Oct 28 (Reuters) - Hygiene company Ecolab Inc (ECL.N) on Thursday agreed to buy Purolite, whose technology can be used in mRNA vaccine purification, in a $3.7 billion all-cash deal to add weight to its pharmaceutical-focused business. The deal helps Ecolabs expand into a field that has gained prominence due to the successful development of messenger-RNA (mRNA) based vaccines for COVID-19 by Pfizer Inc (PFE.N) and Moderna Inc (MRNA.O). Privately held Purolite"s resin-based technology can also be used in the purification of monoclonal antibodies intended to treat cancer. The company would report results within Ecolab"s life sciences business, which provides a range of cleaning products and technical services used in pharmaceutical production. The acquisition, expected to close this year, would also help Ecolab grow in the water purification, food and beverage processing and metal extraction businesses. It would add to the company"s earnings in 2023. "It (the deal) provides another strong and adjacent global growth platform within Ecolab with double-digit growth prospects in both our life sciences and industrial markets," said Ecolab Chief Executive Officer Christophe Beck. 40-year-old Purolite operates in more than 30 countries and is expected to post sales of about $400 million in 2021. J.P. Morgan Securities was the financial advisor to Ecolab. Reporting by Tiyashi Datta and Amruta Khandekar in Bengaluru; Editing by Aditya Soni Our Standards: The Thomson Reuters Trust Principles.