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Acrylic acid, also known as prop-2-enoic acid, is an important unsaturated carboxylic acid that serves as a raw material for a wide range of acrylic products. It is a colorless liquid with a characteristic acrid odor. Acrylic acid finds usage in the production of superabsorbent polymers, adhesives, coatings, plasticizers and more
Manufacturing of Acrylic Acid
Acrylic acid is produced on an industrial scale predominantly through a two-step oxidation of propylene. In the first step, propylene is oxidized to acrolein over metal oxide catalysts at high temperatures. In the second step, acrolein is further oxidized to acrylic acid. Some key aspects of the manufacturing process include:
– Catalysts: The most commonly used catalysts for the oxidation of propylene to acrolein are mixed metal oxides containing molybdenum and bismuth. For the subsequent oxidation of acrolein to acrylic acid, catalysts based on cobalt, manganese or mixed metal ions are employed.
– Reactants: Air or oxygen are typically used as oxidizing agents. Water is removed continuously to drive the exothermic reactions.
– Reactor design: Tubular fixed-bed reactors or fluidized-bed reactors optimized for heat and mass transfer are commonly adopted on an industrial scale.
– Recovery: Acrylic acid is separated from the reaction mixture through distillation. Unreacted acrolein is recycled for further oxidation.
– Yield: The overall yield of the two-step process is around 85-90%. Various process improvements are ongoing to enhance the atom efficiency.
End Uses of Acrylic Acid
Given its reactivity, acrylic acid finds myriad applications either in its monomeric form or after polymerization. Some major end uses include:
Superabsorbent Polymers
Nearly 50% of total acrylic acid demand is from the production of superabsorbent polymers (SAPs). SAPs are crosslinked polyacrylates capable of absorbing hundreds of times their own weight of liquid. They are key components of diapers, adult incontinence products and hygiene articles.
Adhesives and Sealants
Acrylic polymers offer excellent adhesive properties and find extensive application in pressure-sensitive adhesives, hot melts, and structural adhesives. They are used to bond automotive and transportation components, construction materials, medical devices and more.
Coatings
Emulsion polymers of acrylic acid are used as binders and protective coatings in architectural, industrial, and automotive coatings. They provide durability, gloss, flexibility and resistance to UV degradation.
Plasticizers
Acrylic acid esters such as ethyl acrylate and butyl acrylate are important plasticizers. They are blended with PVC to enhance its flexibility, processability and longevity.
Thickeners
Crosslinked polyacrylic acids like carbomers are widely used as thickeners and suspending agents in pharmaceuticals, personal care and household products to improve viscosity.
Others
Other vital applications include production of pesticides, chemical intermediates, flocculants, cement additives, synthetic fibers and more. Acrylic fibers offer sweat and moisture-wicking properties.
Environmental and Economic Impact
With annual global production exceeding 7 million tons, acrylic acid is among the highest volume chemicals manufactured worldwide. The market was valued at $13 billion in 2019 and is expected to grow over 5% each year owing to rising incomes, especially in Asia.
While acrylic acid manufacturing emits greenhouse gases, efforts are ongoing to curb emissions and improve energy efficiency through process intensification and heat integration. Its polymer derivatives also help reduce environmental impact through replacement of less sustainable materials.
Acrylic acid and its polymers have thus emerged as indispensable materials for innumerable industries. Continued material innovations will further expand its diverse applications for enhancing quality of life.
In summary, acrylic acid is a versatile unsaturated carboxylic acid produced through catalytic oxidation of propylene. It serves as a strategic building block monomer for various acrylic polymers finding extensive usage as superabsorbents, adhesives, coatings and plasticizers. With growing global population and demand for better living standards, the importance of acrylic acid and the products derived from it are certain to rise in the coming decades.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
