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$$2\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{Conc. H}_2\text{SO}_4, \, 413\text{ K } (140^\circ\text{C})} \text{CH}_3\text{CH}_2\text{--O--CH}_2\text{CH}_3 + \text{H}_2\text{O}$$
Concept: Primary alcohols undergo bimolecular dehydration in the presence of protic acids like concentrated $$\text{H}_2\text{SO}_4$$ or $$\text{H}_3\text{PO}_4$$ at a lower temperature ($$413\text{ K}$$ / $$140^\circ\text{C}$$) to yield symmetrical ethers. The protonated alcohol molecule is attacked by another unprotonated alcohol molecule via an $$S_N 2$$ pathway. At higher temperatures ($$443\text{ K}$$/ $$170^\circ\text{C}$$), unimolecular/bimolecular elimination ($$E1$$ /$$E2$$) takes over to yield alkenes instead
