Biomass is a promising renewable resource that researchers look forward to building and developing sustainable energy systems to alleviate the energy crisis. Biomass is broadly defined as "a substance produced by the growth of microorganisms, plants or animals." Lignocellulose consists of three parts: cellulose (38-50%), hemicellulose (23~32%) and lignin (15~25%). Lignocellulose is a low-cost, well-stocked biomass component that is often used in fermentation to produce liquid biofuels (e.g., ethanol). The basic process for preparing bioethanol from lignocellulose can be divided into four parts: pre-treatment, hydrolysis, fermentation and purification. The purpose of the bath is to remove the internal structure of the biomass that hinders scarification and fermentation, pulverize the lignin to protect the cellulose, disintegrate the crystal structure of the cellulose, and make it fully contact with the biological enzyme to obtain a good hydrolysis effect. The hydrolysis process uses acid or enzymatic hydrolysis of the polymer to make it a soluble monosaccharide. The fermentation is carried out by fermenting the hydrolysed products (five carbon sugars and six carbon sugars) to obtain ethanol. Purified ethanol can be obtained by further distillation, filtration, and the like.
The process of ethanol conversion is a catalytic application process, which means that the design and application of the catalyst is the key to this process. In the traditional industrial refining process, homogeneous catalysts such as aluminum chloride, ferric chloride, boron fluoride, hydrofluoric acid, etc. are often used for upgrading processing of biomass. However, its conspicuous disadvantages such as the inability to recycle and reuse, the serious environmental pollution, and the corrosive nature of the equipment prompted us to turn our attention to the new heterogeneous catalyst-solid acid catalyst. Among many types of heterogeneous catalysts, zeolite has good industrial applicability, no corrosion to equipment, easy recovery, and easy to modify the zeolite structure and acidity of the catalyst according to different reaction requirements.
In the presence of heterogenous solid acid catalyst, ethanol converts into olefins through a complex process containing a series of intricate elementary reactions. Despite having a broad understanding, the specific reaction mechanisms that dictate the desired production of ethylene remains unresolved by researchers. This is largely due to the large variation of catalyst selection that varies in topology and acidity. On top of that, conversion process is heavily dependent on the specific reaction condition that influences the ETO activity and selectivity – a subtle balance that is still unclear. Thus, this work presents an overview of the proposed reaction mechanisms for the ETO process using H-ZSM-5 catalyst, supplemented by hydrocarbon pool.
Alkylation of arenes by benzyl alcohol was studied on acidic zeolites H-beta (BEA) of mesopore and micropore across various Si/Al ratio with the aim of determine the influence of acidity, molecular and reactant diffusion rate on the rate of reaction. Brønsted acid sites (BAS), achieve through introduction of Al into the silica framework, was verified 29Si and 27Al MAS NMR spectroscopy. Impact of Si/Al ratio was revealed, using 1H MAS NMR spectroscopy, to have an inverse relation with BAS density and positive relation with BAS strength (CD3CN molecules probed). Pore size had direct impact on molecular diffusion resulting in specific performance and preferential of conversion with large arenes performing better with mesoporous zeolites, vice versa for microspores beta zeolites. Benzylation performance improved with BAS strength of H-beta, resultant on formation of aryl cation intermediates the selectively attacks benzyl alcohol. The plausible reaction mechanism based on the role of Brønsted acid sites of the catalyst was discussed.