Metering of Powdered Solids in Gas-Solids Mixtures

Metering of Powdered Solids in I deve'opment I

LEONARD FARBAR Universify of California, Berkeley 4, Calif.

HE metering of true fluids has been thoroughly investigated T 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 to 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 by Carlson, Frazier, and Engdahl (3) investigated the

metering of a powdered coal-air mixture with considerable suc- cess.

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 infor- mation 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 modifica- tions was used for the present investigation.

b

To industrial vacuum cleaner

Sight glns

Figure I. Flow Diagram of General Arrangement of Experimental Equipment

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2948 I N 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. 44, No. 12

Figure 2. Experimental System

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 recircu- lating 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 a t 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.). I ts average size distribution is shown in Table I.

The values indicated in Table I are average values for screen- ings 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 sub- sieve 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

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. In 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

Table 1. Particle Size Distribution by Screening Tyler Equiv. Opening, Weight % Weight %

Screen No. hIicrons Paseed Retained

Figure 3. Solids-Handling System

December 1952 I N 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 2949

were made with air alone. The air rate was set a t a predeter- vacuum unit was shut off; the solids in the cyclone separator mined value and held a t this value while the solids feed slide valve were returned to the feed tank; and the weight of the feed tank was adjusted to a position yielding a uniform solids flow. was observed and compared to the initial weight of the tank

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

Figure 4. Solids Feed Line and Feed Fitting

LSSEMBLY VIEW NOZZLE AND FLANGES

SECTION F-F

Figure 6. 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.

A 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 Cali-

--_ -I--

ORILL IW f llQT

pr(r.l.-c( SECTION A-A

Figure 5.

bration). 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

Metering Nozzles

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-


Figure 7. 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 con- nections. 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

a. Under 12 microns e. 33-49 microns b. 12-1 7 microns 1. 49-74 microns c. 17-25 microns 9. 74-208 microns d. 25-33 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 subse- quent material is based uponthe data takenunder theseconditions.

Periodic calibrations made on the various meters, in terms of the air metering nozzle, served to indicate thc ektent of erosion


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 di- mensions 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. Assum- ing the following conditions:

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

1.

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

0 I I M 0) c

- I, I C

k 9 5

a u - 8 n

W

w LL -

2 7 E 6

13 v)

K P K 5 W k

: 4

3

2

I

0 0 I 2 3 4 5 6 7 8 9 10 I I x l O - ' 0 I 2 3 4 5 6 7 8 P 10~10'~

S O L I D S FLOW RATE "Wi- Pounds Per Second SOLIDS FLOW R A T E "W;- Pounds Per Second

Vol. 44, No. 12 2952 I N 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

a I- d 1.00

9 0.94 :: 0.9; E 0.9c

w 0.98 a 2 0.96

08E 5:

44

42

40

38

36

34

2 32 L

; 30

o 28

26

24

v)

c

-

- e

a W k22 - n w 20 a

2 18 a a a 16

Z 14

12

I O

E

3 cn

W t- W

E

4

2

C

SOLIDS FLOW RATE "&" - Pounds Per Second SOLIDS FLOW RATE '"- Pounds Per Second

Figure 11. Experimental Results for Nozzle Series B


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 pre- dictions 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 pro- longations 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 assump- tion 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 centrifu- gal 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

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

wf (1 - M2) or the V*l position 3 = 1.0 = - and the slope E-

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 by

v/¶ Vf 1 2gA it Pf

Stokes' terminal velocity 1 + 0.150 NR''.@~ vt =

where NE = 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 - - MZ(1 - 31. 2SA2PJ

Since V,, is always greater than V,,

> 1 - - and 1 - - (1 -- v')z ( ' t ) ' ( Vt)rincreasesmore VI2 V/l VfZ

rapidly with Wj than (1 -


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.

In 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

Case 11.

--_ r -.I 1”

11 - $J in which V( represents the difference in

fluid and solid particle velocity, Vc’ = (Vj2 - V,,), and for the

IV I 2gM2A:pj

various conditions is as follows: for the horizontal system in which the solid particles aye not accelerating a t section 2 (long

nozzles) V I , = Va, and - = 0. hence for decreasing values of

the area ratio the slope will increase as -. For the shorter M2 nozzles in the horizontal position, (particle acceleration > 0 a t

8,

V,, 1

section 2), (1 - TI;)z = ($)’, hence the slope will increase V f , 1

in a manner that wii be less than that proportional to ’W’ For the nozzle in the vertical position, VC’ = Vt for the long

nozzle, Vi’ > Vt for the short nozzles, and V j z o( --, which

indicates the slope will increase a t a rate that is more than pro-

portional to - for decreasing values of 111 and that the changes

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

Wf MA1

1 M2

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 to 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

Although this investigation v a s of limited scope, certain conclusions may be drawn with respect to the handling of a gas- solids 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. In- creased 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.


High Molecular Weight Polymers from Propylene and 1-Butene

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

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

cross-sectional area N R = Reynolds number

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 multi- phase flow a t the University of California, was supported in part

EngFnTring

Process development

through a grant by the Research Corp. The writer wishes to ex- press 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.

(7) Stodola and Loewenstein, “Steam and Gas Turbines,” Vol. I, p.

RECEIVED for review February 15, 1952. ACCEPTED August 18, 1952

12 (March 1933).

111, New York, McGraw-Hill Book Co., Inc., 1927.

C. M. FONTANA, R. J. HEROLD, E. J. KINNEY, AND R. C. MILLER Socony-Vacuum Laboraiories, Research and Development Deparimeni, Poulsboro, N. 1.

S A result of previous work (6) on the continuous polymeriza- A tion 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

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.

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

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

I 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. the polymerization of 1-butene

as given in Table I show that mafin __--- 1-Butene . 7-Prowslene----- the above exwectations were in-

Summary of Experimental Conditions and Results for Polymerization of 1 -Butene and Propylene Using Semibatch Technique“

Run No. BS-2 BS-3 BS-16 ,BS-14 BS-15 PSB-2 Pi&-3 PSB-8 deed realized and that molec- HBr/AlBra, mole ratio 0 .40 0 .40 0 . 4 0 0 . 4 0 0.40 0 .30 0 .30 0 . 3 0 Olefin/AlBra, mole ratio 36 64 25 50 75 24 40 80 obtained in the continuous sys- Paraffin/olefin, mole ratio 5 . 7 3 . 1 16 8 6 8 . 3 5 . 0 2 . 5 Olefin feed rateb 0 .41 0 .83 0 . 8 3 0 . 8 3 0 .83 0 . 4 0 0 .33 0 . 3 3 tem were greatly exceeded.

Temp., C. -30 -30 -30 -30 -30 -30 -40 -40 ular weight ceilings previously

_ - ~ __-- _- Times of Addition, Min:-- - It was also observed that the 10 5 5 5 10 9 9 product molecular weight con- 10 10 10 9 9

Olefin 85 77 lo 60 90 60 120 240 tinued t o increase with increas-

AlBra soln. HBr

TPmC of product 35 25 9 . 5 14.1 18.7 3 .35 3 .63 3 .38 ing olefin-to-catalyst mole ratio

all feeds being started simultaneously. Approximately 0.67 of n-butane solvent was initially present in reactor, shown by the results of experi- ments BS-16,BS-14, and BS-15. This indicated the possibility

15 30

lo 15

RTPC of product 1.01 . . . 0 . 9 4 0 .99 1.00 0 .84 0 .86 0 . 8 4 a Aluminum bromide solution in n-butane, HBr gas, and olefin added at constant rate over given time interval,

* Moles of olefin per mole of AlBra per minute.

under certain conditions as

Olefin feed rate was same in both stages of reaction. Thickening power and relative thickening power, defined in (6).

Documents

Metering of Powdered Solids in Gas-Solids Mixtures