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However, the fermentation method is limited by the source of raw materials and high costs, so the synthetic method gradually emerged. The indirect hydration method for ethanol production was reported as early as 1825, but it was not until 1930 that Union Carbide Corporation of the United States realized industrialization. Since the indirect hydration method consumes a large amount of concentrated sulfuric acid, the sulfuric acid medium in the production process has serious corrosion to the equipment and the product separation and purification is difficult, since 1932, the United States and the former Soviet Union have simultaneously started research on the direct hydration method. In 1945, Shell Chemical Company of the United States adsorbed phosphoric acid on granular diatomaceous earth to prepare a solid catalyst, solving the catalyst problem of the direct hydration method.