Temperature rise

The temperature ratio across a compression stage is Tj/t, = (P2 Adiabatic 

N = Poly tropic exponent, (N - 1)/N = (K - l)/KEp Pi, P2 = Suction, discharge pressures, psia Ti, T2 = Suction, discharge temperatures, °R 

Ludwig states that the usual centrifugal compressor is uncooled internally and thus follows a polytropic path. 

Intercooling can be used to hold desired temperatures for high overall compression ratio applications. This can be done between stages in a single compressor frame or between series frames. Sometimes economics rather than a temperature limit dictate intercooling. 

Ludwig, E. E., Applied Process Design for Chemical and Petrochemical Plants, Vol. 3, Gulf Publishing Co. 

Branan, C. R., The Process Engineer s Pocket Handbook, Vol. 1, Gulf Publishing Co., 1976. 

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Where possible, introducing extraneous materials into the process should be avoided, and a material already present in the process should be used. Figure 4.6h illustrates use of the product as the heat carrier. This simplifies the recycle structure of the flowsheet and removes the need for one of the separators (see Fig. 4.66). Use of the product as a heat carrier is obviously restricted to situations where the product does not undergo secondary reactions to unwanted byproducts. Note that the unconverted feed which is recycled also acts as a heat carrier itself. Thus, rather than relying on recycled product to limit the temperature rise (or fall), simply opt for a low conversion, a high recycle of feed, and a resulting small temperature change. 

Adiabatic operation. If adiabatic operation leads to an acceptable temperature rise for exothermic reactors or an acceptable fall for endothermic reactors, then this is the option normally chosen. If this is the case, then the feed stream to the reactor requires heating and the efiluent stream requires cooling. The heat integration characteristics are thus a cold stream (the reactor feed) and a hot stream (the reactor efiluent). The heat of reaction appears as elevated temperature of the efiluent stream in the case of exothermic reaction or reduced temperature in the case of endothermic reaction. 

Figure 13.16 shows two possible thermal profiles for endothermic plug-fiow reactors. This time the temperature falls for low rates of heat addition and/or high heat of reaction. The temperature rises for the reverse conditions. Under conditions between the profiles shown in Fig. 13.16, a minimum can occur in the temperature profile at an intermediate point between the inlet and exit. 

As the temperature of the liquid phase is increased, the system ultimately reaches a phase boundary, the bubble point at which the gas phase (vapour) begins to appear, with the composition shown at the left end of the horizontal two-phase tie-line . As the temperature rises more gas appears and the relative amounts of the two phases are detemiined by applying a lever-ami principle to the tie-line the ratio of the fractionof molecules in the gas phase to that hn the liquid phase is given by the inverse of the ratio of the distances from the phase boundary to the position of the overall mole fraction Xq of the system. 

With most non-isothemial calorimeters, it is necessary to relate the temperature rise to the quantity of energy released in the process by determining the calorimeter constant, which is the amount of energy required to increase the temperature of the calorimeter by one degree. This value can be detemiined by electrical calibration using a resistance heater or by measurements on well-defined reference materials [1], For example, in bomb calorimetry, the calorimeter constant is often detemiined from the temperature rise that occurs when a known mass of a highly pure standard sample of, for example, benzoic acid is burnt in oxygen. 

The heat capacity of a gas at constant pressure is nonually detenuined in a flow calorimeter. The temperature rise is detenuined for a known power supplied to a gas flowing at a known rate. For gases at pressures greater than about 5 MPa Magee et al [13] have recently described a twin-bomb adiabatic calorimeter to measure Cy. 

Dissolve 36 g. of sodium hydroxide in 160 ml. of water contained in a 500 ml. conical flask, and chill the stirred solution to 0-5° in ice-water. Now add io-8 ml. (32-4 g.) of bromine slowly to the stirred solution exercise care in manipulating liquid bromine ) during this addition the temperature rises slightly, and it should again be reduced to 0-5°. Add a solution of 12 g. of acetamide in 20 ml. of water, in small portions, to the stirred hypobromite solution so that the temperature of the mixture does not exceed 20° the sodium acet-bromoamide is thus obtained in the alkaline solution. Now remove the flask from the ice-water, and set it aside at room temperature for 30 minutes. 

Prepare two solutions, one containing i g. of diphenylamine in 8 ml. of warm ethanol, and the other containing 0-5 g. of sodium nitrite in i ml. of water, and cool each solution in ice-water until the temperature falls to 5°. Now add o 8 ml. of concentrated hydrochloric acid steadily with stirring to the diphenylamine solution, and then without delay (otherwise diphenylamine hydrochloride may crystallise out) pour the sodium nitrite solution rapidly into the weil-stirred mixture. The temperature rises at once and the diphenylnitrosoamine rapidly crystallises out. Allow the mixture to stand in the ice-water tor 15 minutes, and then filter off the crystals at the pump, drain thoroughly, wash with water to remove sodium chloride, and then drain again. Recrystallise from methylated spirit. Diphenylnitrosoamine is thus obtained as very pale yellow crystals, m.p. 67 68° yield, 0 9-1 o g. 

Now heat the furnace, so that the temperature rises slowly in the course of about 2 hours to 260-270°, and then maintain this temperature for at least another 4 hours. Then turn off the heating, and allow the furnace to cool and remain untouched overnight. A considerable pressure will now exist in the cold tube, and must be released before the tube is removed from the box A on no account must the unopened... 

It is a well-known fact that substances like water and acetic acid can be cooled below the freezing point in this condition they are said to be supercooled (compare supersaturated solution). Such supercooled substances have vapour pressures which change in a normal manner with temperature the vapour pressure curve is represented by the dotted line ML —a continuation of ML. The curve ML lies above the vapour pressure curve of the solid and it is apparent that the vapour pressure of the supersaturated liquid is greater than that of the solid. The supercooled liquid is in a condition of metastabUity. As soon as crystallisation sets in, the temperature rises to the true freezing or melting point. It will be observed that no dotted continuation of the vapour pressure curve of the solid is shown this would mean a suspended transformation in the change from the solid to the liquid state. Such a change has not been observed nor is it theoretically possible. 

If the system represented by the point D be heated, the solid A will disappear and two partially miscible liquids will remain. The curve ETD is the ordinary solubility curve for two partially miscible liquids (compare Section 1,8, Fig. I, 8, 1). As the temperature rises, the mutual... 

Reflux a mixture of 68 g. of anhydrous zinc chloride (e.g., sticks), 40 ml. (47 -5 g.) of concentrated hydrochloric acid and 18-5 g. (23 ml.) of sec.-butyl alcohol (b.p. 99-100°) in the apparatus of Fig. 777, 25, 1 for 2 hours. Distil oflF the crude chloride untU the temperature rises to 100°. Separate the upper layer of the distillate, wash it successively with water, 5 per cent, sodium hydroxide solution and water dry with anhydrous calcium chloride. Distil through a short column or from a Claisen flask with fractionating side arm, and collect the fraction of b.p. 67-70° some high boiling point material remains in the flask. Redistil and collect the pure cc. butyl chloride at 67-69°. The yield is 15 g. 

Fit up the apparatus shown in Fig. Ill, 31, 1 the capacity of the Claisen flask should be 100 ml. Place 40 g. (24-6 ml.) of redistilled thionyl chloride in the flask and 60 g. (62 ml.) of dry n-butyl alcohol (b.p. 116-117°) in the dropping funnel. Cool the flask in ice and add the n-butyl alcohol, with frequent shaking, over 1 hour (1). Reflux the mixture gently for 1 hour to complete the reaction and to remove the residual hydrogen chloride. Arrange the apparatus for distillation, and distil under normal pressure until the temperature rises to 120° then distil under diminished pressure (Fig. 11, 20, 1) and collect the di-n-butyl sulphite at 116-118°/20 mm. The yield is 66 g. 

Di-n-hexyl ether. Use 50 g. (61 ml.) of n-hexyl alcohol (b.p. 156-157°) and 6 g. (3-5 ml.) of concentrated sulphuric acid, and heat until the temperature rises to 180°. Pour the reaction mixture into water, separate the upper layer, wash it twice with 5 per cent, sodium hydroxide solution, then with water, and dry over anhydrous potassium carbonate. Distil from a 50 ml. Claisen flask, and collect the fractions of b.p. (i) 160-221° (17 g.), and (u) 221-223° (17 g.). Reflux fraction (i) with 4 g. of sodium and distil from the excess of sodium 9 - 5 g. of fairly prure n-hexyl ether, fraction (iii), are thus obtained. Combine fractions (ii) and (iii) and distil from a little sodium collect the pure n-hexyl ether (19 g.) at 221 - 5-223°. 

Ethyl n-butyrate. Use a mixture of 88 g. (92 ml.) of n-butyric acid, 23 g. (29 ml.) of ethanol and 9 g. (5 ml.) of concentrated sulphuric acid. Reflux for 14 hours. Pour into excess of water, wash several times with water, followed by saturated sodium bicarbonate solution until all the acid is removed, and finally with water. Dry with anhydrous magnesium sulphate, and distU. The ethyl n-but3rrate passes over at 119 5-120-5°, Yield 40 g. An improved yield can be obtained by distilhng the reaction mixture through an efficient fractionating column until the temperature rises to 125°, and purifying the crude ester as detailed above under methyl acetate. 

Place 100 g. of adipic acid in a 750 ml. round-bottomed flask and add successively 100 g. (127 ml.) of absolute ethyl alcohol, 250 ml. of sodium-dried benzene and 40 g. (22 ml.) of concentrated sulphuric acid (the last-named cautiously and with gentle swirling of the contents of the flask). Attach a reflux condenser and reflux the mixture gently for 5-6 hours. Pour the reaction mixture into excess of water (2-3 volumes), separate the benzene layer (1), wash it with saturated sodium bicarbonate solution until eflfervescence ceases, then with water, and dry with anhydrous magnesium or calcium sulphate. Remove most of the benzene by distillation under normal pressure until the temperature rises to 100° using the apparatus of Fig. II, 13, 4 but substituting a 250 ml. Claisen flask for the distilling flask then distil under reduced pressure and collect the ethyl adipate at 134-135°/17 mm. The yield is 130 g. 

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