Relation of Space Velocity and Space Time Yield


45, No. 8. Discussions of spectroscopic procedures with G. B. B. AI, Suther- .... defined as the number of moles of desired product recovered per numb...
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INDUSTRIAL AND ENGINEERING CHEMISTRY

1644

Discussions of spectroscopic procedures with G. B. B. A I , Sutherland were extremely valuable. Literature Cited . .

Cullen, R. E., Trans. Am. Soc. ikfech. Engrs., 75, 43 (1953). Cullen, R. E., Univ. Mich. Eatern. Memo. 81 (December 1950). Davis, T., and Sellars, J., Johns Hopkins University, Applied Physics Laboratory, Project Bumblebee, R e p t . 32 (March 1946). Dodge, R. A., Hagerty, W. W., Luecht, J. W.,York, J. L., Glass, D. R., Stubbs, H. E., and Yagle, R. A., Air Force Tech. R e p t . 6067, Part 2, Wright-Patterson Air Force Base, Dayton, Ohio (Sovember 1950). Ethyl Corp., Detroit, blich., “Aviation Fuels aiid Theii Effect on Engine Performance.” SAVAER-06-5-501, USAF T.O. S o . 06--5-4, 1961. Ganiiett, J. R., Univ. M i c h . Estern. Memo. 7 (July 1947). Gaydon, A. G., “Spectroscopy and Combustion Theory,” 2nd ed., London, England, Chapman and Hall, Ltd., 1948. Hicks, H. H., Jr., and Weir, A . , Jr., Uniu. Mich. Extern. Memo. 73 (December 1950). l\Iorrison, R. E., and Dunlap, R. A, Ibid., 21 (May 1948).

Vol. 45, No. 8

(10) l,Iullen, J. IT’., 11,IXD. EXG.CHEM.,41,1935 (1949). (11) Mullen, J. W., 11, Fenn, J . B., and Garmon, R . C., Ibid., 43, 195 (1951). (12) Mullen, J. W., 11, Benn, J. B., and I r h y , 31. R., “Third Symposium on Combustion. Flame. and ExDlosion Phenomena.” 13. 317, Baltimore, I\Id.,’Williamsand Wilkins Co., 1949. (13) Pearse, R. W. B., and Gaydon, A. G., “Identification of Llolecular Spectra,” 2nd ed., New York, John Wiley 8: Sons, Inc., 1950. (14) Perry, J. IT7., ”Chemical Engineer’s Handbook,’’ 3rd ed., 12. 1600, Ken- York, McGraw-Hill Book Co., 1950, (15) Rudnick, J . Aeronaut. Sei., 14, 540 (1947). (16) Weir, A,, Jr., Rogers, D . E., aiid Cullen, R. E., C n i ~ Mich. , Estern. Memo. 74 (September 1950). (17) Williams, G. C., Hottel, H . C., and Scurlock, il. C., “Third Symposium on Combustion, Flame, arid Explosion Phenomena,” p. 21, Baltimore, h l d . , Killiarns and Wilkins Co., 1949.

RECEIVED for review October 27, 19.52. ACCEPTEDMarcli 1.5, 195.3 Presented as past of the Symposium on Chemisisg.of Combustion before the Division of G a s and Fuel Chemistry at the 122nd Meeting, . ~ Y E R I C A N CHEXICALSOCIETY, Btlantic City, N. J. This work was sponsored by the Office of Ordnance Research, U. S. Army.

e e e

e

Relation of Space Velocity and Space Time Yield

e SHlNJlRO KODAMA, KENlCHl FUKUI, A N D AKlRA MAZUME Foculfy of Engineering, Kyofo Universify, Kyofo, Japan

s

EVERAL authors have discussed the relation of space velocity and space time yield in catalytic react,ors of the fixed-bed type (10, 14). Some have treated this problem through considerable simplification and others have considered special cases. I n the present paper the space velocity-space time yield relation is discussed more generally-Le., all the factors that possibly affect this relation are taken into consideration. For this purpose the exact expression for t’he over-all reaction rate must first be obtained preliminarily by a flow method in a laboratory scale experiment. This rate equation can be expressed in terms of the partial pressure of each component of the reaction mixture, the temperature, and the linear velocity, which is related to the reaction rate only implicitly in the material transfer term. I n order to obtain the space velocity-space t,inie yield relation, therefore, the following factors must be considered : Change of partial pressures Change of reaction temperature Change of material transfer rate The third factor, the change of material transfer rate, which is principally due to the change of linear velocity of feed gas, is considered important in some heterogeneous processes, but in most chemical reactions this factor is not so serious as the other two, if the reaction temperature is not extremely high or linear velocity is not extremely small. Accordingly, in the present treat,ment, this factor may be left out of consideration. The second factor, the change of reaction temperature, depends on the type or structure of the reactor-Le., on whether it. is an isothermal reactor, an adiabatic reactor, a heat-erchanger type of reactor, or a self-heat-exchanger type of reactor. I n addition to these three factors, in a practical sense, another

factor det,erniines the quaiitit,?. of desired product that is actually recovered: This factor m a y be called recovery efficiency, defined as the number of moles of desired product recovered per number of moles o i desired product produced in the reactor. The recovery efficiency is considered to be a function of the linear velocity and the temperature of effluent gaa from the reactor and the partial pressure of the desired product in the final reitntion mixture. This functional relation is not, the same in all recovery equipment, and if information concerning this relation is sufficiently complete in a certain piece of equipment,, it is not difficult to take the influence of recover>-efficiency into account in obtaining the actual space time yield-space velocity relation. It is, therefore, rather a meaningless effort than a laborious work t o attempt to discuss this influence generally. Fundamentals. For discussing the phenomena occurring in a reactor in geqeral, a reaction represented by the following st>oichiometric equation is considered : viAi

+ vnA, + V ~ A+S

=o

(1)

Then, the equat,ioiis of mat,erial balance and of heat halarice are

(i

=

1>2,

. . . . .)

and

where

-++ =v o is

-

-+-+

the reaction rate and v, v mean the forward xntl

INDUSTRIAL AND ENGINEERING CHEMISTRY

August 1953

reverse reaction rates, respectively. H may vary with the type of reactor. The space velocity and space time yield which are represented here by the equations u =

Znzo/W

= (Z

ctt/W)mzo

(4)

z

Z

where @[n1/nzo, f(n1/nzo)l =

*(n,/n20)

Equation 14 gives the relation of nl and I , so that the temperature distribution

T = T(Z)

and

Y =

(n1,

- n1o)/W

[(nldnzo)-

=

all

u/qa, z

(5)

respectively, correlate with each other through Equations 2 and 3. The following relation exists between u and Y (IO):

Y

=

i

I n Equation 2, @, which is originally a function of T; z1 zz . . and u, can be brought into a form expressed in terms of T , nl/nzo and u only, using the following relation obtained by stoichiometric considerations zt = [ 01%

+

Q I V ~

-

VL(~I/%O)

I/[

Zar r

+

can be calculated. The relation of Y and u-namely,

nla and nzo-can

be given

bY

(5’)

?U/(V22a!Z)

. .

*

1645

aizvr

r

from Equation 14, when W is given. Heat-Exchanger and Self-Heat-Exchanger Types of Reactor. In these types of reactor, Equation 3 is expressed in the following form :

- Bvr(n~/?z20) 1 (6)

UD

r

Change of Reaction Temperature Depends on Type of Reactor

Isothermal Reactor. In an isothermal reactor Equation 3 can be disregarded and Equation 2 can easily be integrated. Then the integrated form of Equation 2 for component A I is

where T’ is the temperature of the cooling or heating medium outside the catalyst zone. In these two cases the mathematical treatment is extraordiiiarily complicated and troublesome, and no general discussion is possible, but, for each individual reactor even of these types, the relation of and n~is obtainable ( 7 ) as in the case of the adiabatic reactor, when other quantities are known. All Types of Reactor Are Isothermal When u I s Infinitely large

Equation 7 gives nls, and consequently Y,provided the value nzo is given, so that Y can be given as a function of n20,and consequently of u. Adiabatic Reactor. Equation 3, where H is equal to zero, can be written in the form

Using’Equation 2 for component A1 @ (n1/7220,

1 dn1 S dl

T)= --

and Equation 8, the following relation is obtained:

- olll/+i

[(n1/n20)

Relation of Y to u at Very Large u. So far as the limiting case when u is infinitely large is concerned, all types of reactor can be considered as isothermal, because then the temperature distribution in the reactor approaches uniformity. Provided that the inlet temperature, To,does not change with the linear velocity-i.e., if the preheating temperature ie assumed never to be affected by the increase of the linear velocity-the J’-u relation may be discussed by means of Equation 7 . By a simple procedure it may be proved that the value of Y at very large u is found by substituting the feed composition values lim Y in the rate equation, and that nzo+ m is finite or an infinity of lower order than 1230. I n the latter case the approximate Y-u relation can be obtained by the following procedure: Equation 7, where @ is expressed in terms of ( m l / n n 0is) written in the form

=

Z

where

and By Equation 10, the relation of T and nt/nlo can be obtained graphically in the form

T = f(n1/nzo) (13) and by putting Equation 13 into the integrated form of Equation 9, it follows that

and in Equation 15 [l/@(ml/nzo)] is expanded in ascending powers of (ml/neo)which is infinitesimal when n20 is infinitely large: l/@(ml/nzo)

=

(m1/nzo)Tao

+

a1

(m1lnzo)

+

a2

(mlnzo)2+. , , , 1

where s is always positive. Taking only the first term in this equation for approximation and putting it into Equation 15, we have

INDUSTRIAL AND ENGINEERING CHEMISTRY

1646

Table 1. Reaction

Examples of Y-u Relation at Very Large u

Stoichiometric Equation

Catalytic oxidation of SO2 Hydrogenation of iso-octene Dehydrogenation of n-butane

'/20z

-OzHs f Ha

+ CzHa

=

Oxidation of hydrogen Isomerization of 1-butene Water-gas shift reaction Water-gas shift reaction

+ z/s?'JHs

-

1/3Nz

-

9)'

+ Kpz + K' -

kPa3

-

+

?J331*5

+KP)~

(1

_kp2pa _~1 Kps

0

+ i/zNz 4- a/zHz = 0 -Hz0 + Ha + '/zOs = 0 ' -2-Butene + 1-Butene = 0 -COz + CO + HzO - Ha = 0 -Hz + CO + Hz0 - COz = 0

Catalytic decomposition of NH3-H2

m

kp1.5 a 3 0 . 5

P80.6

k'pi

-SHa

Ammonia synthesis

o+

- k'p1 (l+aa+a4)C.5[(l+ora+a4)0.j+K~0~.'aao.~]z (1 + K p P + K'pi)* kpzpt kP2as (1 + Kpa + K'pz + K " P I ) * [ ( I + a8) + KPa8 f K'P]' kpa - k'pips kP kpz

(1 Hydrogenation of ethylene

lim Y'J

R a t e Equation

+ so2 + = 0 -CCsHis + CsHla + HP = 0 -CaHs + CdHlc - HI = 0 -802

Vol. 45, No. 8

(1 f ad [ ( I

+

013)

+ KPW!

2 1

Pi

PZIpa

Z-[-E~O IJ (1

Pl

kpz

0

- k'p1

+ as)

kP

kpa"

m

Plm

-

+

1 ) ~ p n - m ] I l m + 1, m / ' n + l

Partial pressures of reaction products in feed are considered as zero

and accordingly

*

The case where W O ) is infinite can occur-e.g., when one of the products, the partial pressure of which is zero in feed, strongly retards the reaction. Several examples for the Y-o relation a t very large u, when W )is infinite as well as when it is finite, are tabulated in Table I. Mathematical Properties of Y-u Curve. ISOTHERMAL REMTORS. I n an isothermal reactor in which neither consecutive reaction nor side reaction takes place, the Y-u curve must be monotonic. The proof is presented as follows: From Equations 4 and 15,

JI;

dm1

GGa

= Tp

is obtained, and by differentiating this equation with respect t o n20,i t

follom-s that

fC&(4&)d7n1

+ d ~

m 1 s . I = 0

dnlo

satisfies Equation 19. I t is obvious. however. that this condition is never satisfied from the monotonic property of the 0 - (nl/nAo) relation in the present case. ADIABATIC REACTORS. In an adiabatic reactor, a maximum point occurs in some cases, but not in other cases. The condition of occurrence is given as follows: Equations similar to Equations 17 to 19 in the case of an isothermal reactor are obtained, and the desired condition is

where, in place of function +, 9 in Equation 14 is used. When the form of function is known even graphicdy, the $-l (rnl/n,o)relation can be plotted and the value of ( rnlc/n20)which satisfies Equation 20, if it exists, can be found easily by the following procedure:

*

Let a line parallel to the ?n,/nzo axis cut curve I1 in Figure 1 a t two points, B and C, so that area 1 may become equal to area 2. Then, areas ODBFCE and OABGCE, which represent the right-hand and left-hand sides of Equation 20, respectively,

(17)

/

dmla/n20)

If it is assumed that any maximum or minimum point, where (drnl,/dn2o) vanishes, could exist in the Y-u curve, then from Equation 17 the following condition must hold a t that point:

On the other hand, the left side of Equation 18 can also be written in the form

so that by a partial integration Equation 18 becomes c

4

E

0

___r

Figure 1.

Hence, the necessary condition of the occurrence of a maximum or minimum point is that there exists a value of ( rnl,/nzo) which

I. 11.

(

m1/ n20 1 vs. rnl/npo

No maximum occurs Maximum occurs (area 1 = a r e a 2 )

I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY

August 1953

I

t

1647

I'

i: ,10

.

Mlemmw I .ho .io .io .bo
-

Figure 2.

vs. ml/nzo

Maximum occurs 1. W a t e r - g a r shift reaction ( 9 ) II. Catalytic oxidation o f sulfur dioxide (74)

become equal. So the abscissa of C satisfies Equation 20 and represents (ml,/nzo)maz.I n curve I, a line like this cannot be drawn, and therefore no maximum occurs. By differentiating Equation 17 once more with respect to nm, and after some transformations we obtain the relation

I n the case when Equation 20 is not satisfied for any ( mI./nzo) value, the curve has no extreme value. Therefore, the Y-u curve for an adiabatic reactor has either a maximum or no extreme value. Two examples are shown in Figure 2 for the case when a maximum occurs. Optimum Space Velocity for Reactor Design Is Based on Costs as Well as Technical Matters

Therefore, the point which satisfies Equation 20 is a maximum. The (Y)%==, and ( u)mnz.are calculated from the equations

and

It goes without saying that the optimum space velocity is not necessarily the space velocity which promises the maximum space time yield. To obtain the optimum value of space velocity, we must take such factors into consideration as the construction and equipment costs and the operating costs, as well as technical matters-e.g., recovery and preheating device, mechanical strength of catalyst, etc. It is a preliminary requisite, however, for designing a reactor of a given reaction, to know the nature of the space time yield-space velocity relation. The results obtained in the present paper on the space time yield-space velocity relation may be useful in finding the optimum value of space velocity, using only the exact knowledge of the rate equation for the given reaction. By drawing the + - I - (ml/[email protected]) curve in Figure 1, it is also possible t o examine the influence of feed temperature and feed composition upon the space time yield-space velocity relation, which may also be important for determining the values of these two factors in designing reactors. Nomenclature

Ai AI Az CP,

= = = =

i t h component desired component one re resentative component of initial components molalReat capacity of A,, kcal./mole degree

1648

D

INDUSTRIAL AND ENGINEERING CHEMISTRY =

length of periphery of heat transfer

= surface areaof heat transfer/length of catalyst zone, meters

function heat received by catalyst zone per unit volume per unit time through its periphery, kcal. per hour per cu. meter of catalyst kl k’, R“, . . . ., K , K’,K”, , . . = constants in rate equation, which are functions of temperature only = length of catalyst zone, meteis 1 nL = flow rate of 8,. moles per hour P = total pressure in reactor, atmospheres p , = partial pressure of A,, atmospheres = heat of reaction, kcal. per mole of A I produced = total sectional area of catalyst zone, square meters T = reaction temperature, O C. 0’ = over-all heat transfer coefficient, kcal./sq. meter hour C. u = linear velocity of fluid, meters per hour W = packed volume of catalyst, cubic meters Y = space time yield, moles of A I per hour per cubic meter of catalyst zL = mole fraction of A, = mole ratio of A , to A2 in feed = n10/n20 = stoichiometric ratio of A , to A1 in reaction, having posiY$ tive and negative sign accordingly as A1 belongs to the initial or final system-Le., V I = -1, P Z < 0, and v 1 = 0 if = A , is an inert component = space velocity, moles of feed per hour per cubic meter of u catalyst = reaction rate, moles of 41 per hour per cubic +, \E, rp, meter of catalyst = fractional conversion relating to component A2 =

f H

Vol. 45, No. 8

Subscript 0 designates entrance conditions Subscript e designates exit conditions

= a =

.

. .

2

O

n20

- %e

literature Cited (1) Benton, A. F., and Elgin, J. C., J . Am. Chena. Soc., 49, 2426 (1927). (2) Biill, R., J . Chem. Phys., 19, 1047 (1951). ( 3 ) Dodd, R. H., and Watson, K. &I.,TTans. A m . Inst. Chem. Engrs., 42,263 (1946). Hay. R.G.. Coull. J..and Emmett. P. H.. I w . ESG.CHEX..41. 2809 (1949). Kal’kova, K. T., and Temkin, M., Zhur. Fiz. Khim.,23, 695 (1949). Kiperman, S. L., and Granovskaya, V. Sh., I b X , 25,557 (1951). Kodama, S.,Fukui, K., and Tanaka, H., J . Chem. Soc. Japan (Ind.Ghem. Sec.), 54, 303 (1951). Kummer, 5. T., and Emmett, P. H., IND. EXG.CHEU.,35, 677 (1943). Laupichler, F . G., Ibid., 30, 578 (1938). Perry, J. H., “Chemical Engineer’s Handbook,” 3rd ed., p. 329, New York, hlcGraw-Hill Book Co. (1950). Pyzhev, ST., and Temkin, M., Acta Physicochim. (U.R.&’,,S.), 13,327 (1940). Tschernitz, J., Bernstein, S., Beckman, R. B., and Hougen, 0. A , , T?ans. Am. Inst. CLem. Engm., 42, 883 (1946). Uyehara, 0. A., and Watson, K. M., IND.ENG.CHEM., 35, 541 (1943). Wilhelm, R. H., Chem. Eng. Progr., 45, 208 (1948). Winter, E., 2.phys. Chem., B13, 401 (1931). Wynkoop, R., and Wilhelm, R. H., Chem. Eny. Proyr., 46,300 (1950). RECEIVED for review M a y 26, 1952.

n2o

a a a

BCCEPTED

February 12, 1953.

Ion Exchange Process for Recovery of Gold from Cyanide Solution F. H. BURSTALL, P. J. FORREST, N. F. KEMBER,

AND

R. A. WELLS

Chemical Research Laborafory, Teddington, Middlesex, England

T

HE precipitation of gold from cyanide solutions with the aid

of metallic zinc is a well-established procedure of the gold mining industry. It combines the advantages of cheapness and simplicity for the treatment of a large number of ores. There are cases, hon-ever, where the usual procedure of cyanidation, followed by filtration and precipitation of gold in the filtrate with zinc, can be carried out only w-ith difficulty. On grinding, some ores give a large proportion of slimes, which make filtration both difficult and expensive. Others contain elements soluble in cyanide solution t o form complexes, which inhibit the precipitation of gold. Adsorption of the gold on activated carbon has been suggested many times in the past as a means of overcoming these difficulties. More recently, a number of workers ( 2 , 3 ) have demonstrated the possibility of adding activated charcoal directly t o leach pulps and of recovering the charcoal, containing adsorbed gold, by floating or screening. The process ha3 been made cyclic by eluting the adsorbed gold, together with any silver that may be present, from the charcoal n-ith hot sodium cyanide solution (8). The charcoal may then be used for a further adsorption stage. .4 number of gold mills are operating plants based upon this cyclic process. The possibility of using an anion exchange resin for the recovery of gold was first demonstrated using a chloride solution of gold ( 7 ) . Later, Hussey ( 4 ) investigated the possibility of using

the Reakly basic anion exchange resin, Amberlite 1R-4B, for the adsorption of gold from cyanide solutions. By using a countercurrent adsorption and regeneration system an adsorption of 95.4% of the gold and 79.0% of the silver present in a pregnant solution of a leach pulp, prepared from ore from the Buckthorn mining district, was obtained. Loss of resin by attrition mas shown t o be less than 1% after 33 days agitation with a pulp of minus 100-mesh ore containing 31% solids. I n view of the high p H (>10.0) of a normal pregnant solution it is perhaps surprising that the gold capacity of the resin was sufficiently high to make it possible to operate the process, but it must be emphasized that good recovery of gold was achieved only by the use of a very high resin t o pulp ratio. This paper describes an investigation into the adsorption of gold from cyanide solutions on the strongly basic resin, Amberlite IRA-400. The work has been extended to a study of the behavior of other metals, including silver, copper, iron, cobalt, nickel, and zinc and anions other than cyanide, such as sulfate, thiosulfate, and thiocyanate, likely t o occur in commercial cyanide solutions. Experiments were carried out on clear solutions and not on unfiltered pulps, but in view of the experiences of earlier workers, it appears likely that the process suggested could be readily applied, after suitable modification of practical technique] to pregnant pulp solutiona. All the heavy metal complex cyanides examined, including