INDUSTRIAL A N D ENGINEERING CHEMISTRY
August, 1924
sulfuric acid has fallen to 10 per cent or lower. The formation of the sulfone may be ascribed to three possible reactions : 2C"sH~.soaH+(CaHs)zSOz -k (1) 2CsHe HzSO4 +(CaHs)zS02 2H20 (2) ~ (CaH~.)zsOz HzO (3) CeHsSOoH -k C E H---t The first reaction would account best for the apparently constant limiting value which the sulfuric acid attains, as indicated before. The acid formed would in turn be used in the production of more monosulfonic acid with subsequent decomposition, resulting finally in the practically complete decomposition of all the monosulfonic acid into diphenyl sulfone. The second reaction is more likely to occur when the sulfuric acid concentration is high, but the results indicate that very little, if any, sulfone is produced in the early stages of the sulfonation, so that, unless the sulfuric acid present a t this stage would serve to reverse the reaction indicated in the first equation, which does not appear likely, it seems logical to exclude this reaction as a cause of the formation of the sulfone. The third reaction has generally been accepted4 as the chief cause of the formation of the sulfone, but it does not account for the final uniform concentration of sulfuric acid found in the sulfonation samples. It appears logical, therefore, to assign the formation of the sulfone to a combination of the first and third reactions. It has been previously mentioned that in the older process of heating benzene and sulfuric acid together the reaction H2S04 became came to an equilibrium when the ratio HzS0.i 4- HzO 0.78. I n the samples analyzed one of the quantities that was estimated was the water content, provided it was present in sufficient auantitv to make an estimation Dossible. Table I
+
+
gives the ratio H2SOI HzS04HsO and the results obtained indicate that this ratio sufferslittle change as the sulfonation proceeds, even a change in temperature from 130" to 170" C. reducing the ratio only from 0.773 to 0.746. It is obvious, therefore, that the process consists in simply removing the water formed in the reaction, thus making more sulfuric acid available for sulfonation. I n this manner practically all the original sulfuric acid may be converted into monosulfonic acid, and if the reaction is not continued too long the formation of diphenyl sulfone will be negligible. From the standpoint of time consumed and energy required to vaporize the benzene used, the process can best be carried out a t l60"to 170" C. At this temperature the formation of diphenyl sulfone is no more noticeable than at the lower temperatures, as in all cases only traces of the sulfone were observed while the concentration of the sulfonic acid was rising to its well-definedmaximum. The higher temperature might appear to be ideal for the formation of a black charred residue so often found in organic reactions, but even this is scarcely more noticeable than at the lower temperatures at which observations were made. The quantity of charred products rarely exceeded 2 or 3 per cent of the total reaction product. +
4
845
Heat Transfer in Small Pipes' By F. C. Blake and W. A. Peters, Jr. E. 1.DO
PONT DE NEMOUBS & CO., HENRY CLAY, DEL.
ECENTLY the authors had occasion to build a small heater for rapidly heating a liquid to a temperature of 300" C . This heater consisted of 10 feet of copper pipe, '/Isinch internal diameter, l/s-inch external diameter, heated by a low-voltage transformer, using the pipe wall as a resistor. The liquid was forced through the pipe a t B velocity of about 10 feet per second. The high heat transfers obtained with this apparatus led t o an attempt to measure them, a t least approximately, to see how they compared with those obtained by other observers in pipes of larger diameter. The apparatus was modified and arranged as shown in Fig. 1. The temperature of the pipe wall was measured with copper constantan thermocouples, No. 30 wire, soldered to the wall. To measure the water temperature, small holes were drilled in the pipe wall 5 inches apart, opposite the thermocouples, and a small thermocouple was inserted in a glass tube fastened directly opposite the hole with a split rubber stopper. The holes were sufficiently large to permit enough water to escape to give a fair velocity over the thermocouples. The water from the hole near the entrance end of the pipe was not measured. The water from the hole near the exit end and that discharged by the pipe were measured to give the flow through the section between the holes. The holes in crass Section o f r v b b e r x t o p p e t a h o w i n q arronqomint o f thermocouples
n
1
Guyot, Chimie 6' Induslrie, 2, 879 (1919).
N a v a l Stores Commission Goes Abroad for Study Secretary Wallace has appointed J. G. Pace of Pensacola, Fla., a prominent naval stores man of the Gulf Coast, chairman of the Naval Stores Commission which is to visit France and Spain to study the methods used by the French and Spanish turpentine operators in growing and managing the maritime pine and the processes of distillation, manufacture, and distribution of the products of these orchards. The commission is composed of outstanding members of the rosin and turpentine producers of the longleaf pine belt of the South.
FIG.I-RESISTANCE HEATER Steel pipe +inch internal, 0.11-inch external diameter, length 10 inches between thermocouples
the pipe wall were 5 inches from the terminals that brought the heating current into the pipe, this distance being sufficient to prevent errors in the observed temperature of the pipe wall due to conduction along the pipe to the cold massive terminals. This copper pipe was subsequently replaced with steel pipe l/It-inch internal diameter, 0.11-inch external diameter, but with the sample holes and thermocouples 10 inches apart. 1 Received April 16, 1924. Presented as a part of the Heat Transfer Symposium before the Division of Industrial and Engineering Chemistry a t the 67th Meeting of the American Chemical Society. Washington, D. C., April 21 t o 26, 1924.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
846
A series of observations was taken with ea& pipe, usingwater as the fluid. The thermocouples were read with a portable potentiometer accurate to 0.01 millivolt. The water velocities ranged from about 5 to 26 feet per second. The observed data and computed results are given in Table I and plotted in Fig. 2 , using the following notation: h = surface coefficient, B. t. u. per square Eoot per hour pe,r O F.
temperature drop between pipe and liquid K = thermal conductivity of stationary liquid film, B. t. u. per hour per square foot per O F. per foot thickness L0.321 (1 0.00298 t ) where t = water temperature in C.12 D = actual inside diameter of pipe, inches u = average velocity of the liquid, feet per second P = density of the liquid, pounds per cubic foot z = viscosity of the liquid film, centipoises
where Y; = inside radius of pipe r2 = outside radius of pipe H = total heat lost from inside pipe per unit of length k = thermal conductivity of pipe wall t = temperature of pipe wall Then at Z - y 2 dr ~ T Y - y;
K - = g -
Separating the variables and integrating between the limits Y Y
+
The correction for temperature drop through the pipe wall was determined as follows: Neglecting heat loss from the outside and conduction along the pipe, both of which are small compared with the radial heat flow, and neglecting any change in electrical resistance of the pipe wall due to the radial temperature gradient, the heat flowing radially across any section at radius r aiid of unit length is ri Y;
- r2 H - ri
and the area of the section per unit length is 27rr, 2
1-01. 16, No. 8
= r1, t = t; = Y z , t = tz
[ -: :] 1 n 2
tz-jtl=-
27rk
--1
I n computing the corrections, the thermal conductivities of steel and copper were taken as 26 and 220, respectively, in English units. The straight line plotted for comparison is the curve given by Walker, Lewis, and McAdams3 for various experiments with water. The computed data check this curve only approximately in the case of the steel pipe. The results obtained with the copper pipe are considered more accurate. The thermal conductivity of steel varies considerably and the assumed value may be somewhat in error. There was also a possibility of electrical leakage between the heating circuit and the potentiometer in the case of the experiments with the steel pipe. The authors’ method of measuring water temperature by drawing off a portion may give results different from those obtained when a thermocouple is inserted in the center of the pipe. There is a possibility that an undue proportion of the warm and slowly moving film next to the pipe wall was removed, thereby giving a low temperature difference and high heat transfer. This seems improbable, since the heat input calculated from the water flow and its temperature rise was substantially constant for a given voltage. It seems more probable that the disturbance in the stream caused by drawing off a portion of the water may have caused a n undue cooling of the pipe wall a t the hole where the thermocouple was attached, and consequently the measured temperature differences are lower than the average for the whole pipe. The low thermal conductivity of the steel would hinder the smoothing out of such local disturbances. This point could be investigated by attaching a series of thermocouples to the pipe wall in the neighborhood of the sample holes. This has not yet been done. The authors consider it a better method of estimating the pipe wall temperature than a single measurement such as they made. The magnitude of the correction for temperature drop through the steel pipe wall, even with the very thin wall used alid the method of generating the heat in the pipe wall which reduces this drop, serves to emphasize the undesirability of using the steel pipes for measurements of high heat transfers.
Jakol;, Ann. a h y s . , 63, 537 (1920).
8
“Principles of Chemical Engineering,” p. 141.
TABLE I --Entrance--Wall
Water
--Exit-.---. Wall
TEMPERATURES, C-.---
Water -Mean DifferenceMean Flow Obs. Cor. Film Cc./Min. Water CoPPer tube 5 inches effective lenglh, 1 / 1 6 inch inside diameter
Stee2 tube 10 inches effective length, 1 / 1 6 inch inside diameter
hD
h
E-
Dtlp
z
