Catalytic distillation

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Catalytic distillation is a branch of reactive distillation which combines the processes of distillation and catalysis to selectively separate mixtures within solutions. Its main function is to maximize the yield of catalytic organic reactions, such as the refining of gasoline. The earliest case of catalytic distillation was thought to have dated back to 1966; [1] however, the idea was officially patented in 1980 by Lawrence A. Smith, Jr. [2] The process is currently used to purify gasoline, extract rubber, and form plastics.

Contents

Catalysts

The catalysts used for catalytic distillation are composed of different substances and packed onto varying objects. The majority of the catalysts are powdered acids, bases, metal oxides, or metal halides. These substances tend to be highly reactive which can significantly speed up the rate of the reaction making them effective catalysts. [3]

The shapes which the catalysts are packed onto must be able to form a consistent geometric arrangement to provide equal spacing in the catalyst bed (an area in the distillation column where the reactant and catalyst come into contact to form the products). This spacing is meant to ensure the catalysts are spread evenly within the column. The catalyst bed must be largely spacious (about 50% empty) so that any evaporated gaseous reactants may catalyze and form gaseous products. The catalyst bed must also be able to contract and expand as it may have to respond to pressure changes within the column. [4]

Before the catalysts are packed onto the shape, they are first packed onto something porous like a cloth or wire mesh. The cloth may be made from cotton, fiberglass, polyester, nylon, or other similar materials. The mesh is generally made from aluminum, steel, or stainless steel. [5]

In terms of shapes, catalysts are usually packed on rings, saddles, balls, sheets, tubes, or spirals. These shapes tend to be made from fiberglass, teflon, and nonreactive metals. Before the catalysts are introduced into the system, they are either bagged, attached on metal grills or screens, or placed on polymer foams. [6]

Process

Within the catalytic distillation column, liquid reactants are catalyzed while concurrently being heated. As a result, the products immediately begin to vaporize and are separated from the initial solution. By catalyzing and heating the reactants at the same instant, the newly formed products are rapidly boiled out of the system. With the lack of the products, Le Chatelier's principle comes into effect and forms new products from the reactants to replace the removed products. Since the products are continuously exiting, the system never reaches equilibrium. The continuous formation of products causes the reaction to achieve completion. [7]

Reflux

In most reactions carried out by catalytic distillation, the reactants are often more volatile than the products. Because of this, an internal recycling system, known as the reflux, is implemented right after the condenser (an area within the column where escaped gases are cooled down to liquids). The reflux transfers the concentrated vapor back to the catalyst area. [8] The reflux also returns a portion of the condensed liquids to the column to ensure only the products with the lowest boiling points are captured. As the reflux returns impure mixtures, the catalysts are washed for a prolonged usage. [9]

Types of Reactions

Reactions within catalytic distillation columns include: [10]

Improvements from two column distillation

In two column distillation, the obtaining the desired product calls for a column for catalysis and then a column for distillation. This means that the distillation company would have to fund the construction of two large columns as well as a method for transporting the contents of one column to another. With catalytic distillation, the company only needs to fund one column which eliminates both the cost for a second column and the cost to move chemicals from one column to another. This optimization cuts overhead costs to nearly half the original cost. [11]

In addition to cutting costs, catalytic distillation is a milestone in efficiency and efficacy. Less time is spent because it is not necessary to move the contents from column to another. Also, the percent yielded from reactants to products increased in some reactions from 96-97% to 99.9%. [12]

Related Research Articles

<span class="mw-page-title-main">Catalysis</span> Process of increasing the rate of a chemical reaction

Catalysis is the increase in rate of a chemical reaction due to an added substance known as a catalyst. Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice; mixing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process of regenerating the catalyst.

<span class="mw-page-title-main">Chemical reaction</span> Process that results in the interconversion of chemical species

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei, and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.

<span class="mw-page-title-main">Distillation</span> Method of separating mixtures

Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixture and the condensation of the vapors in a still.

<span class="mw-page-title-main">Haber process</span> Industrial process for ammonia production

The Haber process, also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia. The German chemists Fritz Haber and Carl Bosch developed it in the first decade of the 20th century. The process converts atmospheric nitrogen (N2) to ammonia (NH3) by a reaction with hydrogen (H2) using an iron metal catalyst under high temperatures and pressures. This reaction is slightly exothermic (i.e. it releases energy), meaning that the reaction is favoured at lower temperatures and higher pressures. It decreases entropy, complicating the process. Hydrogen is produced via steam reforming, followed by an iterative closed cycle to react hydrogen with nitrogen to produce ammonia.

<span class="mw-page-title-main">Hydrogenation</span> Chemical reaction between molecular hydrogen and another compound or element

Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, often an alkene. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogenation reduces double and triple bonds in hydrocarbons.

In chemistry, reactivity is the impulse for which a chemical substance undergoes a chemical reaction, either by itself or with other materials, with an overall release of energy.

<span class="mw-page-title-main">Heterogeneous catalysis</span> Type of catalysis involving reactants & catalysts in different phases of matter

Heterogeneous catalysis is catalysis where the phase of catalysts differs from that of the reactants or products. The process contrasts with homogeneous catalysis where the reactants, products and catalyst exist in the same phase. Phase distinguishes between not only solid, liquid, and gas components, but also immiscible mixtures, or anywhere an interface is present.

<span class="mw-page-title-main">Catalytic reforming</span> Chemical process used in oil refining

Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil into high-octane liquid products called reformates, which are premium blending stocks for high-octane gasoline. The process converts low-octane linear hydrocarbons (paraffins) into branched alkanes (isoparaffins) and cyclic naphthenes, which are then partially dehydrogenated to produce high-octane aromatic hydrocarbons. The dehydrogenation also produces significant amounts of byproduct hydrogen gas, which is fed into other refinery processes such as hydrocracking. A side reaction is hydrogenolysis, which produces light hydrocarbons of lower value, such as methane, ethane, propane and butanes.

In chemistry, molecularity is the number of molecules that come together to react in an elementary (single-step) reaction and is equal to the sum of stoichiometric coefficients of reactants in the elementary reaction with effective collision and correct orientation. Depending on how many molecules come together, a reaction can be unimolecular, bimolecular or even trimolecular.

<span class="mw-page-title-main">Catalytic cycle</span> Multistep reaction mechanism involving a catalyst

In chemistry, a catalytic cycle is a multistep reaction mechanism that involves a catalyst. The catalytic cycle is the main method for describing the role of catalysts in biochemistry, organometallic chemistry, bioinorganic chemistry, materials science, etc.

Ring-closing metathesis (RCM) is a widely used variation of olefin metathesis in organic chemistry for the synthesis of various unsaturated rings via the intramolecular metathesis of two terminal alkenes, which forms the cycloalkene as the E- or Z- isomers and volatile ethylene.

<span class="mw-page-title-main">Hydrodesulfurization</span> Chemical process used to remove sulfur in natural gas and oil refining

Hydrodesulfurization (HDS), also called hydrotreatment or hydrotreating, is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products, such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils. The purpose of removing the sulfur, and creating products such as ultra-low-sulfur diesel, is to reduce the sulfur dioxide emissions that result from using those fuels in automotive vehicles, aircraft, railroad locomotives, ships, gas or oil burning power plants, residential and industrial furnaces, and other forms of fuel combustion.

In chemistry, a reaction intermediate, or intermediate, is a molecular entity arising within the sequence of a stepwise chemical reaction. It is formed as the reaction product of an elementary step, from the reactants and/or preceding intermediates, but is consumed in a later step. It does not appear in the chemical equation for the overall reaction.

<span class="mw-page-title-main">Membrane reactor</span>

A membrane reactor is a physical device that combines a chemical conversion process with a membrane separation process to add reactants or remove products of the reaction.

A frustrated Lewis pair (FLP) is a compound or mixture containing a Lewis acid and a Lewis base that, because of steric hindrance, cannot combine to form a classical adduct. Many kinds of FLPs have been devised, and many simple substrates exhibit activation.

Reactive flash volatilization (RFV) is a chemical process that rapidly converts nonvolatile solids and liquids to volatile compounds by thermal decomposition for integration with catalytic chemistries.

<span class="mw-page-title-main">Electrocatalyst</span> Catalyst participating in electrochemical reactions

An electrocatalyst is a catalyst that participates in electrochemical reactions. Electrocatalysts are a specific form of catalysts that function at electrode surfaces or, most commonly, may be the electrode surface itself. An electrocatalyst can be heterogeneous such as a platinized electrode. Homogeneous electrocatalysts, which are soluble, assist in transferring electrons between the electrode and reactants, and/or facilitate an intermediate chemical transformation described by an overall half reaction. Major challenges in electrocatalysts focus on fuel cells.

<span class="mw-page-title-main">Supramolecular catalysis</span> Field of chemistry

Supramolecular catalysis is not a well-defined field but it generally refers to an application of supramolecular chemistry, especially molecular recognition and guest binding, toward catalysis. This field was originally inspired by enzymatic system which, unlike classical organic chemistry reactions, utilizes non-covalent interactions such as hydrogen bonding, cation-pi interaction, and hydrophobic forces to dramatically accelerate rate of reaction and/or allow highly selective reactions to occur. Because enzymes are structurally complex and difficult to modify, supramolecular catalysts offer a simpler model for studying factors involved in catalytic efficiency of the enzyme. Another goal that motivates this field is the development of efficient and practical catalysts that may or may not have an enzyme equivalent in nature.

<span class="mw-page-title-main">Heterogeneous gold catalysis</span>

Heterogeneous gold catalysis refers to the use of elemental gold as a heterogeneous catalyst. As in most heterogeneous catalysis, the metal is typically supported on metal oxide. Furthermore, as seen in other heterogeneous catalysts, activity increases with a decreasing diameter of supported gold clusters. Several industrially relevant processes are also observed such as H2 activation, Water-gas shift reaction, and hydrogenation. One or two gold-catalyzed reactions may have been commercialized.

Heterogeneous metal catalyzed cross-coupling is a subset of metal catalyzed cross-coupling in which a heterogeneous metal catalyst is employed. Generally heterogeneous cross-coupling catalysts consist of a metal dispersed on an inorganic surface or bound to a polymeric support with ligands. Heterogeneous catalysts provide potential benefits over homogeneous catalysts in chemical processes in which cross-coupling is commonly employed—particularly in the fine chemical industry—including recyclability and lower metal contamination of reaction products. However, for cross-coupling reactions, heterogeneous metal catalysts can suffer from pitfalls such as poor turnover and poor substrate scope, which have limited their utility in cross-coupling reactions to date relative to homogeneous catalysts. Heterogeneous metal catalyzed cross-couplings, as with homogeneous metal catalyzed ones, most commonly use Pd as the cross-coupling metal.

References

  1. ↑ Hoffman, Achim. "Scale-up of Reactive Distillation Columns with Catalytic Packings" (PDF).
  2. ↑ Smith Jr, Lawrence A. "Catalytic Distillation Process Patent".
  3. ↑ Smith Jr, Lawrence A. "Catalytic Distillation Process Patent".
  4. ↑ Smith Jr, Lawrence A. "Catalytic Distillation Structure".
  5. ↑ Smith Jr, Lawrence A. "Catalytic Distillation Structure".
  6. ↑ Smith Jr, Lawrence A. "Catalytic Distillation Process Patent".
  7. ↑ Smith Jr, Lawrence A. "Catalytic Distillation Process Patent".
  8. ↑ Darton, Richard (1997). Distillation and Absorption '97. IChemE. ISBN   9780852953938.
  9. ↑ Gildert, Gary. "Advances In Process Technology Through Catalytic Distillation" (PDF). Archived from the original (PDF) on 2008-09-06. Retrieved 2012-02-14.
  10. ↑ Smith Jr, Lawrence A. "Catalytic Distillation Structure Patent".
  11. ↑ Gildert, Gary. "Advances In Process Technology Through Catalytic Distillation" (PDF). Archived from the original (PDF) on 2008-09-06. Retrieved 2012-02-14.
  12. ↑ Gildert, Gary. "Advances In Process Technology Through Catalytic Distillation" (PDF). Archived from the original (PDF) on 2008-09-06. Retrieved 2012-02-14.
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