Nanosheet MFI Zeolites for Gas Phase Glycerol Dehydration to Acrolein

Synthesis of Two-Dimensional Zeolite Nanosheets Applied to the Catalytic Cracking of a Waste Cooking Oil Model Compound to Produce Light Olefins

Hierarchical zeolites can provide multidimensional spatial networks and, therefore, have significant potential as catalysts for the cracking of biomass to generate light olefins. The present work synthesized the diquaternary ammonium-type surfactant [C18H37-N+(CH3)2-(CH2)6-N+(CH3)2-C6H13]Br2, incorporating hydrophobic 18-carbon alkyl groups for usage as a structure-directing agent. This compound was subsequently used to prepare nanosheets of a hierarchical ZSM-5 two-dimensional zeolite (HNZSM-5) through a one-pot hydrothermal method. The crystal phase, morphology, and hierarchical structure of the HNZSM-5 were analyzed using various techniques, including X-ray diffraction, electron microscopy, and N2 adsorption/desorption. When applied to the catalytic cracking of a waste cooking oil model compound, the HNZSM-5 exhibited superior activity and stability compared with a conventional ZSM-5. This performance was attributed to the more accessible acid sites and unique lamellar structure of the former material. The HNZSM-5 also outlasted the conventional zeolite, showing deactivation after 45 h of reaction compared with 20 h, indicating exceptional stability and excellent resistance to coking.

Chemicals Production from Glycerol through Heterogeneous Catalysis: A Review

Utilization of biofuels generated from renewable sources has attracted broad attention due to their benefits such as reducing consumption of fossil fuels, sustainability, and consequently prevention of global warming. The production of biodiesel causes a huge amount of by-product, crude glycerol, to accumulate. Glycerol, because of its unique structure having three hydroxyl groups, can be converted to a variety of industrially valuable products. In recent decades, increasing studies have been carried out on different catalytic pathways to selectively produce a wide range of glycerol derivatives. In the current review, the main routes including carboxylation, oxidation, etherification, hydrogenolysis, esterification, and dehydration to convert glycerol to value-added products are investigated. In order to achieve more glycerol conversion and higher desired product selectivity, acquisition of knowledge on the catalysts, the type of acidic or basic, the supports, and studying various reaction pathways and operating parameters are necessary. This review attempts to summarize the knowledge of catalytic reactions and mechanisms leading to value-added derivatives of glycerol. Additionally, the application of main products from glycerol are discussed. In addition, an overview on the market of glycerol, its properties, applications, and prospects is presented.

Heterogeneous Catalysts for Conversion of Biodiesel-Waste Glycerol into High-Added-Value Chemicals

The valuable products produced from glycerol transformation have become a research route that attracted considerable benefits owing to their huge volumes in recent decades (as a result of biodiesel production as a byproduct) as well as a myriad of chemical and biological techniques for transforming glycerol into high-value compounds, such as fuel additives, biofuels, precursors and other useful chemicals, etc. Biodiesel has presented another challenge in the considerable increase in its byproduct (glycerol). This review provides a recent update on the transformation of glycerol with an exclusive focus on the various catalysts’ performance in designing reaction operation conditions. The different products observed and cataloged in this review involved hydrogen, acetol, acrolein, ethylene glycol, and propylene glycol (1,3-propanediol and 1,2-propanediol) from reforming and dehydration and hydrogenolysis reactions of glycerol conversions. The future prospects and critical challenges are finally presented.

Catalytic Conversion of Glycerol into Hydrogen and Value-Added Chemicals: Recent Research Advances

In recent decades, the use of biomass as alternative resources to produce renewable and sustainable biofuels such as biodiesel has gained attention given the situation of the progressive exhaustion of easily accessible fossil fuels, increasing environmental concerns, and a dramatically growing global population. The conventional transesterification of edible, nonedible, or waste cooking oils to produce biodiesel is always accompanied by the formation of glycerol as the by-product. Undeniably, it is essential to economically use this by-product to produce a range of valuable fuels and chemicals to ensure the sustainability of the transesterification process. Therefore, recently, glycerol has been used as a feedstock for the production of value-added H2 and chemicals. In this review, the recent advances in the catalytic conversion of glycerol to H2 and high-value chemicals are thoroughly discussed. Specifically, the activity, stability, and recyclability of the catalysts used in the steam reforming of glycerol for H2 production are covered. In addition, the behavior and performance of heterogeneous catalysts in terms of the roles of active metal and support toward the formation of acrolein, lactic acid, 1,3-propanediol, and 1,2-propanediol from glycerol are reviewed. Recommendations for future research and main conclusions are provided. Overall, this review offers guidance and directions for the sufficient and economical utilization of glycerol to generate fuels and high value chemicals, which will ultimately benefit industry, environment, and economy.

Catalytic Deactivation of HY Zeolites in the Dehydration of Glycerol to Acrolein

The study of the deactivation of HY zeolites in the dehydration reaction of glycerol to acrolein has represented a challenge for the design of new catalysts. HY zeolites with SiO2/Al2O3 molar ratios between 3.5 and 80 were studied. The solids were characterized by XRD, N2 physisorption, SEM-EDXS, Raman and UV-vis spectroscopies, infrared spectroscopy of pyridine (FTIR-Py) and catalytic activity tests from 250 °C to 325 °C. It was found that the total amount of acid sites per unit area of catalyst decreased as the SiO2/Al2O3 molar ratio increased from 3.5 to 80, resulting in the decrease in the initial glycerol conversion. The initial acrolein selectivity was promoted with the increase of the Brønsted/Lewis acid sites ratio at any reaction temperature. The deactivation tests showed that the catalyst lifetime depended on the pore structure, improving with the presence of large surface areas as evidenced by the deactivation rate constants. The characterization of the deactivated catalysts by XRD, N2 physisorption and thermogravimetric analysis indicated that the deposition of coke resulted in the total obstruction of micropores and the partial blockage of mesopores. Moreover, the presence of large mesopores and surface areas allowed the amount of coke deposited at the catalyst surface to be reduced.

Continuous Flow Upgrading of Selected C2-C6 Platform Chemicals Derived from Biomass

The ever increasing industrial production of commodity and specialty chemicals inexorably depletes the finite primary fossil resources available on Earth. The forecast of population growth over the next 3 decades is a very strong incentive for the identification of alternative primary resources other than petro-based ones. In contrast with fossil resources, renewable biomass is a virtually inexhaustible reservoir of chemical building blocks. Shifting the current industrial paradigm from almost exclusively petro-based resources to alternative bio-based raw materials requires more than vibrant political messages; it requires a profound revision of the concepts and technologies on which industrial chemical processes rely. Only a small fraction of molecules extracted from biomass bears significant chemical and commercial potentials to be considered as ubiquitous chemical platforms upon which a new, bio-based industry can thrive. Owing to its inherent assets in terms of unique process experience, scalability, and reduced environmental footprint, flow chemistry arguably has a major role to play in this context. This review covers a selection of C₂ to C₆ bio-based chemical platforms with existing commercial markets including polyols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,4-butanediol, xylitol, and sorbitol), furanoids (furfural and 5-hydroxymethylfurfural) and carboxylic acids (lactic acid, succinic acid, fumaric acid, malic acid, itaconic acid, and levulinic acid). The aim of this review is to illustrate the various aspects of upgrading bio-based platform molecules toward commodity or specialty chemicals using new process concepts that fall under the umbrella of continuous flow technology and that could change the future perspectives of biorefineries.

Glycerol Dehydration to Acrolein over Supported Vanadyl Orthophosphates Catalysts

Biodiesel has been identified as one of the notable options for at least complementing conventional fuels. From a transesterification reaction, crude glycerol is produced as the main by-product. Given the difficultly in upgrading to high-grade glycerin and glycerol market saturation, alternative routes to more value-added products have aroused significant interest. In this work, we proposed supported vanadyl orthophosphates (VOP) as catalysts for the glycerol dehydration to acrolein. VOP supported on γ-Al2O3, TiO2, and ZrO2 were prepared, characterized by inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), N2 physisorption and temperature-programmed desorption of ammonia (NH3-TPD), and tested under different operating conditions. All the samples showed low coke formation in the presence of molecular oxygen in the feed. Acrolein is the main condensable product, with carbon balance being satisfactory under most operating conditions. VOP supported onto alumina provided the best catalytic performance, due to a good balance between the acid (weak and medium acid sites) and redox sites, thereby appearing as a good candidate for glycerol dehydration to acrolein.