Basic Principles of Unit Processes and Unit Operations in Organic Chemical Industries (Part - 1) | Chemical Technology - Chemical Engineering PDF Download

Basic Principles Chemical processes, Unit Processes And Unit Operations In Organic Chemical Industries

Chemical processes usually have three interrelated elementary processes

• Transfer of reactants to the reaction zone
• Chemical reactions involving various unit processes
• Separation of the products from the reaction zone using various unit operations

Processes may involve homogeneous system or heterogeneous systems. In homogeneous system, reactants are in same phase-liquid, gases or solids while heterogeneous system include two or more phases; gas liquid, gas–solid, gas-gas, liquid–liquid, liquid solid etc. Various type reactions involve maybe reversible or irreversible, endothermic or exothermic, catalytic or non-catalytic. Various variables affecting chemical reactions are temperature pressure, composition, catalyst activity, catalyst selectivity, catalyst stability, catalyst life, the rate of heat and mass transfer. The reaction may be carried out in batch, semi batch or continuous. Reactors may be batch, plug flow, CSTR. It may be isothermal or adiabatic. Catalytic reactors may be packed bed, moving bed or fluidised bed Along with knowledge of various unit processes and unit operation following information are very important for the development of a process and its commercialization [Austin,1984] Basic Chemical data: Yield conversion, kinetics

• Material and energy balance, raw material and energy consumption per tone of product, energy changes  
• Batch vs Continuous, process flow diagram
• Chemical process selection: design and operation, pilot plant data, Equipment required, material of construction
• Chemical Process Control and Instrumentation
• Chemical Process Economics: Competing processes, Material and, Energy cost, Labour, Overall Cost of production
• Market evaluation: Purity of product and uniformity of product for further processing 
• Plant Location
• Environment, Health, Safety and Hazard
• Construction, Erection and Commissioning
• Management for Productivity and creativity: Training of plant personals and motivation at all levels
• Research, Development and patent
• Process Intensification Inorder to improve productivity and make the process cost effective and for improving overall economy, compact , safe, energy efficient and environmentally sustainable plant, process intensification has become very important and  industry is looking beyond the traditional chemical engineering.

Unit Processes and Unit Operations in Chemical 

Process Industries 

Chemical process is combination of unit processes and Unit operation. Unit process involves principle chemical conversions leading to synthesis of various useful product and provide basic information regarding the reaction temperature and pressure, extent of chemical conversions and yield of product of reaction nature of reaction whether endothermic or exothermic, type of catalyst used. Unit operations involve the physical separation of the products obtained during various unit processes. Various unit processes in chemical industries are given in Table M-I 3.1. Various chemical reactions and its application in process industries are given in Table M-I 3.2.

Nitration 

Nitration involves the introduction of one or more nitro groups into reacting molecules using various nitrating agents like fuming, concentrated, aqueous nitric acid mixture of nitric acid and sulphuric acid in batch or continuous process. Nitration products find wide application in chemical industry as solvent, dyestuff, pharmaceuticals, explosive, chemical intermediates. Typical products: TNT, Nitrobenzene, m-dinitrobenzene, nitroacetanilide, alpha nitronaphthalene, nitroparaffins  

Table M-I 3.1: Unit Processes in Chemical Process Industries  

TNT is produce in a three-step process: First, toluene is nitrated with a mixture of sulfuric acid and nitric acid to produce mono-nitrotoluene or MNT. The MNT is separated and then renitrated to dinitrotoluene or DNT. In the final step, the DNT is nitrated to trinitrotoluene or TNT using an anhydrous mixture of nitric acid and oleum.