Heterogeneous catalytic reactor

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Heterogeneous catalytic reactors put emphasis on catalyst effectiveness factors and the heat and mass transfer implications. Heterogeneous catalytic reactors are among the most commonly utilized chemical reactors in the chemical engineering industry.

Contents

Types of reactors

Heterogenous catalytic reactors are commonly classified by the relative motion of the catalyst particles.

Reactors with insignificant motion of catalyst particles

Fixed bed reactors

A fixed bed reactor is a cylindrical tube filled with catalyst pellets with reactants flowing through the bed and being converted into products. The catalyst may have multiple configuration including: one large bed, several horizontal beds, several parallel packed tubes, multiple beds in their own shells. The various configurations may be adapted depending on the need to maintain temperature control within the system. Serial connection of two reactors with option to dose oxidant between the stages enable under optimal conditions to increase the product yield in oxidation catalysis. [1] By dosing intermediates or products between the stages, valuable information could be found concerning the reaction pathways.

The catalyst pellets may be spherical, cylindrical, or randomly shaped pellets. They range from 0.25 cm to 1.0 cm in diameter. The flow of a fixed bed reactor is typically downward. Packed bed reactor.

Trickle-bed reactors

A trickle-bed reactor is a fixed bed where liquid flows without filling the spaces between particles. Like with the fixed bed reactors, the liquid typically flows downward. At the same time, gas is flowing upward. The primary use for trickle-bed reactors is hydrotreatment reactions (hydrodesulfurization and hydrodemetalation of heavy crude oil, [2] hydrodeasphaltenization of coal tar [3] ). This reactor is often utilized in order to handle feeds with extremely high boiling points..

Moving bed reactors

A moving bed reactor has a fluid phase that passes up through a packed bed. Solid is fed into the top of the reactor and moves down. It is removed at the bottom. Moving bed reactors require special control valves to maintain close control of the solids. For this reason, moving bed reactors are less frequently used than the above two reactors. Moving bed reactors are most suitable for solid content below 10% and is generally used where the solids (primarily catalyst) have high surface area due to its size in microns.

Rotating bed reactors

A rotating bed reactor (RBR) holds a packed bed fixed within a basket with a central hole. When the basket is spinning immersed in a fluid phase, the inertia forces created by the spinning motion forces the fluid outwards, thereby creating a circulating flow through the rotating packed bed. The rotating bed reactor is a rather new invention that shows high rates of mass transfer and good fluid mixing. RBR type reactors have frequently been applied in high-value biocatalysis reactions, there offering convenient reuse of immobilized enzymes [4] while preventing mechanical damage of the solid-phase catalysts. [5] RBR constructions are also emerging in the nuclear energy industry to purify liquid waste on the scale of 100's of cubic meters. [6]

Reactors with significant motion of catalyst particles

Fluidized bed reactors

A fluidized bed reactor suspends small particles of catalyst by the upward motion of the fluid to be reacted. The fluid is typically a gas with a flow rate high enough to mix the particles without carrying them out of the reactor. The particles are much smaller than those for the above reactors. Typically on the scale of 10-300 microns. One key advantage of using a fluidized bed reactor is the ability to achieve a highly uniform temperature in the reactor. The fluidized bed reactors are best for bio-catalysts or enzymes doped on solids since the solid are fluidized by the working fluid and there is no mechanical impact on the solids.

Slurry reactors

A slurry reactor contains the catalyst in a powdered or granular form. [7] This reactor is typically used when one reactant is a gas and the other a liquid while the catalyst is a solid. The reactant gas is put through the liquid and dissolved. It then diffuses onto the catalyst surface. Slurry reactors can use very fine particles and this can lead to problems of separation of catalyst from the liquid. Trickle-bed reactors don't have this problem and this is a big advantage of trickle-bed reactor. Unfortunately these large particles in trickle bed means much lower reaction rate. Overall, the trickle bed is simpler, the slurry reactors usually has a high reaction rate and the fluidized bed is somewhat in-between.

Related Research Articles

<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.

<span class="mw-page-title-main">Reaction rate</span> Speed at which a chemical reaction takes place

The reaction rate or rate of reaction is the speed at which a chemical reaction takes place, defined as proportional to the increase in the concentration of a product per unit time and to the decrease in the concentration of a reactant per unit time. Reaction rates can vary dramatically. For example, the oxidative rusting of iron under Earth's atmosphere is a slow reaction that can take many years, but the combustion of cellulose in a fire is a reaction that takes place in fractions of a second. For most reactions, the rate decreases as the reaction proceeds. A reaction's rate can be determined by measuring the changes in concentration over time.

In viscous fluid dynamics, the Archimedes number (Ar), is a dimensionless number used to determine the motion of fluids due to density differences, named after the ancient Greek scientist and mathematician Archimedes.

<span class="mw-page-title-main">Fluidization</span> Conversion of a granular material from a solid-like to liquid-like state

Fluidization is a process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid is passed up through the granular material.

<span class="mw-page-title-main">Chemical reactor</span> Enclosed volume where interconversion of compounds takes place

A chemical reactor is an enclosed volume in which a chemical reaction takes place. In chemical engineering, it is generally understood to be a process vessel used to carry out a chemical reaction, which is one of the classic unit operations in chemical process analysis. The design of a chemical reactor deals with multiple aspects of chemical engineering. Chemical engineers design reactors to maximize net present value for the given reaction. Designers ensure that the reaction proceeds with the highest efficiency towards the desired output product, producing the highest yield of product while requiring the least amount of money to purchase and operate. Normal operating expenses include energy input, energy removal, raw material costs, labor, etc. Energy changes can come in the form of heating or cooling, pumping to increase pressure, frictional pressure loss or agitation.

<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">Fluidized bed</span>

A fluidized bed is a physical phenomenon that occurs when a solid particulate substance is under the right conditions so that it behaves like a fluid. The usual way to achieve a fluidized bed is to pump pressurized fluid into the particles. The resulting medium then has many properties and characteristics of normal fluids, such as the ability to free-flow under gravity, or to be pumped using fluid technologies.

<span class="mw-page-title-main">Packed bed</span> A hollow object filled with material that does not fully obstruct fluid flow

In chemical processing, a packed bed is a hollow tube, pipe, or other vessel that is filled with a packing material. The packed bed can be randomly filled with small objects like Raschig rings or else it can be a specifically designed structured packing. Packed beds may also contain catalyst particles or adsorbents such as zeolite pellets, granular activated carbon, etc.

<span class="mw-page-title-main">Fluid catalytic cracking</span> Petroleum conversion process

Fluid Catalytic Cracking (FCC) is the conversion process used in petroleum refineries to convert the high-boiling point, high-molecular weight hydrocarbon fractions of petroleum into gasoline, alkene gases, and other petroleum products. The cracking of petroleum hydrocarbons was originally done by thermal cracking, now virtually replaced by catalytic cracking, which yields greater volumes of high octane rating gasoline; and produces by-product gases, with more carbon-carbon double bonds, that are of greater economic value than the gases produced by thermal cracking.

<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.

Temporal Analysis of Products (TAP), (TAP-2), (TAP-3) is an experimental technique for studying the kinetics of physico-chemical interactions between gases and complex solid materials, primarily heterogeneous catalysts. The TAP methodology is based on short pulse-response experiments at low background pressure (10−6-102 Pa), which are used to probe different steps in a catalytic process on the surface of a porous material including diffusion, adsorption, surface reactions, and desorption.

<span class="mw-page-title-main">Fluidized bed reactor</span> Reactor carrying multiphase chemical reactions with solid particles suspended in an ascending fluid

A fluidized bed reactor (FBR) is a type of reactor device that can be used to carry out a variety of multiphase chemical reactions. In this type of reactor, a fluid is passed through a solid granular material at high enough speeds to suspend the solid and cause it to behave as though it were a fluid. This process, known as fluidization, imparts many important advantages to an FBR. As a result, FBRs are used for many industrial applications.

<span class="mw-page-title-main">Trickle-bed reactor</span> Chemical reactor

A trickle-bed reactor (TBR) is a chemical reactor that uses the downward movement of a liquid and the downward (co-current) or upward (counter-current) movement of gas over a packed bed of (catalyst) particles. It is considered to be the simplest reactor type for performing catalytic reactions where a gas and liquid are present in the reactor and accordingly it is extensively used in processing plants. Typical examples are liquid-phase hydrogenation, hydrodesulfurization, and hydrodenitrogenation in refineries and oxidation of harmful chemical compounds in wastewater streams or of cumene in the cumene process.
Also in the treatment of waste water trickle bed reactors are used where the required biomass resides on the packed bed surface.

<span class="mw-page-title-main">Catalyst support</span> Porous material with a high specific surface area supporting a catalyst

In chemistry, a catalyst support is a material, usually a solid with a high surface area, to which a catalyst is affixed. The activity of heterogeneous catalysts is mainly promoted by atoms present at the accessible surface of the material. Consequently, great effort is made to maximize the specific surface area of a catalyst. One popular method for increasing surface area involves distributing the catalyst over the surface of the support. The support may be inert or participate in the catalytic reactions. Typical supports include various kinds of activated carbon, alumina, and silica.

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

A bubble column reactor is a chemical reactor that belongs to the general class of multiphase reactors, which consists of three main categories: trickle bed reactor, fluidized bed reactor, and bubble column reactor. A bubble column reactor is a very simple device consisting of a vertical vessel filled with water with a gas distributor at the inlet. Due to the ease of design and operation, which does not involve moving parts, they are widely used in the chemical, biochemical, petrochemical, and pharmaceutical industries to generate and control gas-liquid chemical reactions.

<span class="mw-page-title-main">Yurii Matros</span>

Yurii Shaevich Matros was a scientist in the field of chemical engineering, known for his achievement in the theory and practice of heterogeneous catalytic processes. He is acknowledged as a “Godfather” of realization of catalytic processes in forced unsteady state conditions. Matros developed a catalytic reactor with periodic changes of direction of flow rate in packed bed of catalyst. This reactor is widely known in scientific and applied literature as an example of an application of developed theory of forced unsteady processes. Yurii Matros possessed a full doctoral degree of science and was a professor.

The circulating fluidized bed (CFB) is a type of Fluidized bed combustion that utilizes a recirculating loop for even greater efficiency of combustion. while achieving lower emission of pollutants. Reports suggest that up to 95% of pollutants can be absorbed before being emitted into the atmosphere. The technology is limited in scale however, due to its extensive use of limestone, and the fact that it produces waste byproducts.

Ebullated bed reactors are a type of fluidized bed reactor that utilizes ebullition, or bubbling, to achieve appropriate distribution of reactants and catalysts. The ebullated-bed technology utilizes a three-phase reactor, and is most applicable for exothermic reactions and for feedstocks which are difficult to process in fixed-bed or plug flow reactors due to high levels of contaminants. Ebullated bed reactors offer high-quality, continuous mixing of liquid and catalyst particles. The advantages of a good back-mixed bed include excellent temperature control and, by reducing bed plugging and channeling, low and constant pressure drops. Therefore, ebullated bed reactors have the characteristics of stirred reactor type operation with a fluidized catalyst.

Dan Luss is an American chemical engineer, who is the Cullen Professor of Chemical Engineering at the University of Houston. He is known for his work in chemical reaction engineering, complex reacting systems, multiple steady-states reactor design, dynamics of chemical reactors, and combustion.

Gilbert F. Froment is a Belgian Professor Emeritus of chemical engineering at Ghent University, Belgium, and a research professor at Texas A&M University. His career was in the fields of kinetic and chemical reaction engineering studies, as well as the use of that to solve problems in process industry.

References

  1. ↑ Kinetic studies of propane oxidation on Mo and V based mixed oxide catalysts. 2011. pp. 106–118.
  2. ↑ Elizalde, Ignacio; Mederos, Fabián S.; del Carmen Monterrubio, Ma.; Casillas, Ninfa; Díaz, Hugo; Trejo, Fernando (2019-02-01). "Mathematical modeling and simulation of an industrial adiabatic trickle-bed reactor for upgrading heavy crude oil by hydrotreatment process". Reaction Kinetics, Mechanisms and Catalysis. 126 (1): 31–48. doi:10.1007/s11144-018-1489-7. ISSN   1878-5204. S2CID   105735334.
  3. ↑ Dong, Huan; Fan, An; Li, Dong; Tian, Yucheng; Dan, Yong; Feng, Xian; Fan, Xiaoyong; Li, Wenhong (2020-04-01). "Kinetic parameter estimation and reactor simulation of full-range low temperature coal tar during hydrodeasphaltenization over Ni–Mo/γ-Al2O3". Reaction Kinetics, Mechanisms and Catalysis. 129 (2): 899–923. doi:10.1007/s11144-020-01745-4. ISSN   1878-5204.
  4. ↑ Pithani, Subhash; Karlsson, Staffan; Emtenäs, Hans; Öberg, Christopher T. (2019-07-24). "Using Spinchem Rotating Bed Reactor Technology for Immobilized Enzymatic Reactions: A Case Study". Organic Process Research & Development. 23: 1926–1931. doi:10.1021/acs.oprd.9b00240. ISSN   1083-6160. S2CID   199646621.
  5. ↑ Petermeier, Philipp; Bittner, Jan Philipp; Müller, Simon; Byström, Emil; Kara, Selin (2022-08-08). "Design of a green chemoenzymatic cascade for scalable synthesis of bio-based styrene alternatives". Green Chemistry. 24: 6889–6899. doi: 10.1039/D2GC01629J . ISSN   1463-9262. S2CID   251455191.
  6. ↑ "Modernizing liquid waste processing". Nuclear Newswire. American Nuclear Society. Retrieved 2023-04-06.
  7. ↑ Santos, Jackson H. S.; Gomes, Jadiete T. S.; Benachour, Mohand; Medeiros, Eliane B. M.; Abreu, Cesar A. M.; Lima-Filho, Nelson M. (2020-09-05). "Selective hydrogenation of oxalic acid to glycolic acid and ethylene glycol with a ruthenium catalyst". Reaction Kinetics, Mechanisms and Catalysis. 131: 139–151. doi:10.1007/s11144-020-01843-3. ISSN   1878-5204. S2CID   221494771.
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