Chemical reactor materials selection is an important aspect in the design of a

chemical reactor 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 che ...

. There are four main groups of chemical reactors - CSTR, PFR, semi-batch, and catalytic - with variations on each. Depending on the nature of the chemicals involved in the reaction, as well as the operating conditions (e.g. temperature and pressure), certain materials will perform better over others.

Material Options

There are several broad classes of materials available for use in creating a chemical reactor. Some examples include metals, glasses, ceramics, polymers, carbon, and composites.
Busby, J.T. "Challenges for Reactor Materials." Oak Ridge National Laboratory - Fuel Cycle and Isotopes Division. ''U.S. Department of Energy''. 28 Feb. 2012.

Metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

s are the most common class of materials for chemical engineering equipment as they are comparatively easy to manufacture, have high

strength Strength may refer to: Personal trait *Physical strength, as in people or animals *Character strengths like those listed in the Values in Action Inventory *The exercise of willpower Physics * Mechanical strength, the ability to withstand ...

, and are resistant to

fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...

Glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

is common in chemical laboratory equipment, but highly prone to fracture and so is not useful in large-scale industrial use.

Ceramics A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porce ...

are not that common of a material for chemical reactors as they are

brittle A material is brittle if, when subjected to stress, it fractures with little elastic deformation and without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. ...

and difficult to manufacture.

Polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s have begun to gain more popularity in piping and valves as they aid in temperature stability. There are several forms of carbon, but the most useful form for reactors is carbon or graphite fibers in composites.

Criteria for Selection

The last important criteria for a particular material is its safety. Engineers have a responsibility to ensure the safety of those who handle equipment or utilize a building or road for example, by minimizing the risks of injuries or casualties. Other considerations include strength, resistance to sudden failure from either mechanical or thermal shock, corrosion resistance, and cost, to name a few. To compare different materials to each other, it may prove useful to consult an ASHBY diagram and the ASME Pressure Vessel Codes. The material choice would be ideally drawn from known data as well as experience. Having a deeper understanding of the component requirements and the corrosion and degradation behavior will aid in materials selection. Additionally, knowing the performance of past systems, whether they be good or bad, will benefit the user in deciding on alternative alloys or using a coated system; if previous information is not available, then performing tests is recommended.

High Temperature Operation

High temperature reactor operation includes a host of problems such as distortion and cracking due to thermal expansion and contraction, and high temperature corrosion. Some indications that the latter is occurring include burnt or charred surfaces, molten phases, distortion, thick scales, and grossly thinned metal. Some typical high-temperature alloys include iron, nickel, or cobalt that have >20% chromium for the purpose of forming a protective oxide against further oxidation. There are also various other elements to aid in corrosion resistance such as aluminum, silicon, and rare earth elements such as

yttrium Yttrium is a chemical element; it has Symbol (chemistry), symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost a ...

cerium Cerium is a chemical element; it has Chemical symbol, symbol Ce and atomic number 58. It is a hardness, soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it ...

, and

lanthanum Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements bet ...

. Other additions such as reactive or refractory metals, can improve the mechanical properties of the reactor. Refractory metals can experience catastrophic oxidation, which turns metals into a powdery oxide with little use. This damage is worse in stagnant conditions, however silicide coatings have been proven to offer some resistance.

References

{{Reflist Chemical reactors