Metering of Powdered Solids in
I I
deve'opment
LEONARD FARBAR Universify of California, Berkeley
T
HE metering of true fluids has been thoroughly investigated and standards (I, 2 ) have been adopted which ensure an
accuracy of measurement well within the allowable for scientific work. The effect of a second phase on the behavior of metering devices has not been too well established. The effect of water droplets on the flow of steam in nozzles was noted by Stodola and Loewenstein ( 7 ) in discussing the work of Rateau (6); this seems t o be the earliest reference t o the effect of a second phase in metering fluids. It is the purpose of this paper to present some results on the effect of powdered solids in a gaseous mixture when passing through a metering nozzle as a heterogeneous mixture. A recent paper b y Carlson, Frazier, and Engdahl ( 3 ) investigated the
4, Calif.
metering of a powdered coal-air mixture with considerable success. The metering of a mixture of several components in more than one phase becomes increasingly important as the chemical and process industries tend toward increased use of synthesis by catalysis and in the direction of process units of relatively large capacity. The increased use of the continuous-type catalytic processes, the handling of products in the form of powdered solids, the handling of solid combustibles, and numerous other applications makes the metering of solid-gas mixtures a useful tool in the control of plant performance as well as yielding information on the instantaneous changes that may occur in plant operation. I n a previous paper (4)an exploratory study was made of the flow characteristics of solid-gas mixtures in a horizontal and vertical circular conduit using powdered alumina-silica catalyst as the solid phase. The same system with some slight modifications was used for the present investigation.
b
To industrial vacuum cleaner
Sight glns
Figure
I. Flow Diagram of General Arrangement 2947
of Experimental Equipment
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 12
The values indicated in Table I are average values for screenings made under various conditions and over varying Ro-Tap shaking periods. I n view of the relatively large percentage of fines, size determinations were made using an Infrasizer, an elutriation type of analyzer capable of separating particles in the subsieve region. The results of a typical elutriation analysis are shown in Figure 7. Approximately 11.0% (by weight) of the material consists of particles smaller than 12 microns in size. The equivalent particle size indicated is, of course, only a relative measure of the true geometry of the particle. Photomicrographs (magnification of 25OX) of various sized fractions obtained liy elutriation are shown in Figure 8. The particles appear to be of the same general shape regardless of the size range into n hjeh they may fall. The attritional effects, caused by continuous i t s circulation of the solids, were of negligible magnitude with respwt to reproducible results. Screen analysis and elutriation teFts made a t various times indicated a gradual reduction in the percentage of very large particles, with the main bulk of the Tyeiyht shifting to the region of 40- to 80-micron particles. Experimental Procedure
Figure 2.
The air-metering nozzle, -4-1 (Figure I), after calibration I\ ith air and water n a s used as the standard in calibrating all other metering devices when handling gas alone. I n the first group of runs, metering nozzles were installed in the three locations shown in Figure 1. The solids feed tank bed was fluidized and calibration runs
Experimental System
Table 1. Particle Size Distribution by Screening Tyler Screen No.
Equiv. Opening, hIicrons
Weight % Paseed
Weight % Retained
Description of System, Material, and Metering Nozzles The experimental system shown diagrammatically in Figure 1 consists of a flanged connected borosilicate glass conduit (17 mm. inside diameter), a solids feed tank and weighing system, and a multiple-effect cyclone separator forming a closed recirculating system for the handling of solids. The gaseous phase, being air, is handled on a once-through basis by the use of an industrial vacuum cleaner on the outlet of the cyclone separator. A calibrated Ish nozzle was used to meter the air at inlet to the system. The general arrangement of the system details is shown in Figure 2. Figures 3 and 4 show details of the solids feed tank, weighing system, and the solids mixing tee containing a serrated fitting for solids dispersion. Dimensional details for the two series of aluminum metering nozzles used are shown in Figure 5 , aluminum flange details and meter assembly being shown in Figure 6. ,4s may be seen in Figure 1, the metering nozzles were placed in the horizontal and vertical runs of the system with 106 pipe diameters approach for the lower horizontal position, 93 pipe diameters approach for the vertical position, and 54 pipe diameters approach for the upper horizontal position. Pressures were determined by use of calibrated draft gages and vertical U-tube manometers having a least count of 0.01 and 0.1 inch of manometer fluid, respectively. The alumina-silica catalyst used as solids had a specific gravity of 2.45 and an average bulk density of 36 pounds per cubic foot (oven dried to 350" F.). Its average size distribution is shown in Table I.
Figure 3.
Solids-Handling System
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1952
were made with air alone. The air rate was set a t a predetermined value and held a t this value while the solids feed slide valve was adjusted to a position yielding a uniform solids flow. The initial weight of the solids feed tank was recorded as soon as the flow appeared stable, and time intervals for various increments of feed tank weight differential were then recorded. The decrease in the weight of the solids feed tank was plotted against elapsed time as a control curve (Figure 9). Manometer readings were observed and recorded continuously for the duration of the run. Upon completion of a run the solids feed slide valve was closed and the flow system cleared of solids; the
vacuum unit was shut off; the solids in the cyclone separator were returned to the feed tank; and the weight of the feed tank was observed and compared to the initial weight of the tank
SECTION F-F
LSSEMBLY VIEW NOZZLE AND FLANGES
Figure 6.
Figure 4.
Solids Feed Line and Feed Fitting
A --_
-I--
ORILL IW
f llQT
pr(r.l.-c( SECTION A-A
Figure 5.
Metering Nozzles
2949
Metering Flanges
prior to feeding any solids into the system, thus checking losses that may have occurred. The air rate was then re-established and a different solids rate set. The procedure as outlined above was followed for a group of fixed air rates over the range of solids flow rates permitted by the available power on the vacuum unit. Calibration runs were normally made with air alone upon the completion of a series of mixture runs. Pressure differentials were read to 0.01 of an inch of water for a range of 3.0 inches of water differential and to 0.1 of an inch for pressure differentials greater than 3.0. Absolute pressures were obtained to the nearest 0.1 inch of manometer fluid, time to within 0.2 second, and scale weights to within 15 grams (sluggishness observed in platform scale Calibration). Usually after a series of runs all pressure taps were blown clear of solids by removing the pressure lines and applying compressed air to theconnection. During the latter part of the investigation, the number of mixture metering nozzles in the system was reduced to a single nozzle placed either in the lower horizontal run or the vertical run (Figure 1). The experimental procedure remained the same. The &sting of a single metering device was made necessary by the limitations on power and in order to reduce the compressibility effects on the downstream positions. The B series of nozzles were all tested individually in either the lower horizontal or the vertical positions. The A series of nozzles was tested in all three of the nozzle positions and finally checked individually in either the lower horizontal or vertical positions. The solid material handled easily and the many anticipated difficulties were seldom encountered. The main difficulty encountered was that of manom-
2950
INDUSTRIAL AND ENGINEERING CHEMISTRY Figure 7.
Vol. 44, No. 12
Particle Size Distribution
of Alumina Silica Catalyst t-
eter fluid carry-over when working at high solids rates and with a pressure differential quite close to the range of the instrument. This difficulty was quickly cleared up by removing the section affected and cleaning the conduit as well as the nozzle connections. The use of felt pads in eachpressure tap aided materially in eliminating any difficulty from the packing of solids in the pressure taps. The ease with which the solids flowed a t a constant rate (see Figure 9) simplified the operational control considerably. Some difficulty was pncoun-
Figure 8.
Photomicrographs of Sized Catalyst Samples
Under b. 12-1 7 c. 17-25 d. 25-33 a.
12 microns microns microns microns
e. 1. 9.
33-49 microns 49-74 microns 7 4 - 2 0 8 microns
tered in controlling the solids flon rate when the serrated flow fitting \\ as not used in the mixing tee. High speed photography of the mixing section indicated rather large pressure fluctuations in the vertical section of the solids feed line nhen the mixing fitting was not used. To ensure steady state only those runs in which the solids flow was a linear function of time n ere used and all subsequent material is based uponthe data takenunder theseconditions. Periodic calibrations made on the various meters, in terms of the air metering nozzle, served t o indicate thc ektent of erosion
December 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
2951
that might be taking place in the meter. Within the limits of experimental accuracy no effect on the meter performance was noted, even though visual observations indicated a roughening of the initially polished surface, nor could any change in meter dimensions be measured. The roughening or sand blasting effect seemed to be completely uniform. Experimental Data and Results The experimental data obtained are shown graphically in Figures 10 and 11 for the two series of nozzles used in this investigation. Before discussing these data it may be well to consider the energy equation as applied to this particular system. Assuming the following conditions: 1. A closed converging circular conduit with the downstream section (location 2) at a higher elevation than the upstream section (location 1) 2. Incompressible and essentially isothermal flow conditions between the two sections 3. The fluid and solids frictional losses to be proportional to the square of the average fluid velocity a t the downstream location 4. The aggregate mixture of solid particles flowing may be considered to be represented by some average particle size flowing a t the same rate as the aggregate mixture There results upon application of thr energy equation
4
Figure 10,
Experimental Results for Nozzle Series
A
'16
15 14 L
13
3
5 12 M c 0) 0
-
II
I,I C 5
kW 9 a u-8 w
LL n
2 7 13 v)
E 6
K
P
K
W
5
k
:4
3 2 I
0 0
I
2 3 4 5 6 S O L I D S FLOW RATE "Wi-
7
8
9
10
Pounds Per Second
IIxlO-'
0
I
2 3 4 5 SOLIDS FLOW R A T E "W;-
6
7 8 P 10~10'~ Pounds Per Second
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 44, No. 12
a I-
d
1.00 w 0.98 a 0.96
2
9 0.94
::0.9;
E 0.9c 08E 5:
44 42 40
38 36
34 L
2 32
;
30 v)
c o 28
-
e
26 24
a W
-n
k22 w 20 a 3 cn
2 18 a a
a 16 W
tW
Z 14
12 IO
E
E 4
2
C
-
SOLIDS FLOW R A T E "&" Pounds Per Second Figure 11.
SOLIDS FLOW RATE
Experimental Results for Nozzle Series B
'"-
Pounds Per Second
December 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
Rearranging and combining terms
Applying the continuity equation to the fluid phase, letting M equal the ratio of downstream cross-sectional area to the upstream cross-sectional area, and assuming that the fluid density is very small relative to the solids density, Equation 2 becomes
Equation 3 is the general equation accounting for the energy exchanges that must exist in the system previously described and is a linear equation with respect to the solids flow rate in a given system where the fluid gravimetric flow rate is held constant. The first term on the right-hand side of Equation 3 is the intercept (W, = 0 = k,) and is simply the pressure differential of the fluid flowing at the rate Wt. Referring now to Figures 10 and 11 i t appears that the solids friction coefficient does not greatly influence the value of the intercept. Equation 3 indicates that the intercept will increase by an amount that is proportional to the square of the fluid gravimetric flow rate for the horizontally placed nozzle and slightly more for the vertically placed nozzle. The intercept will be further increased by increased nozzle length, and an increase in the intercept will result from a decreasing area ratio, M . These predictions are borne out by the experimental results shown for the A series of nozzle ( M = 0.558) in Figure 10 and the B series ( M = 0.3142) in Figure 11. It is apparent from the experimental results that a linear relationship exists for the pressure differential as a function of solids flow rate for a constant gravimetric flow rate of the conveying gas. This relationship exists, of course, only for the range covered in this investigation. It was originally expected that such a relationship would exist for nozzles provided with cylindrical elongations which would allow the energy exchanges caused by fluid and particle acceleration t o be reflected in the pressure changes that must result from such energy exchange. The prolongations were made in accordance with that shown in Figure 5. The slopes of the curves increase both with increased air rates and increased cylindrical elongation of the nozzles. Nozzle A-2, the standard ISA nozzle modified slightly by use of a single radius to the inlet, shows more than satisfactory performance. Slight elongations of the nozzle outlet, as represented by nozzles A-3 and A-4, perform satisfactorily and in accordance with the assumption made above as to cylindrical length; however, the pressure drop and the energy loss may be considered excessive relative to nozzle A-2. The effect of solids spatial distribution is clearly indicated by nozzle A-5 a t intermediate gas rates. In the vertical run where satisfactory solids distribution existed, the pressure differentials were lower than those for the horizontal (upper) run where the solids distribution in the gas stream was far from uniform, because of the lack of a solids distributor following the 90"ell in the upper horizontal run. This, of course, was true only for the actual conditions that existed for the two locations. Normally, for a uniform mixture flowing through a metering device a greater differential for the meter in the vertical position than in the horizontal position should result. I n this case the solids in the horizontal upper line flowed in more or less stratified fashion through the line and nozzle, concentrated by the centrifugal action in the relatively large radius ell. This resulted in considerable reduction in area (similar to a reduction in the M ratio) for the gas phase in the nozzle; hence there was a considerable increase in velocity and friction, with an accompanying increase
2953
in pressure ditrerential. Regardless of these differences caused by position, the linear relationship still obtains for the unusual condition of Stratified flow. The degree to which the air stream was loaded is best indicated by the range of solids loading rates which varied from zero to approximately 20 pounds of solids per pound of gas flowing. Although not shown on the curves, the differences observed between the lower horizontal and vertical positions for nozzles A-2, A-3, and A 4 were small. It may be well to indicate at this point that where uniform solids distribution does not exist there will be considerable fluctuation in the differential pressure across the meter; this is further amplified by nozzle length. The B series of nozzles (for which the M ratio is 0.3142) yielded the same linear relationship between pressure drop and solids flow for the same constant gas flow rates as shown in Figure 11. I n this series as in the case of series A, the standard nozzle seemed t o respond in a more satisfactory manner than the elongated nozzles. The extent of any compressibility effects for the B series of nozzles is shown by the meter pressure ratio (ratio of the downstream pressure to that a t the upstream pressure tap). These effects may be of considerable importance for the longer nozzles, and in conjunction with the rather high particle velocity may be the cause of the rapid departure from linearity of the pressure differential curves. These effects on the increase in the line slopes are indicated by the second term of Equation 3 or the multiplier to the solids flow rate, Inspection of this multiplier with respect to the elevation difference (nozzle location in either the horizontal or vertical) indicates the slope should always be greater in the vertical position than in the horizontal when all other factors are equal. The incremental increase of this term decreases with an increase in the fluid flow rate; hence at high fluid flow rates this term may contribute a negligible amount to the difference in slope between the horizontal and vertical positions. It will now be assumed that the factors which determine the slope of the lines in Figures 10 and 11 are given by
Case I. Consider first the case of a nozzle'(M = constant) of such length that the solid particles have reached their steady state velocity at the downstream section 2. Now for the horizontal V*l and the slope E- wf (1 - M2) or the position = 1.0 = v/¶ Vf1 2gA it Pf slope is directly proportional to the gas flow rate. I n the vertical position, the solid velocity (for nonaccelerated motion) will always be less than the fluid velocity by an amount necessary to overcome the particle weight or this difference will be the terminal or free fall velocity, V;,the terminal velocity being determined by the particle shape, size, and stream condition. Note that this terminal velocity is not the Stokes' free fall velocity of a spherical particle but is the actual terminal velocity of the particle in the turbulent fluid, which for spherical particles will always be less than the Stokes' velocity. Using the data of Schiller and Naumann (6) for spherical particles, the terminal velocity would be given b y Stokes' terminal velocity vt = 1 0.150 NR''.@~
3
+
where N E = Reynolds number based on the particle diameter, the particle velocity relative to fluid, and the fluid kinematic viscosity. Hence V,1 Vel = V ; = V f 2 V,, (for nonaccelerated particle
-
motion) and slope = 7 wt [(l 2SA2PJ
Since V,, is always greater than V,, (1
- -v')z > VI2
(
1--
rapidly with Wj than (1
't)'
V/l
-
and
- MZ(1 -
(
1
31.
Vt)rincreasesmore -VfZ
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Hence for the long nozzle in the vertical position the slope of the lines will increase at a rate which is more than directly proportional to the increase in gas flow rate. The experimental results on nozzles A-5 and B-5 seem to substantiate these predicted trends. Case 11. I n this case the same size nozzle is considered as in case I ( M ratio equals a constant), but the nozzle length is such that the solid particles are still being accelerated at section 2. For the horizontal position a velocity difference must exist between the solid particles and the fluid in order to provide the force necessary to accelerate the particle mass, that is Ysz< V f , but Val = VI^, since nonaccelerated flow exists in the approach section. For these conditions the expression previously given for line slope predicts a slope for the shortened nozzle that is less than directly proportional to the gas flow rate. For the nozzle in the vertical position the same reasoning as in case I applies but the difference in velocities nil1 be greater than the particle free fall velocity, that is (Vfz - Va2) I I > (Vfz = Vaz)oBse I, and the increase in slope for the shortened nozzle mill be a t a rate that is less than directly proportional to the gas flow rate and less than that for the same nozzle in the horizontal position. The experimental results for all nozzles other than A-5 and B-5 indicate line slopes that change a t a rate that is slightly greater than that resulting from direct proportionality to the gas f l o ~ rate. These deviations may be due to fluid density changes a t the various locations and to the frictional effects that are not included in the expression for the slope given by Equation 3. The final factor contributing to the line slope in Equation 3 is the nozzle area ratio, N , since A,2 = ii2A:. Omitting terms independent of M , the expression for slope may be written as
--_ IV I
r
$J -.I
V,, the area ratio the slope will increase as
-.M12
For the shorter
nozzles in the horizontal position, (particle acceleration
- TI;)z Vf,
in a manner that
=
>0
at
($)’, hence the slope will increase 1
wii be less than that proportional to ’W’
For the nozzle in the vertical position, VC’= Vt for the long nozzle, Vi’
>
investigation, as qualitative observations indicated this influence to be of considerable magnitude. Regardless of these difficulties in evaluating or predicting slopes, use may be made of the metering nozzle for metering the solid phase in gas-solids mixtures where the gravimetric flow rate of the gas phase is maintained constant or where the slope of the pressure differential versus solids flow rate line has been obtained from a calibration a t different gas flow rates. I n an installation where a calibrated blower is not available, a second meter in the dean gas system will be required for the control of the gas rate; this meter may be an orifice plate, but it must be placed in the system where the gas phase alone may be metered and controlled. The mixture metering nozzle (of standard type) may be placed in any section of line carrying the mixture, preferably in a vertical section, and sufficiently far removed from any fittings that would tend to concentrate the solids in a stratified layer. The meter will be quite sensitive to the stability of the mixture, hence any devices used to control the uniformity of the mixture will contribute greatly to the smooth response of the meter for any changes in solids rate. In large installations the mixture meter may be calibrated during the initial filling of the system with solids, and temperature corrections determined during the warm-up period. I n systems not subjected to elevated temperatures, other methods of calibration may be easily employed t o obtain the slope as well as the limit of the straight-line relationship for the nozzle. The nozzle area ratio should be as large as possible, or as indicated by the accuracy possible in metering a h-Pwtonian fluid. Conclusions
1”
11 in which V( represents the difference in 2gM2A:pj fluid and solid particle velocity, Vc’ = (Vj2 - V,,), and for the various conditions is as follows: for the horizontal system in which the solid particles aye not accelerating a t section 2 (long 8, = 0. hence for decreasing values of nozzles) V I , = Va, and -
section 2), (1
Vol. 44, No. 12
Vt for the short nozzles, and
Vjz
o(
Wf --, MA1
which
indicates the slope will increase a t a rate that is more than pro1 portional to - for decreasing values of 111 and that the changes M2 will be greater the shorter the nozzle. Although these trends have been substantiated in a general way by the experimental results, the writer believes neither the experimental data nor the variables contained in Equation 3 are sufficient to allow prediction of line slope for a given metering system geometry without calibration. Carlson et al. (3)found in their investigation on powdered coal that the pressure differential was linear with solids flow rate for light loadings and predicted slopes on the basis of meter constants and mixture flow density. Application of these methods of slope prediction to the nozzles used in this investigation resulted in predicted slopes which were much greater than those actually observed. A further effect that may influence the prediction of meter constants is the particle size distribution which would certainly affect the frictional characteristics within the mixture, depending on whether the particles were an aggregate mixture or a single sized fraction. The influence of solid material distribution in the flowing mixtures on system stability and response requires further
Although this investigation v a s of limited scope, certain conclusions may be drawn with respect to the handling of a gassolids mixture through a metering nozzle. The standard converging nozzle may be used to meter a powdered solids phase in a gas-solids mixture when the gas gravimetric flow rate is maintained constant and the flow is essentially incompressible. The relationship between the meter pressure differential and the solids flow rate is linear over a range of solids to gas flow ratio. The maximum value of the solids t o gas flow ratio appears to depend upon the gravimetric flow rate of the gas phase through the nozzle. The slope of this straight-line relationship appears to depend primarily on the gas flow rate and the nozzle area ratio. Increased slopes result from increasing gas flow rates and decreasing area ratio. Increasing nozzle length merely- increases the pressure differential, hence power loss, without measurably contributing to meter stability or reproducibility of results. Kozzle area ratios should be high in order to reduce power losses, to keep the gas velocities in the range where the linear relationship obtains, and to reduce any tendency toward excessive erosion in the system. Attritional effects appear to have very little, if any, effect on the reproducibility of meter results. The uniformity of the mixture in the approach line to the meter contributes greatly to the stability of both the nozzle and the flow system. The installation of a nozzle in a two-phase flow system appears to stabilize the mi nozzle a t not too great an increase Meter calibration may be carried out in place when installed in large systems where gas rates can be held constant and at least one solids rate determined. Prediction of line slopes and meter accuracy cannot be readily made in view of insufficient experimental evidence on the behavior of metering nozzles when handling flowing mixtures. However, the metering nozzle may be an extremely valuable tool in plant operation where the control of solids flow rates is necessary. Further studies of the various variables, suggested by this investigation, are required in order to determine whether or not constants for the metering of solids may be predicted from system constants.
December 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
Nomenclature A = cross-sectional area, square feet g = gravitational constant = 32.17feetper second per second k = frictional coefficient, dimensionless M = ratio of downstream cross-sectional area to the upstream cross-sectional area N R = Reynolds number P = pressure at section, pounds per square foot B = substance average velocity, feet per second W = substance gravimetric flow rate, pounds per second 2 = section elevation, feet p = substance density, pounds per cubic foot
2955
through a grant by the Research Corp. The writer wishes t o express his appreciation to James M. Powell for the excellent manner in which he handled the flow system and obtained a portion of the data presented. literature Cited (1) American Gas Association, Gas Measurement Committee Rept. 2, New York, NIay 1935. (2) ASME Power Test Codes, “Flow Measurement by Means of Standardized Nozzles and Orifice Plates,” Part 5, Chap. 4, New York, Am. SOC. Mech. Engrs., 1940. (3) Carlson, H.M.,Frazier, P. M., and Engdahl, R. B., Trans. Am. SOC.Mech. Engrs., 70,135 (1948). (4) Farbar, L.,IND. ENG.CHEM.,41, 1184 (1949). (5) Rateau, A,, Ann. mines, 1902. (6) Schiller and Naumann, 2. Ver. deut. Ing., 77, 318, Band 77,K’r. 12 (March 1933). ( 7 ) Stodola and Loewenstein, “Steam and Gas Turbines,” Vol. I, p. 111, New York, McGraw-Hill Book Co., Inc., 1927.
Subscripts 1, 2 refer to upstream and downstream sections, respectively f, s refer to the fluid (gas) and solids phase, respectively Acknowledgment This investigation, a part of the research program in multiphase flow a t the University of California, was supported in part
RECEIVED for review February 15, 1952.
High Molecular Weight Polymers from Propylene and 1-Butene C. M. FONTANA, R. J. HEROLD, E. J. KINNEY,
AND
ACCEPTED August 18, 1952
EngFnTring Process development
R. C. MILLER N. 1.
Socony-Vacuum Laboraiories, Research and Development Deparimeni, Poulsboro,
A
S A result of previous work (6) on the continuous polymerization of 1-butene using promoted aluminum bromide catalyst, polymer products in the molecular weight range suitable for use as viscosity index improvers ( 6 ) in lubricating oils became available. The study of reaction variables indicated, however, that there was a definite molecular weight limit which apparently could not be exceeded in a single-stage continuous polymerization. One of the factors which was believed to be limiting with this method was the possibility that relatively short chains were being removed from the reaction zone before they had sufficient time to grow to their fullest extent. This idea is based on a polymerization mechanism involving a simultaneous slow rate of growth of many polymer molecules in the reaction mixture ( 4 ) . On the basis of this hypothesis the continuous method of polymerization has a limitation not shared by the batch methods. On the other hand, it was observed that in the previously
used batchwise polymerization (6) a considerable portion of the catalyst and promoter was precipitated to form a tarry lower layer during the initial portion of the reaction. The continuous system did not yield a separate tar layer and the reactor effluents were either clear or opalescent. Semibatch Polymerization of Propylene and 1-Butene
The leading thought in turning to the “semibatch” method of polymerization was t o preserve the inherent advantages of the batch method while at the same time fully utilizing the catalyst and promoter and preventing tar formation by initiating the reaction under conditions simulating those used in the continuous method. This is done by feeding catalyst solution, promoter, and olefin simultaneously, over a given time interval, to a stirred reactor containing most of the solvent and thereafter continuing the olefin addition to the end of the polymerization reaction. The experimental results on Table 1. Summary of Experimental Conditions and Results for Polymerization of 1-Butene the polymerization of 1-butene and Propylene Using Semibatch Technique“ as given in Table I show that mafin __--1-Butene 7-Prowslene----the above exwectations were inRun No. BS-2 BS-3 BS-16 ,BS-14 BS-15 PSB-2 Pi&-3 PSB-8 deed realized and that molecTemp., C. -30 -30 -30 -30 -30 -30 -40 -40 ular weight ceilings previously HBr/AlBra, mole ratio 0.40 0.40 0.40 0.40 0.40 0.30 0.30 0.30 36 64 Olefin/AlBra, mole ratio 25 50 75 24 40 80 obtained in the continuous sysParaffin/olefin, mole ratio 5.7 3.1 16 8 6 8.3 5.0 2.5 Olefin feed rateb 0.41 0.83 0.83 0.83 0.83 0.40 0.33 0.33 tem were greatly exceeded. __-- _- Times of Addition, - - : n iM It was also observed that the AlBra soln. 10 5 5 5 10 99 9 product molecular weight conHBr 15 lo 15 10 10 10 9 30 Olefin 85 77 lo 60 90 60 120 240 tinued t o increase with increasTPmC of product 35 25 9.5 14.1 18.7 3.35 3.63 3.38 ing olefin-to-catalyst mole ratio RTPC of product 1.01 ... 0.94 0.99 1.00 0.84 0.86 0.84 under certain conditions as a Aluminum bromide solution in n-butane, HBr gas, and olefin added at constant rate over given time interval, all feeds being started simultaneously. Approximately 0.67 of n-butane solvent was initially present in reactor, shown by the results of experi* Thickening Moles of olefin per mole of AlBra per minute. Olefin feed rate was same in both stages of reaction. power and relative thickening power, defined in (6). ments BS-16,BS-14, and BS-15. This indicated the possibility I
.
_ - ~
-
