Humidity & Vapour Pressure (1990) (1991)

Transcription

1 Humidity & Vapour Pressure 1(i). A mixture of Ethyl Acetate vapor and air has a relative saturation of 50 percent at 30 C and a total pressure of 100 kn / m2. If the vapor pressure of Ethyl Acetate at 30 C is 16 kn / m3, (a). The percentage of air is. (b). The molal saturation is.. (1990) 2. Fill in the blanks: (i). A wet paper pulp contains 75% water. After 100 kg of water removed in a dryer, it is found that the pulp is now containing 30% water. The weight of the original pulp is (ii). The weather bureau reports a dry bulb temperature of ambient air as 29 C and relative humidity of 80%. The barometer read 750 mm hg. The percentage humidity of ambient air is (Vapor pressure of water at 29 C = 30 mm Hg.). (iii). H 2 S is produced from the reaction, FeS + 2HCL FeCl 2 + H 2 S; 120 kg of FeS react with 150 kg of HCL and 0.5 kmol of H 2 S has been produced. The degree of completion of the reaction and the limiting reactant is (iv). The heat absorbed for isothermal reaction,c 4 H 10 (g) C 2 H 4 (g) + C 2 H 6 (g); At 298 k and 1 atm pressure is Standard heat of combustion, kj /mol: C 4 H 10 (g) = ; C 2 H 4 (g) = ,C 2 H 6 (g) = (1991) 2(e) An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates kg of water. The amount of solids handled by the system in kgs is (A) 4000, (B) 9000, (C) 4600, (D) 3000, 2(f) 1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is (A) 520, (B) 200, (C) 400, (D) 500, 2(g) Assuming that CO 2 obeys perfect gas low, calculate the density of CO 2 (in kg/m 3, at 0 0 C and 2 atm.

2 (A) 1, (B) 2, (C) 3, (D) 4, 2(h) Pure O 2 is mixed with air to produce an enriched air containing 50 volume % of O 2. The ratio of moles of air to O 2 used is (1995) 2.17 In a mixture of benzene vapour and nitrogen gas at a total pressure of 900 mm Hg, if the absolute humidity of benzene is 0.2 Kg benzene/kg nitrogen, the partial pressure of benzene in mm Hg is : a. 180, b. 60.3, c. 720, d. 200, (1996) 7. CaCO3 slurry has to be dried. The drier is designed to remove 100 kg moisture per hour. Air at 20 C and 40% relative humidity, enters the drier and leaves at 650C and 65% relative humidity. What is the weight (in kg) of bone-dry air required per hour? The atmospheric pressure is 103 kpa. If the humidity of the air entering the drier can be varied, what is the minimum amount of dry air required? The constants for Antoine equation for vapour pressure of water in mm Hg may be taken as A = , B = , and C = (1999) 2.11 Fresh orange juice contains 12% (by weight) solids and the rest water. 90% of the fresh juice is sent to an evaporator to remove water and subsequently mixed with the remaining 10% of fresh juice. The resultant product contains 40% solids. The kg of water removed from 1 kg fresh juice is (2002) A) 0.4 B) 0.5 C) 0.6 D) ) Air at a temperature of 20 0 C & 750 mm Hg pressure has a relative humidity of 80%. What is its percentage humidity? Vapour pressure of water at 20 0 C is 17.5 mm Hg. a) b) 80 c) d) (2003) 42. A vessel of volume 1000 m 3 contains air which is saturated with water vapour. The total pressure and temperature are 100 kpa and 20 0 C, respectively. Assuming that the vapour pressure of water at 20 0 C is 2.34 kpa, the amount of water vapour (in kg) in the vessel is approximately (A) 17 (B) 20 (C) 25 (D) 34

3 (2004) 4. A dehumidifier (shown below) is used to completely remove water vapor from air. Which ONE of the following statements is TRUE? (2009) A. Water is the ONLY tie component B. Air is the ONLY tie component, C. BOTH water and air are the components D. There are NO tie components Solutions 5(vi). A binary hydrocarbon liquid mixture of A and B (K = 1.5) containing 60 mole percent A in flash vaporized. The mole fraction of A in the liquid product is (1990) Q.37 The vapor-liquid equilibrium curve of a binary mixture A-B, may be approximated by a linear equation over a narrow range of liquid mole fractions ( 0.2 < xa < 0.3) as follows * ya xa ya is the mole fraction of A in the vapor. 100 moles of a feed ( xa,f = 0.28) is batch distilled to a final residue ( xa,w = 0.2). Using the Rayleigh equation, the number of moles of the residue left behind in the distillation unit, up to 2 digits after the decimal point, is (2013) Stoichiometry, Ideal Gas & Fundamentals 11(i). Pure propane (C5H8) is burnt in an excess of air to give following analysis of combustion products in volume percent: CO2 = 5.0, CO = 3.5, H2 O = 11.4, O2 = 7.0 and N2 = 73.1 Calculate the percentage of excess air used. (1990)

4 12(ii). Limestone mixed with coke is being burnt kiln. An average analysis of the limestone is CaCO 3 : 84.5%, MgCO 3 :11.5% and the rest inert. The coke contains 76% carbon, 21% ash and 3% moisture. The calculation of CaCO 3 is only 95% complete and that of MgCO 3 90%. The carbon in the coke is completely burnt of CO 2. The kiln is fed with 1 kg of coke per 5 kg limestone. Calculate weight percent CaO in the product leaving the kiln. (1991) 2(a). It is desired to make 100 kg of a solution containing 40% salt by mixing solution A containing 25% salt and solution B containing 50% salt. The mass in kg of solution A required is. 2(b). (1992) 1.2 g atoms of carbon and 1.5 g moles of oxygen are reacted to give 1 g mole of carbon dioxide. The limiting reactant is. The percent excess reactant supplied is. 11. The concentration of SO 2 in the flue gases from a boiler was found to be 0.2 kg/m 3 at N.T.P. Determine the concentration of SO 2 in parts per million at N.T.P. Assume that the gases are perfect. (1992) 12(a). The analysis of the gas entering the secondary converter in a contact Sulphuric acids plant 4% SO 2, 13% O 2 and 83% N 2 (volume %). In the converter SO 2 is oxidized to SO 3. The gases leaving converter 0.45% SO 2 on an SO 3 free basis (volume %). Calculate the percent conversion of SO 2. 12(b). Dry methane is burned with dry air. Both are at 25 C initially. The flame temperature is If complete combustion is assumed how much excess air is being used? The reaction is, CH 4 + 2O 2 CO 2 + 2H 2 O Standard heat of reaction = x 10 3 J/g mole of CH 4 reacted. Mean molal specific heat of gases between 25 C and 1300 are in J/(g mole) ( K). CO 2 = 51.88; H 2 O = 40.45; O 2 = 34.01; N 2 = 32.21; (1992)

5 2(a) kg of a solution containing 50% by weight of a salt dissolved in it is cooled. 400 kg of anhydrous salt is separated out. The solubility of the salt at the lower temperature is kg/100 kg of water is, (A). 80; (B). 50; (C). 40; (D). 20 2(b). Methane is completely burned with air. The possible volume percent of carbon dioxide (on dry basis) in the flue gases is, (A) (B) (C) (D) (1993) 12. Iron pyrites (FeS 2 ) is burned with air in 100% excess of that required to oxidize all iron to Fe 2 O 3 and all sulphur to sulphur dioxide. Calculate the composition of exit gases, if 80% of sulphur is oxidized to sulphur trioxide and the rest to sulphur dioxide. All iron is oxidized to Fe 2 O 3 (1993) 11. The Orsat analysis of a flue gas is CO % O 2 7.1% N2 80.2% Determine the percent excess air used in the combustion. The nitrogen present in the flue gas is contributed by air only. (1995) 11. A hydrocarbon is burnt with excess air. The Orsat analysis of the flue gas shows % CO 2, 3.78 % O 2 and % N 2. Calculate the atomic ratio of C : H in the hydrocarbon and the % excess air. (1996) 12. Methanol vapour can be converted into formaldehyde by the following reaction scheme CH 3 OH + ½ O 2 HCHO + H 2 O ; CH 3 OH HCHO + H 2

6 The fresh feed to the process was 0.5 kg mol/ h O 2 and an excess methanol. All of the O 2 reacts in the reactor. Formaldehyde and water are removed from the product stream first, after which H 2 is removed from the recycled methanol. The recycle flow rate of methanol was 1 kg mol/h. The ratio of methanol reacting by decomposition to that by oxidation was 3. Draw the flow diagram and then calculate the per pass conversion of methanol in the reactor and the fresh feed rate of methanol (1996) 2.4 Pure carbon is com,pletelly burnt in oxygen. The flue gas analysis is 70% CO 2, 20% CO and 10% O 2. The percent excess oxygen used is A) 20, B) 12.5, C) 0, D) 10, (1997) 2.7 A sample of well water contains 140 g/m 3 Ca 2+ ions and 345 g/m 3 Na + ions. The hardness of the sample of water, expressed in terms of equivalent CaCO 3 in g/m 3 [assuming atomic masses of Ca : 40, Na : 23, C : 12 and O : 16 ] is A) 350, B) 485, C) 140, D) 345, (1998) kg/h of an aqueous solution of 20% Na 2 CO 3 is cooled gradually to t 0 C, to crystallize out Na 2 CO H 2 O. The solubility of Na 2 CO 3 at t 0 C is 2.1%. Calculate the percentage of Na 2 CO 3 recovered in the form of crystals. (Assume no loss of Na 2 CO 3 through the mother liquor adhering to the crystals and no carry over of crystals with the mother liquor). Draw a neat block diagram showing the inlet and exit compositions and flow rates. [ Molecular weight of Na 2 CO 3 can be assumed to be 106 and that of water to be 18 ]. (1998) 1.5. A solution of specific gravity 1.0 consists of 35% A by weight and the remaining B. If the specific gravity; of A is 0.7, the specific gravity of B is A) 1.25, B) 1.3, C) 1.35, D) 1.2, (1999) 1,7 The molar composition of a gas is 10% H 2, 10% O 2, 30% CO 2 and balance H 2 O. If 50% H 2 O condenses, the final mole percent of H 2 in the gas on a dry basis will be A) 10 %, B) 5 %, C) %, D) 20 %, (2000)

7 1.11 Methane is mixed with stoichiometric proportion of oxygen and completely combusted. The number of additional specifications required to determine the product flow rate and composition is A) 0 B) 1 C) 2 D) 3 (2002) 38) 6 g of carbon is burnt with an amount of air containing 18 g oxygen. The product contain 16.5 g CO 2 and 2.8 g CO besides other constituents. What is the degree of conversion on the basis of disappearance of the limiting reactant? a) 100% b) 95 % c) 75 % d) 20 % (2003) 39) An aqueous solution of 2.45% by weight H 2 SO 4 has a specific gravity of The composition expressed in normality is a) b) c) d) (2003) 42) A sample of natural gas containing 80% Methane (CH 4 ) and the rest Nitrogen (N 2 ) is burnt with 20% excess air. With 80% of the combustibles producing CO 2 and the remainder going to CO the Orsat analysis in volume percent is a) CO 2 : 6.26 CO : 1.56 O 2 : 3.91 H 2 0 : N 2 : b) CO 2 : 7.42 CO : 1.86 O 2 : 4.64 N 2 : c) CO 2 : 6.39 CO : 1.60 O 2 : 3.99 H 2 0 : N 2 : d) CO 2 : 7.60 CO : 1.90 O 2 : 4.75 N 2 : (2003) 6. The weight fraction of methanol in an aqueous solution is The mole fraction of methanol X M satisfies. (A) X M < 0.5 (B) X M = 0.5 (C) 0.5 < X M < 0.64 (D) X M > 0.64 (2004) Statement for Linked Answer Questions 80 & 81 : kg of C 3 H 8 is burnt with 1160 kg of air (Mol. Wt. = 29) to produce 88 kg of CO 2 and 14 kg of CO C 3 H O 2 = 3 CO H 2 O

8 What is the percent excess air used? A) 55 B) 60 C) 65 D) What is the % carbon burnt? A) 63.3 B) 73.3 C) 83.3 D) 93.3 (2007) 31. Air (79 mole % nitrogen and 21 mole % oxygen) is passed over a catalyst at high temperature. Oxygen completely reacts with nitrogen as shown below, 0.5 N 2(g) O 2(g) NO (g) 0.5 N 2(g) + O 2(g) NO 2(g) The molar ratio of NO to NO 2 in the product stream is 2:1. The fractional conversion of nitrogen is A) 0.13 B) 0.20 C) 0.27 D) 0.40 (2008) Common Data for Questions 71, 72 and 73 : Methane and steam are fed to a reactor in molar ratio 1 : 2. The following reactions take place, CH 4(g) + 2H 2 O (g) CO 2(g) + 4H 2(g) CH 4(g) + H 2 O (g) CO (g) + 3H 2(g) where CO 2 is the desired product, CO is the undesired product and H 2 is a byproduct. The exit stream has the following composition Species CH 4 H 2 O CO 2 H 2 CO Mole % The selectivity for desired product relative to undesired product is A) 2.3 B) 3.5 C) 7 D) The fractional yield of CO 2 is (where fractional yield is defined as the ratio of moles of the desired product formed to the moles that would have been formed if there were no side reactions and the limiting reactant had reacted completely) A) 0.7 B) 0.88 C) 1 D) The fractional conversion of methane is A) 0.4 B) 0.5 C) 0.7 D) 0.8 (2008) Q.32 A saturated solution at 30 C contains 5 moles of solute (M.W.=50 kg/kmol) per kg of solvent (M.W.=20 kg/kmol). The solubility at 100 C is 10 moles of the solute per kg of the solvent. If 10 kg of the original solution is heated to 100 C, then the weight of the additional solute that can be dissolved in it, is (A) 0.25 kg (B) 1 kg (C) 2 kg (D) 3.34 kg

9 (2010) Q.33 The products of combustion of methane in atmospheric air (21% O 2 and 79% N 2 ) have the following composition on a dry basis : Products Mole % CO O CO 0.53 N The ratio of the moles of CH 4 to the moles of O 2 in the feed stream is (A) 1.05 (B) 0.60 (C) 0.51 (D) 0.45 (2010) Q. 32 The following combustion reactions occur when methane is burnt. CH O 2 CO H 2 O 2 CH O 2 2 CO + 4 H 2 O 20 % excess air is supplied to the combustor. The conversion of methane is 80 % molar ratio of CO to CO 2 in the flue gas is 1 : 3. Assume air to have 80 mol % N 2 and rest O 2. The O 2 consumed as a PERCENTAGE of O 2 entering the combustor is (A) 20 (B) 62.5 (C) 80 (D) 83.3 (2011) Material Balance 11(ii). For the reaction A B, the process flow diagram is shown in figure.1.the fresh feed of A contents 0.5 % of inert by volume. 80% conversion per pass of A fed to the reactor is obtained. The concentration of inert going into the reactor (after mixing with the recycle stream) must be held at 2% by volume. All streams are ideal gases and the process is at steady state. How many moles need to be recycled per mole of total feed to the reactor at (1). (1990)

10 6. Methanol is produced by the reaction of CO with H 2 CO + H 2 CH 3 OH Only 15% of carbon monoxide entering the reactor is converted to methanol. The methanol formed is condensed and recovered completely. The unreacted CO and H 2 are recycled back to the reactor. The feed will contain H 2 and CO in the ratio of 2 : 1. For 3200 kg/hr of methanol produced, calculate I. Kg mole/hr of fresh feed, II. Kg mole/hr of recycle gas, Mole. Weight of CH 3 OH = 32. (1995) 2.2 The reaction A + B C has been conducted in a reactor as shown

11 2.2 (i) The number of boundaries around which material balances can be written are a. 1, b. 6, c. 3, d. 4, 2.2 (ii) The number of independent balances (material) that can be made around the reactor are a. 1, b. 2, c. 3, d. 4, (1996) 1.5 In the system as shown in Fig. 1.5 each stream contains three components. The maximum number of independent material balances is

12 A) 3, B) 4, C) 6, D) 9, (1997) 2.5 A flow sheet is given in Fig If the single-pass (once-through) conversion of A to B is 20%. Then the rate of recycle R (moles/hr) is A) 300, B) 400, C) 500, D) 600, (1997) 12. Sea water is desalinated by reverse osmosis as shown in Fig. 12.

13 All compositions are on mass basis. Calculate R/E. (1997) 3. Ethylene Oxide is produced by the oxidation of Ethylene over a catalyst. Safety considerations dictate that the gaseous mixture entering the reactor should contain 10 mol Air per mol Ethylene. The conversion per pass is 22%. The Ethylene oxide formed is completely condensed out and the remaining gases recycled. Make up oxygen is added to maintain the requisite oxygen levels. For a plant producing 440 kg/h of Ethylene oxide. (a) Calculate the quantity of pure makeup oxygen to be supplied, in kg/h, in steady; state operation, (b) Draw a neat block diagram showing the major units, flows and compositions, and indicate the envelope / boundary around which the requisite mass balance(s) is/are being made. The relevant reaction is represented by 2 C 2 H 4 + O 2 2 C 2 H 4 O (g) (g) (g) [ Assume atomic masses as : C = 12, 0 = 16, H = 1 ] (5) (1998) 6. It is proposed to produce acetaldehyde by oxidation of ethanol in gas phase C 2 H 5 OH (g) + ½ O 2 (g) CH 3 CHO (g) + H 2 O (g)

14 The ratio of air to ethanol in the fresh feed (before it is mixed with recycle stream) is 10 to 1. The conversion of ethanol on a single pass through the reactor is 25%. The unreacted ethanol is completely separated from the reaction products and recycled. What is the ratio of recycle stream to the fresh feed stream? What is the composition of the outlet stream from the reactor in mass fraction and mole fraction? (1999) 19. The reaction A 2B + C takes place in a catalytic reactor (see diagram below). The reactor effluent is sent to a separator. The overall conversion of A is 95%. The product stream from the separator consists of B, C and 0.5% of A entering the separator, while the recycle stream consists of the remainder of the unreacted A and 1% of B entering the separator. Calculate the single pass conversion of A in the reactor. molar ratio of recycle to feed. (2000) 2.3 A butane isomerization process produces 70 kmol/h of pure isobutane. A purge stream removed continuously contains 85% n butane and 15% impurity (mole %). The feed stream is n- butane containing 1% impurity (mole %). The flow rate of the purge stream will be A) 3 kmol/h B) 4 kmol/h C) 5 kmol/h D) 6 kmol/h (2001)

15 CH-5 The process schematic of a propane dehydrogenation plant is shown below. It is desired to set up a simplified version of the material balance for this plant. Assume that the only reaction is the dehydrogenation of propane to propylene there are no side reactions. The yield of propylene per pass is 30% (i.e., 30% of the propane entering the reactor is converted to propylene). Assume that the amount of carbon formed on the catalyst is negligible. The product flow rate (stream S 5 ) is 50 kmol/h. Calcutta the flow rtes of all the other streams. Notice that all streams except stream S, are pure. (2001) kg of saturated aqueous solution of a highly soluble component A at 60 0 C is cooled to 25 0 C. The solubility limits of A are (0.6 kg A)/(kg water) at 60 0 C and (0.2 kg A)/(kg water) at 25 0 C. The amount, is kgs, of the crystals formed is A) 0.4 B) 0.25 C) 0.2 D) (2002) 41) Na 2 SO 4, 10 H 2 O crystals are formed by cooling 100 kg of 30% by weight aqueous solution of Na 2 SO 4. The final concentration of the solute in the solution is 10%. The weight of crystals is a) 20 b) 32.2 c) d) (2003)

16 5. A distillation column separates 10,000 kg/h of a benzene-toluene mixture as shown in the figure below. In the figure, X F, X D, and X W represent the weight fraction of benzene in the feed, distillate, and residue, respectively. The reflux ratio is (a) 0.5 (B) 0.6 (C) 1.0 (D) 2.0 (2004) kg of Na 2 SO 4 (molecular weight = 142) is present in 330 kg of an aqueous solution. The solution is cooled such that 80 kg of Na 2 SO H 2 O crystals separate out. The weight fraction of Na 2 SO 4 in the remaining solution is (A) 0.00 (B) 0.18 (C) 0.24 (D) 1.00 (2004) 5. A process flow sheet analysis results in the degrees of freedom having a value of 2, which one of the following steps must be next carried out? (a) Identify and add two new independent equations from process model (b) Remove two equations that have been wrongly assumed to be independent (c) Assign values of two variables in the process. (d) Assign value to one variable and remove one equation that was wrongly assumed to be independent. (2005) 41. A metal recovery unit (MRU) of intake capacity 5000 kg/hr treats a liquid product from a plant and recovers 90% of the metal in the metal in the pure form. The unrecovered metal and its associated liquid are sent to a disposal unit along with the untreated product from the plant (see figure below). Find the flow rate (m6) and the weight fraction of the metal (w6). The liquid product flow rate is 7500 higher of composition 0.1 (wt fraction), Assume steady state.

17 (a) m 6 = 7500 kg/hr, w 6 = 0.0 (b) m 6 = 7050 kg/hr, w 6 = (c) m 6 = 4500 kg/hr, w 6 = (d) m 6 = 5600 kg/hr, w 6 = (2005) 42. In the triangular diagram represented below for a batch separation process, a stream F is mixed with a solvent B to produce products R and E. Substance A is the carrier liquid and C is the solute to be extracted. The amounts of B ad E are 1 kg and 1.20 kg respectively. The length FM is 3.1 and length FB is 8.5 units on the figure. The ratio R/E is estimated to be Note : Figure not to scale (a) (b) 2 (c) (d) 2.5 (2005) 43. A feed stream (S1) at 100 kg/hr and containing only A mixes with recycle stream S5 before entering the reactor (see figure below), where the reaction A B takes place. The operation is at steady state. The stream S3 leaving the reactor is separated, without either phase or

18 composition change, into two streams S4 and S5. If the mass fraction of B in S4 is 0.95 and total flow rate of S5 is 10 kg/hr, then the ratio of flow rates of streams (S3/S5), and the flow rate of A in S3 are, respectively. (a) 11 and 110 kg/hr (b) 24 and 240 kg/hr (c) 11 and 5.5 kg/hr (d) 70 and 330 kg/hr (2005) Statement for Linked Answer Questions 76 & 77 : Solvent C is used to extract solute B selectively from, 100 kg/hr feed mixture A+B in a steady state continuous process shown below. The solubility of C in the raffinate and the solubility of A in the extract are negligible. The extract is distilled to recover B in the bottom product. The overhead product is recycled to the extractor. The loss of solvent in the bottoms is compensated by make up solvent S d. The total flow rate of the solvent stream S going to the extractor is 50 kg/hr. The mass fractions (X i s) of some selected streams are indicated in the figure below.

19 76. Distillation bottoms flow rate W and solvent dosing rate S d in kg/hr are (A) W = 50, S d = 50 (B) W = 100, S d = 20 (C) W = 10, S d = 50 (D) W = 50, S d = Feed rate E to the distillation column and overhead product rate T in kg/hr are (A) E = 90, T = 40 (B) E = 80, T = 40 (A) E = 90, T = 50 (B) E = 45, T = 20 (2006) Statement for Linked Answer Questions 78 & 79 : 78. A simplified flowsheet is shown in the figure for production of ethanol from ethylene. The conversion of ethylene in the reactor is 30% and the scrubber following the reactor completely separates ethylene (as top stream) and ethanol and water as bottoms. The last (distillation) column gives an ethanol-water azeotrope (90 mol% ethanol) as the final product and water as waste. The recycle to purge ratio is 34.

20 The reaction is : C 2 H 4 (g) + H 2 O (g) C 2 H 5 OH (g) For an azeotrope product rate of 500 mols/hr, the recycle gas flowrate in mols/hr is A) 30 B) 420 C) 1020 D) For the same process, if fresh H 2 O feed to the reactor is 600 mol/hr and wash water for scrubbing is 20% of the condensables coming out of the reactor, the water flowrate in mols/hr from the distillation column as bottoms is A) 170 B) 220 C) 270 D) 430 (2007) 32. A 35 wt% Na 2 SO 4 solution in water, initially at 50 C, is fed to a crystallizer at 20 C. The product stream contains hydrated crystals Na 2 SO 4.10H 2 O in equilibrium with a 20 wt% Na 2 SO 4 solution. The molecular weights of Na 2 SO 4 and Na 2 SO 4.10H 2 O are 142 and 322, respectively. The feed rate of the 35% solution required to produce 500 kg/hr of hydrated crystals is A) 403 kg/ha B) 603 kg/hr C) 803 kg/hr D) 1103 kg/hr (2008) 34. Carbon black is produced by decomposition of methane : CH 4(g) C (s) + 2H 2 (g) The single pass conversion of methane is 60%. If fresh feed is pure methane and 25% of the methane exiting the reactor is recycled, then the molar ratio of fresh feed stream to recycle stream is A) 0.9 B) 9 C) 10 D) 90 (2008)

21 5. Dehydrogenation of ethane, C 2 H 6 (g) C 2 H 4 (g) + H 2 (g), is carried out in a continuous stirred tank reactor (CSTR). The feed is pure ethane. If the reactor exit stream contains unconverted ethane along with the products, then the number of degrees of freedom for the CSTR is (A) 1, (B) 2, (C) 3, (D) 4 (2009) 28. Pure water (stream W) is to be obtained from a feed containing 5 wt % salt using a desalination unit as shown below: If the overall recovery of pure water (through stream W) is 0.75 kg/kg feed, then the recycle ratio (R/F) is (A) 0.25 (B) 0.5 (C) 0.75 (D) 1.0 (2009) Common Data for Questions 55 and 56 : A flash distillation drum (see figure below) is used to separate a methanol-water mixture. The mole fraction of methanol in the feed is 0.5, and the feed flow rate is 1000 kmol/hr. The feed is preheated in a heater with heat duty Q h and is subsequently flashed in the drum. The flash drum can be assumed to be an equilibrium stage, operating adiabatically. The equilibrium relation between the mole fractions of methanol in the vapor and liquid phases is y* = 4 x. The ratio of distillate to feed flow rate is 0.5.

22 55. The mole fraction of methanol in the distillate is (A) 0.2 (B) 0.7 (C) 0.8 (D) If the enthalpy of the distillate with reference to the feed is 3000 kj/kmol, and the enthalpy of the bottoms with reference to the feed is 1000 kj/kmol, the heat duty of the preheater (Qh in kj/hr) is (A) 2x10 6 (B) 1x10 6 (C) 1x10 6 (D) 2x10 6 (2009) Q. 31 Ammonia is synthesized at 200 bar and 773 K by the reaction N 2 + 3H 2 2NH 3. The yield of ammonia is 0.45 mol/mol of fresh feed. Flow sheet for the process (along with available compositions) is shown below. The single pass conversion for H 2 in the reactor is 20%. The amount of H 2 lost in the purge as a PERCENTAGE of H 2 in fresh feed is (A) 10 (B) 20 (C) 45 (D) 55 (2011) Common Data for Questions 50 and 51 : The reaction A (liq) + B (gas) C (liq) + D (gas), is carried out in a reactor followed by a separator as shown below

23 Notation : Molar flow rate of fresh B is F FB Molar flow rate of A is F A Molar flow rate of recycle gas is F RG Molar fraction of B in recycle gas is Y RB Molar flow rate of purge gas is F PG Molar flow rate of C is F C Here, F FB = 2 mol/s; F A = 1 mol/s; F B /F A = 5 and A is completely converted. Q. 50 If Y RB = 0.3, the ratio of recycle gas to purge gas (F RG /F PG ) is (A) 2 (B) 5 (C) 7 (D) 10 Q. 51 If the ratio of recycle gas to purge gas (F RG /F PG ) is 4 then Y RB is (A) 3/8 (B) 2/5 (C) 1/2 (D) ¾ (2012) Common Data for Questions 48 and 49: A reverse osmosis unit treats feed water (F) containing fluoride and its output consists of a permeate stream (P) and a reject stream (R). Let CF, CP, and CR denote the fluoride concentrations in the feed, permeate, and reject streams, respectively. Under steady state conditions, the volumetric flow rate of the reject is 60 % of the volumetric flow rate of the inlet stream, and CF = 2 mg/l and CP = 0.1 mg/l. Q.48 The value of CR in mg/l, up to one digit after the decimal point, is Q.49 A fraction f of the feed is bypassed and mixed with the permeate to obtain treated water having a fluoride concentration of 1 mg/l. Here also the flow rate of the reject stream is 60% of the flow rate entering the reverse osmosis unit (after the bypass). The value of f, up to 2 digits after the decimal point, is (2013)

24 Energy Balance - Thermophysics 7. The heat reaction at 300 K and at one atmosphere pressure for the following gas phase reaction: A + 3B C; is 50,000 calories per mole of A converted. Data on the molar heat capacity at constant pressure (cal/mol.k) of the various components are: C p for A = x 10-3 T, T in K C p for B = 7 C p for C = 26 Calculate the heat of reaction at 500 K and at one atmosphere pressure (1994) 13. Bituminous coal with a calorific value of KJ/Kg is used for generating steam in a boiler. How much coal has to be burnt to generate 1 MW of energy. Efficiency of combustion is How much air is needed if 50% excess air is to be used. Assume that coal contains 87% carbon and 33% ash. (1995) 13. A feed at 1298 K, consisting of flue gas (CO 2, O 2 and N 2 ) and air, is passed through a bed of pure carbon. The two reactions that occur both go to completion. CO 2 (g) + C(s) 2CO (g), H 0 R at 298 K = 170 kj/mol O 2 (g) + 2C(s) 2CO (g), H 0 R at 298 K = kj/mol The combustor is adiabatic and the product gases exit at 1298 K. Calculate the required moles of CO 2 per mol of O 2 in the feed stream, so that the net heat generated is zero and the bed temperature remains constant at 1298 K. Data : Mean Molar Heat Capacities, Cpm Substance Cpm, kj/(mol)(k) C 0.02 O CO 0.03 CO (1997) 1.5 For the case of a fuel gas undergoing combustion with air, if the air/fuel ratio is increased, the adiabatic flame temperature will A) increase B) decrease C) increase or decrease depending on the fuel type D) not change (2001)

25 2.22 A rigid vessel, containing three moles of nitrogen gas at 30 0 C, is heated to C. Assume the average heat capacities of nitrogen to be Cp = 29.1 J/mol 0 C and Cv = 20.8 J/mol 0 C. The heat required, neglecting the heat capacity of the vessel, is A) J B) J C) 4576 J D) J (2002) 43) Heat capacity of air can be approximately expresses as Cp = x 10-3 T where Cp is in J/(mol)(K) and T is in K. The heat given off by 1 mole of air when cooled at 1 atmospheric pressure from C to C is a) kj b) kj c) kj d) kj (2003) Q are based on the data supplied in the paragraph below One mole of methane undergoes complete combustion in a stoichiometric amount of air. The reaction proceeds as CH 4 + 2O 2 CO 2 + 2H 2 O. Both the reactants and the products are in gas phase. H = kj/mol of methane. 40. Mole fraction of water vapour in the product gases is about (A) 0.19 (B) 0.33 (C) 0.40 (D) If the average specific heat of all the gases/vapour is 40 J/(mol k), the maximum temperature rise of the exhaust gses in C would be approximately equal to (A) 1225 (B) 1335 (C) 1525 (D) 1735 (2004, Both Stoichiometry and Thermophysics) kg/hr of saturated steam at 1 bar (enthalpy kj/kg) is mixed adiabatically with superheated steam at 450 C and 1 bar (enthalpy kj/kg). The product is superheated steam at 350 C and 1 bar (enthalpy kj/kg). The flow rate of the product is A) 711 kg/ha B) 1111 kg/hr C) 1451 kg/hr D) 2051 kg/hr (2008) Common Data for Questions 55 and 56 : A flash distillation drum (see figure below) is used to separate a methanol-water mixture. The mole fraction of methanol in the feed is 0.5, and the feed flow rate is 1000 kmol/hr. The feed is preheated in a heater with heat duty Q h and is subsequently flashed in the drum. The flash

26 drum can be assumed to be an equilibrium stage, operating adiabatically. The equilibrium relation between the mole fractions of methanol in the vapor and liquid phases is y* = 4 x. The ratio of distillate to feed flow rate is The mole fraction of methanol in the distillate is (A) 0.2 (B) 0.7 (C) 0.8 (D) If the enthalpy of the distillate with reference to the feed is 3000 kj/kmol, and the enthalpy of the bottoms with reference to the feed is 1000 kj/kmol, the heat duty of the preheater (Qh in kj/hr) is (A) 2x10 6 (B) 1x10 6 (C) 1x10 6 (D) 2x10 6 (2009, ALSO IN MATERIAL BALANCE) Energy Balance - Thermochemistry 1(ii). The following data on heats of combustion at 25 C are given Compound Heat of combustion at 25 C. n-heptane C7H10 (g) kj / mol Ethyl Alcohol C2H5OH (g) kj / mol Heats of formation of CO2 (g) and H2O (l) are -380 kj / mol and 280 kj / mol respectively. (a). The heat of formation of gaseous n-heptane at 25 C is (b). The heat of formation of gaseous Ethyl Alcohol at 25 C is.. (1990) 12. Pure CO is mixed with 100% excess air and burnt. Only 80% of CO burns. The reactants are at 1000C and the products are at 3000C. Calculate the amount of heat added or removed per Kg mole of CO fed to the reactor.

27 Data : Mean molal specific heats between 25 0 C and T 0 C (given below) in KJ Kg.mole.K are Gas T = C T = C CO CO O N Standard heat of formation at 250C in KJ/Kg mole are CO CO (1995) Q.35 Calculate the heat required (in kj, up to 1 digit after the decimal point) to raise the temperature of 1 mole of a solid material from 100 C to 1000 C. The specific heat (Cp) of the material (in J/mol-K) is expressed as Cp = T, where T is in K. Assume no phase change. (2013)