Report Experiment Crystalization

Exp 2: CRYSTALLIZATION OF BIOPRODUCTS

CSB 30103

OBJECTIVES:

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To perform batch crystallization process utilizing the evaporation method.

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

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To dete determ rmin inee the the effe effect ct of circ circul ulat atio ion n flow flow rate rate and and heat heatin ing g rate rate on the 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 1


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assume. For each chemical compound, 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 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 material handled. handled. Therefore, Therefore, each crystalli crystallization zation plant requires requires many unique features 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 cause caused d by conta contact ct of the the crys crysta tals ls with with each each othe otherr and and with with the the pump pump impe impell ller er,, 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.

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OPERATING PROCEDURES:

4.2 General Start-Up Procedures for Evaporation Crystallization

1. All valves valves are ensured ensured closed closed except except the the ventilati ventilation on valve valve V12. 2. The produc productt vessel vessel B2 is is checked checked empty empty of liqu liquid. id. 3. 10 L of saturated saturated salt salt solution solution was was prepared prepared by dissolvi dissolving ng the appropria appropriate te amount of salt in water. 4. The saturat saturated ed salt solution solution was poured poured into into the crysta crystalli llizer zer vessel vessel B1 throug through h valve V10 until the liquid overflows at the conical inlet. Valve V10 was closed. 5. The remaini remaining ng solution solution was poured poured into the feed/r feed/reac eactio tion n vessel vessel R1 through through the charge point. 6. The stirrer stirrer M1 was switc switched hed and adjusted adjusted the the speed to mid-range mid-range.. 7. The crystall crystallizer izer pump P1 P1 was switched switched on and the the circulati circulation on flow rate 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 cooling water water was turned turned on on by opening opening valves V14 and and V15. 9.

The The ther thermo most stat at T1 was was ensu ensure red d conta contain in suff suffic icie ient nt heat heat tran transf sfer er flui fluid d whil whilee thermostat T2 contains sufficient water and was refilled as necessary.

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

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11. Valve V12 was closed to operate the crystalliz crystallization ation under vacuum. vacuum. The vacuum pump P3 was switched on and pressure was set at 0.3 bars on the controller. 12. The temperature temperature rise in the feed/reactio feed/reaction n vessel vessel was observed observed until it has reached reached a constant value. 13. The circulation circulation line was allowed to heat up until boiling boiling and evaporation evaporation occurs and condensate starts to appear in the condensate vessel B4. 14. The units now were ready ready for experiments experiments..

4.3 General Start-Up Procedures for Batch Cooling Crystallization

1. All valves valves were ensured ensured closed closed except the ventila ventilation tion valve valve V7. V7. 2. Abou Aboutt 10 L satu satura rate ted d oxal oxalic ic acid acid solu soluti tion on was was prep prepar ared ed by diss dissol olvi ving ng the the appropriate amount of oxalic acid in clean water. 3. The oxalic oxalic acid soluti solution on was poured poured into into the feed/rea feed/reaction ction vessel vessel R1 R1 through through the charge port. 4. The stirrer stirrer M1 was switc switched hed and adjusted adjusted the the speed to mid-range mid-range.. 5. The The ther thermo most stat at T2 was was ensu ensure red d cont contai ain n glyc glycol ol-w -wat ater er and and was was refi refill lled ed as necessary. 6. Thermostat Thermostat T2 T2 was switch switched ed on. The temper temperature ature of thermostat thermostat T2 was set set to 60 °C. 7. The temperatu temperature re rise in the the feed/reacti feed/reaction on vessel was was observed observed until until it has reached reached a constant value. 8. The appropriat appropriatee amount of oxalic oxalic acid acid was added into into the feed/rea feed/reaction ction vessel 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.

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9. The circu circulat lation ion line line was was allowe allowed d to cool cool down. down. 10. The units now were ready ready for experiments experiments..

4.5 Product Collection

1. The product vessel vessel B2 was empty. empty. 2. If the unit operating at atmospheric atmospheric pressure, pressure, valve V6 was opened and let the slurry solution flow from the circulation line into the product vessel. 3. If the unit operating operating under vacuum, vacuum, vent valve V7 and V8 were slowly slowly opened to released the vacuum. 4. Valve V6 was opened to collect collect the required required amount of slurry solution 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. 6. The product vessel was cleaned before placing placing it back into the unit. 7. From the collection collection bottle, the slurry solution solution was poured through through the filter 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 unit operati operating ng at atmospher atmospheric ic pressure, pressure, valve valve V13 was was opened to to drain drain the condensate vessel B3. 2. If the unit unit operat operatin ing g under under vacuum vacuum,, the the vess vessel el was isol isolat ated ed from the vacuum vacuum system by closing valve V11.

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3. Vent valve V12 was was opened opened slowly slowly to releas releasee the vacuum. vacuum. 4. Valve V13 V13 was opened opened to fully fully drain drain the the vessel. vessel. Valve Valve V13 was was closed. closed. 5. Vent Vent valve valve V12 was closed closed and valve valve V11 V11 was was opene opened d slow slowly ly to return return the condensate vessel B3 to vacuum.

4.4 General Shut-Down Procedures

1. The temper temperatu ature re set point point was reduce reduced d for both thermo thermosta statt T1 and T2 to below below room temperature and the liquid in the thermostats was allowed to cool down to room temperature. 2. The cooling cooling water water was keep keep running running through through condens condensers ers W2 W2 and W3. W3. 3. The stirr stirrer er M1 M1 was switched switched off off and dosing dosing pump pump P2. 4. The The circul circulat atio ion n flow flow rate rate of pump pump P1 was was set to 200 L/hr and the the liqu liquid id was allowed to cool down to room temperature. 5. The circ circula ulatio tion n pump P1 was was turne turned d off. off. 6. Valves V14 and V15 were were closed closed to stop the the cooling cooling water water flow. flow. 7. The quick quick removable removable connections connections were were opened opened carefully carefully at product product vessel vessel B2 and the vessel was removed. Any remaining liquid or solid residue was discarded and cleaned in the vessel. 8. The sampling sampling bottle bottle B5 B5 was removed removed and valve valve V5 was opened opened to to drain all liquid liquid from the circulation line. 9. A hose was attac attached hed to valve valve V9 to clean clean the solid solid residue residue in the circul circulati ation on 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.

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11. If required, required, the liquid liquid in the feed/reacti feed/reaction on vessel were drained by opening valves V1, V2 and V3. 12. The product product vessel vessel B2 and sampli sampling ng bottle bottle B5 were placed placed back back into into the unit. unit. Valves V5 and V6 were closed.

EXPERIMENT PROCEDURES:

1. The general general start-up start-up procedures procedures were were performed performed as described described in Section Section 4.2. For For batch crystallization, thermostat T2 need not be switched o n. 2. The circulat circulation ion flow rate, rate, vacuum vacuum pressure pressure and the the temperatur temperaturee of thermosta thermostatt T1 were set to a suitable value. The feed solution was ensured boil at the specified temperature and pressure. 3. The circul circulati ation on line was allowed allowed to heat up until until boiling boiling and evaporat evaporation ion occurs occurs and condens condensate ate starts starts to appear appear in the condensat condensatee vessel vessel B3. The timer timer was started. 4. The circulati circulation on flow rate rate and inlet/out inlet/outlet let temperatu temperatures res were recorde recorded d of both feed feed solution and thermal fluid through the heat exchanger W1. 5. The formation formation of crysta crystals ls was observed observed in the circulat circulation ion line. Once Once crystals crystals start start to appear, the timer was stopped and the time duration was recorded. 6. The amount amount of condensa condensate te was measure measured d accumulat accumulated ed in condens condensate ate vessel vessel B3 and the condensate vessel was drained. Section 4.6 was referred. The timer was restarted. 7. The followin following g steps steps were perform performed ed at every every 15 minute minute interva intervals: ls:

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i.

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The The circul circulat atio ion n flow flow rate rate and inlet inlet/o /out utle lett temper temperat atur ures es were were record recorded ed of both slurry solution and thermal fluid through the heat exchanger W1.

ii. ii. iii. iii.

The amount amount of condens condensate ate was measur measured ed accu accumul mulate ated d in vessel vessel B3. The The condens condensat atee vesse vessell B3 was drai draine ned d by openi opening ng valve valve V13. V13. Secti Section on 4.6 4.6 was referred.

8. Step 7 above was was carried carried out until until the liquid liquid level in the the crystalli crystallizer zer vessel vessel B1 has dropped to about halfway below the conical inlet. 9. The total total time time taken was was recorded recorded for for the cryst crystalli allization zation process. process. 10. About 2 L of product slurry was collected from the circulation circulation line as explained in Section 4.5. 11. The amount of crystals obtained obtained and the crystal crystal concentration concentration were determined determined in the crystallizer at the end of the batch process. 12. The entire experiment experiment was repeated by varying varying the circulati circulation on flow rate, vacuum pressure and heating rate (temperature at thermostat T1).

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RESULTS

Time 9.50 am

FI301 L/hr 665

FI302 L/hr 798

PIL201 °C 0.301

10.20 am 10.50 am 11.20 am 11.50 am 12.20 pm 12.50 pm 1.20 pm 1.50 pm 2.20 pm

480 550 405 361 301 301 290 284 276

801 805 806 805 802 808 806 807 805

0.301 0.301 0.301 0.302 0.300 0.297 0.306 0.302 0.302

Panel No/Unit TI101 TI102 TI103 °C °C °C 58.8 77.3 25.2

58.8 58.5 58.2 58.9 62.4 61.9 67.4 66.6 64.1

74.9 75.2 75.9 76.4 77.0 75.5 77.4 77.7 77.7

26.5 26.8 27.0 27.3 27.6 28.0 28.3 28.6 28.9

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Amount of Salt water that used = 6 Liter

Weight of crystal + container = 529.09 g

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TI104 °C 26.7

TI105 °C 107.3

TI106 °C 101.0

27.0 27.5 27.7 27.9 28.3 28.8 29.0 29.2 29.4

107.5 107.7 107.8 107.8 107.8 107.9 107.9 107.9 107.9

100.8 101.1 101.2 101.4 101.6 101.7 101.7 101.8 101.7


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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 characteristi characteristics. cs. High levels levels of supersaturat supersaturation ion around crystallizat crystallization ion 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 possibly inhibits the growth of crystalline crystalline nuclei. nuclei. Imperfect Imperfect mixing 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


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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 characteristi characteristics. cs. High levels levels of supersaturat supersaturation ion around crystallizat crystallization ion 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 possibly inhibits the growth of crystalline crystalline nuclei. nuclei. Imperfect Imperfect mixing 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). 1994). Moreover, the content of solution in the cake after filtration is too high, which lowers the quality of crystals conside considerab rably. ly. This This necess necessit ity y compli complicat cates es the filtra filtrati tion on technol technology ogy,, raises raises costs 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 these proble problems ms relate related d to product product quality quality requir requireme ements nts is an excess excess of fine 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. 11


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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 nucleation is supersatur supersaturation, ation, which is defined defined as the difference difference in chemical chemical potential between the solid and the liquid phase. A distinction is made between two mechanisms of format formation ion of new crysta crystalli lline ne materi material, al, known known as primar primary y nucleat nucleation ion and seconda secondary ry nucleati nucleation. on.

The formatio formation n of new crystal crystalli line ne materi material al from from a clear clear liqui liquid d is called 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. particles. In homogeneous homogeneous nucleation, nucleation, these foreign particles particles are absent and primary primary nucleati nucleation on occurs occurs as a result result of local local fluctu fluctuati ations ons of concent concentrat ration ion in the liquid liquid.. In practice, the liquid will always contain small particles and he terogeneous 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 material in the liquid is attritio attrition. n. Attritio Attrition n is the discontinuo discontinuous us 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 moderate level. The next step in the crystallisati crystallisation on 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 from melt crystallisation. crystallisation. In general crystals 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 characteristic crystal length is often used. Dissolution Dissolution of crystals crystals takes place 12


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when the solution is under saturated. Dissolution is not quite the opposite of growth as it does not require require the surface surface integratio integration n step and the rate-limiting rate-limiting step is therefore therefore mass transf transfer er away from from the crysta crystall surfac surface. e. Theref Therefore ore,, when when the dissol dissoluti ution on takes takes place, 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 material from which new crystals 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, agglome agglomerat ration ion is usuall usually y an undesir undesired ed phenom phenomenon enon as the agglome agglomerat rates es can entrap entrap mother liquid. liquid. Mother liquor inclusions inclusions can result result in caking behavior behavior downstream 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 evaporates and the supersatur supersaturated ated mother liquor crystall crystallizes. izes. This gives considerable 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 concentratio concentration n corresponds corresponds to relatively relatively high pressure pressure and whose final mother liquor 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

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

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Whiting Equipment Canada Inc. Swenson Crystallization Equipment

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APPENDIX

CRYSTAL FORM

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Report Experiment Crystalization

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