fcc process of heavy feed stock with improved yield of light olefins

8/9/2019 FCC PROCESS OF HEAVY FEED STOCK WITH IMPROVED YIELD OF LIGHT OLEFINS

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FCC PROCESS OF HEAVY FEED STOCKWITH IMPROVED YIELD OF LIGHT OLEFINS

Bulatov R.M., Jirnov B.S.Ufa State Petroleum Technological University

There is written about most perspective method of FCC process with improved yield oflight olefins using in industry. It is described FCC process for heavy feed stock which modifiedto produce greater yields of light olefins particularly! ethylene! propylene and butylene withless production of dry gas i.e.! hydrogen! methane and ethane at relatively high conversion.

Keywords: c atalytic cracking process! FCC process! propylene! heavy feed stock! lightolefins! "S# additives! medium pore $eolite! coked catalyst

Propylene is second in importance only to ethylene as a petrochemical raw

material building bloc . Propylene has traditionally been obtained as a by!product "rom

steam crac ing to produce ethylene and "rom re"inery "luidi#ed catalytic crac ing

processes to produce gasoline. Propylene is conventionally produced through $%%

processes, dehydrogenation processes, and predominantly "rom steam crac ing

processes. &he pro'ected growth in demand "or propylene has started to e(ceed that o"ethylene so that e(isting processes cannot satis"y the "oreseeable "uture growth in the

demand "or propylene. &ypically, however, $%% units produce only around ) wt ! * o"

propylene. +s a result, propylene production "rom $%% units is "orecast to grow by

more than - * over the ne(t - years, with a large part o" this demand coming

"rom +sia. %onse/uently, modi"ications to $%% units can increase propylene production

are necessary. Several re"erences disclose modi"ied $%% processes to improve

propylene yields 0)1.&he propylene demand "rom $%% is growing at a "aster rate than global

$%% capacity, and the propylene yields "rom $%% are increasing to eep up with

demand 2$igure 3.

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$ igur e : $ or ecas t $%% capacity and pr opy lene pr oduction2Source: %hemical Mar et +ssociates, nc 7--;3

$luidi#ed catalytic crac ing, or $%%, is a well! nown and widely practiced

process "or converting heavy hydrocarbons, gasoils and residues into lighter hydro!

carbon "ractions. &he process "or the catalytic crac ing o" heavy hydrocarbons, gasoils

and residues is well nown and currently practiced in all types o" $%% units processing

a variety o" these "eedstoc s 0 1.

n general terms, the process "or the crac ing o" hydrocarbon "eedstoc s relies

on contact with "luidi#ed catalytic particles in a reaction #one maintained at appropriate

temperatures and pressures.


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and hot catalyst temperatures. 5ne such process called deep catalytic crac ing 2>?%%@3

re/uires ) to - seconds o" contact time to increase propylene yields. Aowever, this

process also yields a relatively substantial /uantity o" undesirable dry gas i.e.,

hydrogen, ethane and methane. Cew $%% catal ys t t echnologies ar e being developed t o

enable r e"iner s t o ac hie ve t he challenging pr opylene yields r e/ uir ed t o mee t t he

growing demand " or pr opylene "r om $%%. n some cases, ancillary reactors and other

treatment vessels have been provided to treat a particular "raction or reaction product

stream. n some instances, multiple reactors are provided each with a di""erent "eed, in

order to derive a particularly desired product stream. +n $%% process is modi"ied to

produce greater yields o" light ole"ins particularly, ethylene, propylene and butylene

with less production o" dry gas i.e., hydrogen, methane and ethane at relatively high

conversion.

$%% process "or obtaining light ole"ins comprises contacting a hydrocarbon "eed

stream with blended catalyst comprising regenerated catalyst and co ed catalyst. &he

catalyst has a composition including a "irst component and a second component. &he

second component comprises a #eolite with no greater than medium pore si#e wherein

#eolite comprises at least * wt. o" catalyst composition. &he contacting occurs in a

riser to crac hydrocarbons in the "eed stream and obtain crac ed stream containinghydrocarbon products including light ole"ins and co ed catalyst. &he crac ed stream is

passed out o" an end o" the riser such that hydrocarbon "eed stream is in contact with the

blended catalyst in the riser "or less than or e/ual to 7 seconds on average. &he

hydrocarbon products including light ole"ins are separated "rom the co ed catalyst. &he

"irst portion o" co ed catalyst is passed to regeneration #one in which co e is combusted

"rom catalyst to produce regenerated catalyst. Second portion o" co ed catalyst is

blended with regenerated catalyst and introduced to the riser. &he regenerated catalysthas substantially the same relative proportions o" the "irst component and the second

component as the blended catalyst that contact the hydrocarbon "eed stream 081.

Recycling co ed catalyst including large pore #eolite or active amorphous

material and #eolite with no greater than medium average pore si#e and blending it with

regenerated catalyst improves the yield o" light ole"ins and the overall conversion. t is

the case even at lower residence times. +dditionally, the lower temperature o" the


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catalyst resulting "rom blending hot regenerated catalyst and cooler recycled catalyst

improve ole"in selectivity.

+n embodiment o" this method is a process "or "luidi#ed catalytic crac ing o" a

hydrocarbon "eed stream to obtain light ole"ins. &he process comprises contacting the

hydrocarbon "eed stream with a catalyst composition including at least .- * wt. o" the

#eolite having no greater than medium average pore si#e and at least -. * wt. co e.

&his method is more "ully e(plained in the conte(t o" a $%% process that is

modi"ied to yield greater /uantities o" light ole"ins. Eight ole"ins are ole"ins with si( or

less carbon atoms and, pre"erably, less than "ive carbon atoms.

&he catalyst comprises two components that may or may not be on the same

matri(. &he two components are circulated throughout the entire system. &he "irst

component may include any o" the well! nown catalysts that are used in the art o"

"luidi#ed catalytic crac ing, such as an active amorphous clay!type catalyst or high

activity, crystalline molecular sieve. Molecular sieve catalysts are pre"erred over

amorphous catalysts because o" their much!improved selectivity to desired products.

Feolites are the most commonly used molecular sieves in $%% processes.

Pre"erably, the "irst catalyst component comprises a large pore #eolite, such as an G!

type #eolite, an active alumina material, a binder material, comprising either silica oralumina and an inert "iller such as aolin 0H1.

&he #eolitic molecular sieves appropriate "or the "irst catalyst component should

have a large average pore si#e. &ypically, molecular sieves with a large pore si#e have

pores with openings o" greater than -.; nm in e""ective diameter de"ined by greater than

- and typically 7 membered rings. Pore Si#e nde( o" large pores are above about D .

Suitable large pore #eolite components include synthetic #eolites such as I!type

and G!type #eolites, mordenite and "au'asite. G #eolites with low rare earth content are pre"erred in the "irst catalyst component. Eow rare earth content denotes less than or

e/ual to about .-* wt. rare earth o(ide on the #eolite portion o" the catalyst.

&he second catalyst component comprises a catalyst containing, medium or

smaller pore #eolite catalyst e(empli"ied by FSM!), FSM! , FSM! 7, FSM!7D,

FSM! D), FSM!DH, FSM! H, and other similar materials. &his second catalyst

component pre"erably disperses the medium or smaller pore #eolite on a matri(

comprising a binder material such as silica or alumina and inert "iler material such as



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aolin. &hese catalyst compositions have a crystalline #eolite content o" - to 7) wt!*

or more and a matri( material content o" ;) to 8- wt!*. %atalysts containing 7) wt!*

crystalline #eolite material are pre"erred. %atalysts with greater crystalline #eolite

content may be used, provided they have satis"actory attrition resistance. Medium and

smaller pore #eolites are characteri#ed by having an e""ective pore opening diameter o"

less than or e/ual to -.; nm, rings o" - or "ewer members and a Pore Si#e nde( o" less

than D .

FSM!) and S&!) type #eolites are particularly pre"erred since their high co e

resistivity will tend to preserve active crac ing sites as the catalyst composition ma es

multiple passes through the riser, thereby maintaining overall activity. FSM!) additives

are a very e""ective solution "or increasing propylene yield in the $%% unit. &his

approach gives the re"iner a great deal o" "le(ibility, as additive usage can be ad'usted

according to changes in propylene demand and to optimi#e operation within unit

constraints such as wet gas compressor loading. FSM!) generates propylene by

selectively crac ing ole"ins in the gasoline boiling range. +s the amount o" FSM!)

additive in the catalyst inventory increases, the incremental yield o" propylene produced

per percent o" additive decreases. Propylene yield reaches a plateau once the FSM!)

concentration reaches around - *. &he diminishing e""ectiveness o" FSM!) at higherconcentrations occurs because the ole"ins in the gasoline become depleted 0)1.

&he "irst catalyst component will comprise the balance o" the catalyst

composition. &he relative proportions o" the "irst and second components in the catalyst

composition will not substantially vary throughout the $%% unit.

&he high concentration o" the medium or smaller pore #eolite in the second

component o" the catalyst composition improves selectivity to light ole"ins by "urther

crac ing the lighter naphtha range molecules. But at the same time, the resulting smallerconcentration o" the "irst catalyst component still e(hibits su""icient activity to maintain

conversion o" the heavier "eed molecules to a reasonably high level.

$%% "eedstoc s, suitable "or processing by this method, include conventional

$%% "eeds and higher boiling or residual "eeds. &he most common o" the conventional

"eeds is vacuum gas oil which is typically a hydrocarbon material having boiling range

o" "rom D D!))7 % and is prepared by vacuum "ractionation o" atmospheric residue.

Aeavy or residual "eeds, i.e., boiling above 88 %, are also suitable.


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&he amount o" blended catalyst that contacts the "eed will vary depending on

the temperature o" the regenerated catalyst and the ratio o" recycled to regenerated

catalyst comprising the catalyst blend. 6enerally, the blended catalyst to "eed will be in

a ratio o" "rom - to )-. Pre"erably, the blended catalyst to "eed will be in ratio "rom -

to D- and more pre"erably in ratio "rom ) to 7). &he high catalyst!to!"eed ratio will

operate to ma(imi#e conversion which tends to "avor light ole"in production.

+lthough it has been well established within the art o" $%% that increasing

catalyst!to!"eed ratios will increase conversion, catalyst!to!"eed ratios cannot be easily

increased since this ratio is not an independent variable in standard $%% units. Rather

the ratio o" catalyst to "eed is dependent on the heat balance limitations o" the unit.

%onse/uently, only relatively low catalyst!to!"eed ratios o" to - are typically obser!

ved. Such a means o" increasing catalyst!to!"eed ratios, however, was not e(pected to

maintain high catalyst activities due to the co e deactivation o" the catalyst. Reduction

the catalyst!to!"eed contact results in an increased light ole"in yield and a decreased dry

gas yield.

Blends o" co ed and regenerated catalyst have comparable activity to that o" the

regenerated catalyst. %onse/uently, recycling co ed catalyst can be e""ectively utili#ed

to increase the catalyst!to!"eed ratios, thereby, allowing operation at very short catalyst!to!"eed contact times with catalyst that has been heavily diluted with catalyst containing

medium to small pore #eolite while still maintaining high conversions. Ma(imi#ing

conversion is particularly important in order to ma(imi#e yields o" ey light ole"ins.

&he catalyst composition with a relatively low concentration o" the "irst catalyst

component and relatively high concentration o" second catalyst component still e(hibits

improved conversion and selectivity to light ole"ins. ven when a portion o" the catalyst

composition is co ed and when the riser residence time is very short were completelyune(pected 0H1.

Pre"erably, the blended catalyst will comprise a : ratio o" recycled catalyst to

regenerated catalyst. &he amount o" co e on the recycled catalyst portion returning to

regeneration will vary depending on the number o" times the catalyst particle has

recycled through the riser. Cevertheless, the co ed catalyst portion entering to the

regeneration as well as the recycled catalyst portion could range "rom average co e

concentration.


L


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Reduction riser contact time e""ects in the presence o" a catalyst composition

containing a large /uantity o" a small to medium pore #eolite component, and in a pro!

cess system where the temperature o" the catalyst contacting the "eed is representative

o" a recycled catalyst system. &he study was conducted in a $%% riser operating under

conditions "avorable to obtain greater yields o" light ole"ins. &ests were per"ormed using

three riser residence times: 7.) seconds, .) seconds, and -.; seconds. + riser in the

$%% process was run at -, MPa, a regenerator temperature o" around L) % an

outlet temperature o" )LL %, a "eed temperature o" about 7 %, a riser hydrocarbon

partial pressure o" about -,-;L MPa, and a catalyst!to!"eed ratio o" about 7H. &he results

"or each o" the residence times in the riser are presented in &able .

&able

Gield o" light products against residence time

Riser Time (sec.) 0 ! " # $ #?ry 6as 2wt!*3 7,78 7,;H ,

thylene 2wt!*3 ),8L L,HH L,-7Propylene 2wt!*3 7 ,L 77,D- 8,DLButylene 2wt!*3 , 7 D, 7,)L

?ecreasing the residence time in the riser "rom 7,) seconds to -,; seconds

increased the relative propylene yield by 7 * with a corresponding decrease in dry gas

o" *. &his corresponds to an absolute yield increase o" 7,D * wt. propyl ene and

,H * wt. decrease in dry gas. ?ecreasing the residence time in the riser "rom 7,)

seconds to ,) seconds increased the relative propylene yield by ) * with the

corresponding decrease in dry gas o" D7 *. thylene production increased in ,) second

riser residence time and nominally decreased at -,; second riser residence time.

+dditionally, butylene production increased with reductions in riser residence time.

Surprisingly, the 7,) second residence time actually e(perienced lower conversion than

the shorter times o" ,) or -,; seconds. t attributed this drop in conversion due to a

reduction o" secondary reactions such as ole"in oligomeri#ation, which produce higher

molecular weight components.

5ne o" the bene"its o" the present method is that recycling o" co ed catalyst and

mi(ing it with regenerated catalyst can reduce the catalyst temperature entering the riser

by 7H % to HD %, depending on the regenerator temperature and the co ed catalyst


;


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recycle rate. + study was conducted to demonstrate the e""ect o" lower catalyst

temperature contacting the "eed in a short riser residence time system where the catalyst

contained a high concentration o" a medium pore #eolite. &he e""ect o" catalyst

temperature contacting the "eed was observed at L 8 % and ;D7 % with catalyst

composition containing 7- * wt. o" an additive containing about 7) * wt. medium pore

#eolite and H- wt!* o" catalyst containing G!type #eolite. &he high catalyst tempe!

rature, ;D7 %, was chosen to represent a standard $%% regenerator temperature. &he

lower catalyst inlet temperature o" L 8 % resulted in a catalyst!to!"eed ratio o" 7H

compared to the catalyst!to!"eed ratio o" 7 used "or the hotter catalyst inlet temperature

o" ;D7 %. Since the riser outlet temperature was maintained at )LL % in both cases,

decreasing the catalyst inlet temperature "orces operation at higher catalyst!to!"eed ratio

in the riser. &he results are presented in &able 7.

&able 7

Gield o" light products against temperature

C%&%' s& Tem er%&*re !+$ ,C - / ,C%atalyst!to!$eed Ratio 7 7H

nert %atalyst 2wt!*3 - L-?ry 6as 2wt!*3 ,-; 7,8;

thylene 2wt!*3 ),D ),DPropylene 2wt!*3 L,8; 7-,L8Butylene 2wt!*3 7,L; ,)76asoline 2wt!*3 7L,D7 77,8H

&he comparison o" the e""ect o" catalyst temperature on propylene yield

indicates that reducing the catalyst inlet temperature by LL % results in a 77 * relative

increase and a D,; * wt. absolute increase in propylene yield. +dditionally, a ) *

relative increase and a ,8 * wt. absolute increase in butylenes and a 7; * relative

decrease and a , * wt. absolute decrease in dry gas was observed with the reduction

in catalyst inlet temperature. %onversion "or the lower catalyst temperature was also

improved.

+nother comparison was conducted "eed conversion over varying concentrations

o" a component additive containing FSM!). &he additive level was varied "rom - to

- *. +ll tests were run with a catalyst to "eed ratio o" about 7H, a riser outlet

temperature o" )LL %, a riser partial pressure was -,-;8D MPa, and a "eed!to!catalyst

contact time in the riser o" ,) seconds. ncreasing the additive to very high levels had


H


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only a marginal a""ect on the conversion to light materials that boil under D; %. &he

data is illustrated in &able D. +lthough the conversion does drop slightly "rom L ,8 to

L-.- * wt. as the additive level is increased "rom - to - * wt., the data indicates that

the activity o" the standard, G!type #eolite, $%% catalyst has been well maintained even

a"ter high dilution. Since the FSM!) additive can only crac lighter, naptha!range

molecules, FSM!) addition had been thought to signi"icantly reduce "eed conversion at

higher levels. &his tests show that signi"icant "eed conversion can be achieved at very

high medium pore #eolite additive levels and short catalyst!to!"eed contact time using

higher than typical catalyst!to!"eed ratios.

&able D

Gield o" light products against temperature

+dditive Eevel. 2wt!*3 - - 7- D- -%o e 2wt!*3 D,) 7,;H 7, L 7,D- ,HH?ry 6as 2wt!*3 D,DL D, L D, H 7,; 7,HD

thylene 2wt!*3 7,H- ),- ),L L, ) ;,)Propylene 2wt!*3 L,7 7-,D7 7-,;H 7 ,DD 7 ,;DButylene 2wt!*3 ,)) , D , H D,L; 7,8;

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fcc process of heavy feed stock with improved yield of light olefins

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