Catalysts And Processes for C4's Cuts Upgrading

T. Inui (Editor), Successful Design of Catalysts © 1988 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

167

CATALYSTS AND PROCESSES FOR C4'S CUTS UPGRADING

G. MARTINO, B. JUGUIN and J.P. BOITIAUX. Institut Fran~ais du Petrole, B.P. 311, 92506 Rueil-Malmaison (France)

ABSTRACT The C 's olefinic cuts produced by steam-cracking and fluid catalytic cracking ~re used as chemical feedstocks and automotive fuels. Their elaboration requires several processes, among them many are catalytic. INTRODUCTION ~ The C4' s di 01efi ns and 01efi ns cuts are produced by two major processes : steam-cracking and fluid-catalytic cracking. Their use is achieved either in petrochemistry to produce chemical feedstocks, either in refining to produce automotive fuels. The upgrading of these raw cuts requires several processes such as amines wash, soda wash, hydrogenation, oligomerizations, alkylation (1,2,3,4,5,6). The main components of these cuts are always similar, their concentrations depending on the cracking processes: see table 1. TABLE 1

COMPOSITION OF Cos CUTS (%W)

I STEAM CRACKING ISOBUTANE BUTANE ISOBUTENE I-BUTENE T-2-BUTENE C·2·BUTENE i-a BUTADIENE VINYLACETYLENE 1-BUTYNE

I

0.7 2.0 21.9 16.0 7.0 4.0 48.0 0.2 0.2

FLUID CATALYTIC CRACKING 34.9 11.0 15.0 13.0 16.0 10.0 0.1

STEAM-CRACKING C4'S CUTS The C4's cuts from steam-cracking are mainly used to make chemicals or polymers and the date in table 1 show the high content of butadiene in this C4

168

raw cut. This stream is treated by extractive distillation, which separates three main cuts:

an olefinic raffinate,

a pure butadiene stream and an

acetyl eni c concentrate, that has to be burned. However, for safety reasons, this acety1enic stream cannot be pure, it is diluted by C olefins and 4's butadiene. The selective hydrogenation of vinyl acetylene increases consequently the total butadiene recovery: see figure 1. Three implantations of the hydrogenation unit are possible: fresh feed hydro (feed 1), acetylenic concentrate hydro (feed 2), fresh feed + acetyl eni c recycle hydro (feed 3). The butadi ene yi e 1din each case changes with the requested vi nyl acetyl ene content at outlet of the reactor. Fi gure 1 clearly emphasi zes that recyc 1e before hydrogenati on is hi gh1y favorable if compared hydrogenation.

with the fresh feed

The hydrogenation of the acety1enic concentrate itself appears

co 0

·ti

.s .... +

5

C. RAW CUT

100

.~

e

~

;s ~

e>>-

c::J

9T

1;3 a:

~

i'5

is

;=: ::J

98

EO

~ ~

c::J

97

--l~. ~~.~.L.I~,~~-'

96LL-<---1 L 5 2 1 0.5 0.1 005 0.01 VINYLACETYLENE IN HYDROGENATED C4 (wt %1

Fig. 1. Rich butadiene C cut hydrogenation. 4's to be attractive for high conversion levels, but this figure is difficult to obtain, due to the high exothermicity of the treatment of such a stream with high acety1enic levels. Moreover, the standard palladium containing catalysts are "washed out" after one month and the operati on is very tremendous

and

costly. For solving this problem, a new generation of bimetallic catalysts have been designed, which are more resistant to this palladium extraction (7, 8) : see figure 2.

169

0.3r-------------------------,

LD 277

'E
VACin: 1.5%-VACout : 0.5%

o

u u

a.. LD 277 8%-6%

o

6 7 8 On-stream (months)

Fig. 2. Palladium elution by vinylacetylene.

28

-. ?Po .....,

•• _··-·_·_·_·_·-·_·o·....::c,...--==·_·_·-

••

<,

.... ~ ....c:

u 27

0

....

Q)

eQ)

~

BUTADIENE- 1 - BUTENE 26 \..

l

-.

2-BUTENES--- BUTANE

10 2

5.101

10

5

1

Residual butadiene content (ppm)

Fig. 3. Raffinate hydrogenation - 1 butene yield.

170

After the butadiene extraction, the raffinate contains valuable olefins and roughly 1 % butadiene. The use of these olefins requires the selective hydrogenation of this butadiene. Following the final destination of the C4 olefin, one can be interested to promote the l-butene to 2-butenes isomerization (butan-2-01 production) or to avoid this isomerization (linear low density polyethylene production). Two different catalysts have been designed for both applications. Figure 3 illustrates how the new bimetallic LD 271 minimizes the l-butene isomerization and maximizes the l-butene yield (9). F.C.C. C4'S CUTS The F. C.C. C4 S processed to produce fuels and the producti on of the gazoline blending stocks requires a complex treatment, as can be seen in the figure 4. The catalytic units of these schemes are oligomerization, alkylations and selective hydrogenation. I

OLiGOMERIZAnON

L..;

BUTAOIENE HYDROGENATION

Fig. 4. F.C.C. C4's cut treatment block diagram. Oligomerization processes (10) The transformation by oligomerization, of the C4 olefinic cuts, leads to an isoolefinic oligomers : dimers to pentamers. The choice of the catalysts depends on the nature of the required products; the mostly used is supported phosphoric acid (11). More recently, amorphous silica-aluminas (12, 13) and zeolithes such as HZS~1 5 (14) and mordenites have been introduced; IFP uses amorphous silica-aluminas and special mordenites. They are rather stable : po1ar compounds (water, oxygenated products, sul fur products) act only as i nhi bitors and the acti vity of the catalyst can be recovered by stri ppi ng ; high polymers produced by the dienes present in the feedstock and, also, basic nitrogen stick on the catalyst and can be removed by air burning. This catalysts lead to a broad range of processes: SELECTOPOL, POLYNAPHTA, POLYDIESEL. By changing the operating conditions, particularly the reaction temperature, one can promote (table 2) :

171

TABLE 2 IFP OLIGOMERIZATION PROCESSES

PROCESS

PRDDUCTION DF CATALYSTS CHARACTERISTICS OF THE PRODUCTS • Specific gravity (200e) • Distillation curve (TOP) · initial boiling point · 20% volume · 50% volume · 90% volume · end boiling point

SElECTOPOL AND POLYNAPHTHA PDLYDIESEl POLYNAPHTHA [CAR GASDLlNE

JETFUel

DIESel

AMDRPHDUS SILlCAALUMINA

AMDRPHOUS SILlCAALUMINA

ZEOLITHES

D.735 to 0.740

0.798

0.806

45°C 10rC 121°C 230°C 230°C

155°C

155°C 208°C 274°C 382°C 439°C

nrc

209°C Z63°C 285°C

• Octane numbers

[lead-fr..) · research clear

· motor clear • Freezing point* • Smoke point* • Aromatics content (w%)'

97 to 102 84 to 86

< - 60°C 33 millimeters

< - 60°C 1.4%

• Cetane number

(CFR engine)'

41.5

• Kinematic viscosity

(40"CI'

4.2 'sk

*After hydrogenation of the product. 1) either the formation of 1ight 01 igomers (dimers or trimers), thus obtaining only a gasoline with and 97 - 102 octane number (lead free RON) 2) or the formation of heavier oligomers (trimers, tetramers and pentamers) that can be used as bases for jet-fuel. TABLE 3 IFP OLIGOMERIZATION PROCESSES FEEDSTOCK SPECIFICATIONS, CATALYST CONTAMINANTS CATALYST CONTAMINANTS

• Sulfur compounds as mercaptans and sulfides

FEEDSTOCK SPECIFICATIONS ,,-; 5 ppm

COMPLEMENTARY PRETREATMENT UNITS NEEDED Soda-wash

or merox

~

, Soda • Basic nitrogen as NH3 Dr amines , Oxygenated compounds as acids, ketones, aldehydes, alcohols -; Water • Traces of sulfur , Dienic hydrocarbons such as butadiene , Acetylenicshydrocarbons such as vinylacetylene

,,-; 1 ppm

-

-

,,-; 2 ppm Water-wash ,,-; 50D ppm ,,-; 10 ppm ,,-; 5 ppm ,,-; 500 ppm ,,-; 10 ppm

Dryer molecular sieve

treatment

Selective hydrogellation unit

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The use of a special mordenite promotes the formation of monobranched olefins due to its geometrical selectivity, after hydrogenation the resulting monobranched paraffins present a high cetane number. The contaminants contained in the industrial C4 cuts, particularly the F.c.C.'s one, have a big influence on this type of catalyst, some upstream purification units are needed to meet the feedstock specifications (table 3). Aliphatic alkylation (10, 15, 16, 17, 18) The world capacity for the production of alkylates is about 40 millions tons per year. In this operation, isobutane reacts with an olefin to produce branched paraffins which are components with high octane number. The alkylation reaction is carried out in liquid phase at low temperature (0-50 °C), in presence of sulfuric acid (95-98 %) or water free hydrofluoric acid. Consumption of catalyst and all operations of the plant are especially TABLE 4 ALIPHATIC ALKYLATION PROCESSES

CATALYSTS CDNTAMINANTS Sulfur compounds • Soda • Basic nitrogen • Oxygenated compounds

SUBSEQUENT TECHNICAL PRDBLEMS Foam formation

FEEDSTDCK SPECIFICATlDNS .;; 15D ppm .; 1 ppm ~ 2ppm

.; 5D ppm

Water-wash

Drastic corrosion

Dryer molecular sieve Treatment Isobutane extraction plant or MTBE unit

• Dianic hydrocarbons such as butadiene • Acetylenic hydrocarbons

sludge formation

.; 100ppm

such as vinyl acetylen

acidconsumption

Acid consumption and

.; 5%

Isobutane

Sludge formation

and acidconsumption Isobutane shortage

f--

Soda wash or merax

Acid coftSumption

:;;:; 1 ppm

Water

CDMPLEMENTARY PRETREATMENT UNITS NEEDED

or selectopol unit

Selective hydrogenation Planl

!

n-butane to isebutane isomerization plant

Alkylate octane Butene-l to butenes·2 number maximizing isomerization unit

TABLE 5 ALKYLATION OF ISOBUTANE ON THE BUTENES HF

TO = 25°C

ISOBUTANE/BUTENES = 13

C. OLEFIN C. ISOMERS

OCTANE NUMBER BUTENES 2 ISOBUTENE BUTENE 1 QFTHE C. ISOMERS

Trimethyl 2,2,3 pentane

1.4

1.3

1.5

Trimethyl 2,3,3 pentane

13.B

11.7

13.3

100.6

Trimethyl 2,3.4 pentane

20.3

13.4

15.6

100.2

Trimethyl 2,2.4 pentane

54.4

62.6

46.3

Oimethylhexanes

10.1

11

ALKYLATE RON CLEAR

97

96.5

:~-+~

f--.

*Average value.

101.2

, I

100

173

sensitive to the contaminants contained in the C4 cuts coming from F.C.C. Some purifi cat i on units of the feedstock are requi red. The most important one is the butadiene (as indicated in table 4) which can be removed by selective hydrogenati on. Noreover , the structure of the different i sooctanes obtai ned vary accordi ng to the nature of the butenes (tab 1e 5), the alkyl ates comi ng from butenes-2 have a higher octane number than the one coming from butene-l. Selective hydrogenations The raw C effluent from F.C.C. is very often highly contaminated for two 4 main reasons the feedstock of F.C.C. is heavy and is not always hydrotreated. The C4's contain consequently a lot of sulfur and the final use bei ng fuels, the performances of ami ne and soda washs are very often not efficient enough. It is necessary to use catalysts which are selective (no saturation of olefins into butane and isobutane) and sulfur resistant. Moreover, in the case of HF alkylation, these catalytic hydrogenations are required to promote the isomerization of l-butene into 2-butenes. A summary of the industrial results is presented in table 6. It clearly appears that the mixed bed arrangement is optimum. The catalyst B is sulfur resistant enough to the catalyst A promoting the l-butene hydrogenate the butadiene, i someri zati on. This prehydrogenati on of butadi ene is mandatory to avoi d the hindrance of l-butene isomerization which is inhibited by butadiene, but not by sulfur. TABLE 6 HYDROGENATION OF BUTADIENE IN A FCC C. CUT

T" = BO°C

P = 25 bar

VVH = 20

BUTADIENE IN FEEDSTOCK = 6000 ppm

BUTADIENE AT OUTLET

CATALYSTS

A

B

B +A

PALLADIUM ON ALUMINA PROMOTED PALLADIUM ON ALUMINA -----MIXED BED

SULFUR = 20 ppm

I

I-BUTENE ISOMERIZATION

1000 ppm

35%

~

10 ppm

56%

~

10 ppm

78%

CONCLUSION The world market'situation, which is characterized by local shortage of 01 efi ns for petrochemi stry (for instance propyl ene) and i ncreasi ng demand of high quality automotive fuels (unleaded gasoline), makes mandatory the transformation of C4's cuts. Such a treatment requires many tatalytic

174

processes which use acidic catalysts (oligomerizations, alkylation) and metal catalysts (selective hydrogenation). The constant improvement of these catalysts is, therefore, an every day work for catalyst designer. REFERENCES 1 W. KRONIG and K. HALCOUR, Processes for hydrogenating pyrolysis naphtha, Brennstof Chemie, (D) 50, n? 9, 1969, 258. 2 W. KRONIG, Cold hydrogen treat pyrolysis cuts, Hydrocarbon Processing, march 1970, 121. 3 M. DERRIEN, J.W. ANDREWS, P. BONNIFAY and J. LEONARD, The IFP selective hydrogenation process, Chem. Eng. Prog. 70, n° 1, 1974, 74. 4 A.E. ELEAZAR, R.N. HECK and M.P. WITT, Hydroisomerization of C 4's, Hydrocarbon Processing, 1979, 112. 5 K.M. BROWN, Treating jet fuel to meet specs, Hydrocarbon Processing, feb. 1973, 69. 6 R. UGO, Catalysis Reviews, 1975, vol. 11, 225. 7 J.P. BOITIAUX, J. COSYNS, M. DERRIEN and G. LEGER, Newest hydrogenation catalysts, Hydrocarbon Processing, 1985, 51. 8 M. DERRIEN, Catalytic Hydrogenation, in studies in Surface Science and Technology, 1986, p. 613, Elsevier. 9 J.P. BOITIAUX, J. COSYNS, M. DERRIEN and G. LEGER, AIChE Spring National Meeting, Houston, march 1985. 10 B. JUGUIN, B. TORCK and G. MARTINO, Upgrading of C4 cracking cuts with acid catalysts. B. Imelik et al. (Editors), Catalys l's by acids and bases, p. 255, 1985, Elsevier Science Publishers B.V., Amsterdam. 11 E. WEISANG and P.A. ENGELHARD, Bul. Soc. Chim. F., 1811 (1968). 12 B. JUGUIN and J. MIQUEL, IFP, French Patent FR 2.547.830 (1984). 13 B. JUGUIN, J. COSYNS and J. MIQUEL, IFP, US Patent 4.423.264 (1983). 14 S.A. TABAK, F.J. KRAMBECK, W.E. GARWOOD, Conversion of propylene and butylene over ZSM-5 catalyst, AIChE Journal, september 1986, vol. 32, n° 9. 15 B. TORCK, Catalyse acido-basique en phase homoqene , Techniques de 1 Ingenieur , J. 1186 (1983). 16 G.H. DALE, PD 8 (3), 11th World Petroleum Congress, London 1983. 17 G.R. MUDDARIS, M.J. PETTMAN, Hydrocarbon Processing, 91, oct. 1980. 18 J. WEITKAMP, S. MAIXNER, Erdal and Kohle, 36 (11) 523, 1983. I