Hydrothermal conversion of biomass into acetic acid

Hydrothermal process is one of the most promising processes for the conversion of biomass waste into resources among the several biomass conversion processes, because water of high temperature and high pressure has remarkable properties as a reaction medium. This paper described advances in our research involving overall reaction pathways for acetic acid production from biomass, mainly including (1) acetic acid production by controlling pathways of hydrothermal reaction, (2) acid-base behavior of water in the subcritical region and (3) effect of lignin on the acetic acid production in WO of lignocellulosic biomass.     

Two-stage pyrolytic conversion of different types of biomass into synthesis gas

Possibilities of using the method of two-stage pyrolytic processing of the main types of biomass for the production of synthesis gas are considered. A comparison of the biomass characteristics (volatile content, ash content, elemental composition, and heating value) and the characteristics of gas mixtures obtained from it (volume, composition, and heating value) is performed. From the results obtained, it follows that the considered method of pyrolytic processing allows obtainment of 1.25 to 1.39 m³ of synthesis gas (per kg of combustible mass of the raw material) with heating value at 10–12 MJ/m³, and a high degree of energy conversion as compared with other methods for biomass gasification.     

Influence of salt addition on the hydrothermal conversion of rhyolitic pumice into zeolite

The influence of the presence of anions in zeolite synthesis systems starting from rhyolitic pumice has been examined. The anions may play a double role, sometimes determining the formation of certain phases (mainly feldspathoids), in other cases favouring or disfavouring the growth of a species at kinetic level (zeolite Na-P).A novel phase (denominated K), the formation of which is dependent on the presence of carbonate ions, has been obtained and described. The possibility that the valence more than the nature of the anions in the parent solution may be effective in accelerating the growth of some phases is emphasized.     

Application of hydrothermal reaction to conversion of plant-origin biomasses into acetic and lactic acids

In this paper, some recent advances in our research on hydrothermal conversion of biomass into useful substances are presented. Here, we mainly focus on the production of acetic acid and lactic acid from carbohydrates including aldose, lignocellulosic biomass, and glycerin along with the discussion of some reaction mechanisms and the interaction between the main components of natural material, such as cellulose and lignin in lignocellulosic biomass. A large-scale continuous flow reactor system was also presented.     

Recent progress in the development of solid catalysts for biomass conversion into high value-added chemicals

Abstract

In recent decades, the substitution of non-renewable fossil resources by renewable biomass as a sustainable feedstock has been extensively investigated for the manufacture of high value-added products such as biofuels, commodity chemicals, and new bio-based materials such as bioplastics. Numerous solid catalyst systems for the effective conversion of biomass feedstocks into value-added chemicals and fuels have been developed. Solid catalysts are classified into four main groups with respect to their structures and substrate activation properties: (a) micro- and mesoporous materials, (b) metal oxides, (c) supported metal catalysts, and (d) sulfonated polymers. This review article focuses on the activation of substrates and/or reagents on the basis of groups (a)–(d), and the corresponding reaction mechanisms. In addition, recent progress in chemocatalytic processes for the production of five industrially important products (5-hydroxymethylfurfural, lactic acid, glyceraldehyde, 1,3-dihydroxyacetone, and furan-2,5-dicarboxylic acid) as bio-based plastic monomers and their intermediates is comprehensively summarized.     

Recent progress in the development of solid catalysts for biomass conversion into high value-added chemicals

In recent decades, the substitution of non-renewable fossil resources by renewable biomass as a sustainable feedstock has been extensively investigated for the manufacture of high value-added products such as biofuels, commodity chemicals, and new bio-based materials such as bioplastics. Numerous solid catalyst systems for the effective conversion of biomass feedstocks into value-added chemicals and fuels have been developed. Solid catalysts are classified into four main groups with respect to their structures and substrate activation properties: (a) micro- and mesoporous materials, (b) metal oxides, (c) supported metal catalysts, and (d) sulfonated polymers. This review article focuses on the activation of substrates and/or reagents on the basis of groups (a)–(d), and the corresponding reaction mechanisms. In addition, recent progress in chemocatalytic processes for the production of five industrially important products (5-hydroxymethylfurfural, lactic acid, glyceraldehyde, 1,3-dihydroxyacetone, and furan-2,5-dicarboxylic acid) as bio-based plastic monomers and their intermediates is comprehensively summarized.     

Hollow carbon nanostructures obtained from hydrothermal carbonization of lignocellulosic biomass

Here we describe a new method for obtaining carbon nanocages at relatively low temperatures using a low-cost lignocellulosic waste material as carbon precursor. Coconut coir dust has been submitted to hydrothermal carbonization in the presence of clays minerals such as sepiolite, attapulgite, and montmorillonite followed by a demineralization step. Just after hydrothermal treatment, the samples prepared in the absence of the clays presented a sponge-like morphology as typically described for hard-plant tissues submitted to this treatment while the samples heated in the presence of clays were fundamentally heterogeneous. After chemical etching with hydrofluoric acid, the sample free from clays exhibited irregular round-shaped particles with poorly defined cavities. For samples containing clays, on the other hand, the chemical etching lead to well-defined carbon nanocages as long as the particles were successfully etched such as attapulgite and montmorillonite. For sepiolite, however, the presence of residual inorganic particles was observed along with irregularly shaped hollow nanostructures. Finally, Raman measurements revealed the typical features of amorphous carbons.     

Efficient hydrothermal synthesis of nanostructured SAPO-34 using ultrasound energy: Physicochemical characterization and catalytic performance toward methanol conversion to light olefins

A comparative synthesis of SAPO-34 was carried out via conventional and ultrasound assisted hydrothermal methods and tested toward methanol conversion to light olefins. The synthesized catalysts were characterized using XRD, FESEM, PSD, EDX, BET and FTIR analysis. Sonochemically synthesized SAPO-34 showed higher surface area, prefect crystallinity and uniform particles size in comparison to conventional hydrothermal synthesized sample. XRD patterns showed suitable crystalline structure of sonochemically synthesized SAPO-34 and its nanoscale structure. FESEM images confirmed prefect crystallinity and narrow size distribution of sonochemically synthesized SAPO-34. BET analysis indicated remarkable surface area of sonochemically synthesized SAPO-34. Catalytic performance tests of synthesized SAPO-34 toward methanol to light olefins conversion showed higher activity of sonochemically synthesized SAPO-34. Olefins selectivity of sonochemically synthesized SAPO-34 was considerably higher than that of the conventional SAPO-34. Time on stream performance of the synthesized catalysts at 400 °C confirmed higher stability of sonochemically synthesized SAPO-34.     

生物质原料的组分选择性拆分-功能经济性利用

在充分认知生物质原料在化学成分、结构组成、酶解及发酵性能上的不均一性的基础上,提出"组分选择性拆分-功能经济性利用"的生物质炼制新途径,即最大限度保持生物质大分子原有结构、尽可能激活适于酶解组分的生物活性,同时实现中间产物最大价值化。基于生物质原料特性、转化过程和产品要求的关联,笔者创新性地构建了多条生物质炼制产业链,验证了生物质"组分选择性拆分-功能经济性利用"的生物质炼制工业技术体系的可行性、合理性和可靠性。"组分选择性拆分-功能经济性利用"是突围生物质炼制生物燃料、生物材料和生物化学品的经济技术问题的必由之路。     

微波水热转化制备多孔羟基磷灰石微球

提出对球形碳酸钙进行精细化加工来制备羟基磷灰石的方法。通过与Na2HPO4-(NH4)2HPO4混合溶液在微波加热条件下进行阴离子交换反应,对粒度约15μm的球形碳酸钙进行水热转化并利用ESEM、XRD和EDS等手段对反应产物进行表征。反应15min后,碳酸钙转化为羟基磷灰石主相,无其它磷酸钙盐相存在,产物保留了原料的球形骨架结构,其显微结构为约0.2μm的细小颗粒聚集体,孔径约为100nm。EDS分析表明产物的表面组成为[Ca9.04Mg0.40Na1.16][(PO4)5.22(CO3)0.61](OH)3.12,属部分CO32-离子取代的羟基磷灰石。结果表明,在微波加热下碳酸钙能在较短时间内不经其它磷酸盐中间态而直接转化成单一的羟基磷灰石相。     

Synthesis of hydroxyapatite nanorods from abalone shells via hydrothermal solid-state conversion

Hydroxyapatite (HAP) has been widely applied as a biomaterial for repairing or substituting human hard tissues. In this paper, HAP nanorods were successfully produced from abalone shell powders via hydrothermal solid-state conversion without surfactants or complex agents. The field emission scanning electron microscopy (FESEM) showed that the produced HAP exhibited the typical rod-like structure. Based on the X-ray diffraction (XRD) and thermal analysis (thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)), these samples contain a small amount of aragonite and calcite crystals, and their content gradually decreases by prolonging the hydrothermal time. However, this decrease only slightly changes for the longer times. The Fourier transform infrared spectroscopy (FTIR) revealed that organic matter was detected in the samples without adding surfactants or complex agents. This study provides a solution to the resource waste and environmental pollution caused by abandoned abalone shells, and we also synthesized HAP for potential bone repair materials.     

Stability and direct conversion of mineral barite crystals in carbonated hydrothermal fluids

The pseudomorphic replacement of mineral barite (BaSO₄) crystals into barium carbonate was investigated in the present work by using carbonated alkaline hydrothermal fluids. Hydrothermal treatments were carried out over the temperature range from 150 up to 250 °C for intervals between 1 and 192 h, with different filling ratios (40–70%), and molar ratios of 1, 5, and 10. The reaction products were characterized by XRD and SEM techniques. The chemical reactivity of mineral barite crystals was markedly limited at temperatures below 200 °C, and only a tiny BaCO₃ layer on the surface of the original BaSO₄ crystal was formed on the crystal treated for 192 h. The rate of the pseudomorphic conversion of BaSO₄ into BaCO₃, was accelerated by increasing the reaction temperature and the molar ratio . Powder X-ray diffraction results showed that under hydrothermal conditions the replacement of ions by ions, in barite crystals was completed at 250 °C with a molar ratio = 10 for an interval of 192 h, resulting in the Witherite structure. The morphology of the completely converted BaCO₃ at 250 °C in a Na₂CO₃ solution for 192 h, showed that the conversion proceed without severe changes of the original shape and dimension of the original crystal, similar to that observed in mineral pseudomorphic replacement process.     

Comparison of the characteristics of hydrothermal carbons derived from holocellulose and crude biomass

The effects of lignin removal on hydrochar were investigated by comparing the structural, chemical, and thermal characteristics of holocellulose and wood powder-derived carbon materials (hydrochar). The hydrochar samples were obtained from hydrothermal carbonization (HTC) of holocellulose and wood powder at 210–230 °C for 9 h. The characteristics of the obtained products were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetric analysis. The observations reveal that the onset temperature of the HTC of holocellulose is lower than that of wood powder. The holocellulose-derived hydrochar samples exhibit higher carbon content and thermal stability with higher coalification degree and less complex chemical composition compared with resultant products based on wood powder. These results reveal that the holocellulose is easier to be disintegrated and hydrocarbonized without the shielding effects of lignin and suggest that the lignin removal is beneficial for increasing the rate and efficiency of the polysaccharide in biomass converting into hydrochar.     

Reaction mechanisms in the geopolymeric conversion of inorganic waste to useful products

High-performance materials for construction, waste immobilisation and an ever-growing range of niche applications are produced by the reaction sequence known as 'geopolymerisation'. In this process, an alkaline activating solution reacts with a solid aluminosilicate source, with solidification possible within minutes and very rapid early strength development. Geopolymers have been observed to display remarkable chemical and thermal stability, but due to their largely X-ray amorphous nature have only recently been accurately characterised. It has previously been shown that both fly ash and ground granulated blast furnace slag are highly effective as solid constituents of geopolymer reaction slurries, providing readily soluble alumina and silica that undergo a dissolution-reorientation-solidification process to form a geopolymeric material. Here a conceptual model for geopolymerisation is presented, allowing elucidation of the individual mechanistic steps involved in this complex and rapid process. The model is based on the reactions known to occur in the weathering of aluminosilicate minerals under alkaline conditions, which occur in a highly accelerated manner under the conditions required for geopolymerisation. Transformation of the waste materials to the mixture of gel and nanocrystalline/semicrystalline phases comprising the geopolymeric product is described. Presence of calcium in the solid waste materials affects the process of geopolymerisation by providing extra nucleation sites for precipitation of dissolved species, which may be used to tailor setting times and material properties if desired. Application of geopolymer technology in remediation of toxic or radioactive contaminants will depend on the ability to analyse and predict long-term durability and stability based on initial mix formulation. The model presented here provides a framework by which this will be made possible.     

Creation of dense hydroxyapatite (synthetic bone) by hydrothermal conversion of seashells

Strombus gigas (conch) shells and Tridacna gigas (Giant clam) shells have dense, tailored structures that impart excellent mechanical properties to these shells. In this study, conch and clam seashells were converted to hydroxyapatite (HAP) by a hydrothermal method at different temperatures and for different conversion durations. Dense HAP structures were created from these shells throughout the majority of the samples. High temperatures were found to accelerate the conversion process, however, cracks were found on the surface of the samples converted at high temperature or for very long conversion times. The conversion at 180 °C, refreshing the diammonium hydrogen phosphate [(NH₄)₂HPO₄] solution every 2 days, produced samples of good quality. Different morphologies of HAP were found in different regions of the converted shells, which may be caused by different structural morphologies and in different amounts of porosity in the original shells. Partially converted shell samples with dense HAP layers on the surface growing inward and original shell structures inside have an average fracture stress about 137–218 MPa, which is close to the mechanical strength of compact human bone.     

One-step hydrothermal synthesis,characterization and visible-light catalytic property of Ag-reduced graphene oxide composite

In this paper, a nanocomposite consisting of Ag nanoparticles and reduced graphene oxide sheets was synthesized via a one-step hydrothermal method using glucose as a reducing agent. The as-prepared sample was characterized systematically, and the results indicated that the graphene oxide was reduced and an Ag-reduced graphene oxide hybrid material was formed. It was shown that the as-prepared Ag-reduced graphene oxide was in a layered structure stacked by reduced graphene oxide sheets. The Ag nanoparticles decorated on the reduced graphene oxide sheets. The analysis revealed that there was strong interaction between the Ag nanoparticles and reduced graphene oxide sheets. A photodegradation study was also performed on the Ag-reduced graphene oxide composite. It showed that the composite exhibited a high catalytic activity for the photodegradation of Rhodamine B pollutant under visible-light irradiation, which made Ag-reduced graphene oxide a promising candidate as photocatalyst for Rhodamine B.     

Enhanced hydrothermal stability of ZSM-5 formed from nanocrystalline seeds for naphtha catalytic cracking

We successfully synthesized hydrothermally stable ZSM-5 with crystalline nano seeds. We employed a template-free method using ZSM-5 crystalline nano seeds and sodium silicate as a silica source. The prepared ZSM-5 exhibited uniform crystal size and relative crystallinity greater than 100 %. The size of the crystalline nano seed in the scale of 100 nm was found to be the optimum size for obtaining uniform, highly crystalline ZSM-5 with structural stability. After P-modification, the synthesized ZSM-5 with the optimally sized seed showed high hydrothermal stability and improved catalytic naphtha cracking activity compared to a commercial ZSM-5 catalyst. In order to find the elements for the increased hydrothermal stability, the samples were evaluated by studying crystallinity, aluminum spectrum, and acidity using XRD, solid-state NMR, and NH₃-TPD, respectively after steaming at 800 °C for 24 h. It is speculated that the increased hydrothermal stability of the ZSM-5 resulted mainly from the increased aluminum structural stability.