• Author / Uploaded
• Valentina Baldovinos

Citation preview

1)

.DEPARTMENT OF CHEMICAL ENGINEERING BALANCE OF MATERIAL IN NON-REACTIVE SYSTEMS 300 kg of a mixture containing 10 wt. % of a component A, 10 wt. % of B and 80wt % of C is in a storage tank. The goal is to obtain 500 kg of a mixture with the composition of 20 wt. % of A, and 30 wt. % of B. The following is available: a mixture AB containing 90 wt.% of A and 10 wt. % of B, A mixture of BC containing 8 wt. % of B and 92 wt. % of C, and pure component B. What amounts of mixtures AB and BC and pure component B have to be added to the original mixture?

2)

A mixture of ethanol (A) and water (B) is separated in a distillation column. The volumetric flow rate of the feed stream is 5 m3/h. The concentration of ethanol in the feed is cA = 2.800 mol/m3. The distillate leaves the column with a concentration of ethanol cA = 13.000 mol/m3. The volumetric flow rate of distillate is one cubic meter per hour. How much ethanol is lost through the bottoms of the column, in kilograms of ethanol per hour?

3)

A ternary mixture of benzene, ethylbenzene, and toluene is fed to a distillation column at a rate of 105 mol/h. The composition of the mixture in % moles is: 74% benzene, 20% toluene, and 6% ethylbenzene. The distillate flows at a rate of 75 mol/h. The composition of the distillate in % moles is 97,33 % benzene, 2% toluene, and the rest is ethylbenzene. Find the molar flow rate of the bottoms stream and the mass fractions of the three components in the distillate and bottoms stream.

4)

A complex mixture of aromatic compounds leaves a chemical reactor and is fed to a distillation column. The mass fractions and flow rates of distillate and bottoms streams are given in Table 4.25. Compute the molar flow rate and composition, in molar fractions, of the feed stream. Flow rate and composition of distillate and bottoms streams. (kg/h) Flow ωBenzen ωToluen ωBenzaldehid ωBenzoicAci ωMethylBenzoat rat e e e d e e

Distillat e Bottom s 5)

125

0.1

0.85

0.03

0.0

0.02

76

0.0

0.05

0.12

0.8

0.03

The indicator dilution method is a technique used to determine flow rate of fluids in channels for which devices like rotameters and orifice meters cannot be used (e.g., rivers, blood vessels, and large diameter pipelines). A stream of an easily measured substance (the tracer) is injected into the channel at a known rate and the tracer concentration is measured at a point far enough downstream of the injection point for the tracer to be completely mixed with the flowing fluid. The larger the flow rate of fluid, the lower the tracer concentration at the measurement point. A gas stream that contains 1.50 mole% CO2 flows through a pipeline. 20.0 kg of CO2/min is injected into the line. A sample of the gas is drawn from a point in the line 150 m downstream of the injection point and

found to contain 2.3 mol% CO2. (a) Estimate the gas flow rate (kmol/min) upstream of the injection point (after steady state has been reached). (a) If the CO2 concentration at the measurement points (150 m downstream) begins to rise at 18 s after the additional CO2 was first injected. Assuming that the tracer travels at the average velocity of the gas in the pipeline (i.e. neglecting diffusion of CO2), estimate the average velocity (m/s). If the molar gas density is 0.123 kmol/m3, what is the pipe diameter? 6)

A feed stock available at the rate of 1000 mol/h and consisting of (all in mol%) 20% propane (C3), 30% isobutane (i-C4), 20% isopentane (i-C5) and 30% n-pentane (nC5) is to be separated into two fractions by distillation. The distillate is to contain all the propane fed to the unit and 80% of the isopentane fed to the unit and is to consist of 40% isobutane. The bottoms stream is to contain all the normal pentane fed to the unit. Calculate the complete distillate and bottoms analysis.

7)

The conventional method for separating ethyl alcohol from an alcohol/water mixture is by distillation. However, this procedure can at best only produce a product 95% by volume alcohol because alcohol and water form a constant boiling mixture, called an azeotrope, of that composition. Simple distillation cannot eliminate the azeotrope. Instead, if a pure alcohol product is desired, benzene is added to the feed solution. The benzene itself forms an azeotrope with water but one, which has a lower boiling point than the alcohol, and thus the alcohol can be purified.

8)

A liquid mixture containing 30.0 mole% benzene (B), 25.0% toluene (T), and the balance xylene (X) is fed to a distillation column. The bottom product contains 98.0 mole% X and no B, and 96.0% of the X in the feed is recovered in this stream. The overhead product is fed to a second distillation column. The overhead product from the second column contains 97.0% of the B in the feed to this column. The composition of this stream is 94.0 mole% B and the balance T. Calculate a. the percentage of the benzene in the process feed (i.e. the feed to the first column) that emerges in the overhead product from the second column. b. the percentage of toluene in the process feed that emerges in the bottom product from the second column.

9)

An equimolar liquid mixture of benzene and toluene is separated into two product streams by distillation. The vapor stream leaving at the top of the column, which contains 97 mole% benzene, is fed to a condenser to undergo complete condensation. The condensed liquid is split into two equal fractions: one is taken off as the final overhead product stream and the other (the reflux) is recycled to the top of the column. The final overhead product contains 89.2% of the benzene fed to the column. The liquid leaving the bottom of the column is fed to a partial reboiler in which 45% of it is vaporized. The vapor generated in the reboiler (the boilup) is recycled to the column, and the residual reboiler liquid is taken as the final bottom product stream. The compositions of the streams leaving the reboiler are governed by the relation: (yB/(1– yB))/(xB/(1–xB)) = 2.25. where yB and xB are the mole fractions of benzene in the vapor and liquid streams, respectively. Using 100 mol of feed as a basis, calculate: a. the molar amounts of the overhead and bottoms products. b. the mole fraction of benzene in the bottoms productc. the percentage recovery of toluene in the bottoms product. Ans. 97% recovery.

10) Given the process shown, find the recycle flow in pounds/hour, the production rate of potassium nitrate, and the recycle ratio.

11) Una lechada compuesta de un precipitado de TiO2 en una solución de agua salada se va a lavar en tres etapas como se muestra en el diagrama de flujo. Si la lechada de alimentación consiste de 1000 lb/h de 20% de TiO2, 30% de sal y el resto de agua, calcúlese la alimentación de agua de lavado a cada etapa. Supóngase que: a) El 80% de la sal alimentada a cada etapa sale con la solución de desperdicio. b) Se operan las etapas de manera que la lechada de salida contenga una tercera parte de sólidos. c) En cada etapa, la concentración de sal en su solución de desperdicio es la misma que la concentración de sal acarreada con la lechada de salida de la etapa.

12) Un material que contiene 75% en masa de agua y 25% de sólidos se alimenta a un granulador a una velocidad de 4000 kg/h. Este material se mezcla dentro del granulador con el producto recirculado de un secador el cual se encuentra después del granulador. El material que sale del granulador y que alimenta al secador tiene 50% en masa de agua. El producto que sale del secador tiene 16,666% en masa de agua. En el secador se pasa aire sobre el sólido que se está secando. El aire que entra al secador contiene 3% en masa de agua y el aire que sale del secador contiene 6% en masa de agua. (a) ¿Cuál es la cantidad de producto recirculado al granulador? (b) ¿Cuál es la cantidad de aire alimentado al secador? 13) Se tiene una planta desalinizadora de agua de mar por ósmosis inversa usando el proceso que se muestra en la figura. Utilizando los datos del diagrama, calcule: a) La velocidad de extracción de salmuera de desperdicio. b) La velocidad de producción de agua desalinizada. c) La fracción de salmuera que sale de la celda de ósmosis que es recirculada. d) La velocidad de alimentación de salmuera a la celda de ósmosis inversa.