Chemical Reactors in Chemical Engineering Processes

Introduction

In many chemical engineering processes, the use of vessels intended to hold chemical reactions known as chemical reactors are used. Designing chemical reactors entail multiple chemical engineering aspects. The chemical reactions occur in reactors, where they can be controlled and monitored for efficiency and safety. Such chemical reactors are useful in production of many chemicals such as pharmaceutical compounds components (Roberts, 2009). They operate in numerous dissimilar ways. There are many scientific specialty organizations, which manufacture chemical accessories and reactors such as substitute components for broken devices. In our daily lives, we operate an assortment of chemical processes but generally, we do not perceive them in any scientific way. Such chemical processes include running washing machines or fertilizing lawns.

 

Chemical Reactors

The paper discusses reactors with particular emphasis on chemical reactors as equipment used in the Chemical Engineering Design. Through in-depth analysis, this essay will provide a brief discussion about chemical reactors, their importance, and functions. Moving forward, the paper will seek to explain how chemical reactors are constructed, which materials are important in construction of chemical reactors, their quantity, and size. Lastly, this essay will provide the demerits of using chemical reactors and determine whether large energy amounts are used. Moreover, this paper will address safety issues including toxic materials, explosive situations, etc. The essay will further seek to find out whether these problems can be solved by exploring possible improvements.

In quantifying a washer’s dirt removal efficiency or fertilizer’s soil distribution patterns, it is important to comprehend which chemical transformation will occur within a definite volume and the speed. Reactor engineering and chemical kinetics are the basic scientific foundations for chemical engineering processes analysis. Both are invented by man and occur in nature. The design of chemical reactors aims at optimizing a reaction’s present value. Chemical engineers ensure that reactions proceed with high efficiency in realizing desired output products. The normal operating costs include costs of labor and raw materials, energy removal, and energy input. Energy changes yield cooling or heating, pumping to pile pressure, agitation, or loss of frictional pressure (Gianetto, Silveston, & Baldi, 1996).

Description and Function

Designs of Laminar Flow Reactors (LFRs) require tubular reactors or pipes and tanks. These indispensable vessels are used as batch reactors or even continuous reactors (Caccavale, 2011). Solids such as catalysts, inert materials, and reagents are accommodated in such reactors. However, reagents and products are fluids that react in the reactors. Most reactors run at steady states but it is also important to note that they can work in transient states (Aris, 1999). In reactors, residence time, chemical species concentrations, coefficients of heat transfer, pressure, and temperature are the major process variables. Chemical reactors may be designed as pipes or tanks. It depends on the need of the reactor. The reactors considerably vary in their sizes. Chemical reactors with small bench tops are used in laboratories, while big tanks may be used in industrial scale chemical production.

Chemical reactors such as typical tubular reactor have packed bed. The design of the chemical reactor may include varying features of its controlling conditions. The packing within the bed may contain catalyst of chemical reactions. Batch and continuous reactors are among the most common types of reactors (Perlmutter, 1992). When reactors are in operation after maintenance, they are considered to be in transient state. In a transient state, major process variables are changing with time. Since chemical reactions involve transformation of an assortment of chemical substances, chemical reactors are important in transformation of the chemicals to another chemical substance set. Chemical reactions that occur within the reactor can be either exothermic, when heat is given off, or endothermic, when heat is absorbed.

Chemical reactor vessels may have a heating or cooling jacket or heating or cooling tubes (coils) around the vessel wall to heat up or cool down the content. Industrial chemical reactors vary in their sizes. Some of them are of few cm3, while others are vast structures often depicted in industrial plants’ photographs. For instance, kilns producing lime from huge limestone may be 25 meters high and contain over 400 tons of material. Reactor’s design is dependent on many factors. Particularly, the kinetics and thermodynamics of chemical reactions being conducted are of central importance. There are three primary models used in estimation of the most significant process variables for dissimilar chemical reactors: batch reactor, plug flow, and continuous stirred-tank reactors. Moreover, there is also a catalytic reactor, which requires distinct treatment.

In batch chemical reactors, the components are added upon the reactor and consequently controlled allowing reaction to occur. When the reaction is over, the batch is removed and then, the reactor is prepared for another reaction round. Such reactor is ideal for people in need of chemicals in small quantities, for instance, a chemists researcher requiring compounds for their pharmaceutical research. Batch reactors are commonly used in laboratories. Reactors are contained in a beaker, flask, or test-tube. The content is mixed together and then heated for reaction to occur. After the reaction, there is a cooling stage followed by pouring the products out, and purification, if necessary. At the end, the batch reactor is cleaned to allow for addition of different reactants. Batch reactors are useful for companies manufacturing products that involve dissimilar reactor conditions and reactants. Manufacture of margarine and colorants are processes, which require batch reactors.

On the contrast, a continuous chemical reactor operates continuously and requires a steady supply of reaction materials. In industrial chemicals manufacture, continuous reactors provide consistent and high level chemicals. Such reactors are periodically shut down for maintenance or when they are not in need. To restart them, special steps are taken to ensure that their functionality is not impaired. Continuous reactors are used in feeding reactants. When the reaction is about to occur, products are withdrawn to another point. There must be equivalent flow rate of products and reactants. Continuous reactors are rarely used in laboratories. However, water-softeners can be considered as continuous reactors. Hard water from mains goes through the tube that contains ion-exchange resin. Reaction occurs down a tube and then, soft water gets out through the exit.

Designers familiar with chemical reactors’ needs create such devices. Custom reactors are built for special purposes. In designing reactors, chemical engineers ensure conformity with existing safety guidelines. Enterprising chemists may build their personal chemical reactors for certain projects. While there are certain safety steps important in ensuring that reactors work properly and safely, the basics of designing chemical reactors remain relatively simple. Continuous reactors are used in catalytic cracking at oil refineries. Tubular, fixed bed, fluid bed, and Continuous Stirred Tank (CST) are kinds of continuous reactors. Tubular reactors are used for fluids, liquids and gases, flowing at high velocities. While reactants flow, they are converted into products. The products cannot diffuse back, and there is no or little back mixing. It decreases side reactions occurrence and increases productivity of desired products. Fixed bed continuous reactors are used in sulfuric acid, ammonia, and nitric acid manufacture. Fluid bed continuous reactors are used when catalyst particles are involved, for instance, in ethene oxychlorination to vinyl chloride. Lastly, impellers are essential in stirring reagents inside CSTRs. More importantly, continuous CSTRs are used in polythene manufacture. The major functions of reactors include mixing of contacting catalysts and substrates, heat transfers, mass transfers, environment control, and containment of chemicals.

Technologically, design of chemical reactors aims at providing the maximum quantity of products within the minimal time. It ensures maximum profits. However, the design of reactors faces numerous constraints such as limited availability of raw materials. The demand for reactors may also be low. Moreover, safety issues accompany the use of reactors. Therefore, it is important to affect proper pollution control strategies to ensure that reactors do not affect the environment and us. It can be done through proper application of kinetics, stoichiometry, and thermodynamics in manufacture of chemical reactors. With tube, stirred tank, fluidized, fixed bed, and tubular reactors, it is important to incorporate process intensification. It is because most chemical reactions are exothermic releasing excessive heat that is hazardous to human health.

Chemical reactors major demand is in manufacture of vanaspati, shortenings, and margarine. Moreover, such reactors may be used in production of vegetables and blend of triglycerides, that is, fatty acids and glycerol. Chemical reactors may also be used in hydrogenation of fatty acids like saturated, diunsaturated, and monosaturated ones to reduce color or odor, as well as bolster melting point and improve stability. In design of chemical reactors, process intensification is important. It entails a reduction strategy in a chemical plant’s physical size to achieve given objectives. Process intensification is essential with increasing competition, stringent environment norms, and scarce resources. Additionally, it is important to incorporate multifunctional reactor systems, where many functions are elaborately designed to happen together. Process intensification is a major drive in petrochemicals and refining sector.

Reactors are used in catalytic reforming with the intention of increasing octane number. Moreover, chemical reactors assist in conversion of napthenes, cyclo paraffin, and paraffin to branced paraffin and aromatics. Such process involves isomerization, cyclization, and dehydrogenation. Momentum transfer occurs in a radial flow reactor, while energy transfers occur because of heat exchange within the chemical reactors. In fact, bioreactor operates due to interactive relations between the physical environment and bio system. During the biotic phase, the external environment regulates the chemical reactors while in the abiotic phase, interaction of energy, momentum, and mass is culminating in huge environmental gradients, especially in time and space (Levenspiel, 1992).

In most industries, there are many chemical reactions between liquids and gases. First, gas purification entails removal of carbon dioxide, nitrogen oxides, and hydrogen sulphide gases from chemical process streams. Secondly, production processes such as fermentation, polymerization, chlorination, oxidation, carbonization, and carboxylation also involve the use of reactors. Reaction technologies cover production of many fine chemicals as well as intermediates from some antibiotics to additives, dyes, phenol, adipic acid, esters, hydrogen peroxide, acetaldehyde, etc. (Trambouze, Landeghem, & Wauquier, 1998). The importance of reactor performance in technology has been overlooked. Partially, this is the reason of poor chemical process performances. In such chemical processes, the function of kinetics is not as vital as that of mass transfer and fluid dynamics. In chemical reactors, exothermic polymerization reactions are controlled using cold water held in jackets. Pressure may vary with the intent of controlling the rate of chemical reactions. Further, emulsion concentration and productivity is attained within pilot plants but is not reproduced in industrial autoclaves exhibited through lower performances.

Potential for Improvement

In future, chemicals may be produced inside reactors approximately the size of large desktop computers called micro reactors. Therefore, extensive knowledge about processes within industrial reactors may help chemical manufacturers reduce costs and bolster energy efficiency. The reduction of reactor sizes will culminate to reduction of chemical amount and capital costs in a given time. Consequently, chemical processes will be inherently safe. Such reactors can keep temperatures constant. The surface will be large enough to accommodate more volume. It will allow efficient and effective heat transfer from the chemical reaction to the environment. It is even for exothermic reactions such as aromatic hydrocarbon nitration, which may be explosive. Considerable research concerning development micro reactors has been achieved paving way for possible improvements of reactors.

There exists the possibility of direct conversion of benzene into phenol. A mixture of oxygen and benzene is directed through alumina tube that is packed with some palladium. Hydrogen gas passes over the mixture. Such a micro reactor is thus important in production of phenol from some benzene. Oxygen atoms react with hydrogen to release species of reactive oxygen like hydroxyl radicals. The hydroxyl radicals then react with benzene forming phenol. Oscillatory flow amalgamation is another development that spells potential development of reactors. Chemical engineers are working towards designing reactors, which allow fluids that are to be reacted get oscillated within reactors with baffles at 0.5Hz and 15Hz and amplitudes ranging from 1mm to 100mm. It permits effective reactants mixing as well as heat transfer to the environment. It provides similar conditions as those experienced in plug flows that are hard to achieve where small material quantities are used.

There are many disadvantages resulting from the use of chemical reactors. Huge amounts of energy used by reactors is one of them. Equally, there are huge amounts of waste released by chemical reactors. Moreover, many safety issues such as toxic materials and explosive situations arise. There may be uncontrolled chemical reactions because of overpressure and energy release through exothermic reactions. Also, toxic materials may be suddenly released from reactors due to human errors and work-related accidents. Additionally, chemical reactors expose people to heat stress. Moreover, teratogenic, mutagenic, and carcinogenic substances presenter in reactors may be released during maintenance work and cleaning. Also, there may be musculoskeletal problems arising from prolonged shut-down (Nauman, 2002).

However, such problems can be militated through good repair of reactors. Additionally, the use of control systems for reactors to achieve consistent, economic, and safe operations of such equipment is fundamental. It is important to sensitize chemical engineers and practicing students of safety issues regarding chemical reactors as an overarching concern in reactor control and design. Some waste materials and toxic substances from chemical reactors may be hazardous to people. For this reason, a healthy debate regarding an avalanche of issues relating to reactors is essential in the wider chemical industry spectrum. Development of practical and stable control systems and effective reactors is vital as well. When this is coupled with proper control schemes and keen examination of controllers’ algorithms, it will ensure that safety against reactors.

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Steady chemical reactors operations require provision of copiousness of area for cooling and heat transfer or even heating medium to handle dynamic disturbances. Temperature control will also guarantee that reactors will not discharge excessive heat. Specifications of physical properties, including viscosity, density, as well as molecule weight distribution and economic objectives relating to selectivity, yield, and conversion, ensure that reactors are not overworked. Reactors require high pressure in order to achieve high temperature. Fabrication of reactors is expensive, and fission activity poses a huge challenge for reactors operators (Rodrigues, Calo, & Sweed, 1999). Moreover, there is a need of control rods and a heat exchanger. It is important to shut down reactors to reload and load newfangled ones. It is equally important to ensure that coolant radioactivity is short-lived by keeping the reactors pure. Also, it is important to facilitate fuel processing and shut down reactors when required to ensure moderate heat transfer.

In addition, it is necessary to have homogeneous catalytic chemical reactors to facilitate flow mixing and pattern. Chemical reactions are affected by the thermodynamic equilibrium. Additionally, chemical engineers should focus on application and computation of energy conservation and matter. Good ideas, chemical engineering knowledge, and experience are fundamental in scaling up chemical reactors as well as unit operations. For this reason, anemometers, conductimeters, capacitors, and pilot tubes as well as model reactions and fluids are instrumental in this scale up. Industrial reactors are used in benzene conversion. In industrial reactors, proper polymerization rate and intense agitation increase stirrer speed in emulsion stability within these reactors. Emulsion stability within reactors is especially important in exothermic chemical reactions (Whitaker, & Cassano, 1996). In chemical engineering processes, bolstering efficiency and environmental sustainability of chemical reactors are important factors that dictate the posterity of this equipment.

Another potential improvement is scale up of chemical reactors, which should be chief for any chemical engineer. It is a basic step towards optimization and realization of many industrial plants. Such scale up involves synthesis of knowledge accumulated in process development phases from laboratory experiments design and kinetic correlations derivation to mathematical modeling, operation of industrial and pilot plants, and dynamic experiments. Reactor technologies affect selection of design, modeling, and heat exchanges. Therefore, these reactor technologies are important in flow pattern, catalyst, effectiveness factor, as well as pressure drop. Heat exchange is obtained through multi-tubular reactors, fluidized beds, and adiabatic intercooled layer (Aris, 1999). Flow pattern directly influences yield and is effectively managed through proper design of reactors as well as operating conditions such as swapping with pressure drops.

Conclusion

Chemical reactions concerning oil, chemical, and petrochemical industries occur in reactors. Different kinds of reactors face extremely varying operating conditions. It concerns the involved chemical species’ nature, both products and reactants, as well as operating physical conditions. Chemical reactors should provide the requisite residence time to reactants in order to complete the chemical reaction, allow any necessary heat exchange, and place phases in close contact in facilitating the reaction. Tubular reactors are important for gaseous reactants. The paper has demonstrated that batch reactors are non-continuous as well as mixed-closed vessel, while CSTR operate in steady state and is never closed. Mass inflows and outflows within the reactor cannot be canceled. The essay has shown that indeed, most chemical engineering processes widely use reactors in chemical reactions.

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