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here, I have explained two parts of chemical engineering i.e Unit Process and Unit Operation with examples.
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Unit Process and Unit Operation Topics Covered: 1. Unit Process 2. Unit Operation 3. Analysis of Manufacturing Processes:
Unit Process Definition: Unit processes involves principal chemical conversions leading to synthesis of various useful products and provide basic information regarding reaction temperature and pressure, extent of chemical conversions, yield of products, nature of reaction whether it is endothermic or exothermic and type of catalyst used. It is a process in which chemical change occurs. Examples: oxidation, reduction, calcination, etc. Unit Processes in Chemical Industry: ❑ Combustion ❑ Oxidation ❑ Neutralization ❑ Silicate Formation ❑ Causticization ❑ Electrodialysis ❑ Double Decomposition ❑ Calcination and Dehydration ❑ Nitration ❑ Esterification ❑ Ammonolysis ❑ Reduction ❑ Halogenation ❑ Ion Exchange ❑ Sulfonation ❑ Hydrolysis and Hydration ❑ Hydrogenation and Hydrogenolysis ❑ Alkylation ❑ Condensation ❑ Polymerization ❑ Diazotization and Coupling ❑ Fermentation ❑ Pyrolysis and Cracking ❑ Aromatization ❑ Isomerization ❑ Hydroformylation
Unit Operation Definition: Unit operations involve the physical separation of products obtained during various unit processes. Here no chemical change is there. e.g. Screening, Distillation, Evaporation, Decantation, etc. Types of Unit Operations in Chemical Engineering: ❖ Mass Transfer Operations: It includes the operations in which mass is transferred by using chemical potential difference as driving force. E.g. gas absorption, extraction etc. ❖ Fluid Flow Operations/ Momentum transfer Operations: It includes the operations which involve fluid transportation, filtration and solid fluidization. ❖ Heat transfer Operations: It includes the operations in which temperature difference is main driving force. E.g. Heat Exchange, Evaporation etc. ❖ Mechanical Operations: It includes the operations in which external mechanical force is used as a driving force. E.g. Crushing, Screening etc. ❖ Thermodynamic Operations : It includes the operations in which energy is transformed from one place to another so that we get desired output E.g. Refrigeration, Liquefaction etc. There are some operations in which two operations take place simultaneously. E.g. Distillation, Humidification etc.
Analysis of Manufacturing Processes: 1. Ammonia Manufacturing using Haber’s Process: Steps Unit Process/Unit Operation Reason In this step, CO and CO2are converted into CH4and removal of traces of H2S, H2O,P and Arsenic is done. Here catalytic hydrogenation of nitrogen takes place Purification of input stream (Feed Guard Reactor) Unit Process Main Reaction Unit Process Cooling of product stream (condenser) Unit Operation Here, ammonia from vapor mixture is converted into liquid ammonia i.e. only physical state of ammonia is changed. Here, liquid ammonia is separated from vapor mixture. No chemical reaction is there. Here, remaining ammonia is get condensed. Again, only physical state of ammonia is changed. Separation of liquid ammonia (Separator) Unit Operation Refrigeration of remaining ammonia (refrigerator) Unit Operation
2. Nitric Acid Manufacturing using Ostwald’s Process: Steps Unit Process/Unit Operation Reason In this step ammonia reacts with oxygen to produce nitric oxide (NO). Oxidation of Ammonia (Platinum – Rhodium catalyst is used.) Unit Process Here, The temperature of mixture is reduced. Cooling of mixture Unit Operation First of all, NO is get converted into NO2 due to the addition of excess air. Then NO2 gas is absorbed into water to get Nitric acid. Absorption in water. (Excess air is added to gaseous stream before entering the absorption column) Unit Process ❑ Many times, Unit operation and unit processes are integrated. Gas absorption is a unit operation because ,gas is absorbed over the liquid and does not react with it. But if absorbed gas reacts with that liquid, then we cannot say that, it is a unit operation. In this case a unit process is done by using the technique of unit operation. In Ostwald’s process NO2is absorbed in the water, but it react with water to form Nitric acid. Hence we have considered that as a unit process. ❑ Sometimes side reactions take place while performing a unit operation. Those reactions do not alter the classification of that particular step. Because the extent of such reactions is very low. In Ostwald’s process, output mixture of catalytic reactor is cooled using direct contact with water, during this process small amount of nitrous acid is formed which is removed in that step only.
