSH 4Cu2+ + 2RSSR 4Cu+ + 4H+(a) Oxidation of mercaptans by the ion Cu2+:

In this reaction the cupric ion Cu2+ s transformed into a cuprous ion Cu’.(b) Regeneration of th e cupric sal t by the oxygen in th e air:

4Cu+ O2 4H+ + 4Cu2+ 2H20(regenerated)

The presence of even traces of copper in gasoline is unacceptable (gum for-mation and color change) and is a major drawback.

15.2.1.5 Hypochlorite Process

After the mercaptans have been transformed into salts, the attack byhypochlorite is direct and rapid:

2RSH+20H-+2RS-+2H20

2 RS- C10- H,O + RSSR + C1- + 2 OH-(hypochlorite ion)

The drawbacks come from a large number of side reactions caused by thestrong reactivity of hypochlorite, with th e formation of sulfonates, sulfonesand chlorine derivatives in particular. As a result, pollution phenomena occurand reagent consumption is significant.

15.2.1.6 “Solutiter” Extraction Process

Developed by Shell after the Second World War, the process consists in dis-

solving the mercaptans in an alkaline solution. Dissolution is made easy by theaddition of some organic compounds such as fatty acids, aromatic acids andalkylphenols. The reaction proceeds as follows:

(a) Extraction of mercaptans by the alkaline solution:

RSH OH- + RS- H2O(b) Oxidation of mercaptides to disulfides and regeneration of OH-:

12

2RS- + - 0, H,O + RSSR + 2OH-(regenerated)

The extractive solution, called “solutizer”, is a solution of potassiumhydroxide and tricresol in water.

The following drawbacks can be noted:

several extraction stages;

disulfides difficult to sepa rate from the solution;


9/30

Chapter 15 WHITE PRODUCTS REFINING BY SWEETENING 51 1

smell problems due to tricresol;

large volumes of solution in operation.

15.2.2 Current Technologies

Generally speaking, the sweetening feed (LPG, gasolines, kerosene) is treatedby air in the presence of caustic so da with a soluble catalyst. It is a catalyticoxidation process working in liquid phase. The pressure is adjusted so that theair required for the reaction is dissolved in the medium. In a later improvedversion of t he process, the catalyst was adsorbed on a solid support, thereby

giving rise t o the second generation of processes.

15.2.2.1 Reaction Steps. Types of Catalyst

Mercaptan sweetening requires the use of a catalyst active at low temperature,as the reaction is usually carried out between 30 and 50°C. Of all the catalyststhat have been studied in the past thirty years, organic chelates have provedto be t he most effective. Today th e catalytic formulas generally used in indus-try have a cobalt phthalocyanine base (Fig. 15.2), where hydrophilic groupshave been grafted in order to make the catalyst soluble in aqueous alkaline

solutions.The catalyst’s mode of action determines the reaction mechanism of this

type of oxidation: i.e. th e dyestuff’s redox properties. In the presence of mer-captides (reduced form of RSH), cobalt phthalocyanine oxidizes them to disul-fide and thus goes into its reduced form (called th e “leuco” form in thedyestuff industry).

The air present in the medium reoxidizes the dye and the catalytic cyclecontinues. The determining ste p is therefore the dye reoxidation rate.

With these considerations, t he mercaptan oxidation reaction sequence cannow be described. It takes place in three steps:

(a) Transformation into mercaptides by aqueous caustic sod a treatment:

2RSH+20H-+2RS-+2H20(caustic soda) (mercaptide)

(b) Conversion into disulfide by means of th e dyestuff in its oxidized form:

2 RS- + catalo + RSSR cata12-(oxidized form of dye) (reduced form of dye)

(c) Reoxidation of the catalyst by the oxygen of air and regeneration of thecaust ic soda for recycle. This is th e slow st ep of the process.

1

2cata12- - 0 t

1. Other dyestuffs than phthalocyaninesdyestuffs.

H 2 0 + catalo 2OH-

have also been proposed, for example sulfur


10/30

51 2 Chapter 15 WHITE PRODUCTS REFININGY SWEETENING

-

Figure15.2

I

R N- N ‘i‘

Cobalt phthalocyanine. Sweetening catalyst base.

The sum of these three reactions gives th e overall reaction of t he process:

1

22 R S H -02 + RSSR HZO

15.2.2.2 Process Design

Two types of approach have been developed for the reaction sequence pre-sented above:

Sweetening oxidation: here th e “mercaptan” sulfur is transformed by oxi-dation into “disulfide” sulfur, which remains in the medium. In o therwords, after this chemical refining process the total sulfur remainsunchanged, but th e mercaptans have disappeared.

Extractive oxidation: this process uses physical extraction of mercap-tans, and th e extractive solution (i.e., th e alkaline solution containing thephthalocyanine) is regenerated afterward by air oxidation.

The extraction coefficients of mercaptans by industrial caust ic soda areexamined versus their carbon content (Table 15.7) for the second approach.The mercaptans in light cuts are extracted satisfactorily, contrary to heavy


11/30

Chapter 15 WHITE PRODUCTS REFINING BY SWEETENING 513

Mercaptan K Boiling range at 1 atmosphere “C)

C lCZc

c

c

c6

c7

mercaptans, especially the C6+. In actual practice, extraction is possible up toC5 mercaptans.

Consequently:

- 1000 6220 3530 52-685 64-98

1-2 105-1250.2-0.3 150-160

0.1 170-180

The extractive process is sufficient for LPG to obtain a product comply-ing with specifications 2.

Extraction can be performed for light gasolines, but t he operation mustbe supplemented by a sweetening oxidation to make products complywith specifications.

Extraction can not be used to treat heavy naphthas and jet fuels(kerosenes). The first technique, i.e. sweetening oxidation, must beapplied.

- Table

15.7

15.3 Industrial Processes

Equilibrium constants caustic soda/hydrocarbon) of mercaptans (C, to C7).K = RSH concentration in the caustic soda */RSH concentration in the hydro-

There are two main types of processes:

The first uses technologies of th e liquid/liquid contact type.

The second is more conventional and implements a fixed bed catalyst.

15.3.1 LiquicULiquid Contact Technologies

Two technologies of different design have been developed in this area: one byUOP (Merox process) and t he o ther more recently by Merichem (Thiolex andMericat processes).

2. According th e sodium plurnbite test Doctor Test).


12/30

Extraction tower

Figure

15.3

Treated LPG or gasoline

IExtractive process (Memx extractive).

Gasoline

or LPG-

Refinery

Filter

Steam

Regenerator(Rashig rings)

Disulfide s eparato

F* a

Catalyst h ak e up

Caust ic soda circulation

P

I VSteel GratesWool


13/30

Chapter 15 WHITEPRODUCTS REFINING BY SWEETENING 51 5

15.3.1.1 UOP Technology Merox)[6]

a Merox f i t r a c t l v e ProcessThe Merox extractive process unit (Fig. 15.3) comprises three sections:

The countercurrent exfraction tower: It extracts mercaptans with causticsoda and is generally equipped with perforated trays. Operating conditionsare as follows:

- apparent contact time: 15 to 20 min;- linear feed velocity (LPG, gasoline): 0.5 cm/s;- caustic soda 12-18 wt (expressed in pure caustic);- caustic soda/feed ratio: 15 to 25 vol;- sufficient pressure to prevent evaporation phenomena;- the lowest possible extraction temperature to achieve better extraction.Nota bene:(a) Extractive caustic soda ages with time due to the formation of carbon-

ates and phenates, as well as thiosulfates from the oxidation of traces of H,Spresent in the feed (less than 10 ppm). In any case, the caustic soda concen-tration must be kept above 11 wt by make up with the solution or with puresoda.

(b) The feed must contain the least possible dissolved oxygen to prevent

side reactions.The ah-actioe solution regenemtor. Here the alkaline solution coming

from the bottom of the extraction tower (and charged with mercaptides) isregenerated by air oxidation with disulfide formation. It is packed with Raschigrings. The operating conditions are as follows:

- contact time: 40 min;- linear velocity (in empty vessel): 0.1 to 0.2 cm/s;- air: approximately 1.9 Normal m3/kg of RSH sulfur;- temperature: 20 to 60°C.Nota bene: The “active” catalyst content varies between 100 and 250 ppm

in the solution. Excess catalyst results in regenerator fouling. Moreover, freshcatalyst make up must be added at regular intervals.

The disulfide separator. Disulfides are separated from the alkaline solu-tion in a horizontal drum that operates under the following conditions:

- contact time: 25 to 30 min;- linear velocity: 0.3 to 0.5 cm/s;- a steel wool coalescer improves the disulfide/alkaline solution separation.Nora bene: The disulfides exiting the separator are sent to the gas oil

hydrodesulfurization unit or to the atmospheric distillation overhead hydretreating unit.

b. Merox Sweetening Process

The Merox sweetening unit (Fig. 15.4) includes three sections:

The mixing tower: Gasoline, the alkaline catalytic solution and air areinjected in the bottom of the tower. The reaction takes place in the tower and


14/30


15/30

Chapter 15 WHITE PRODUCTS REFININGY SWEETENING 51 7

Meroxextraction

the total effluent is recovered at t he to p and sent to the separator. The toweris packed with Raschig rings or equipped with perforated trays. It operatesunder th e following conditions:

- contact time: 3 to 12 min;- catalytic solution/gasoline ratio: 10 to 20 vol;- linear velocity: 0.5 to 3 cm/s;- temperature: approximately 40°C.

The separator. The gasoline is separated from the catalytic solution in a

- contact time: 25 to 30 min;- linear velocity: 0.3 to 0.5 cm/s.After settling, the catalytic solution is recycled t o the mixing tower, while

the gasoline is sent to a sand filter.

The sand filter. The settled and sweetened gasoline is sometimes cloudy(a slight emulsion due to caustic soda solution entrainment) and t he sand fil-ter acts as a coalescer. In the sand filter vessel, the linear velocity is approxi-mately 0.3 to 0.5 cm/s. The refined gasoline is drawn off laterally in the lowerpart of the sand filter.

Nora bene: Despite the sand filter, soda entrainments can sometimes beobserved in th e gasoline du e to surges in flow rate or pressure.

The possible areas of application for Merox technology are summarized inTable 15.8.

horizontal drum that operates under the following conditions:

Meroxsweeteningeed

-Table

15.8

LPGLight straight

run gasolinesCatalytic cracked

gasolines

Thermal crackedgasolines

Jet fuels**

Possible areas of application for Merox liquid/liquid technology

+

Combination Meroxextraction then

sweetening

Note that th e Merox extractive process can a lso be applied t o treat s our gases.

* * Possible but not done in actual practice.

This table requires some comments:

1. RSH extraction is accomplished to 98-100 for LPG (C3 /C , cuts).


16/30

51 8 Chapter 75 WHITE PRODUCTS REFINING BY SWEETENING

2. Sweetening or th e extraction sweetening combination are possible forlight straight run gasolines, but hydrotreating is currently preferredChapter 16).

3. A sweetening operation is generally performed for catalytic or thermalcracked gasolines. However, it may be advantageous to implement extra-ction before sweetening in anticipation of lower sulfur specifications forgasolines. Experience has shown that the mercaptans present in the C,cut i.e. the light gasoline overhead) can be extracted satisfactorily.

4. Jet fuels can be sweetened by means of a soluble catalytic solut ion andwith this technology. However, as discussed later on, a simpler solution

uses a catalyst adsorbed on a fixed bed under a slight trickle of causticso da and in the presence of air.

From a refining standpoint as such, the resulting products have an RSH sul-fur content lower than 3 ppm in general). However, two major drawbacksabout this type of process should be pointed out:

1. Use of large volumes of aqueous soda, leading to spent alkaline solutiondisposal problems.

2. Soda can sometimes be found entrained in the refined products.

15.3.1.2 Merichem Technology [1,3 ,41

This technology is also of the liquid/liquid type, but of a totally differentdesign. The process uses the principle of the fiber contactor patented byMerichem in 1975.

The hydrocarbon feed and the alkaline solution are sent to a cylindricalcon tactor Fig. 15.5) packed with stainless steel fibers. The metallic fibers arewetted with the aqueous phase which runs down along them. The hydrocar-bon phase flows parallel to the fibers. In this way, the contact between thehydrocarbon and the aqueous phase films is excellent. The resulting masstransfer is highly efficient without any problems of emulsion or pressure loss.The two phases can be separated without any entrainment in either one.

a. Process Flow Scheme (Thiolex, Mericat)There are two possibilities: mercaptan extraction by caustic so da Thiolexprocess) or sweetening Mericat process) Fig. 15.6). A combination of the twoprocesses can also be used if the aim is to sweeten while eliminating maximumRSH sulfur from the medium at the same time. The flow scheme represented inFigure 15.7 illustrates treatment of a light coking gasoline. It includes threemain sections:

A caustic soda prewash t o remove the H,S present in the feed.A mercaptan extraction section with two in-series contactors Thiolex

A Mericat catalytic sweetening section for the mercaptans that could notprocess).

be extracted in the Thiolex section.


17/30

Chapter 75 WHITE PRODUCTS REFINING BY SWEETENING 51 9

Acid hy drocarbon feed

Figure

15.5 Basic diagram of the Merichem technology.

Alkalinesolution I Fibc3r contactor

i iTreated hydrocarbon

r

Spent aqu eous solution

b. Results

The advantages of this technology can be summarized as follows:(1) Very high efficiency achieved in mercaptan extraction and sweetening.(2) Minimum caustic soda and catalyst consumption.(3) N o caustic soda entrainment in the refined product.(4) Simple operating conditions.

Areas of application: the Merichem technology can treat a wide range of

LPG (as well as gases) with the extraction process;

straight-run, orcatalytic

or thermal cracking gasolines;jet fuels.

Table 15.9 gives the results for treatment of a light coking gasoline by thecombination of so da prewashing Thiolex Mericat processes. Despite thevery high mercaptan sulfur content of the feed (2 400 to 2 700 ppm), the result-ing efficiency is excellent and the product complies with specifications.

white products:


18/30

520 Chapter 15 WHITE PRODUCTSREFINING BY SWEETENING

Figure

15.6

Feed

Mericat sweetening p rocess.

Treated hydrocarbon

-

Oxidationair

Caustic sodarecycle

- - - _ - -

Spent caustic soda Fresh caustic soda

Table15.9 Treatment of a light coking gasoline. Com bined process [?’I

Flow rate (rn3/d)

Feed:

Sp.gr. d i 0Initial boiling point “C)

End point “C)

H2S @Pm>Mercaptan sulfur (pprn)Total sulfur (ppm)

Product:

Sodium (pprn)

Mercaptan sulfur (pprn)

Total sulfur (pprn)

Doctor test

HZS @Pm>

Efficiency ( ):

Prewashing sectionRSH extraction sectionSweetening section

Test

256

0.67531867-8

2 400-2 7063 500-3 700

< 10

< 11 150-1 280

Negative

10094

> 99

Design

318

0.6903010020

3 0004 020

s 50

151 300

Negative


19/30


20/30

522 Chapter 15. WHITE PRODUCTS REFININGY SWEETENING

3 causticsoda

15.3.2 Fixed Bed Catalyst Processes

This type of process uses cobalt phthalocyanine as its catalytic base,adsorbed on activated carbon. Industrial processes were developed aroundthis formula, for example Minalk and Kerox UOP) and later Mericat I1(Merichem).

-

15.3.2.1 Process Flow Diagrams

The processes involve mercaptan sweetening rather than extraction. The fixedbed of catalyst (impregnated activated carbon) is wet by a trickling solution of

caustic soda.

a. Minalk Process Minimum Use o f Alkali) [ 6 ]The process was designed especially to treat light and heavy gasolines fromcatalytic cracking. The flow diagram (Fig. 15.8) is simple: after the gasoline ismixed with dilute 3 weight caustic soda and air, it is treated in a reactor con-taining a bed of activated carbon previously impregnated with Merox catalyst.The soda itself is injected at a very low flow rate (5 to 20 ppm of NaOH in rela-tion to the gasoline). The fixed bed reactor also serves as a soda settler andcoalescer, so there is one single vessel with a slow flow velocity. The tempera-

ture ranges from 40 to 50°C and the pressure from 8 to 20 bar, depending onthe type of feed.

L2

Catalytic

Air

. . . . . . .. . .. -.:, .. :. Activated carbon bed. . . . . . . . . .;.;;: ; i imp regnated with Merox c atalyst. :.:.. .: ....

. . . . . . . . . ............

. . . . . ... . . . . . ........... :- + Treated gasoline.'.'

Antioxidant

Figure

15.8 Minalk process (UOP).


21/30


The refined gasoline is withdrawn from a side stream and sent to storageafter an oxidation inhibitor is added on line. The settled caustic soda, with apH between 9 and 12, is withdrawn a t the bottom of th e reactor. The Merox cat-alyst has a lifetime of one to three years. The procedure of reimpregnating thecatalyst on th e bed of activated carbon requires a series of washingsequences.

b. Kerox Process [6,2]

The process was designed especially to treat kerosenes. It comprises sevensections (Fig. 15.9):

Prewashing with dilute caustic soda removes the acidity due to naph-thenic acids and phenols from the kerosene.

The sand filter removes suspended particles and emulsions. In somecases an electrosettler is used to perform these two operations.

The reactor works with caustic so da recirculation (10 to 15 wt), anoperating temperature between 40 and 50°C and a pressure ranging from5 to 10 bar.

The settler separates out the spent caustic soda exiting the reactor. Thesoda is recirculated back to the reactor two or three times at the mostand then routed to the refinery’s spent caustic circuit.

Washing with water eliminates entrained caustic.

The salt filter dries the kerosene.

The clay treatment, with a clay filter, winds up the refining process byeliminating polar compounds.

c. Mericat I . Process [5]

Developed to treat jet fuels, this process uses fiber contactors with several

stages. It includes (Fig. 15.10):A caustic soda pretreatment to eliminate naphthenic acids and phenols.

A fixed bed sweetening section (Mericat II .

Washing with water without any settling vessel, which is not considered

Kerosene drying on salt, followed by a final clay treatment.

necessary in this process.

15.3.2.2 Results

a. Minalk Process

The process allows production of gasoline with character istics that meet thedoctor test a lu mbit e test) specification. During normal operation, the exitingmercaptan sulfur concentration is less than 3 ppm. Neither the copper c o r r esion test nor t he color is affected.


22/30

Caustic soda Sandprewash filter

Figure

15.9

Feed I

Kerox process (UOP).

Reactor Settler Waterwash

IRecycled caustic soda_ _ _ _ _ _ _ _ _ _ _ I

Water Spentwater


23/30

c M zz c

Q ?

0 u

u

.

b.

aE 2 (Y

U

5


24/30

526 Chapter 15. W H I T E PRODUCTS REFININGY SWEETENING

If the process is compared to th e liquid/liquid Merox sweetening process,

a dramatic reduction in caustic soda consumption;

a decrease in alkaline solution entrainment in the gasoline;

a simplification in the process (see Section 15.4) which results in lower

three major advantages can be noted:

investments and operating costs.

6 Kerox Process

The process allows production of kerosenes that meet present-day specifica-tions:

negative plumbite test with an RSH sulfur content lower than 10 ppm on

free sulfur content 0.2 ppm;

acid number 0.012 mg KOH/g;

Saybolt color 20;

WSIM (water separometer index modified) 3 85 (without additive);

silver corrosion 1.

However, some kerosenes are more difficult to refine. Table 15.10 classifiescrude oils according to how readily th e kerosene cut can be refined. UOP hasproposed a new catalyst, Merox 10, for the most difficult cases.

c. Mericat II Process

Like th e Kerox process, t he Mericat I1 process allows production of kerosenesthat meet present-day specifications.

exiting th e unit;

15.4 Economic Data15.4.1 General Information

Table 15.11 gives the areas of application of chemical refining and hydrotreat-ing processes for various white products.

This table requires two comments:

1. Fixed bed sweetening is in competition with hydrotreating for the kero-se ne cut (jet fuel). Today one of th e essential specifications laid downfor jet fuel is on mercaptan sulfur. It is therefore preferable to perform

chemical refining because hydrotreating consumes hydrogen, which isnever in very abundant supply in the refinery. Moreover, with theincreasingly stringent sulfur specification on diesel oils (sulfur 0.05 ),there may be a risk in some cases of a shortfall in desulfurization capac-ity. Sweetening kerosene should therefore be a good way to make moredesulfurization capacity available or maintain it the same.


25/30


1

1

4

Easy refiningArabian LightArabian MediumArabian HeavyHassi-MessaoudKuwaitKirkukMurbanQatar LandQatar MarineSouediehZuetinaZarzaitineBerriDubaiSirticaOmanBrass RiverSafaniyaSaharaArzewKhafi

3

3

1

1

~

Possible refining

Table15.1 1

AdmaBasrahBasrah MediumFereidon

Areas of application for hydrotreating and chemical refining proc esses .

Difficult refiningAgha JariJamburTujmazaEoceneGash SaranAin ZalaDariusUralBelaymKirkuk BlendBasrah HeavyAbu A1 Bukhoosh

Kerox unit. Effec tof the parent crude oil on refining the co rrespondingkerosene.

Feeds

Liquidpiquid

Fived bedchemicalExtraction

Hydro-treating

sweetening

LPGStraight run

Conversion

Kerosene

light gasolines

pasolines**

*

1

3I I


26/30


2. Today conversion gasolines from coking, catalytic cracking, visbreak-ing) are generally chemically refined rather than hydrotreated. Heretoo, with the increasingly stringent sulfur specification on the gasolinepool, chemical refining technologies by extraction should gain popular-ity since the investments and operating costs are lower than forhydrotreating. Furthermore, for the same reason some fractions of lightcatalytic cracking gasoline middle cuts) a re hydrotreated, while theoverhead cut is treated by sweetening, generally of the extractive type.

15.4.2 Process Licensors. Treatment Capacity

The market for white product chemical refining by sweetening processes , i.e.:

mercaptan extraction units,chemical sweetening units,combined units with extraction followed by sweetening,

is today mainly dominated by two licensors: UOP and Merichem. The first,UOP, had licensed over 1 500 units worldwide by 1994 for a total treatmentcapacity of more than 680 million m3/year of various products LPG, gasolinesof all origins) Appendix 15.1). The second, Merichem, had licensed 280 unitsby mid-1994, accounting for a treatment capacity of 160 million m3/year ofwhite products and 30 million m3/year of gas Appendixes 15.2, 15.3 and 15.4).

15.4.3 Basis for an Economic Estimate

15.4.3.1 Investments

Investments in white product chemical refining units depend on th e feed to betreated and the type of process. Table 15.12 gives battery limits investmentranges for refining three types of feeds kerosene, catalytic cracking gasoline,LPG) .

15.4.3.2 Operating Costs

Operating cos ts can be estimated as shown below for two typical cases.

a. Ke ros ene R efiningAn estimate of operating costs for fixed bed sweetening ranges from € 0.25 to0.4 per ton (€ 1999), and is broken down a s follows:

( IUtilities kWh, cooling water, instrument air) .............................. 2Catalyst.. ........................................................................... 7Chemicals NaOH, sal t, clay, reaction air) ................................... 45Manpower. ......................................................................... 46


27/30

Chapter 15 WHlTE PRODUCTS REFININGY SWEETENING 529

Light catalyticcracking gaso-line

Feed tobe refined

1.6-1.9 Liquid/liquid tech-nology

0.8-1.0 Minalk type fixedbed technology

1700 Sweetening

Kerosene

-

1700 Sweetening

Table15.12 Investments for white product chemical refining units battery limits).

Investments106 f 1999)

Utilities (kWh/t)Caustic (g/t)Catalyst @/t)Manpower h/d)

4.0-5.5

Liquidfliquid process Werox) Fixed bed process Winalk)

0.09 0.07

1 0.530 15

12 4

Comments

-

Investments dependon the type of tech-nology used

Table15.13 Sweetening of a light catalytic cracking gasoline. Estimate of operating costs.

I II I

LPGExtraction

sweetening

Merox extract ive800 without 1.4-1.6 type

6 Ga soline RefiningTable 15.13 gives an estimate of operating costs for two kinds of process(Merox and Minalk). The use of a fixed bed technology reduces operating costssubstantially:

caustic soda consumption is lower by half,

catalyst consumption is also halved,

manpower is divided by three.

Overall, calculation shows that operating costs for fixed bed sweeteningare an estimated 2.5 times lower than for liquid/liquid light gasoline sweeten-ing.


28/30


References

1 Mueller T., Rosenstock G. (1983) Sweetener lowers costs. HydrocarbonProcess. Int. Ed ., Oct., 10, 95.

2 Verachtert T.A., Staehle B.E., Salazar J.R. (1985) Merox catalyst innovationsolves difficult kerosene treating problems. Natl. Petr Refine rs Ass oc. Annu.Meeting, San Antonio.

3 Vasquez R.G. (1989/1990) Reduced operating costs by caustic treating jetfuel stream. Hydrocarbon Technology International.

4 Maple R. (1994) Caustic treating of MTBE and TAME feedstocks.Hydrocarbon Technology International 9 1.

5 Franqoise G., Varadi T. (1993) A new kerosene mercaptan oxidation process.Hydrocarbon Technology International 63.

6 Holbrook D.L., Arena B.J., Verachtert T.A., Brick J.C. (1983) Merox processesfor caustic minimization and management. Natl. P e p Refiners Assoc. Annu.Meeting, San Antonio.

7 Wizig H.W., Vasquez R.G., Maeda K. (1986) Increase lead susceptibility ofsour coker naphta stream via caustic treating. Natl. Petr Refin ersAss o. Annu.Meeting, Los Angeles.

Appendixes

Operating companies

Conoco Inc.Chevron Canada Ltd.Petr. Brasileiro SA

-

-Petrox SAAdmin. Nacl. CombustiblesAlcoholy Portland SARAS SpAERTOIL SA

--

Kukdong Oil Co. Ltd.

Kyung-in Energy Co.Thai Oil Ltd.BP Kwinana My. Pty. Ltd.

-

Place

Billings, USABurnaby, CanadaPaulinia, Brazil

-Con cep cih , ChileMontevideo, UruguaySarroch, ItalyHuelva, Spain

-Seosan, South Korea

Inchon, South KoreaSriracha, ThailandKwinana, Australia

-

-

Capacity(m3/d>

18751 3502 7003 000

1 000

950Extension

620940300480

2 385875

3 0201 5903 510

-

Units using Merox process UOP).Source: HPI Construction Boxscore Hydrocarbon Processing 1992-1997)).


29/30


DerbyHydrocarbons Great BritainUS Oil Refining

Operatingcompanies

Wichita, USA 480 Kerosene

Barrow-in-Furness,UK 960 Condensa teTacoma, USA 555 Jet fuel

ANIC

ARC0 OIL GASBP

-

ChamplinChevronChines Petroleum Co.

ClTGO

Appendix

15.3 Units using Mericat 11 process.(Source : HPI Construction Boxsco re Hydrocarbon Processing (1992-1997)).

ConocoCosmo

KyokutoLiquid EnergyLittle AmericaMarathonMobil

NavajoNes te OyPemexPetrosarSarpomShell

Place

Gela, ItalyBakersfield, USAGrangemouth,UK

Rock Springs, USAEl Paso, USAKaohsiung, Taiwan

Lake Charles, USA

Commerce City, USAChiba, Japan

Chiba, JapanBridgeport, USACasper, USARobinson, USAChalm ette, USA

Artesia, USAPorvoo, FinlandSalina Cruz, MexicoSarnia, CanadaTrecate, ItalyPulau Bukom, Singapore

480205795

1750160

2 3852 580

3 1803 1801190

4001 4301190

32019101590

400

4 61018102 7802 385

51016701 525

Feed

PentenesCondensate

Heavy cracked gasolineLight cracked gasoline

CondensateLight cracked gasoline

Cracked gasoline

Heavy cracked gasolineHeavy cracked gasoline

NaphthaLight cracked gasoline

Light naphthaLight naphtha

NaphthaCracked gasoline

Naphtha/coking gasolineNaphtha/coking gasoline

Cracked gasolineCracked gasolineCracked gasoline

NaphthaLPG

Light cracked gasolineHeavy cracked gasoline

Units using Mericat process.

(Source: HPI C onstruction Boxscore Hydrocarbon Processing (1992-1997)).

Place


30/30

532 Chapter 75 WHITE PRODUCTS REFININGY SWEETENING

Operatingcompanies

Enterprise---

h e n , USAFina Oil ChemicalFletcher Oil

Gulf Coast Fractionators-

Idemitsu KosanJavelinaKochMarionMobil

-

TexacoTexaco Oil &ChemicalTOATonkawa

UDS

Ultramar CanadaUnion

ValeroWarren Petro

Yukong

Appendix

Place

Mt. Belvieu, USA

Baytown, USAPort Arthur, USACarson, USAMt. Belvieu, USA

Aichi, JapanCorpus Christi , USACorpus Chris ti, USA

Theodore,USAChalmette, USA

-

Wilmington, USAVidor, USAKawasaki, JapanArnett, USA

Arkansas, USASt. Romuald, Canada

Lemont, USACorpus Christi , USAVenice, USA

Ulsan, South Korea

780

1 600

3 200

3 200

480

1030

480

2 420

5 090

1 530

490

400

525

9 900

480

71511 300

1160

28 300

1160

1110

2 700

2 860

1670

610

Feeds

Butane

PropaneButaneButane

Aromatic naphthaButane

c3 &Butane

PropaneLPG

Butane

LPGNaphtha

Fuel gas

Propane

ButanelbutenesFuel gas

LPGFuel gas

c3/c4

c3/c4

C4for alkylation

c3 Ic4C4for alkylation

LPG

Units using Thiolex proces s.(Source: HPI Construction Boxscore Hydrocarbon Processing (1992-199 7)).

tratamento glp

Documents