report experiment crystalization

Exp 2: CRYSTALLIZATION OF BIOPRODUCTS CSB 30103

OBJECTIVES:

To perform batch crystallization process utilizing the evaporation method.

To examine the rate of evaporation and crystallization in a batch process.

To determine the effect of circulation flow rate and heating rate on the

evaporative crystallization processes.

INTRODUCTION

Batch evaporative crystallization

Crystallization is the process by which a chemical is separated from solution as a high-

purity, definitively shaped solid. A crystal may be defined as a solid composed of atoms

arranged in an orderly, repetitive array. The infer-atomic distances in a crystal of any

definite material are constant and characteristic of that material. Crystals are, in short,

high-purity products with consistent shape and size, good appearance, high bulk density

and good handling characteristics. Because the pattern or arrangement of the atoms is

repeated in all directions, there are definite limitations on the shapes which crystals may

assume. For each chemical compound, there are unique physical properties differentiating

that material from others, so the formation of a crystalline material from its solution, or

mother liquor, is accompanied by unique growth and nucleation characteristics. While

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crystallization is a unit operation embracing well known concepts of heat and mass

transfer, it is nevertheless strongly influenced by the individual characteristics of each

material handled. Therefore, each crystallization plant requires many unique features

based upon well established general principles. Each application must be evaluated on an

individual basis to achieve optimum results. The mechanical design of the crystallizer has

a significant influence on the nucleation rate due to contact nucleation (that which is

caused by contact of the crystals with each other and with the pump impeller, or

propeller. when suspended in a supersaturated solution). This phenomenon yields varying

rates of nucleation in scale up, and differences in the nucleation rates when the same

equipment is used with different materials.

OPERATING PROCEDURES:

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4.2 General Start-Up Procedures for Evaporation Crystallization

1. All valves are ensured closed except the ventilation valve V12.

2. The product vessel B2 is checked empty of liquid.

3. 10 L of saturated salt solution was prepared by dissolving the appropriate amount

of salt in water.

4. The saturated salt solution was poured into the crystallizer vessel B1 through

valve V10 until the liquid overflows at the conical inlet. Valve V10 was closed.

5. The remaining solution was poured into the feed/reaction vessel R1 through the

charge point.

6. The stirrer M1 was switched and adjusted the speed to mid-range.

7. The crystallizer pump P1 was switched on and the circulation flow rate was set to

200 L/hr. The liquid solution was observed flowing from the crystallizer vessel

B1 through the pump to the heat exchanger W1 and then overflowing at the

conical inlet back to the crystallizer vessel.

8. The cooling water was turned on by opening valves V14 and V15.

9. The thermostat T1 was ensured contain sufficient heat transfer fluid while

thermostat T2 contains sufficient water and was refilled as necessary.

10. Both thermostat T1 and T2 were switched on. The temperature of T1 (containing

thermal-oil fluid) was set to 110 °C and thermostat T2 (containing glycol-water)

was set to 80 °C. The pump speed was set for both thermostats to a value of 8.

11. Valve V12 was closed to operate the crystallization under vacuum. The vacuum

pump P3 was switched on and pressure was set at 0.3 bars on the controller.

12. The temperature rise in the feed/reaction vessel was observed until it has reached

a constant value.

13. The circulation line was allowed to heat up until boiling and evaporation occurs

and condensate starts to appear in the condensate vessel B4.

14. The units now were ready for experiments.

4.3 General Start-Up Procedures for Batch Cooling Crystallization

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1. All valves were ensured closed except the ventilation valve V7.

2. About 10 L saturated oxalic acid solution was prepared by dissolving the

appropriate amount of oxalic acid in clean water.

3. The oxalic acid solution was poured into the feed/reaction vessel R1 through the

charge port.

4. The stirrer M1 was switched and adjusted the speed to mid-range.

5. The thermostat T2 was ensured contain glycol-water and was refilled as

necessary.

6. Thermostat T2 was switched on. The temperature of thermostat T2 was set to 60

°C.

7. The temperature rise in the feed/reaction vessel was observed until it has reached

a constant value.

8. The appropriate amount of oxalic acid was added into the feed/reaction vessel R1

through the charge port and let it dissolved. Saturated oxalic acid should remain in

60 °C temperature. Solubility data of oxalic acid was referred.

9. The circulation line was allowed to cool down.

10. The units now were ready for experiments.

4.5 Product Collection

1. The product vessel B2 was empty.

2. If the unit operating at atmospheric pressure, valve V6 was opened and let the

slurry solution flow from the circulation line into the product vessel.

3. If the unit operating under vacuum, vent valve V7 and V8 were slowly opened

to released the vacuum.

4. Valve V6 was opened to collect the required amount of slurry solution and valve

V6 was closed.

5. The quick removable connections were opened carefully at product vessel B2

and the vessel was removed. The slurry solution was poured into a collection

bottle.

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6. The product vessel was cleaned before placing it back into the unit.

7. From the collection bottle, the slurry solution was poured through the filter to

obtain the crystallized solid. The solid was dried by putting it under the sun or in

an oven.

4.6 Draining Condensate

1. If the unit operating at atmospheric pressure, valve V13 was opened to drain the

condensate vessel B3.

2. If the unit operating under vacuum, the vessel was isolated from the vacuum

system by closing valve V11.

3. Vent valve V12 was opened slowly to release the vacuum.

4. Valve V13 was opened to fully drain the vessel. Valve V13 was closed.

5. Vent valve V12 was closed and valve V11 was opened slowly to return the

condensate vessel B3 to vacuum.

4.4 General Shut-Down Procedures

1. The temperature set point was reduced for both thermostat T1 and T2 to below

room temperature and the liquid in the thermostats was allowed to cool down to

room temperature.

2. The cooling water was keep running through condensers W2 and W3.

3. The stirrer M1 was switched off and dosing pump P2.

4. The circulation flow rate of pump P1 was set to 200 L/hr and the liquid was

allowed to cool down to room temperature.

5. The circulation pump P1 was turned off.

6. Valves V14 and V15 were closed to stop the cooling water flow.

7. The quick removable connections were opened carefully at product vessel B2 and

the vessel was removed. Any remaining liquid or solid residue was discarded and

cleaned in the vessel.

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8. The sampling bottle B5 was removed and valve V5 was opened to drain all liquid

from the circulation line.

9. A hose was attached to valve V9 to clean the solid residue in the circulation line

and the pipeline was flushed with tap water. Valve V5 and V6 were drained

through water.

10. The condensate vessel B4 was drained by opening valve V13.

11. If required, the liquid in the feed/reaction vessel were drained by opening valves

V1, V2 and V3.

12. The product vessel B2 and sampling bottle B5 were placed back into the unit.

Valves V5 and V6 were closed.

EXPERIMENT PROCEDURES:

1. The general start-up procedures were performed as described in Section 4.2. For

batch crystallization, thermostat T2 need not be switched on.

2. The circulation flow rate, vacuum pressure and the temperature of thermostat T1

were set to a suitable value. The feed solution was ensured boil at the specified

temperature and pressure.

3. The circulation line was allowed to heat up until boiling and evaporation occurs

and condensate starts to appear in the condensate vessel B3. The timer was

started.

4. The circulation flow rate and inlet/outlet temperatures were recorded of both feed

solution and thermal fluid through the heat exchanger W1.

5. The formation of crystals was observed in the circulation line. Once crystals start

to appear, the timer was stopped and the time duration was recorded.

6. The amount of condensate was measured accumulated in condensate vessel B3

and the condensate vessel was drained. Section 4.6 was referred. The timer was

restarted.

7. The following steps were performed at every 15 minute intervals:

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i. The circulation flow rate and inlet/outlet temperatures were recorded of

both slurry solution and thermal fluid through the heat exchanger W1.

ii. The amount of condensate was measured accumulated in vessel B3.

iii. The condensate vessel B3 was drained by opening valve V13. Section 4.6

was referred.

8. Step 7 above was carried out until the liquid level in the crystallizer vessel B1 has

dropped to about halfway below the conical inlet.

9. The total time taken was recorded for the crystallization process.

10. About 2 L of product slurry was collected from the circulation line as explained in

Section 4.5.

11. The amount of crystals obtained and the crystal concentration were determined in

the crystallizer at the end of the batch process.

12. The entire experiment was repeated by varying the circulation flow rate, vacuum

pressure and heating rate (temperature at thermostat T1).

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RESULTS

Panel No/UnitFI301 FI302 PIL201 TI101 TI102 TI103 TI104 TI105 TI106

Time L/hr L/hr °C °C °C °C °C °C °C9.50 am 665 798 0.301 58.8 77.3 25.2 26.7 107.3 101.0

10.20 am 480 801 0.301 58.8 74.9 26.5 27.0 107.5 100.810.50 am 550 805 0.301 58.5 75.2 26.8 27.5 107.7 101.111.20 am 405 806 0.301 58.2 75.9 27.0 27.7 107.8 101.211.50 am 361 805 0.302 58.9 76.4 27.3 27.9 107.8 101.412.20 pm 301 802 0.300 62.4 77.0 27.6 28.3 107.8 101.612.50 pm 301 808 0.297 61.9 75.5 28.0 28.8 107.9 101.71.20 pm 290 806 0.306 67.4 77.4 28.3 29.0 107.9 101.71.50 pm 284 807 0.302 66.6 77.7 28.6 29.2 107.9 101.82.20 pm 276 805 0.302 64.1 77.7 28.9 29.4 107.9 101.7

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Amount of Salt water that used = 6 Liter

Weight of crystal + container = 529.09 g

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DISCUSSION

Crystallization processes are usually carried out in agitated mixing tanks (Wachi and

Jones, 1995). Conditions of mixing in crystallizers with internal circulation forced by

mechanical stirrer significantly influence the final size of product crystals (Mersmann,

1999) and their characteristics. High levels of supersaturation around crystallization

points in the mixer due to a cooling surface, evaporative interference and or liquid

reactants contact lead to an inhomogeneous solution and non-uniform mixing especially

in fast precipitation systems. This causes very strong effects of homogeneous nucleation

and possibly inhibits the growth of crystalline nuclei. Imperfect mixing conditions are

generally observed in most industrial crystallizers. They are caused by supersaturation

phenomena, which create crystals of small final sizes, making downstream operations

such as filtration difficult and inefficient (Mersmann, 1994). Moreover, the content of

solution in the cake after filtration is too high, which lowers the quality of crystals

considerably. This necessity complicates the filtration technology, raises costs of

production and does not guarantee the expected specification of produced crystals.

Crystallisation is a separation and purification process, used in the production of a wide

range of materials. It involves the formation of one or more solid phases from a liquid

phase or amorphous solid phase. Crystallisation is one of the older unit operations in the

chemical industry and it differs from most unit operations because of the presence of a

solid product. The main advantages of crystallisation are a high purity in one process

step, a low level of energy consumption and relatively mild process conditions. Although

crystallisation is widely used it is still not well understood. This is a disadvantage and

problems in terms of product quality and process operation is frequently encountered.

One of these problems related to product quality requirements is an excess of fine

particles, resulting in bad filterability. Applications of crystallisation can be found in

producing inorganic materials such as potassium chloride (fertiliser), organic materials

such as paraxylene (raw material for polyester). An enormous number of and diversity in

crystallisation processes is found in the pharmaceutical, organic fine chemical and dye

industries.

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Among the crystallization mechanism that influences the crystal population discussed

above. Nucleation is the formation of new crystalline material. The driving force for

nucleation is supersaturation, which is defined as the difference in chemical potential

between the solid and the liquid phase. A distinction is made between two mechanisms of

formation of new crystalline material, known as primary nucleation and secondary

nucleation. The formation of new crystalline material from a clear liquid is called

primary nucleation. This type of nucleation can be subdivided in heterogeneous and

homogeneous nucleation. In heterogeneous nucleation, the liquid contains microscopic

foreign particles such as dust or dirt and the primary nucleation takes place on these

particles. In homogeneous nucleation, these foreign particles are absent and primary

nucleation occurs as a result of local fluctuations of concentration in the liquid. In

practice, the liquid will always contain small particles and heterogeneous nucleation is far

more likely to occur than homogeneous nucleation. The formation of new nuclei at the

surface of parent crystalline material is referred to as ‘birth’ or secondary nucleation. The

main source of parent material in the liquid is attrition. Attrition is the discontinuous

separation of very small particles from a parent crystal due to collisions of the parent

crystal with the impeller in the pump, the vessel wall and other crystals. Whereas primary

nucleation requires a very high level of supersaturation, secondary nucleation occurs at a

moderate level. The next step in the crystallisation process is the growth of the small

sized particles formed during nucleation. In the absence of agglomeration and breakage,

growth, together with nucleation, determines the final particle size distribution of the

crystal population. The driving force for crystal growth is again supersaturation. Crystal

growth is a process of mass transfer, surface integration and heat transfer. The mass

transfer step involves the diffusion of growth units such as ions, atoms or molecules

towards the crystal surface. Next, orientation and adsorption of the growth unit takes

place in the surface integration step. Heat transfer occurs simultaneously with both steps

and is usually not rate-limiting apart from melt crystallisation. In general crystals have

different growth rates at different surfaces, referring to the increase in length per time of a

surface in the direction normal to that specific surface. However, a single linear growth

rate of the characteristic crystal length is often used. Dissolution of crystals takes place

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when the solution is under saturated. Dissolution is not quite the opposite of growth as it

does not require the surface integration step and the rate-limiting step is therefore mass

transfer away from the crystal surface. Therefore, when the dissolution takes place,

crystals are easily rounded off as its corners and edges are the regions where mass

transfer is least rate limiting. Attrition and breakage are both a result of crystal collisions

with the pump, the vessel wall or other crystals. The impact of these collisions can result

in increased internal crystal stress. The stress will accumulate with repeated collisions,

ultimately leading to crystal fracture. The distinction between attrition and breakage is

made by the size of the particles after the original crystal has fractured. Breakage is

referred to as the separation of a crystal into two or more similar sized crystals. The

separation of a crystal into one slightly smaller crystal and many much smaller fragments

is named attrition. The amount of impact energy required for breakage is considerably

more than for attrition. As stated before in the part on secondary nucleation, attrition is a

main source for parent material from which new crystals are born. The mass formed by

the cementation of individual particles is referred to as agglomerate. For agglomeration to

take place, first of all two or more crystals have to collide. When these crystals are held

together by interparticle forces, such as Van der Waals, electrostatic and steric forces,

they form a mass called an aggregate. Growth between the crystals in the aggregate is the

final cementation step, resulting in agglomerate. In solution crystallisation processes,

agglomeration is usually an undesired phenomenon as the agglomerates can entrap

mother liquid. Mother liquor inclusions can result in caking behavior downstream the

crystallization process or during storage. Caking means the inclusions fracture and the

contained mother liquid comes out, cementing multiple crystals together as the solvent

evaporates and the supersaturated mother liquor crystallizes. This gives considerable

problems in product storage and processing.

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CONCLUSION

As conclusion, to get the better sizing of crystallization products, these parameters of

mechanism should be controlled during the process. For applications involving relatively

small amounts of material it is often convenient to use a batch crystallizer. Another

reason to make use of a batch process is when losses must be kept to a minimum, usually

when expensive materials are involved. Batch operation also has useful applications

where the cooling range is very wide, such as in handling material whose initial feed

concentration corresponds to relatively high pressure and whose final mother liquor

temperature corresponds to room temperature or significantly lower. In such systems the

use of batch crystallization avoids the shock introduced to the system in continuous

equipment by mixing high-temperature feed solutions with relatively low-temperature

mother liquor.

REFERENCES

http://sundoc.bibliothek.uni-halle.de/diss-online/02/03H046/t4.pdf

Whiting Equipment Canada Inc. Swenson Crystallization Equipment

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http://sundoc.bibliothek.uni-halle.de/diss-online/02/03H046/t4.pdf


APPENDIX

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CRYSTAL FORM

report experiment crystalization

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