Biomass hydrothermal conversion

The Plato (Proving Lasting Advanced Timber Option) process is derived from a technology that was originally developed by Royal Dutch Shell, and was a spin-off from research into the hydrothermal conversion of biomass into liquid fuels. The Plato thermal modification process involves four stages (Figure 8.3) ... 

Jin F, Yun J, Li G, Kishita A, Tohji K, Enomoto H (2008) Hydrothermal conversion of carbohydrate biomass into formic acid at mild temperatures. Green Chem 10(6) 612-615... 

The different process routes, in particular with reference to pressure applications, will now be described in more detail. Hydrothermal conversion of highly water-containing biomasses will be described in a different section, due to the special features of these processes. 

High pressure hydrothermal conversion of Spirulina was studied with iron as catalyst (Matsui et al., 1997). It showed that the bio-oil yield increased linearly from 54.4 to 63.7 wt. % with increasing amount of Fe(CO)5-S from 0 to 1 mmol. The conversion and gas yield were nearly constant. In a similar study, brown macroalga Laminaria saccharina was hydrothermally liquefied to bio-crude in a batch reactor (Anastasakis and Ross, 2011). A maximum bio-crude yield of 19.3 wt. % was obtained with a biomass to water ratio of 1 10 at 350°C and 15 min of residence time. The solid residue contained large proportion of calcium and magnesium, whereas the liquid phase was rich in sugars, ammonium, potassium and sodium. 

TABLE 12.3 Hydrothermal Conversion of Biomass in Hot Compressed Water... 

Knezevic, D., van Swaaij, W., Kersten, S. Hydrothermal conversion of biomass. II. Conversion of wood, pyrolysis oil, and glucose in hot compressed water. Ind Eng Chem Res 2010,49,104-112. 

Waste biomass (poplar sawdust, wheat straw, paper sludge, etc.) Hydrothermal and chemical Hydrothermal conversion of feedstock in the presence of an acid catalyst Levulinic acid Galletti et al. (2012)... 

Jin, F.M., Enomoto, H., 2009. Hydrothermal conversion of biomass into value-added products technology that mimics nature. Bioresources 4, 704-713. 

Modern research in hydrothermal processing has concentrated on the utilization of biomass and wet wastes. The process has clear advantages for wet feedstocks but biomass with low moisture content such as woody biomass has also been investigated. Most biomass can be processed by hydrothermal conversion but one of the main considerations is often the ease of pumping and material transfer. The feed is typically fed as a water slurry due to the hydrophilic nature of biomass and the reasonable ease in forming water slurries with biomass particles at pumpable concentrations. This is typically possible up to 30% solids, details on biomass slurry pumping are review by Elliott et al. (2015). 

Kruse, A., Funke, A., Titirici, M.-M., 2013. Hydrothermal conversion of biomass to fuels and energetic materials. Current Opinion in Chemical Biology 17 (3), 515—521. 

Thermal conversion involves the use of elevated temperature with or without the presence of oxygen to break down the structure of the feedstock. It includes torrefac-tion, pyrolysis, gasification, and combustion. Thermal conversion of biomass can also be carried out in a solvent (e.g. as in hydrothermal processing) [1], but in this chapter, only torrefaction fast pyrolysis gasification with air, oxygen, or steam and combustion in air will be considered. 

One can envisage the future production of liquid fuels and commodity chemicals in a biorefinery Biomass is first subjected to extraction to remove waxes and essential oils. Various options are possible for conversion of the remaining biofeedstock, which consists primarily of lignocellulose. It can be converted to synthesis gas (CO + H2) by gasification, for example, and subsequently to methanol. Alternatively, it can be subjected to hydrothermal upgrading (HTU), affording liquid biofuels from which known transport fuels and bulk chemicals can be produced. An appealing option is bioconversion to ethanol by fermentation. The ethanol can be used directly as a liquid fuel and/or converted to ethylene as a base chemical. Such a hiorefinery is depicted in Fig. 8.1. 

Hydrothermal liquefaction is a process for the conversion of biomass into an organic product oil. It has been widely studied in the early 1980 s (see the recent extensive literature survey in [1]), Starting in 1983 Shell Research performed process development based on experiments in autoclaves and a continuous bench scale unit. This resulted in a conceptual design for the HTU process including cost estimate [2,3]. The work was discontinued in 1988. 

Conversion of biomass at a temperature of 300 350 °C and a pressure of 120-180 bar within the so-called HydroThermal Upgrading (HTU) process yields a mixture of hydrocarbons, carbon dioxide, water and dissolved organics, which can be further processed in a catalytic HydroDeOxygenation (HDO) step to yield diesel with characteristics similar to fossil diesel. A major advantage is that wet biomass feedstocks can be employed without drying in contrast, water at hydrothermal conditions acts as a solvent and reactant at the same time, leading to a product with less oxygen compared to biocrude prepared by pyrolysis. 

Jin F, Enomoto H (2011) Rapid and highly selective conversion of biomass into value-added products in hydrothermal conditions chemistry of acid/base-catalysed and oxidation reactions. Energy Environ Sci 4(2) 382-397... 

Hydrothermal carbonization is an effective method and has been extensively studied for the synthesis of carbonaceous material from different organic sources, especially from biomass. Pyrolysis is one of the most promising thermochemical processes for the conversion of biomass mainly into liquid (bio-oil), gaseous (gaseous C1-C4 hydrocarbons), and solid (char) products [167,168]. 

Hydrothermal technology has emerged as a most powerful tool because of its environmental-friendly approach. Hydrothermally synthesized carbons have been applied in various fields of research including electronics, nanotechnology, mechanical, biotechnology, and biomedical. Conversion of biomass and waste materials into alternative energy sources open new potentials for future research. A considerable amount of research is still required to fully understand the carbonization process of biomass and polysaccharides. 

As known, hydrothermal processes have been successfully used for conversion of organic wastes to fuels or useful materials, for example, biocrude oil, hydrogen, glucose, lactic acid, acetic acid, and amino acids [14,46,47]. Among these chemicals, acetic acid is an important chemical reagent and industrial chemical which is widely used for the production of poly(ethylene terephthalate), cellulose acetate, and poly(vinyl acetate). As a stable and recoverable intermediate, it can be produced from biomass, terrestrial plants, and microalgae during the process of hydrothermal treatment [48,49]. 

Hydrothermal carbonization is a thermochemical process involving the conversion of carbohydrate components (i. e., cellulose and hemicellulose) of biomass into carbon-rich solids in water at elevated temperature and pressure (Titirici et al., 2007b). Under acidic conditions with catalysis by iron salts, the reaction temperature during carbonation may be as low as 200°C (Titirici et al., 2007a). Iron oxide nanoparticles and iron ions were found to be effective in catalyzing hydrothermal carbonization of starch and rice grains under mild temperatures of < 200°C and gave attractive nanostructures (Cui et al., 2006). 

There is not only a need but also an urge to use waste biomass resources in the production of biofuels, due to the many envirorunental and economic impacts from the conventional fossil-based transportation fuels. The conversion routes applied to biomass for fuel production widely include thermo-chemical, hydrothermal and biochemical. All the three conversion methods are well-suited to achieve the energy requirements for being ecofriendly processes. However, in the present context both thermochemical and hydro-thermal conversion are foimd effective to produce an energy dense liquid bio-oil that could not only be used as a transportation fuel but also for heat and power generation. 

Kong, L., Li, G., Wang, H., He, W., Ling, F. Hydrothermal catalytic conversion of biomass for lactic acid production. J Chem Technol Biotechnol 2008, 83, 383-388. 

As discussed previously, the production of lactic acid via fermentation has many difficulties. Consequently, research on novel routes is required. Many experiments have been carried out, and research has been focused on chemocatalytic methods for the conversion of sugars into lactic acid or alkyl esters. Different processes are being explored using biomass feedstock, notably liquid phase processes based on both mild catalytic and subcritical hydrothermal conditions (Jin and Enomoto, 2011 deClippel et al., 2012). 

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