In recent years, with increasing environmental protection requirements and the continued growth in demand for clean fuels, the market demand for fuel ethanol has risen significantly, driving the rapid development of ethanol production technologies and processes. Chinese researchers have been actively exploring new ethanol production processes and technologies through continuous research and development. Traditional ethanol production processes mainly rely on bio-fermentation, while modern technologies include ethylene hydration and carbonylation-hydrogenation routes based on C1 feedstocks. From a chemical conversion perspective, commercially available ethanol production processes mainly include three types: biomass fermentation via sugars, ethylene hydration, and carbonylation-hydrogenation of oxygen-containing compounds.
Grain Fermentation Method
Grain fermentation is the earliest developed method for ethanol production and is still widely used, especially in the production of alcoholic beverages. The basic principle of this method is that, under the action of a fermenting agent, glucose (C6H12O6) is converted into ethanol through a series of biochemical processes such as cooking and saccharification. Specifically, a saccharifying agent (such as acids or amylase catalysts) is first used to convert the starch in the raw material into fermentable sugars, which are then used to produce ethanol through fermentation. In industrial practice, starch is typically pretreated with starch-saccharifying enzymes to achieve saccharification, providing a foundation for subsequent fermentation.
Ethylene Hydration Method
To meet the rapidly developing needs of the basic organic synthesis industry, it is essential to use inexpensive and widely available raw materials to produce ethanol. Industrially, the most important synthetic route is the ethylene hydration method, which involves reacting ethylene with water using chemical methods to produce ethanol. The product obtained by this method is usually called synthetic ethanol, to distinguish it from fermented ethanol produced by traditional fermentation methods.
Carbonylation Reduction Method
Based on the phase state of the catalytic system, the process of preparing ethanol by the carbonylation reduction of methoxy compounds is mainly divided into two categories: one is the traditional homogeneous catalytic process, and the other is the dimethyl ether heterogeneous carbonylation reduction process, which was industrialized in 2017. Although the catalytic systems differ, the reaction mechanisms of the two methods are consistent, both involving two core steps: first, the methoxy compound is carbonylated to generate an acetyl compound, and then the acetyl compound is reduced to obtain ethanol and corresponding byproducts. The first step, extending the carbon chain of C1 oxygen-containing compounds to C2 oxygen-containing compounds through a carbonylation reaction, is the key to the entire process and directly determines the technical and economic feasibility of producing ethanol via different carbonylation reduction pathways.
Syngas Catalysis
Direct catalytic production of ethanol from syngas is one of the important pathways for coal-based ethanol production. This technology uses syngas (CO + H2) as raw material, directionally converting it into a low-carbon mixed alcohol, primarily ethanol, under the action of a catalyst. Its core technology lies in the development and selection of high-performance catalysts. Due to the complex composition of coal-based syngas, this process places high demands on the adaptability, stability, and anti-toxicity of the catalyst. In industrial applications, catalysts are needed to improve carbon monoxide conversion and ethanol selectivity.
Methyl Acetate Hydrogenation
In recent years, the hydrogenation of methyl acetate to ethanol technology has received widespread attention from researchers both domestically and internationally. The catalysts used in this reaction can be mainly divided into two categories: one is noble metal-based catalysts, represented by ruthenium (Ru), rhodium (Rh), palladium (Pd), and platinum (Pt); the other is non-noble metal systems, represented by copper-based catalysts.
