Device for Feeding Liquids at Specified Rates H A R V E Y DIEHL, Iowa State College, Amos, Iowa, AND CLIFFORD H A C H , G. Frederick Smith Chemical Company, Columbus, O h i o
THE
problem of feeding two liquids into a reaction vessel continuously in specified amounts may be solved by the apparatus shown in Figure 1. Liquids of densities d, and d, which must be delivered in volumes vi and 02 are contained in chambers 1 and 2, respectively. T h e pressure above the liquids, P I , is sufficiently below atmospheric pressure, P , in the mixing chamber so that the liquids flow only when stopcocks 3 and 4 are opened and if air is bled into !he apparatus through capillary tube 5 and bubbler 6 . The relation between P, and P when stopcocks 3 and 4 are open and no liquids are flowing is Pi dihl = P Pi dnhz = P Since the pressure is the same above and below each liquidt h a t is, PI and P,respectively-it follows that dih = d 2 h Thus,the heights of the two liquids are inversely proportional t o their densities. When air is admitted through the bubbler, PI decreases and this is offset by a flow of both liquids from the chambers. The rate at which the height of each liquid falls is inversely proportional to the densities of the liquids. Obviously the lighter liquid must be placed in the taller chamber, as its height will fall faster. T h e volume of liquid delivered depends on the cross-sectional area of the chamber; the radius of the chambers may be computed by the relations
+ +
7M,*hl*
*r,'h'
= =
d 2 di I n designing the apparatus, the dead spares indicated by hl'and h' cannot be used, but theapparatusshould be constructedso that
and
=
h,'
h' di -.
. I convenient size is chosen for rl and hl', and r, di a n i h' are then computed. r or illustration, consider the vapor-phase bromination of pyridine ( I ) : CJHsN 2Rr = k C s H 4 S E r HBr The molecular weights of the pyridine and bromine are 79 and 2(80), the densities 1 and 3, and the volumes 79 and 53, respectively. As i t is neceasary to 1:sve an excess of hrornine the volumea selected are SO rnl. of pvridine and 65 ni!. of bromine, which must be added slowly hut in these proportions. the reaction taking place in the hot tube attached at 7. If it is desired to run a 6 mole hatch, the volumes involved are 480 ml. of pyridine, V h and 390 ml. of bromine, VI. A convenient radius for the pyridine chamber might be 2.4 cm.; and using
h,' =
+
+
m-lzb* = I't (3:14;(2.5)zh' = 180 it is found that b' = 23.7 cm. h,' i j then found from d 1 hi' = 111'2 = 23.7 - = 7.9 cm. di
VI
h,'
3
and r, is calculated b y
v,
rrl*hl' = VI (3.14) (rIz)7.9= 390 r; = 4.0 cm.
IO
I n practice the exact sizes of glass tubing for the chambers will not be available, but the chambers can be made approximately and the cross-sectional area of one or both adjusted by inserting glass rods. I n the case of a dense material like bromine, glass rods will float, hut a suitable rod cnn easily he made from glass tubing filled nith wire solder or mercury and sealed. The number of these rods required can he determined best by filling the chambers to heights h,' and hZ' with water. Volume VI of water is then added to chamber 1 and V t to chamber 2. Height h," is measured, h,' calculated by
and the level of liquid 2 adjusted to the calculated height by adding glass rods. T o set the apparatus in operation volumes VI and V , are placed in their respective chambers, and the pressure above the liquide is decreased by applying suction a t 10. With stopcock 8 closed and screw clamp 9 closed, stopcock 3 or 4 is cautiously opened and air allowed to bubble up through the liquid until it stops and liquid begins to drip out. Both stopcocks, 3 and 4, are then opened. An initial flow of one liquid will probably occur, aut* matically adjusting heights hl and hl, so that hidl = h,d, after which the flow stops. Air is then admitted b y opening screw clamp 9, which permits liquids in chambers 1 and 2 to flow. The bubbles of air passing are a convenient indicator for adjusting the rate of flow of the liquids. The reaction vessel to which the apparatus is attached should be arranged so that pressure P remains constant. I n the case of the bromination of pyridine, where the vapors pass over pumice in a tube, the accumulation of liquid on the pumice may cause the pressure to change slightly, disrupting the Bow of the liquids from the chambers. I n such a csse a stopcock such as 11 placed on the mixing chamber can be left open to the atmosphere.
Figure 1. Diagram of Apparatus
LITERATURECITED
(1) Hertog and Wibaut, Rec. trap. chim.. 51, 381 (1932): U. 9. Patent 1,977,662(Oct. 23, 1934), asfiianed to Dow Chemical CO.
119
