ChE Refresher I November 2017 [PDF]

Zitiervorschau

CHEMICAL ENGINEERING REFRESHER October - November 2017 For CHEMICAL ENGINEERS LICENSURE EXAMINATION On November 18, 19 and 20, 2017

DR. LEONARDO C. MEDINA, JR.

1.

Formation of large crystals is favored by (A). a low nucleation rate (B). a high degree of supersaturation (C). a high magma density

(D). a low magma density

High degree of supersaturation Unless a solution is supersaturated, crystals can neither form nor grow. After the building up of a supersaturated solution, the first step in crystallization is the ‘phase separation’ of solid from liquid giving rise to ‘birth’ of new crystals. Since the supersaturated solution is not in equilibrium and in a meta stable state, crystal formation gets started in order to relieve supersaturation and the process moves towards equilibrium. As a thumb rule more rapid the supersaturation, faster is the nuclei formation, i.e. faster precipitation of the solids out of the solution, resulting in a lower control on crystallization process. Typical supersaturation value defined as a ratio of the concentration of solute at a particular temperature and equilibrium concentration at the same temperature, lies in the range of 1.1 to 1.5. However, supersaturation affects nucleation and crystal growth in radically different manners. The relation of the degree of nucleation with crystal growth controls the crystal size and size distribution of the products, and is crucial for industrial crystallization process.

2.

The change in enthalpy per unit weight of gas adsorbed on gas free or degassed adsorbent to form a definite concentration of adsorbate is called its (A). integral heat of adsorption (B). differential heat of adsorption (C). heat of wetting (D). hysteresis

Integral heat of adsorption – enthalpy of the adsorbate-adsorbent combination minus the sum of the enthalpies of unit weight of pure solid adsorbent and sufficient pure adsorbed substance to provide required concentration all at the same temperature

Differential heat of adsorption – heat liberated at constant temperature when unit quantity of vapor is adsorbed upon a large quantity of solid already containing adsorbate Heat of wetting – evolution of heat when an adsorbent solid is immersed in a pure liquid Hysteresis – observed when the desorption equilibrium pressure is always lower than that obtained by adsorption

3.

With the lowering of equilibrium pressure at a given temperature, the amount of adsorbate on adsorbent (A). Increases (B). remains the same (C). decreases

(D). may increase or decrease

The amount of an adsorbate adsorbed or desorbed per unit mass of the adsorbent largely depends on the prevailing temperature and pressure. Lower temperature and higher pressure favor adsorption while higher temperature and lower pressure favor desorption. By taking the advantage of these phenomena, both adsorption and desorption are usually carried out in the same vessel in case of batch adsorption. When the adsorbent is nearly saturated, the flow of feed is stopped and the temperature is raised when desorption takes place. A carrier gas or superheated steam may be passed through the bed of adsorbent for carrying away the desorbed substance.

4.

A separation process in which a liquid mixture contacts a non-porous perm-selective membrane and one component is transported through the membrane preferentially is called (A). electrodialysis (B). ultrafiltration (C). pervaporation

(D). microfiltration

Pervaporation (page 20-63)

A membrane separation process used to separate volatile substances from dilute solutions in which the membrane provides a selective barrier. Being independent of vapor–liquid equilibria, pervaporation operates by permeation of a substance through the membrane followed by its evaporation into the vapor phase. The separation is based on a difference in transport rates of individual components in the liquid retentate and vapor permeate on either side of the membrane. The upstream side of the membrane is typically at ambient pressure and the downstream side is under vacuum to allow the evaporation of the selective component after permeation through the membrane. The driving force for the separation is the difference in the partial pressures of the components on either side of the membrane. Electrodialysis (page 20-66) A membrane separation process in which ionic species are separated from water, macrosolutes, and all uncharged solutes. Ions are induced to move by an electrical potential, and separation is facilitated by ion-exchange membranes. Membranes are highly selective, passing either anions or cations and very little else.

Ultrafiltration (page 20-50)

The separation of very fine particles and molecules by filtration through a microporous or semi-permeable membrane . It is used to separate molecules with a molecular weight in the range of 3,000 to 100,000. Ultrafiltration therefore can separate out macromolecules such as proteins, polysaccharides, and fat globules while allowing smaller water and lactose molecules to pass through the membrane as permeate. Microfiltration ( page 20-54) a membrane filtration separation process used to separate fine particles and molecules. The membrane consists of a polymeric microporous material with a pore size of between 0.1 and 10 micrometers. The filtration separation uses an applied pressure across the membrane as the driving force. It is typically used for the separation of proteins from yeast cells following the process of fermentation, clarification of liquid beverages, separating cream from whey in milk, and the sterilization of liquids by filtering out microorganisms.

Problems 5 to 8 are based on the following information: Particles having a size of 0.10 mm, a shape factor of 0.86 and a density of 1200 kg/m3 are to be fluidized using air at 25°C and 202.65 kPa absolute pressure. Air has a density of 2.374 kg/m3 and viscosity of 1.845 x 10-5 Pa-s at 25°C and 202.65 kPa. The void fraction at minimum fluidizing conditions is 0.43. The bed diameter is 0.60 m and the bed contains 350 kg of solids. Calculate the following: 5. The minimum height of the fluidized bed is (A). 2.79 m

(C). 1.03 m

(B). 1.18 m

(D). 1.81 m

6. The pressure drop at minimum fluidizing conditions is (A). 21.2 kPa

(C). 12.12 kPa

(B). 18.2 kPa

(D). 8.95 kPa

7. The minimum velocity for fluidization is (A). 4.374 x 10-3 m/s

(C). 0.04374 m/s

(B). 3.744 x 10-3 m/s

(D). 4.34 m/s

8. Using 4.0 times the minimum velocity, the porosity of the bed is (A). 0.75

(C). 0.46

(B). 0.604

(D). 0.0314

9. Purification of a chemical species by solidification from a liquid mixture where no diluent solvent is added to the reaction mixture and the solid phase is formed by cooling is called a. falling film crystallization

b. melt crystallization c. fractional crystallization d. solution crystallization

Page 18-39 to 18-45

Melt Crystallization A crystallization process used to separate components of a liquid mixture by cooling until a particular component is crystallized as a solid from the liquid phase within a crystallizer. It involves either a gradual deposition of a crystalline layer on a chilled surface of a flowing or static melt, or the fast generation of discrete crystals dispersed in the crystallizer.

Fractional Crystallization A process used to produce pure crystals that involves dissolving crystals in a small amount of a hot solvent and cooling the solution to produce crystals. The process is repeated until a required purity of crystal has been obtained.

Solution Crystallization It is commonly conducted with aqueous solutions of dissolved in organic salts.

Falling Film Crystallization This crystallizes solution with heat sensitive components.

10. A coarse, stationary or vibrating screen consisting of parallel steel bars is (A). stationary screen (B). grizzly (C). reciprocating screen (D). oscillating screen

Grizzly – used for screening large sizes, particularly of 1 inch and over. The large and oversize particles are discharged over the lower right end and the smaller particles pass through the slots between the bars into the hopper directly below. Stationary Screens – are made of punched metal plates or woven wire mesh, usually set at an angle with the horizontal up to about 60°. Suitable for small scale operation such as screening sand, gravel or coal

Oscillating Screens – are characterized by low-speed (300 to 400 rpm) oscillations. Screens in this group are usually used from ½ inch to 60 mesh. Silk cloth are often used. Reciprocating Screens – are standard equipment processing plants for handling fine separations even down to 300 mesh. Used to handle usually dry, light or bulky materials, light metal powders, powdered foods and granular materials.

11. Which of the following changes causes a Type II liquid-liquid system to become a Type I system? (A). an increase in temperature (B). a decrease in temperature

(C). an increase in pressure (D). a decrease in pressure

Type II system – two binary pairs have limited miscibility Type I system – one binary pair has limited miscibility

Type I, one miscible pair

Type II, two miscible pairs

12. In ternary liquid equilibria, the apex of the equilateral triangular diagram represents (A). a pure component (B). a binary mixture

(C). a ternary mixture (D). an insoluble binary system

Each apex of triangle represents 100% pure component

Problems 13 and 14 are based on the following information:

Two thousand kilograms per hour of an aqueous solution of sodium nitrate containing 57.6% NaNO3 is being cooled in a continuous crystallizer from 90°C to 40°C. Cooling water flows counter-currently and its temperature rises from 16°C to 21°C. Water amounting to 2% by weight of the initial solution is being evaporated during cooling. A saturated solution of sodium nitrate at 40°C contains 1.045 kg NaNO3 per kg water. The average specific heat of NaNO3 solution is 0.59 kcal/kg-°C and that of solid NaNO3 is 0.287 kcal/kg-°C. The heat of crystallization of NaNO3 is 59.17 kcal/kg. The average latent heat of vaporization of water may be taken as 575 kcal/kg. The overall heat transfer coefficient has been estimated to be 120 kcal/h-m2-°C. Using the given data: 13. The cooling water rate to be used is (A). 6972.5 kg/h (B). 7962.5 kg/h (C). 9672.5 kg/h (D). 9726.5 kg/h 14. The heat transfer area to be provided is (A). 4.96 m2 (B). 6.49 m2 (C). 5.86 m2 (D). 9.46 m2

15. Partition ratios can be particularly sensitive to temperature when mutual solubility between the feed and extraction solvent involves hydrogen bonding. An interesting example is the extraction of citric acid from water using 1-butoxy-2-propanol as a solvent. Its partition ratio at a temperature of 20°C is (A). 0.65 (B). 0.40 (C). 0.35 (D). 0.20

16.

Rate of leaching increases with increasing (A). temperature (B). pressure

(C). viscosity of solvent (D). size of the solid

Temperature (Page 18-65) The temperature of the extraction should be chosen for the best balance of solubility, solvent-vapor pressure, solute diffusivity, solvent selectivity, and sensitivity of product. In some cases, temperature sensitivity of materials of construction to corrosion or erosion attack may be significant. Temperature is an important parameter in leaching. Temperature of leaching should be as high as possible since at high temperature the solute is more soluble, the concentration of solute in the leach solution is more, the diffusivity of the solute through the solid is higher and the viscosity of the solution is lower, all of which contribute to higher leaching efficiency. However, at higher temperature solvent loss may be more and some undesirable materials may be extracted. Process and Operating Conditions The major parameters that must be fixed or identified are the solvent to be used, the temperature, the terminal stream compositions and quantities, leaching cycle (batch or continuous), contact method, and specific extractor choice. The leaching process will be favored by increased surface per unit volume of solids to be leached and by decreased radial distances that must be traversed within the solids, both of which are favored by decreased particle size. Fine solids, on the other hand, cause slow percolation rate, difficult solids separation, and possible poor quality of solid product. The basis for an optimum particle size is established by these characteristics.

17. To extract copper, pyrite cinders are subjected to chlorinating and roasting with sodium chloride. The copper is contained in the roasted material in the form of cupric chloride (CuCl2) whose content is 11%. The roasted product is leached in a counter-current battery using acidified water obtained as result of washing the flue gas. The inert solid material retains 2 kg of water per kg of solid. Equilibrium is reached in each stage. The number of stages needed in the battery to produce a solution containing 12% (mass) of CuCl2 and extract 98% of the copper from the roasted product is (A). 8 (B). 11 (C). 6 (D). 15

18. An available crusher has been accepting hard rock with a volume-surface mean diameter of 0.069 m and providing a product with a volumesurface mean diameter of 5 x 10-3 m. The power required for crushing 10,000 kg/h of this specific rock is 6.35 kW. Assume that the mechanical efficiency of the unit will remain unchanged. The power consumption using Bond’s law if the capacity were reduced to 9000 kg/h with the same feed characteristics but with a reduction in the volume surface mean diameter of the product to 4 x 10-3 m is (A). 7.35 kW (B). 7.0 kW (C). 6.64 kW (D). 8.64 kW

19. What is the bowl diameter of a disc type sedimenting centrifuge with the following specifications and performance characteristics: speed = 4,000 rev/min, liquid throughput rate = 20 – 200 gal/min and typical motor size = 7.5 Hp? (A). 7.0 in (B). 13 in (C). 24 in (D). 10 in

20. The following equilibrium relationship was obtained during the treatment of an aqueous solution of a valuable solute by decolorizing carbon for removal of coloring impurities: where X = adsorbate concentration per kg of carbon and Y = equilibrium color units per kg of solution measured on an arbitrary scale proportional to the concentration of the colored impurity. It is proposed to reduce the color of the solution to 20% of its original value of 9.0. The quantity of fresh carbon required per 100 kg of the solution in single stage operation is (A). 4.18 kg (B). 5.6 kg (C). 7.2 kg (D). 1.84 kg

Problems 21 and 22 are based on the following information: An acetaldehyde-toluene solution containing 6% acetaldehyde by weight is being treated with water in a three stage co-current extraction battery to remove acetaldehyde. Water and toluene are completely immiscible and the equilibrium distribution of acetaldehyde between them is given by the relation: Y = 2.2 X where: Y = kg acetaldehyde per kg water and X = kg acetaldehyde per kg toluene

21. If 60 kg water is used in each stage per 100 kg of feed, the percentage acetaldehyde extracted is (A). 92.8% (B). 78.2% (C). 83.9% (D). 97.85% 22. The percentage acetaldehyde extracted is, if 100 kg of feed is extracted once with 180 kg of water (A). 93.87% (B). 73.83% (C). 80.83% (D). 88.03%

23. The mutual solubility of two salts can be plotted on the X and Y axes with temperatures as isotherm lines. If both solid-phase KCl and NaCl are present, the solution composition at equilibrium can only be represented by the invariant point (at constant pressure). The solubility ratios in parts per 100 parts water of KCl and NaCl at 40°C are: (A). 34.3 and 27 (B). 20.4 and 28.4 (C). 35 and 27.5 (D). 22.6 and 31.4

24. The sphericity of a cylindrical needle with a height, H, equal to 5.0 times the diameter, D is

(A). 0.696 (B). 0.727 (C). 0.569 (D). 0.277

25. A laboratory test was conducted with a small, tubular-bowl centrifuge on a fermentation broth. At the operating conditions, a sigma value of 7400 ft2 was computed, with a measured volumetric flow rate of 0.11 gal/min. For the commercial plant that will process the same broth, the largest tubular bowl centrifuge available has the following characteristics: bowl speed = 15000 rpm, r2 = 5 cm, r1 = 2 cm, and bowl depth = 100 cm. Using the sigma scale-up theory, the volumetric flow rate of this unit can process is (A). 0.92 gal/min (B). 0.37 gal/min (C). 0.47 gal/min (D). 0.59 gal/min

26. It is desired to recover lead from an ore containing 10% lead sulfide (PbS) and the balance assumed to be silica, 500 tons of ore being treated per 24 hr-day. It is assumed that the concentrate from a single cell is of acceptable purity but the tailings are to be retreated in scavenger cells with return of scavenger concentrate to the rougher. Laboratory findings indicate that if the water to solids ratio L/S = 2.0 and the contact time is 8 min in the rougher and L/S = 4.0 for 15 min in scavenger with mechanically agitated machines of the Denver type. The following compositions will be found for the various products: PbS

SiO2

Feed

10%

90%

Final Concentrate

80%

20%

Rougher Tailings

2%

98%

Scavenger Concentrate

11%

89%

Final Tailings

0.5%

99.5%

The densities of PbS and SiO2 are 7.5 and 2.65 g/cc respectively. The volume needed in the scavenger is

(A). (B). (C). (D).

750 ft3 570 ft3 680 ft3 840 ft3

27. The average work index of CaSO42H2O in kWh/ton is (A). 13.11 (B). 8.16

(C). 25.17 (D). 45.03

28. In liquid-liquid extraction, if the selectivity (or relative separation) is unity, then (A). separation of constituent is most effective (B). no separation is possible (C). amount of solvent requirement is minimum (D). solvent flow rate should be very high

Solute Selectivity (page 15-12) In certain applications, it is important not only to recover a desired solute from the feed, but also to separate it from other solutes present in the feed and thereby achieve a degree of solute purification. The selectivity of a given solvent for solute i compared to solute j is characterized by the separation factor αi,j = Ki/Kj. Values must be greater than αi,j = 1.0 to achieve an increase in solute purity (on a solvent-free basis). When solvent blends are used in a commercial process, often it is because the blend provides higher selectivity, and often at the expense of a somewhat lower partition ratio. The degree of purification that can be achieved also depends on the extraction scheme chosen for the process, the amount of extraction solvent, and the number of stages employed.

29. During distribution of a solute between two partially miscible solvents, the selectivity at the plait point is (A). zero (B). one (C). less than zero (D). very large

Plait Point Composition conditions in which the three coexisting phases of partially soluble components of a three-phase liquid system approach each other in composition.

30. For economy in liquid extraction, the partition ratio (or distribution coefficient) must be (A). less than one (B). equal to one (C). greater than one (D). as large as possible

Partition ratio Ki = Yi/Xi (page 15-12) Partition ratios on the order of Ki = 10 or higher are desired for an economical process because they allow operation with minimal amounts of solvent (more specifically, with a minimal solvent-to-feed ratio) and production of higher solute concentrations in the extract—unless the solute concentration in the feed already is high and a limitation in the solvent’s loading capacity determines the required solvent-to-feed ratio. Since high partition ratios generally allow for low solvent use, smaller and less costly extraction equipment may be used and costs for solvent recovery and recycle are lower. In principle, partition ratios less than Ki = 1.0 may be accommodated by using a high solvent-to-feed ratio, but usually at much higher cost.

31. For a solid spherical particle of 0.80 mm in diameter and a density of 2600 kg/m3 that is immersed in a fluid of density 1200 kg/m3 and a viscosity of one centipoise, the unhindered terminal velocity is (A). 0.975 m/s (B). 0.0975 m/s (C). 0.0795 m/s (D). 0.0579 m/s

32. Calculate the power to move a load of 850 tons/h of a granular material on a conveyor belt, 1.0 m wide and 100 m long. The conveyor operates at 150 m/min and its moving parts weight 5,000 kg respectively. Constants F and Lo have been evaluated as 0.04 and 38 respectively. (A). 24 Hp (B). 27.2 Hp (C). 19.8 Hp (D). 35.3 Hp

33. An extraction process in which the primary purpose is to transfer solute from the feed phase into the extract phase in a manner analogous to stripping in distillation (A). fractional extraction (B). cross current or cross flow extraction

(C). countercurrent extraction (D). standard extraction

Standard extraction (page 15-11) process is one in which the primary purpose is to transfer solute from the feed phase into the extract phase in a manner analogous to stripping in distillation. Fractional extraction refers to a process in which two or more solutes present in the feed are sharply separated from each other, one fraction leaving the extractor in the extract and the other in the raffinate. Cross-current or crossflow extraction is a series of discrete stages in which the raffinate R from one extraction stage is contacted with additional fresh solvent S in a subsequent stage.

Countercurrent extraction is an extraction scheme in which the extraction solvent enters the stage or end of the extraction farthest from where the feed F enters, and the two phases pass each other in countercurrent fashion.

34. The first appearance of adsorbate in fluid from an adsorber is called

(A). throughput (B). break point (C). breakthrough (D). critical point

Breakthrough The point where an adsorbate first appears in the fluid from an adsorber. The maximum concentration of unwanted ions such as calcium ions that are left in a treated liquid in an ion exchange unit. Throughput

The total amount of material fed to or produced as a product from a process per unit time. It can be expressed as either a mass or a volumetric rate. In oil refineries, the throughput refers to the stream of feedstock supplied. Critical point The temperature and pressure of a substance at equilibrium when two phases become identical and form a single phase. The critical state is the condition in which the density of both the liquid and vapor phases of a substance are the same as occurs at the critical point. Breakpoint Point at which the required level of adsorption has been satisfied

35. A hollow-fiber permeator with Do = 300 microns and Di = 200 microns gives a water flux of 10 gal/day-ft2 with 0.1 M sodium chloride solution at 20°C and the salt rejection is 97%. Feed solution flows normal to the fibers at an average superficial velocity of 0.50 cm/s. For 0.1 M sodium chloride solution at 20°C, the density and viscosity are 1.0 g/cm3 & 0.01 g/cm-s and the volumetric diffusivity of the salt, Ds = 1.6 x 10-5 cm2/s. The concentration polarization is (A). 0.12 (B). 0.1268

(C). 0.68 (D). 0.068

36. A crusher is fed with limestone having particles of 2.0 cm median equivalent diameter and discharges a product consisting of particles of 0.50 cm median equivalent diameter. The feed particles can be considered very coarse and so Kick’s law would be the most appropriate. The equipment operates at a capacity of 1.2 x 104 kg/h consuming a power of 10 Hp. If the requirements of the process demand a finer size of the product (0.4 cm of median equivalent diameter) decreasing the capacity to 1.0 x 104 kg/h, the theoretical power consumption under the new conditions is (A). 5.3 kW (B). 7.2 kW (C). 6.2 kW (D). 8.6 kW

37. The average pore diameter and surface area of polyacrylic ester for purification of pulping wastewaters and antibiotics recovery are (A). 0.3-0.6 and 0.5-20 (B). 10-25 and 0.15-0.4 (C). 2-4 and 0.9-1.2 (D). 4-20 and 0.3-0.7

38. The solubility of strontium acetate in water at 0°C is _____parts per 100 parts water. (A). 53.5 (B). 33 (C). 25.4

(D). 36.9

39. The terminal settling velocity in water at 70°F of a particle with a specific gravity of 5.0 and diameter of 100 microns is ____ ft/s (A). 0.135 (B). 0.014 (C). 0.081 (D). 0.028

40. The viscosity of ethyl benzene is ____cp at 60°C (A). 0.24 (B). 0.56 (C). 0.14 (D). 0.44

41. A suspension of glass beads in ethylene glycol has a hindered settling velocity of 1.8 mm/s while the terminal settling velocity in a single glass bead in ethylene glycol is 18 mm/s. If the Richardson and Zaki hindered settling index is 6.5, the void fraction of solids in the suspension is (A). 0.702 (B). 0.66 (C). 0.61 (D). 0.902

42. The composition of feed and underflow (percent solids) in the design of a typical thickener for the sugar beet carbonation process are

(A). 2 - 5 and 15 - 20 (B). 0.01 - 0.05 and 2 - 8 (C). 10 - 30 and 25 - 65 (D). 1 - 5 and 6 - 25

43. The terminal velocity of spherical air bubbles with an average diameter of 4 mm rising in contaminated water is _____cm/s (A). 22 (B). 5.0 (C). 41 (D). 17

44. A 10,000 lb batch of a 32.5% MgSO4 solution at 120°F is cooled without appreciable evaporation to 70°F. At 70°F the concentration of solids is 26.3 lb MgSO4 per 100 lb solution. Assuming that the mother liquor leaving is saturated, the mass of MgSO47H2O crystals that will be formed is

(A). 4174 lb (B). 6655 lb (C). 2756 lb (D). 3345 lb

45. A mixture of particles in packed bed contains the following volume percent of particles and sizes: 15%, 10 mm; 25%, 20 mm; 40%, 40 mm and 20%, 70 mm. The effective mean diameter, Dpm if the shape factor is 0.74 is (A). 23.43 mm (B). 16.81 mm (C). 12.38 mm (D). 18.34 mm

46. An aqueous solution of acetic acid is to be extracted with isopropyl ether. The solution contains 24.6 kg of acetic acid and 80 kg of H2O. Water and isopropyl ether may be considered as completely immiscible under these conditions. At the temperature of the extraction, the following equilibrium data apply: kg acetic acid/kg isopropyl ether kg acetic acid/kg H2O

0.03 0.046 0.1 0.15

0.063 0.2

0.07 0.22

0.078 0.28

0.086 0.26

If 100 kg of isopropyl ether is added to the solution, the weight of acetic acid that will be extracted by isopropyl ether if equilibrium conditions are attained is (A). 18 kg (B). 15 kg (C). 24.6 kg (D). 7 kg

47. Air at 101.3 kPa absolute at 25oC is flowing at a velocity of 10 m/s in a wind tunnel. A long cylinder having a diameter of 90 mm is placed in the tunnel and the axis of the cylinder is held perpendicular to air flow. For air at 25oC and 101.3 kPa: ρ = 1.187 kg/m3 and µ = 1.845 x 10-5 kg/m-s. The force on the cylinder per meter length is

(A). 6.94 N (B). 4.69 N (C). 9.46 N (D). 5.49 N

48. Powdered coal with the screen analysis given below as “Feed” is fed to a vibrating 48-mesh screen in an attempt to remove the undesired fine material. When the screen was new the undersize and oversize analyses were listed under the columns headed “New”. After 3 months’ operation, the analyses are as headed “Old”. Screen Analyses – Mass Fractions Oversize Undersize Mesh Size Feed New Old New Old -3+4 0.010 0.012 0.014 …… ……… -4+6 0.022 0.027 0.031 …… ……… -6+8 0.063 0.078 0.088 …… ……… -8+10 0.081 0.100 0.112 …… ……… -10+14 0.102 0.126 0.142 …….. ……… -14+20 0.165 0.204 0.229 …… ……… -20+28 0.131 0.162 0.182 …… ……… -28+35 0.101 0.125 0.104 …… 0.093 -35+48 0.095 0.117 0.065 …… 0.171 -48+65 0.070 0.029 0.025 0.246 0.186 -65+100 0.047 0.015 0.008 0.183 0.146 -100+150 0.031 0.005 ……… 0.141 0.111 -150+200 0.020 …… ……… 0.105 0.071 -200 0.062 …… ……… 0.325 0.222 The effectiveness of the screen when new and when old is (A). 58.85% and 71.6% (B). 82.75% and 81.06% (C). 65.28% and 61.8% (D). 75.82% and 72.08%

49. It is desired to extract phenol from water using methyl isobutyl ketone as extraction solvent at 30°C. The partition ratio is (A). 39.8 (B). 7.06

(C). 2.13 (D). 3.44

50. In the Tyler standard screen scale series, when the Mesh number increases from 3 mesh to 10 mesh (A). the clear opening decreases (B). the clear opening increases

(C). the clear opening is unchanged (D). the wire diameter increases

Tyler Standard Screen Scale