17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
New Butene Dimerization Technology
Nobuhiro Kimura , Takashi Morikita, Tatsuo H amamatsu
Nippon Oil Corporation,
Chemic al Refinery Integrati on R& D Group, Fuel Research Laboratory,
Research & Development Di vision, 8, Chidoric ho, Naka- ku, Yokoham a,
231- 0815 Japan
e-mail: nobuhi ro .kimura @e neos. co .jp
Abstract
Ne w bute ne di me ri zation tec hnol ogy with hi gh di mer se l ectivit y has be en
devel oped at Ni ppon Oil . The obta ine d isoocte ne ha s be en us ed a s a ra w
mat erial of hi gh Res earc h Octa ne Number (RON) gasoline. The key
technology of the process i s a novel phos phoric aci d catalyst different fr om
prior sol id phosphoric aci d ( SPA) catal yst s. The a uthors found that
phosphori c aci d monome r ( ortho phosphori c acid) ha s excelle nt di mer
selecti vity, developed a nove l cata lyst that consists of only of phosphoric
acid monomer s upported on sil ica.
1. Int ro d uct i on
A mi xtur e of bra nched C8 ol e fi n is call ed isooctene. Isooct ene i s a di mer
of C4 fra c tion that c ontai ns is obut ene . I t is us e ful as a ra w mat erial of hi gh
RON gasoline and a ra w mat erial of chemical i ntermediates such as alkyl
phe nol a n d isonona noic a cid. The de mand for aromatic compounds i s rising
rapidl y. Aroma tic compounds s uc h as x yl e ne are t he ra w mat erials o f
chemicals. Ar omati c compounds have high RON value s, a nd ar e pr esent i n
gasoline
today.
Therefore,
ar omati c
c ompounds
producti on
coul d
be
increased by extr act ion of the aromatic compounds fro m ga solin e. Ho we ver,
other mat erials of high RON value become n ec essar y t o mai nt ai n t he R O N
value
of
the
gasoline .
In
addition,
octa ne
number
i mpr ove me nt
of
automotive gasoline is being studi ed, with t he goal of energy conservation.
Use of t he hi gh- RON methyl tert-but yl ether (M TBE) i s ba nne d or re stricted
[1-3], and so the search is on for materials of high RON values as substitutes
for M TBE. Mea n whi le, the de ma nd for propyle ne is ri sing r apidl y. Pr opyl ene
is the raw mat erial of pol ypropylene , a commodit y pl as tic. The vigorous
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17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
de mand has led t o increa sed propyle ne producti on. ABB Lummus Global’s
OCT ( Ole fi n Conve rsion Te c hnol ogy), a pr oces s which pr oduces pr opyl ene
fr om n-butene and ethylene , has bee n installe d in var i ous pla ce s. Thi s
technology was also adopted by Nippon Oil Corporation. OCT is a
technology that manufactur es pr op yl ene by t he metat hesis rea ction of
n-butene and ethylene. Isobutene from the C4 fr action is unneces sa ry i n t he
metathesis reaction. On the other hand, the manufacturing process of
poly mer gasoline by oli gomeri zation of light ol efin has been researched
since the past . Concerni ng the di me riz ation pr oc ess usi ng FCC-C4 f eedst oc k,
whi ch is rich i n n- butene, t h ere ar e some examples of commercialization
such as UOP's I n Al k process [7-13] and the NExOCTANE proc ess develope d
by Neste Oil and Kell ogg Brown & Root [14-16]. However, there ar e no
examples of selective di merization using solid acid catalysts with high
conc entr a tion of is obut ene , whi ch has high rea c tivity. To use t he i s obut ene
in t he C4 fracti on effecti vel y, we de veloped new is obut ene di me r ization
technology. Pr oduc t is ooct e ne bec omes a ra w materi al for hi gh RON
gasoline. A commercial pl ant has been onstre a m sinc e 2006 in Kawa saki
Japa n ( Fi g. 1), a nd producti on of is ooc tene is 40,000 t ons per year.
Fig. 1
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Commercia l pla nt
17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
2. Tec hnology Sum mary
2-1. Cat a lyst
The key t echnology of t he pr oces s i s a novel phosphoric ac id catal ys t tha t
differs from prior SPA catalysts. The outline of the developed catalyst is as
follows.
2-1-1. Dimer Selectivity
The re acti vity of i s obut ene i s higher t han n-but ene, a nd oligomeri zation
of isobut e ne oc cur s easily usi ng a n aci d catalyst. Its use i n di mer pr oducti on
was me nti one d a bove. On the ot her hand, it is no t use d for pr oduction of
heavy pr oduct s l arg er t han tri mer s at pr esent . Therefore, the development o f
catalysts with hi gh di me r selectivity is of utmost i mpor tance. However,
oligomeri zation of butenes is a consecutive reaction, so it is diff icult to
obtai n t he di mer only. Al s o, di mer selecti vi ty decrea ses a s is obut ene
conversi on
i ncre as es.
Fig.
2
s hows
t he
re lation
be twee n
is obut ene
conversion and dimer selectivity in the reaction of isobutene using silica
alumina and the developed catalyst. With solid acids such as t he sili ca
alumina catalyst , as isobutene conversi on r ose , di mer selec tivity dec rease d.
On t he ot her ha nd, the de ve lope d cat alyst s howe d hi gh di mer se lectivit y
even at higher conver sion rates. Di mer yi eld is obt ai ned as is obut ene
conversion multiplied by dimer selectivity. Di mer yiel d can be r aised by
20% or more wit h t he de veloped cat alyst compared with th at with the silica
alumina catalyst.
The re sult ca n be explained by t he difference i n reaction me cha nis m. The
reaction progresses by cation reaction mechanism and passes the alkyl cation
with the silica alumi na catalyst. Reactivity of the alkyl cation does not
change,
regar dless
of
the
carbon
number.
Ther efore,
di me r
easily
poly merizes, and the di mer selectivit y decreases. On t he ot her hand, with the
phosphori c ac id c atalyst t he reaction progresses by t he ester reactio n
me cha nis m. Is obut ene react s wit h phosphori c acid, pr oduci ng phosphori c
acid est er (Fig. 3) . Since the re is thr ee-di me nsi ona l restr icti on in phos phor ic
acid ester, it is thought that bulk high polymers are difficul t to form. It was
found that the esterification reaction th at ha s hi gh di me r s electivit y occurs
most re a dily whe n the phosphori c acid i n t he cat alyst is a monomer.
Conventi onal SPA c atalyst s c ontai n sil icon phos phate a nd phos phor ic aci d
poly mer [4-6]. Sili con phos phate i s a compound of phosphoric aci d bonde d
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17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
with silica, and the phosphoric acid polymer is a compound that is condensed
by dehydration of phosphoric acid monomer. This is because the catalyst is
ma nufactured at a p proxi mate ly 300 de grees . There fore , it was not easy to
take an ester react ion me chanis m tha t ha d high di me r selecti vity. The
devel oped catal yst a chieves hi gh acti vit y a nd hi gh di mer s el ectivit y, because
it consist s onl y of phosphor ic acid monome r s upporte d on sili ca. In ot her
wor ds , we de vel oped a novel cat alys t that is different fr om prior SPA
catalysts.
Dimer selectivity, %
100
High-yield
＞Δ20%
Developed catalyst
Sillica alumina catalyst
Isobutene conversion, %
Fig. 2
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Perfor ma nc e of de vel ope d c atal yst
100
17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
O
+
HO
P
OH
HO
isobutene
phosphoric acid
HO
P
P
OH
buthyl phosphate
O
O
O
O
OH
+
OH
O
HO
P
OH
OH
isobutene dimer
O
HO
P
Fig. 3
O
OH
steric hindrance
isobutene trimer
Ester intermediate reaction mechanism
2-1- 2. Catalyst life
Fact ors t hat decr ease the acti vity of the developed catalyst are both the
out fl ow of phos phoric aci d a nd t he c ha nge i n phosphori c a cid st ates fr om th e
dehydra ti on-c ondensation of phosphori c aci d.
Outflow of phosphoric acid
Conventional SPA catalyst consists of silicon phosphate, which is
phosphoric acid chemically bonded to silica. On the other hand, the
developed catalyst consists of only phosphoric acid monomer supported on
silica. There i s no chemical bonding between the phosphoric acid and
support . This fa ct is confir me d by X-ra y di ffra ction. Wh en there is no
bonding, it is not able t o obtain t he crystall ine pea k. Thus , the develope d
catalyst had a demerit in that the out fl ow of t he phosphoric aci d on t he
catalyst i s more than t he c onve ntiona l catal yst. As a result of our deeper
knowl edge re gardi ng the outfl ow of pho sphori c aci d, we lear ned that the
out fl ow of phos phoric a ci d can be controlled to levels typical with
conventi onal t echnology through opti mi zation of the ope rat ional met hod.
De hy drati on conde nsation of phos phor ic ac id
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17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
Wit h moi sture , phosphoric a cid on the catal yst changes phosphori c aci d
states. When moist ure densit y is l ow, phosphor ic acid is conde nse d fro m
phosphori c aci d monomer to a phos phoric aci d poly mer by de hydrati on. The
change of phosphoric acid states can be deter mined by the P 3 1 -MAS NMR of
the catal yst ( Fig. 4). The chemi cal shift of phosphoric a cid monomer i s 0
ppm, and phosphoric acid polymer is below -20 pp m. When water of t he
necessary quantity is not added, it becomes a lower activity catalyst. Our
exami nati ons showed t hat when phosphori c acid st ates cha nge from
monomer to polymer, both activity and selecti vit y dec reas e. The phosphori c
acid state of the developed catalyst is phosphoric acid monomer. In order to
contr ol t h e de hydra tion condensati on of t he phos phor ic a ci d on t he c atalyst ,
the nece ss ary qua nti ty of wate r is added to the C4 feedstock in this process.
Low active catalyst
Fresh catalyst
80
60
Fig. 4
40 20
0
-20 -40 -60 -80 ppm
P 3 1 MAS NMR spectr a of cat al ysts
By controlling t he activit y decrease by the above-mentio ned method, th e
devel op ed cat alyst mai nt ai ne d t he t a rget yield for six mo nths or more (Fi g.
5). The re actor te mperat ure r ose s ever al de grees duri ng si x months , and it s
activit y hardly decr eased. There fore , a long cat al yst li fe c a n be e xpe cted.
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Yield of isooctenes, %
17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
Target
0
50
Fig. 5
100
Days on feeds
150
200
Life of develope d cat alyst
2-1- 3. Re generat ion
It is i mpossi ble to regenerat e conventional SPA catalysts when activity
decreases. This i s because they consist of phosphori c a cid c he micall y
bonded to the silica support. On the other hand, the developed catalyst has
an advant age i n t hat the catal yst can be easil y r egenerate d by s oaking i n a
phosphori c a cid s ol ution i n a reactor. Th is is because the developed catalyst
is a simple catalyst that is phosphoric acid monomer adsorbed on silica. It is
thus possible to greatly reduce the amount of waste ca talyst . Al so, the
per for ma nce of t he catalyst a fter re- soaking i s e qual to be fore.
2-2. Proc ess
Wit h t hi s t echn ology, the high dimer selectivity of the developed catalyst
allowed us to achieve a more si mpl e pr oces s.
2-2- 1. Reactor
Sinc e ol i gomeri zat ion of butene s is a consecutiv e reaction, di mer
selecti vit y i ncreases as but ene conv ersion is lowered in mild reaction
conditions.
Wit h a low select i vity catalyst, butene convers ion i s kept low in the first
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17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
reactor in order to obtai n hi gh di mer selectivit y. Unreact e d butenes are then
separ ated by distillation, and i t is necessary to repeat t he same met hod i n t he
second r eactor. High di mer yiel d can be achieved t his way, but it
necessitates a large investment in equipment . I n contrast , we can achieve
high di me r yiel d i n a single- s tep re acti on wit h t he de vel oped c atalys t tha nks
to i ts hi gh di mer selecti vity. There i s t hus one re actor invol ve d in t he
proc ess , whi ch tra nslate s t o lower i nvest ment c osts .
2-2- 2. Quench
Di meri zat ion of butenes i s an exot he r mic reac tion. Wit h convent ional
technology, the reaction heat is removed using the unreacted raffi n ate. This
is t he way that t he unreact ed r a ffinate separat ed from effl uents of the reactor
by distillation feeds to the catalyst beds. Therefore, reaction heat in the
upper bed is removed. With this technology it is di fficult to for m heav y
product s large r tha n tri mers beca use the rea cti on progre sses by t he est er
reaction mechanism. Therefore, it is pos sible t o re move the re acti on heat by
the fact that the reactor effl uent which is not distilled is circulated back t o
the react or top. There is no decreas e of dimer selectivity because it is
di fficult for di mers to form heavi er pr oducts. There fore, it was possible to
use an inexpensive adiabatic reactor. Thus, as shown in Fi g. 4, thi s process
becomes a si mple one invol ving one adiabatic reactor and t wo di stillation
towers.
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17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
Isobutene fraction
Butane
Isooctene
Dimerization reactor
Butane stripper
Heavy oil fraction
Product stripper
Fig. 6
Develope d di merizati on proces s
2-3. Product char acteristi cs
Pr oduct isooctene, whi ch is the dime r of isobutene , is the isomer of C8
ole fin. The ma in product s of is ooct ene are 2,4,4-tri me thyl pent e ne-1 and
2,4,4-t ri methyl pent ene- 2. These are c a lled diis obute ne. I s oocte ne is use ful
as a raw mat erial for high RON gasoli ne. Me anwhil e, dii sobutene is use ful
as a c he mic al i nt er mediat e for al kyl phenol, isonona noic aci d a nd ot her
product s. The Bl ending Rese arch Oct a ne Number (BRON) of isooct ene is
115, whi c h is hi gh. There for e, it can contri but e to ene rgy c ons ervation by
improving the fuel consumption of gasoline automobiles. In addition, the
RON and distillation characteristics of isooctene rival those of aromatic
compounds s uc h as t olue ne, meaning it is possible to substitute isooctane for
aromatic compounds i n gasoline. In other words, it bec ome s possi ble to
increase producti on of aromatic co mpounds i ndirectly. Though phosphori c
acid catal yst i s use d, t her e is no phosphorus i n t he fi nal product.
3. Conclusion
We found that phosphoric acid monomer has excellent dimer selectivity,
and developed a novel cat alyst that consists only of phosphoric acid
monome r s upporte d on sili ca. Because the devel oped cat alyst can be
rege nerat ed, waste catalyst c an be re duced. BRON of isooctene i s 115, and it
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17th Saudi Arabia-Japan Joint Symposium
Dhahran, Saudi Arabia, November 11-12, 2007
can
cont ribute
to
the
energy
conservati on
thr ough
fuel
economy
improvement for gasoline automobiles. In addition, the RON and distillation
chara cteri stics of i sooc tene rival t hos e of ar omatic comp ounds . Is oocte ne
can be used to repl ace ar omatic compounds in gasoli ne. I n ot her words, it
become s pos sible t o increa se pr oducti on of aromati c c ompounds indire ctly.
A c ommer cial pla nt has bee n onstr ea m since 2006, with annual production of
40,000 t o ns.
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[13]
T. R.Kr awietz,
P.Lin,
K.E.
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[14] PEP Re vie w 2003- 12
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[15] H.D.Ploa n, R.Birkho ff, M.F. Gilbert, M.Nurminen and A. Pyhalahti,
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