Catalysts - Increasing the Rate of Reaction - Essay Example

Catalysts Increase or Decrease the Rate of Reaction Humans have always been familiar with catalysts in their everyday lives, for example in making of soaps, fermentation of wine to vinegar. The name Catalyst was first proposed by Swedish chemist Jöns Jakob Berzelius in the years 1835. The word has been derived from the two Greek terms ‘kata’ which means down and ‘lyein’ which means loosen. Berzelius used this term to describe that the process loosens the bonds through which chemical compounds are held together. A Catalyst is a substance that is usually used to speed up a chemical reaction, but remains unchanged even after the reaction. When the reaction is complete, the mass of the catalyst will be the same as it was at the beginning of the reaction. A catalyst is a substance that is added to a reaction in order to alter the rate of the reaction. The catalyst can increase the rate of reaction by reducing the activation energy of the reaction or decrease the rate of reaction by increasing the activation energy of the reaction. A catalyst changes the procedure of the reaction and consequently changes the activation energy of the reaction. A catalyst can be obtained back unchanged after the reaction is complete (Chisholm-Burns, 2008, p 371). “A catalyst combines with a reactant known as the substrate and forms an intermediate known as complex, which then decomposes to regenerate the catalyst and yield the products. In this way the catalyst decreases the activation energy by changing the mechanism of the process and the rate is accordingly increased.” (Sinko and Martin, 2005, p 416). Negative Catalysts are certain materials when present during a chemical reaction, create an unfavorable or hindering influence. The presence of these catalysts increases rather than decreasing the chemical friction. Negative catalysts can sometimes stabilize a chemical system. For example the addition of a few hundredths of one percent of hydrochloric or sulfuric acid to a 30 volume hydrogen peroxide is said to considerably boost its stability (Sabatier, 2007, p 2-4) Catalytic reactions are generally categorized into either homogenous or heterogeneous reactions. A homogenous catalysis reaction is one in which both the catalyst and the substances that the catalysts work on are in the same phase, i.e. solid, liquid or gas. An example of this can be seen in the reaction studied by Kirchhof. During this reaction both sulfuric acid and starch were in the same phase, i.e. a water solution. A heterogeneous catalysis reaction is one in which the catalyst is in a different phase from the compounds or substances it acts on. For example in a catalytic converter, the catalyst is a solid, usually a valuable metal such as platinum or rhodium, whereas the substances on which it acts is a gas such as nitrogen dioxide or any other gaseous byproducts of combustion. Catalysts are also classified into electrocatalysts and organocatalysts. In electrochemistry, especially in fuel cell engineering many metal-containing catalysts are utilized to increase the speed of half reactions in fuel cell. One common type of fuel catalyst used is the nanoparticles of platinum and these are supported on larger carbon particles. Organocatalysts need a higher loading than metal-based catalysts. However these catalysts are usually available in bulk thus reducing costs. Enzymatic reactions operate on a principle of organic catalysts. Catalytic Reactions have certain basic characteristics. Firstly, during a chemical reaction, the catalyst remains unchanged. It has the same mass and chemical composition at the end of the chemical reaction as it did in the beginning of the chemical reaction. However its physical properties may be subject to change. Secondly, a very small portion of catalyst can produce significant effect on the speed of the chemical reaction. Thirdly, a catalyst cannot start off any chemical reaction. It can purely effect the reaction, i.e. it can increase or decrease the rate of reaction. A catalyst does not contribute to the energy system during the chemical reaction, since it is reproduced at the end of each chemical reaction. The free energy change will hence be the same in the presence or absence of the catalyst. A catalyst merely functions as an agent to identify an alternate path for the chemical reaction. Lastly, the catalyst does not stimulate the final state of equilibrium. Equilibrium remains constant (Upadhyay, 2006, p 146-147). Catalysts are used in a number of industrial processes today, during the manufacturing of a number of things. A wide variety of catalysts are used in the refining of petrol, production of ammonia, manufacturing of rubber, soaps, detergents and polymers. One of the most prominent processes to use catalysts extensively is the refining of petroleum. The petroleum refining process used catalysts for reforming, catalytic cracking and alkylation. Reforming is a process that uses heat, pressure and a catalyst to cause chemical reactions that promotes naphthas contained in petroleum, into high octane petrol and petrochemical feedstock. The naphthas are hydrocarbon mixtures comprising of many paraffins and naphthenes. The catalyst usually used in this Reforming process is one containing platinum. The platinum based catalyst speeds up the process of udgradation of naphthas into high octane petrol and petrochemical feedstock. Once this reforming process is done with the platinum based catalyst, paraffins are converted into isoparaffins, paraffins are converted into napthenes and naphthenes are converted into aromatics. Cracking is a process of breaking down heavy hydrocarbon molecules into lighter products, namely petrol and diesel. Cracking involves catalytic cracking, thermal cracking and hydrocracking. Catalytic cracking converts heavy hydrocarbon fractions got by vacuum distillation into lighter products such as petrol and light fuel oil. The feedstock goes through a chemical breakdown, under controlled heat and pressure, in the presence of a catalyst. The catalyst used in this process includes either small pellets of silica-alumina or silica-magnesia. Fluid catalytic cracking uses a very fine powder as catalyst. This fine powder is usually a mixture of aluminum oxide and silica and flows like liquid when disturbed by steam or gas. Thermal cracking uses heat to breakdown the residue from vacuum distillation. Hydrocracking is nothing but catalytic cracking in the presence of hydrogen. Hydrocracking is capable of increasing the yield of petrol components. Propylene and butylenes are Olefins that are produced during catalytic and thermal cracking. Alkylation is the chemical bonding of these light molecules with isobutane to form larger molecules that make high octane petrol. Olefins and Isobutane are mixed with an acid catalyst and cooled (Australian Institute of Petroleum, 2002). The production process of the commercially important gas ammonia also makes use of catalysts. Ammonia is produced by combining nitrogen gas and hydrogen gas under high pressure and temperature in the presence of a catalyst. The catalyst used in this process is powdered iron. In the absence of the catalyst the reaction of nitrogen and hydrogen gases to produce ammonia would not occur. But the presence of a catalyst such as powdered iron the reaction occurs and is made to occur fast enough to produce large quantities of ammonia gas for commercial use. Catalysts are also widely used in the production of rubbers. Rubbers can be classified into two, namely natural and synthetic rubber. While natural rubber is obtained from latex, synthetic rubber is obtained from synthetic latex. Synthetic rubber is basically produced from two substances, namely butadiene- 1,3 and sterol. Butadiene-1,3 is a gas obtained from oil and sterol is obtained from oil coal. Butadiene-1,3 and sterol are placed in large containers with soap solution. The soap solution assists in the formation of some parts of the rubber. Catalysts are added to this mixture. The catalyst used here is metal sodium. After mixing gradually, the mixture turns into a liquid that has dairy colour. When the synthetic latex reaches a certain point and obtains the necessary standards, inhibitors or negative catalysts are added to stop the reaction. The latex is placed into another container with an acid and a hydrochloric solution where the reaction is stopped and latex is curtailed. The curtailed slices of rubber are then washed to remove residue. Among synthetic rubbers Polybutadiene Rubber (PBR) is one of the most important and widely used synthetic rubbers. Catalysts are also used in the production of PBR. Alkali metals are used as catalysts in the production of PBR. Al oxide is also used as a filler and an acid catalyst in the manufacturing of rubber and as a lubricant (Sheftel, 1995, p193). Tin and Amines are used as catalysts in the production of foam rubber as they speed up the chemical reaction and and allow large volume of production runs. Soap manufacturing process also used catalysts to a large extent. Soap is a combination of sodium and potassium salts of stearic acids and other fatty acids. Fatty acids are found in animal fats and in plant oils such as palm oil, coconut oil, olive oil, castor oil etc. The reacting of these oils and fats with a strong alkaline solution in the presence of a catalyst is a process called saponification. Soap is usually made using any of two processes, namely, hot process and cold process. However for both hot and cold process heat is required for saponification. Sodium Hydroxide popularly referred to as lye is used as catalyst in both processes. Lye is the catalyst that induces the fats and oils to saponify and turn into soap and glycerin. The sodium hydroxide reacts with oils and fats and is chemically changed into soap and glycerin and hence does not remain in the final bar of soap. In the hot-process lye and fat are boiled together at 80-100oC until saponification occurs. The soap maker can identify this point either by tasting or by observing closely. After saponification the soap is separated from the solution by adding salt. In the cold process the soap maker has to make a note of the saponification values of the fats, in order to calculate the amount of lye (sodium hydroxide) to be used. Excess lye can cause high pH levels which will irritate the skin. The lye is dissolved in water and the oils are heated or melted at room temperature. Once both the substances have cooled to about 100-110oC, they may be combined. The lye fat mixture is stirred and blended. Essential oils, fragrance etc are added to mixture and then poured into moulds to cool off (Willcox, 2000, 453) Detergent manufacturing processes also make use of catalysts. Many types of detergents are manufactured. The feedstocks used are benzene and propene. Propene reacts in the presence of phosphoric acid as a catalyst to form a tetramer. This tetramer combines with benzene to form dodecylbenzene in the presence of the catalyst aluminum chloride. Treatment if this with strong sulfuric acid results in sulfonic acid which is neutralized to give the required sodium salt. Various materials are added to synthetic detergents to improve their cleansing ability. Many bulk industry chemicals are manufactured with the help of various catalysts. Large scale industry chemicals are manufactured using oxygen as a catalyst through the process of catalytic oxidation. Examples of chemicals produced by this process include, nitric acid derived from ammonia, sulfuric acid, converted from sulfur dioxide to sulfur trioxide using the chamber process, terephthalic acid from p-xylene and acrylonitrile from propane and ammonia. Other chemicals are products generated through large-scale reduction through hydrogenation. The biggest example of a chemical produced through hydrogenation is ammonia which is made using the Haber process from nitrogen. Methanol is made from carbon monoxide. Bulk Polymers are obtained from ethylene and uses a catalyst called Ziegler-Natta. Ziegler-Natta catalysts are based on titanium compounds and organometallic aluminium compounds like undefined methylaluminoxane or well defined triethylaluminium. Some of the polymers prepared using Ziegler-Natta catalyst include, Polyethylene, Polypropylene, Amorphous Poly-alpha-olefins (APAO), Polyvinyl alcohol and Polyacetylene. Polyethylene pr polythene as it is commonly known is thermoplastic commodity used in the packaging of consumer products. Polypropylene is is also a thermoplastic polymer used in packaging, textiles, stationery, plastic parts, containers, laboratory equipment, automotive parts etc. Amorphous Poly-alpha-olefins (APAO) have an amorphous structure which makes them widely used in the production of hot melt adhesives. Polyvinyl alcohol is a water soluble synthetic polymer and has very good adhesive properties. Polyacetylene has high electrical conductivity and is used in microelectronics. Dye manufacturers use a series of catalysts namely, Anhydrous Cupric Chloride, Di hydrate Cupric Chloride, Nickel Sulphate, Nickel Chloride etc. Copper Stearate is used as a catalyst in Wood Preservative. Cupric Acetate is used as a catalyst in making pesticides and pigments. It is also used as catalyst in organic synthesis (Shan Chemicals, Online). Many fine chemicals are prepared with the help of catalysts. The methods used in producing fine chemicals are ones used in producing bulk chemicals also. However production of fine chemicals involves a few other specialized processes that can prove to be very expensive on a large scale. One prominent example of such a process would be Friedel-Crafts reaction. The Friedel-Crafts alkylation of benzene concerns the replacement of a hydrogen atom on benzene ring by an alkyl group like methyl or ethyl. Aluminium chloride is used as a catalyst in the process. Benzene is treated with a chloroalkane in the presence of aluminium chloride, the catalyst. The Friedel-Crafts acylation of benzene is treated with mixture of ethanol chloride and aluminium chloride as a catalyst. Acyllation means replacing an acyl group into a benzene ring in this process. At the end of the process a ketone known as phenylethanone is formed. Food processing also uses catalysts extensively. One chief example of the use of catalysts is the hydrogenation of fats with nickel as the catalyst during the production of margarine. Food Hydrogenation is done by exposing the oil to hydrogen gas in the presence of a catalyst. The catalysts used here is nickel. Oil is hydrogenated in carbon steel vessels in which the correct temperature, hydrogen gas pressure, agitation of oil and the concentration of the catalyst nickel, can be well controlled. After the process of hydrogenation the nickel catalyst is removed through filteration. Hydrogenation results in the conversion of certain double bonds to saturated bonds (J. Scott Smith, Yiu H. Hui, 2004, p346). Catalysts are extensively used in the industry of organic chemistry. From the refining of petroleum to the manufacturing of ammonia gas, soaps and detergents, industry bulk chemicals, industry fine chemicals, rubber and polymers to the processing of food. Hence catalyst is one of the most important substances in the field of chemistry, without which the production and manufacturing of many industrial products would be impossible. References Australian Institute of Petroleum (2002). Refining of Petroleum. Retrieved June 19, 2009. http://www.aip.com.au/ Chisholm-Burns, M A (2008). Barron's PCAT: Pharmacy College Admission Test. Barron's Educational Series, 2008. p 371 Sabatier, P (2007). Catalysis In Organic Chemistry. READ BOOKS, 2007. p 2-4 Sheftel, V O (1995). Handbook of Toxic Properties of Monomers and Additives. CRC Press, 1995. p193 Shan Chemicals. Shan Chemicals: Industrial Chemicals. Retrieved June 19, 2009. http://www.indiamart.com/shanchemicals/industrial-chemicals.html Sinko, P J and Martin, A N (2005). Martin's Physical Pharmacy and Pharmaceutical Sciences: Physical Chemical and Biopharmaceutical Principles in the Pharmaceutical Sciences. Lippincott Williams & Wilkins, 2005. p 416 Smith, J S and Hui, Y H (2004). Food Processing: Principles and Applications. Wiley-Blackwell, 2004. p346 Upadhyay, S K (2006). Chemical Kinetics and Reaction Dynamics. Springer, 2006. p 146-147 Willcox, Michael (2000). "Soap". in Hilda Butler. Poucher's Perfumes, Cosmetics and Soaps (10th edition ed.). Dordrecht: Kluwer Academic Publishers. pp. 453. Read More

A heterogeneous catalysis reaction is one in which the catalyst is in a different phase from the compounds or substances it acts on. For example in a catalytic converter, the catalyst is a solid, usually a valuable metal such as platinum or rhodium, whereas the substances on which it acts is a gas such as nitrogen dioxide or any other gaseous byproducts of combustion. Catalysts are also classified into electrocatalysts and organocatalysts. In electrochemistry, especially in fuel cell engineering many metal-containing catalysts are utilized to increase the speed of half reactions in fuel cell.

One common type of fuel catalyst used is the nanoparticles of platinum and these are supported on larger carbon particles. Organocatalysts need a higher loading than metal-based catalysts. However these catalysts are usually available in bulk thus reducing costs. Enzymatic reactions operate on a principle of organic catalysts. Catalytic Reactions have certain basic characteristics. Firstly, during a chemical reaction, the catalyst remains unchanged. It has the same mass and chemical composition at the end of the chemical reaction as it did in the beginning of the chemical reaction.

However its physical properties may be subject to change. Secondly, a very small portion of catalyst can produce significant effect on the speed of the chemical reaction. Thirdly, a catalyst cannot start off any chemical reaction. It can purely effect the reaction, i.e. it can increase or decrease the rate of reaction. A catalyst does not contribute to the energy system during the chemical reaction, since it is reproduced at the end of each chemical reaction. The free energy change will hence be the same in the presence or absence of the catalyst.

A catalyst merely functions as an agent to identify an alternate path for the chemical reaction. Lastly, the catalyst does not stimulate the final state of equilibrium. Equilibrium remains constant (Upadhyay, 2006, p 146-147). Catalysts are used in a number of industrial processes today, during the manufacturing of a number of things. A wide variety of catalysts are used in the refining of petrol, production of ammonia, manufacturing of rubber, soaps, detergents and polymers. One of the most prominent processes to use catalysts extensively is the refining of petroleum.

The petroleum refining process used catalysts for reforming, catalytic cracking and alkylation. Reforming is a process that uses heat, pressure and a catalyst to cause chemical reactions that promotes naphthas contained in petroleum, into high octane petrol and petrochemical feedstock. The naphthas are hydrocarbon mixtures comprising of many paraffins and naphthenes. The catalyst usually used in this Reforming process is one containing platinum. The platinum based catalyst speeds up the process of udgradation of naphthas into high octane petrol and petrochemical feedstock.

Once this reforming process is done with the platinum based catalyst, paraffins are converted into isoparaffins, paraffins are converted into napthenes and naphthenes are converted into aromatics. Cracking is a process of breaking down heavy hydrocarbon molecules into lighter products, namely petrol and diesel. Cracking involves catalytic cracking, thermal cracking and hydrocracking. Catalytic cracking converts heavy hydrocarbon fractions got by vacuum distillation into lighter products such as petrol and light fuel oil.

The feedstock goes through a chemical breakdown, under controlled heat and pressure, in the presence of a catalyst. The catalyst used in this process includes either small pellets of silica-alumina or silica-magnesia. Fluid catalytic cracking uses a very fine powder as catalyst. This fine powder is usually a mixture of aluminum oxide and silica and flows like liquid when disturbed by steam or gas. Thermal cracking uses heat to breakdown the residue from vacuum distillation. Hydrocracking is nothing but catalytic cracking in the presence of hydrogen.

Hydrocracking is capable of increasing the yield of petrol components.

Read More