ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
Propylene Polymerization in Packed Reactor LIQUID PHOSPHORIC ACID CATALYST S. R. BETHEA Humble
c
0;I and
AND
Refining
J. H. KARCHMER Co., Boyfown, T e x .
ATrlLYTIC polpiierization has been eniploj-ed ill the petroleum industry t o convert large quantities of the olefins from catalytic cracking operations t o more valuable materials such as high-octane gasoline components and polymers t h a t are used in the preparation of synthetic detergents. T h e L-niversal Oil Products process ( 7 , 9,13, 26) and t h e California process are frequently employed ( 1 8 ) . I n the former, the olefin-containing gases, usually propylene and/or butylene, are passed over a catalyst of solid phosphoric acid on kieselguhr a t a pressure above about 200 pounds per square inch gage and a temperature of approximately 400" F. to convert them t o a mixture of dimers, trimers, and tetramers. I n the California process a bed oi quartz .sand netted n-ith a Etatic film of pho3phoric acid i. eniployed as t.he eatal>-st. Ipatieff (12, 1 4 ) poll-merized both prop!-lene and butylene ( 1 5 ) with liquid l U O 7 , phosphoric acid t o mono-olefin polymer at a temperature of 400' F. and pressures up to 750 pounds per square inch. I n siihseclucnt norli, Ipatieff and Pines ( 1 7 ) pol)-merized propylene a t 630" t o 700" F. in the presence of 90% phosphoric :?.rid with initial pressure of 1200 pounds per square inch. T h e liroducts ol~tainetlunder these more severe conditions contained appreciable amounts of cyclic compounds. Investigators a t the 1la.ssachuFetts Institute of Technology ( 2 ? ) >w i n g 10 t o 30% phoiphoric acid with pressures of 2500 t o 6000 pounds per eqrmre inch and temperature3 of 500" to 580" F., found that the percentage of higher boiling products increased x i t h increasing conversion. I n a semiplant scale equipment, using silver-lined reactors, German iiivchgators a t the I. G. Farlienindustrie ( 2 1 ) polymerized propylene with concentrated liquid plioq~horic acid a t 590 pounds per ;quare inc,h gage arid 302" 1:. 1:)Imth t h e German work and that of IpatiefT i t vas found that the molecular weight of the polymer could be varied by varying acid htrciigth and adding certain metallic salts t o the phosphoric :icitl. Inasmuch a s liquid phosphoric acid appeared t o have definite possibilities as a means of controlling the molecular n-eiglit of polymer, i t TI-as decided t,o investigate its 1 1 s ~zs a catalyst t o produce motor gasoline components of high qunlitj- :md certain . not only to i i i w - t i molecular iveight olefins. It TTRS nece gate the effects of pertinent process va CY on conversiori aut1 product quality, but also t o design and faliriciite a reactor n11d auxiliary equipment t h a t would enslire mnsimum yields : i ~ ~nt l4 - t the corrosive effects of hot phosphoric acid. Preliminary batch reactor investigations demoiistr:tte t h a t 85 t o liquid phosphoric acid could be used as a cat:ilyst for producing predominantly CSt o Clz olefin polymers from propylene-containing gases a t 350" F. and a t 40 atm. p concentration of the acid was varied from 85 to 109G5, the yieltl of polymer increased for a given reaction time nnd t h e concentration of the heavy polymers iiicreased. K h e n the arid coilcentration was 85 t o lO07,, t8henumber of carbon at'oms in tlie polymer was found to be principally multiples of 3 , indicating t h a t t,he polymer is formed b y a combination of tv-o or more propylene units. However, with 100% pho~phoric acid, a
370
greater smear of molecular neights \vas found in the products, indicating appreciable fragmentation and recombination. K h e n 0.5 t o 2.07, arsenic trioxide was added t o t h e 1007, phosphoric acid catalyst, its corrosive action on Type 304 (18:8, C r : S i ) and Type 316 (18:8:3, C r : S i : 3 I o ) stainless steels a t 3(iO" F. u-as controlled satisfactorily and the average molecular w i g h t of the product v a s foiind t o he slightly lower than the corresponding polymer prepared from 1007, phosphoric acid. Preliminary pilot unit runs led to modification of reactor system
I n the initial pilot unit work, cont,act between catalyst a n d hydrocarbon n-as obtained by jetting the vaporized feed into the bottom of a pool of liquid catalyst. The conversions obtained n-ith this type of contactor ivere Ion-; apparently, the small pas i)uhblrs from the jet, coalewed in the pool of acid arid thu? prevented t h e maintenance of sufficient interfacial area betn.ceri tlie liquid cutslyst and t h e hydrocarlion t o effect a prartical amount of conversion. T r o similar runs were made after thtl reartor was packed with 3/l,-inch copper pellets but, again, relatively IO\T conversions Lvere obtained. I n vien of these limitations, the reactor system ivah niodified so t h a t the hj-drocarbon retention time could be co~itrollrdhy v:irying the feed rate. Preheated, vaporized olefinic feed and recirculated liquid phosphoric acid v e r e introduced into the top of the picked reactor and brought in contact as they flon-ed d ~ \ v n over the packing. -kcid and hydrocarbon from the bottom of thv reactor paFsed through a cooler and into a separator from nhicli the acid vas pumped back t o the reactor inlet. T h e hydrocarbon phase leaving the scparkttur floli-ed t o a stabilizer, where cont,inuou separation of tail gar and polymer n-a$ cffected. Pilot unit operations in downflow packed reactor gave useful data on polymerization process
Equipment and Procedure. ;1 flon- plan of the pilot unit is shon-n in Figure 1. T h e olefin feed was pumped into the first preheater, which consisted of a 20-foot coil of */&-inchextraPtrong Ptainless steel (Type 301) pipe. T h e temperature in this preheater T as controlled by adjusting steam pressure in the jacket. T h e partially heated feed then flon-ed into the second prehratcr, ivhere its temperature was adjusted t o the deeiretl level. This preheater consisted of a 10-foot coil of 1/4-inch estrastrong T y p e 304 ?tee1 pipe. T h e temprr:iture \raj controlled punipcd by the nniount of the temperature of Dowtherm t h t \\-as through the jncliet. T h e vaporized feed flowed throiigh a 1,'4-inrh Haatelloy Alloy B line and entered the side of the reactor t,hrough a 1/32-inchjet a t a level 5 inches below t h r top. T h e rciit,tor T V ~ Pfabricated from an 11-foot length of 1.5-inch estra-lir.:i\-y Hastelloy - I3 pipe. Thermocouple ~vellsof tnnces of 0.5, 2.5, 4.5, 6.5, 8.5) and this alloy \yere located a t 10.5 feet nhove t,he hottoni of the packed eection. T h e bottom of the reactor \\-as equipped n-ith a pair of 1500-series Hastelloy
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 48, No. 3
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
7 ---I
Lh-
GAS METER
~
Figure 1 .
Olefin polymerization unit
%faced ring groove flanges to facilitate the insertion and removal of reactor packing and corrosion t r s t pieces. An 11-foot section of the reactor n-as packed with 3/ls-inch copper pellet,s after run 1'13-8. The copper packing n-as replaced by a 10.5-foot section O F 8- to 16-mesh crushed carbon aft,er run PH-16. T h e temperature of the react,or &-as controlled by passing the h a t i n g medium from the second feed preheater and from the recycle acid preheater (descrihrd subsequently) through a water cooler and then into a 50-foot section of 1/4-inch pipe that was I\-ound around the entire length of the reactor. The reactor product (hydrocarbon plus liquid catalj-st) passed through a water-cooled condenser that consisted of a 10-foot coil of I/4-inch Hastelloy B extra-strong pipe. The condensate and acid then flowed into the acid settler. T h e settler consisted of 12-inch section of 4-inch extra-strong stainless steel pipe. . ileg 5 inches long and 2 inches in diameter was welded to the bottom of the settler, which was equipped with a 2000-pound ctainless steel gage glass, on n-hich the volume of the acid in the wttler could be read. The recycle acid was pumped from the bottom of the settler leg by nieans of a variable-stroke reciprocating pump, which n-as protected by an oil seal, into the acid recycle preheater. Samples of the catalyst for anal>-sis and discard were taken on the discharge side of the acid pump. Periodically, the acid recycle rate \vas measured by diverting the circulating catalyst into a calibrated gage glass. After the rate had been determined, the acid was returned to the system. The acid preheater %-as constructed
March 1956
of an 11-foot coil of l/a-inch Ilastelloy 13 standard pipe. The circulating acid temperature was controlled by the amount and temperature of Dowtherm t h a t passed through the preheater jacket. From this preheater the recycle acid floried through a '/r-inch Hastelloy B pipe that extended down into the reactor approximately 4 inches. The hydrocarbon effluent from the top of the acid settler passed through a back-pressure regulator and was discharged iit 200 pounds into the product filters to remove acid carry-over. The first filter contained alumina and the second filter (in series) contained a mixture of alumina and Ascarite. The product from the filters flored through another backpressure regulator and was discharged into the stabilizer. The stabilized pol>-mer was n-ithdrann from the bottom of the stabilizer into an ice-cooled accumulator. T h e overhead from the stabilizer xvas n-ithdrawn, as a gas, through a back-pressure ~ in a wet-test meter. Representaregulator and ~ 7 - ameasured tive samples were analyzed by mpans of a mass spectrometer. Inasmuch as traces of unconverted feed remained in the polymer bottoms, the polymer from each yield period mas "debutanized" in a coliimn 1.5 inches in diameter, having a &foot section packed with ':,-inch steel helices, at 10 t o 1 reflux ratio. I n order t o determine the 1-ield of motor gasoline fraction (initial boiling point to 430" F.) on the debutanized polymer, the latter frartions nere rerun in a column 1.25 inches in diamet)er by 18 inches, packed n-ith 3/la-inch helices :tt a take-off of approximately 20y0 per hour. At the 430" F. cut point no external reflux n-as applied, because heat losses from the column n-ere so
INDUSTRIAL AND ENGINEERING CHEMISTRY
371
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT great t l i ~t , the npplicaiion oi' external reflnx rvould hu1.e resulted in coluii,ii flooding. Bromine iiunilier (131, ASTM distillation, AI'I Rr:ivit.-. and Research cle:ir trctu.ne nuniljer d a h iwre 01)taincd on the motor gssoiine fraction, ant1 similar data (n-itli the exception of iiiforniation on octane numlxlr) n-we olit:iinetl on t h e tlc-hiitmized polymer. I\Iolecul:ir \\-eight5 of t h e !ml?mc.r frnciioir. were e2timated from the ASTN t l i ~ t i l l : , t i u ~ idata. eniployiiig tlic> cr,rrelation; sli,:,n-n by AIaun-t~ll(201. Propylene Feed Stack. .!'lie feed qtock t'illlJlo!.tvl in theae studies \Tab liridiiced I,?. frn:.tionntion of t lie C j IJius iii'otluct from the catalytic: cr:~cki~ig of p r o ~ e gas s nil aiitl cont:iin,xi 38, 41, (1.5,
pent oxide. The arid coiicc,ntration i r i t h e reactor diirin: a run \I :i* r i j l l o \ d ljy detprrcining n-:iter, cxl-ron, and pho.phori8: Licid. Aleid strength then K X c:rlciilated on a hydroc:irboi The amount oi phosphoric acid in a sani~ile. . the titratahle acidity cslculnted a ? RJ'O, ( content was determined by combustion ( B )il:i, content n-ai: calculntetl on the iimptiori th:it :(I1 iIir c:irl)i)ri
Table
I.
present 3s mono-olefins. Tlie n-ater content was dctermiricd by d i d l a t i o n of the snnil?le with dry tnliiene aft,er the free phosphoric acid had reacted :vith anilirie. The dYTII distillstion :ipp:~rut-iii: for determiiiiiig n-zter in hydrocarbons (8)TKLQ modified t o permit more accur:tte measuremeiit of the x i t e r . This d e t ~ m i n a t i o nJVW aiigiiiented by sn stlaptation of the I k l Fischer ( 1 ) dead-stop end-point nirtliod (8,10) for tleterniiiiing n a t e r whenever the nnionnt of saniple limited or rapid rwiilt-: WAI'C clc~irerl. One of tlic convciitions :itioptecl I to expreis a11 :xiti ronrc~rtr:itioii$ ill term; of pcr cent o ophosphoric acid, H,l'04. . ihoiigli it is ltnon-ii t h a t thoie concentrations of aciti i n of 100yo H,PO, are actually inixtures of tiic ortlto-, tri-, tet;.n-: ~ i i dmetaphosphoric acids (4) Observations of Flow in a Glass Model of Reactor. In orcler t o o1Jt:iin n 1)c.tter iindc~retantliiigof gaseous hytlroc,nrl,on-lirliiiil plioy,horii. :i*,itlcontact in tlic pilot unit reactor, n gl:t,s coliiinn 1.5 iiirlie. i n diameter i w s p i ~ c i i ~n-it11 l 3 / l s - i ~ copper ~ ~ h 1viitie. were provided t o flow S570 phosphoric :~citi (vi*co-of 32 c p , :tt 80' F.)and air down through the pnc>ketl tied :it ruoni tcniperatnre. In riiiis t h a t n-ere v a r r i d out :it suprrfwinl g L s :ind liyiiid velorities eqiiiv:dent to those nor:ii:iIly ~11~plo:~~cd i n tlic pilot unit, marked mixing of g iiqiiitl. WLS ol)+erved. .is :t rtwil lie "voil-ls" in the p i n liquid. In effect gas, /,e inch n e r c diipcrvd in a phase, Coa1esreric.c nnil I C -
Summarized Data Obtained with Cxurrent Downflow Packed ReactDr
R u n 1'11 Pacling
7 '5
.
I'RP
A-ozRT' hr
CS+
pn;?-!i.i
r 5i-U. n t.
?: or.
B
0.15;
0.1Bi 0 04.5
12 R
62.2
23 i
5: 0
8') 4
02
92.8
84.6 90.2
!i
(loof)
? ! 0 .4 100 i 9.6
Hydrocarhon recor.cri-. x t . 5 First-ordcr r a t e c o n s t a n t , lir. -'(k)
R u n I'JI-
13.90
okfins
chareerl Ca to 4:3OC i , "Raoline Yield. n t . ? on Cs; p d y r l c r Research clear octane S o . Olefin conrerii.,n f r o m t n i l "-" :::iaIySIS,
13 1 2
68 9 90 :i 11 0
1
97.1" 108.,-
372
IN D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Vol. 48, No. 3
54% final conversion, 3 2 0 ' F., 400 Ib./sq. inch gage,
Example.
z =
0.83
~
1, 2. 3. 4.
Av. v s . final conversion 360 360 400 320 360
5. 6. 7. 8.
300
400 500 400
500 500 500 700
320 306 360 290 276
9.
1 ci. 11.
500 500
-4
0
.
5
v
~
~
I
q0: y 1
'~
~.
~~.
~
,
'
~~
:.
-,
~
g
,
0.4
0
G
0
20
gage. I t foiind that propj,lenc conversion could be cvrrc.i:itod by asliming t h a t t h e propylene polymerizntion r e ~ h i j ~ proi ceeded as nil irreversiiik liviriogeiieous g;i.-phse fir-t-order process. .llthoiigh c:ilciilationi indicated th:Lt imth gas a n d liquid h>-tlrocarbon p1ia.e. n-ere prcsent in the p i k t unit reactor a t high olefin convcrqiony, ereellent correlations w r e o1it:iined rvhen deviation of t?ie hJ-tlrocnri7on mixture from the perfect 93s la\y v-xs taken iiitZ3 account. The following integrated Grrtorrler eyiintion for ii iion- w:ictor \vas i i w d to correlate the ri:lta.
40 60 Average Conversion, Per Cant
100
BO
I;'
Figure 2. Compressibility factors of reactor hydrocarbons vs. propylene conversion
( S L ;)
1 I (1 1 -"f
in
t7het.e
X.
tli~per4oii of tile gas l7ui)liles occurred as the mixturc f l o w d don-ti tiiroiigii the pacl;eci [mi. ~ ~ i ewater i i (viscosity at^ 0.86 c p , :it 8U" F , ) n-as w e d in place of the S57c phosphoric acid, no mixing of Ea- and liquid rrns observed; the gas phase was colitinuoils :inrl the Iiiluiti :ippenred to flow .;lon-i?- ilvo:' t l L c,snrfacc of :he packing. Althoiigli t h c vizcoqitirq of n i mid ~ S 5 7 c plioiphOi.iC' nritl a t room tcnipcratiire n-ere e d 1natw1 131. 2.4) to be sonierrliat !iigher than t h e ii!-rirocar?ion n:,d liquid acid: respectivel?-, i n the pilot iinit, recictor, it i.c IF- ~ _ _ _ lieved that tlie pilot unit renctor acted :IS
a mixing d e v i v t o p r o d i m n continiial1~er.-ion of gweoiia hydroearcntn!:--t. Thus t,he surface : L W R of the p:icliirig ~.~:oiildl-ie tw :I le-z ciitii:J v:irinhle it] t tli:iti is the area of ;!le packing in the prorers ( 1 8 ) . dierein the c:itnlyyt consists of :ist:itic iil?ii (if 1)limTiliorir w i d oii quartz
kT',tP
~
,.I-,,
(1)
Ai-,Jzri 7'
first order reaction rate constant, voluiix oi' olefin per volume of r e x t o r per hour fed per hour grsnl-molee of of olefins fed per hour of olefin required t o produce 1 nioie of polymer
= =
-
~
~
~
.
~
~
.
~
~
~
~
~
.
.~~
-,
-1c
-
0
-~~
5:Llltl.
Olefin conversions up i o 99% ware obtained
L):it:i th:it n-cre oiitnined ii, ti,? tlorrnilow re:wtor :it :i c n t n l p t of polvnii:r :ire siinimnrized
iii
C.05
G
0.10
0.20
0.i5
0.25
0.30
0.35
0.40
VRP, tir. NO ZRT
T:il,!c I.
Figure 3.
Polymerization of propylene as first-order process Propyienc feed, 58.2 mole % olefins Temperature, 360" F. Catalyst circulation rate, 0.61 v./v./hr. Run PH-
0
A 0 0
A
March 1956
11 16
15 17 18 19
% Hap04 92 96. 98, 98( 103 109,
8~
16-inch copper pailet packing
8 - to 16-mesh c a r b o i ~ a c k i n g
I N D U S T R I A L A N D E N G I N E E R IN G C H E 31 I S T R Y
373
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT
01
!
of the resulting straight line passing through the origin is equal to k , t,he first-order reaction rate constant. This constniit, is characteristic of the specific reaction system that was used i n the pilot unit lyork. Figire 3 shorn the corrrlations that were obtained m-hen the pilot unit data were plotted in this niriniier. A linear relationship vias obtained for opmitions R-it11 the 98% acid wherein pressure n-as varied from 300 t o 700 pound. per square inch gage and feed rate TI-^ varied froni 0.5 to 2.2 volumes per hour. Correlations for the acids of higher and l o w r strength m r e based on data obtained in a constant pressure of 500 pounds per square inch gage. .An attempt was madc to increase the over-all rate of reaction by employing smaller reactor packing. F o r this reason the to I"-16 3/16-inchcopper packing that was used in runs 1"-9 (inclusive) v a s replaced with 8- to 16-mesh carbon packing prior to run PH-17. Although it is estimated t h a t the carbon packing had about 50y0 more surface area than the copper packing, the pilot unit data indicate no advantage for the smaller packing. This conclusion is supported bj- the data for t.he 98% acid correlation of Figure 3: which indicates that the same rates of reaction were obtained in runs I"-15 and li, rrhen the copper and carbon packing, respectively, were employed.
I
1
100 105 I IO 115 Cotolyst Strength, Wt. % H3P04, Hydrocarbon Free Basis
95
90 Figure
4.
Effect of catalyst strength on rate of propylene polymerization
Temperature,
400
360
OF.
320
280
I
401
Propylene feed, 5 8 . 2 mole % oleflns Temperature, 3 6 0 ' F. Catalyst, 0.61 v./v./hr. phosphoric acid charged to Hastelloy B reactor packed with 1 1 feet of a/~6-inch copper pellets or 10.5 feet of 8- to 16-mesh carbon packing
f = fraction of olefins converted V R = reactor volume, liters P = absolute reactor pressure, atmospheres z
=
R T
= =
average compressibility factor of hydrocarbons in the reactor gas constant,, atm./liter/" K. absolute reactor temperature, ' IC.
By use of the terms n and
;v. allowance is made in the preceding
and dividing by F . The left-hand side of Equation 2 is dependent only on olefin concentration in the feed, average molecular weight of the polymer produced, and olefin conversion. When this conversion function is plotted against the reciprocal space velocity, the slope
2.2
IO00
2.4
2.3
I 2.5
Temperature,°K
a l a y 25, 1955.
. A C C E P T E D December 3 , 1955. Division of Petroleum Chemistry, 127th hleeting, ACS, Cincinnati, Ohio, March-April 1955.
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