Thermochemical Biomass Conversion Process Research Articles

Roles of mineral matter in biomass processing to biofuels

AbstractMinerals in biomass have a significant impact on both biofuel quality and yield. This is especially true for current thermochemical biomass conversion processes. However, the roles of plant minerals in biochemical conversion have not been studied extensively, even though they are generally considered to lower the sugar yield because they reduce the feedstock proportion of carbohydrates. A successful strategic solution is thus necessary to overcome the challenges caused by the minerals in biomass, which include (1) decreased quality of biomass feedstocks; (2) reduction of process efficiency; and (3) reduction of the product quality and quantity from biomass conversion. This review summarizes the roles of plant minerals in a biorefinery, focusing on these key challenges. The discussion covers many issues related to plant minerals in biofuel production, including their sources, functions, and distribution in plant biomass, methods of characterizing them, their influence in a biorefinery, and the strategic handling required to manage their occurrence in biomass, based on reported studies. It could inspire better strategies to deal with the variance of mineral content in biomass feedstocks to increase process efficiency and reduce costs while supporting the concept of a circular bioeconomy. © 2023 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd.

Phytotoxicity of hydrochars obtained by hydrothermal carbonization of manure-based digestate

The management of digestate, the main by-product of the anaerobic digestion (AD) process, is one of the most serious environmental issues. Although digestate is used on arable land as a fertilizer, it can have a negative impact on the environment due to nitrate leaching into the groundwater and ammonia volatilization into the atmosphere, with high economic and environmental disposal costs. Therefore, hydrothermal carbonization (HTC), a thermochemical biomass conversion process, could represent a sustainable and efficient alternative for digestate management. Hydrochar, the solid product of the HTC process, has been recently proposed as a plant growing medium in soilless culture systems (SCS). Here, using cow manure digestate as feedstock, we investigated the influence of the HTC process reaction temperature (180, 220 and 250 °C) and residence time (1 and 3 h) on the physical-chemical properties (pH, electrical conductivity, and mineral element concentrations) of the resulting hydrochars. Furthermore, in order to fully valorize hydrochar as a growing medium, their possible phytotoxic effects and those of their water extracts (prepared at two different concentrations and at different pHs) were tested in germination tests with cress seeds (Lepidium sativum L.). Concentrations of nutrients, heavy metals, organic acids, sugars and furan compounds were determined in the water extracts. Characterization analysis of these hydrochars revealed that they can be distinguished from each other by their physical-chemical properties, which were significantly affected by the two process parameters. Specifically, the HTC temperature had a greater effect on the composition of hydrochars than the residence time. Germination tests found hydrochar water extracts to show significantly lower phytotoxicity than the hydrochars themselves. Notably, the phytotoxic effect of the extracts decreased with increasing extraction ratio and decreasing pH. The chromatographic characterization of extracts identified the presence of potential phytotoxins, such as furan compounds (i.e., hydroxymethylfurfural and furfural). However, before using hydrochars as potential and innovative growing media for plants, their phytotoxicity should be limited, for example through their dilution with other substrates. Overall, AD-HTC coupling could represent a valuable eco-sustainable expedient in the field of biomasses, green economy and waste conversion and, therefore, further investigations in this direction are necessary.

Upgrading of biomass-derived liquids in a biorefinery context: Hydroisomerization and fluid catalytic cracking of heavy naphtha on bench and pilot scale

The development of efficient processes for the upgrading of low value bio-derived liquid intermediates to high added value products in biorefineries is critical for the establishment of a robust and competitive bio-based economy. We show in this paper that low quality surrogate heavy naphtha, representative of biofuels from thermochemical biomass conversion processes, can be efficiently converted to high quality fuel and chemicals (olefins) via hydroisomerization and catalytic cracking, respectively. Hydroisomerization over a low loading 0.1 wt% Pt/ZSM-5 catalyst leads to the conversion of normal paraffins to C5-C8 isoparaffins with limited cracking, and produces a fuel with higher octane and lower cetane number, suitable for use in future powertrains such as HCCI engines. Catalytic cracking of the naphtha on a commercial ZSM-5 based FCC catalyst results in the production of a significant amount of olefins at 600 °C, primarily propylene followed by ethylene, n-butene, pentene and i-butene. Both processes are validated on pilot scale. Some differences observed between bench and pilot scale results are due to scalability phenomena and different reaction conditions. Still, excellent agreement with regards to the composition of the products at similar conversion level exists, demonstrating the scalability and applicability of these upgrading processes in thermochemical biorefineries.

A novel chemical looping partial oxidation process for thermochemical conversion of biomass to syngas

The Biomass-to-Syngas (BTS) chemical looping process is an advanced thermochemical biomass conversion process for the production of sustainable fuels and chemicals. The BTS process is novel in that it converts biomass feedstock to high purity syngas with adjustable H2:CO molar ratio without needing an air separation unit (ASU), a tar reformer, a steam reformer, or a water-gas-shift (WGS) reactor. In the BTS process, biomass feedstock is partially oxidized to produce syngas by oxygen carriers in a reducer that is operated in a co-current gas-solid moving bed contact mode. The reduced oxygen carriers are regenerated in a fluidized bed combustor via the oxidation reaction with air. The BTS process uses the iron-titanium composite metal oxide (ITCMO) material as the oxygen carrier, which is capable of cracking the volatiles produced in biomass pyrolysis as well as regulating the syngas composition. The co-current moving bed reducer eliminates back-mixing, channeling, or bypassing of solid and gas reactants, resulting in a syngas composition that is close to the thermodynamic equilibrium. In this paper, the rationale of a successful BTS process is discussed along with the thermodynamic characteristics of the ITCMO oxygen carrier, that can effectively react with a woody biomass feedstock, analyzed based on an ASPEN Plus model. Bench scale moving bed reducer experiments are presented, indicating the conversion of wood pellets to syngas with a H2:CO ratio of 2, which is suitable for methanol or liquid fuel synthesis. The gas and solid composition produced in the bench scale reducer matches the prediction from the ASPEN Plus thermodynamic model. This model is further used to analyze the performance of the BTS process under autothermal conditions for methanol production, with a comparison with a baseline indirectly heated gasification process. The results indicate that the BTS process significantly reduces the biomass and steam consumption and appreciably improves the biomass conversion efficiency over that obtained from the baseline process.

Bio-CCS: Feasibility comparison of large scale carbon-negative solutions

Abstract The urgency to stabilize the global temperature rise at 2 °C as highlighted in the IPCC Fifth Assessment Report calls for solutions that can remove CO 2 from the atmosphere. Achieving negative CO 2 emissions by removing CO 2 from the atmosphere is possible by applying carbon capture in processes using biomass (Bio-CCS). Biomass has the capability of withdrawing and storing atmospheric CO 2 . As a result, CO 2 released during biomass combustion can be captured and stored permanently underground, thus depriving the atmosphere of CO 2 . The objective of this paper is to assess the background for most rational deployment opportunities of Bio-CCS from climate and economic point of view; to evaluate what is the best way to use constrained biomass resources by assessing the effects that raw materials types, different processes and end products have on carbon stocks and on the overall GHG mitigation from the global perspective. A concrete example on how more thorough deployment of Bio-CCS could penetrate in near-term markets is given as a Finnish Bio-CCS roadmap with scenarios highlighting the bottlenecks and constrains. The roadmap assessment is based on power plant, industrial plant and emission database calculations with future projections for existing installations. The technical implementation of Bio-CCS in different industrial sectors goes hand in hand with the development of conventional CCS technology deployment. In general, similar solutions are suitable for capturing CO 2 from biomass applications as for fossil fuels. The main differences relate to the size and the location of emission sources (biomass-based installations are often decentralized and of smaller scale compared to fossil-based installations) or to the different kind of impurities in the combustion process, ash and flue gas. However, no principal technical restrictions to the capture of biogenic CO 2 exist in energy generation applications or industrial processes. As a consequence, certain Bio-CCS applications are low-hanging fruits for near future deployment of carbon capture assuming that negative emissions are accounted for. In this paper the potential technologies for Bio-CCS and the feasibility of some solutions are compared both from a sustainability and cost point of view. There are four major biomass conversion routes where Bio-CCS is applicable; biochemical conversion (fermentation and hydrolysis), thermo-chemical conversion (e.g. gasification), power production (gasification and combustion) and industrial processes. In addition to ethanol fermentation the thermo-chemical biomass conversion processes are considered the first-phase targets for applying capture of CO 2 , both from a logistic and cost point of view. The main Bio-CCS technologies assessed in this study are Fischer-Tropsch diesel production, bio-SNG production, lignocellulosic ethanol production, torrefaction and biomass based power production such as co-firing biomass in a coal-based condensing power plant and biomass-based CHP (combined heat and power) production. The most applicable industry sector forintroduction of Bio-CCS is obviously pulp and paper industry but some potential exists also in cement industry, iron and steel industry and oil and gas refineries. The emission reduction potential in different technologies is very much bound to the scale of installations which again is generally limited by the scale of technologies and availability of biomass raw material. The biggest reduction potential for the studied cases per industrial site can take place in iron and steel industry (∼3 Mt/a), pulp and paper industry (∼1.3 Mt/a) and in combined heat power (CHP) production (∼2.5 Mt/a) as opposed to straw ethanol production of smaller scale (∼0.1 Mt/a). However, the CO 2 avoidance potential per unit of biomass raw material utilized is highest in co-firing (20tCO 2 /toe), iron and steel industry (10tCO 2 /toe) and in CHP production (8tCO 2 /toe) whereas straw ethanol has lowest potential also in this category (1.5tCO 2 /toe). The cost estimations show a theoretical economic advantage of Bio-CCS over fossil CCS on carbon prices when the carbon sink effect is accounted for. The total costs for Bio-CCS vary from 35€/ton to 300€/ton CO 2 stored depending on the technology. As the potential of Bio-CCS is bound to the availability and usage of biomass raw materials, the sustainability of the raw materials is of essence. The current biomass flows and potentials set the initial limits for the wider deployment of Bio-CCS. Efficient utilization of constrained resources is an essential question, when the target is to optimize the impact on the system level, from the society point of view. The ultimate objective is to suggest whether deployment of CCS has the desired impact on the atmospheric CO 2 concentration. As biomass can be used in many ways, the primary purpose of utilization and products containing biogenic carbon also adds up to this. When biomass is utilized for products other than energy, the impact to environment and economy differs. The opportunities with these solutions, realistic potential and the main threats related to Bio- CCS are discussed in the light of sustainability and economic potential.

Tar content and composition in producer gas of fluidized bed gasification of wood—Influence of temperature and pressure

AbstractIn thermochemical biomass conversion processes, especially gasification, the tar content, and composition is a major subject. Because of the various processes examined at VUT, this work picks up the opportunity to compare the different tar amounts and its composition at different temperatures and process parameters. Gasification of biomass was carried out at the 100‐kW steam‐blown dual fluidized bed gasifier pilot plant III (800–870°C) and the 70‐kW air‐blown pressurized research unit (800–900°C; 1–5 bar) at VUT. Olivine is a catalyst for tar conversion; hence it was used as bed material in steam gasification and also in pressurized air gasification. For better understanding of tar formation during thermochemical conversion of biomass, the tar content and composition in the producer gas were analyzed with a gas chromatograph coupled with a mass spectrometer.Basic differences between the two thermochemical conversion processes occurred especially at higher temperatures or higher pressures. The tar composition was shifted to higher molecular tars such as polyaromatic hydrocarbons. Decreasing tar amounts were found at higher temperatures or higher pressures. Therefore, in future, an optimization of gasification processes should be easier to accomplish, which means lower tar content in the producer gas, which results in a better utilization of the biomass. © 2009 American Institute of Chemical Engineers Environ Prog, 2009

Mechanisms of Thermochemical Biomass Conversion Processes. Part 2: Reactions of Gasification

Gasification as a thermochemical process is defined and limited to combustion and pyrolysis. The gasification of biomass is a thermal treatment which results in a high proportion of gaseous products and small quantities of char (solid product) and ash. Biomass gasification technologies have historically been based upon partial oxidation or partial combustion principles, resulting in the production of a hot, dirty, low Btu gas that must be directly ducted into boilers or dryers. In addition to limiting applications and often compounding environmental problems, these technologies are an inefficient source of usable energy. The main objective of the present study is to investigate gasification mechanisms of biomass structural constituents. Complete gasification of biomass involves several sequential and parallel reactions. Most of these reactions are endothermic and must be balanced by partial combustion of gas or an external heat source.

Mechanisms of Thermochemical Biomass Conversion Processes. Part 1: Reactions of Pyrolysis

The present work is a study on the pyrolysis mechanisms of biomass structural constituents. Biomass resources include wood and wood wastes, agricultural crops and their waste byproducts, municipal solid waste, animal wastes, waste from food processing, and aquatic plants and algae. The major organic components of biomass can be classified as cellulose, hemicelluloses, and lignin. The pyrolysis is thermal degradation of biomass by heat in the absence of oxygen, which results in the production of charcoal (solid), bio-oil (liquid), and fuel gas products. Thermal degradation of cellulose proceeds through two types of reaction: a gradual degradation, decomposition, and charring on heating at lower temperatures; and a rapid volatilization accompanied by the formation of levoglucosan on pyrolysis at higher temperatures. The hemicelluloses reacted more readily than cellulose during heating. Of the hemicelluloses, xylan is the least thermally stable, because pentosans are most susceptible to hydrolysis and dehydration reactions. Dehydration reactions around 473 K are primarily responsible for thermal degradation of lignin. Between 423 K and 573 K, cleavage of α- and β-aryl-alkyl-ether linkages occurs. Around 573 K, aliphatic side chains start splitting off from the aromatic ring.

98/03101 Yields of oil products from thermochemical biomass conversion processes

This paper examines the use of organic co-solvent (n-heptane, toluene and anisole, up to 10 wt.%) in the hydrothermal liquefaction of macroalgal biomass as a means of achieving in situ fractionation of the biocrude product according to polarity. The filamentous freshwater macroalga Oedogonium was grown under nutrient-depleted conditions to achieve a low nitrogen content, 1.1 wt.% N. Its hydrothermal liquefaction in a continuous pilot plant reactor (300–350 °C, 3–5 min and 2–5 wt.% loadings) yielded up to 25 wt.% (dry ash-free basis, daf) extractable biocrude. More severe conditions led to biocrudes in higher yields, with reduced oxygen and slightly increased nitrogen contents, and with lower viscosity. The presence of co-solvents had little effect on the total biocrude yield but gave rise to in situ separation of the biocrude into distinct fractions associated with the organic phase (designated solvent oil) and the aqueous phase (designated DCM oil). The amount of solvent oil produced exceeded the amount that could be extracted at room temperature, by that solvent, from the product mixture obtained in the absence of co-solvent. The relative proportions and properties of the solvent and DCM fractions varied with the polarity of the co-solvent. Anisole co-solvent dissolved nearly all the biocrude and the resulting viscous oil was similar to that obtained without co-solvent. On the other hand, solvent oil produced with n-heptane (~ 7.4 wt.% daf yield, or ~ 37% of the total biocrude) had significantly reduced levels of nitrogen (1.1 wt.%) and oxygen (12.5 wt.%) and possessed relatively low viscosity. Toluene co-solvent HTL produced a solvent oil with intermediate yield and properties. Co-solvent HTL offers a simple and effective means of fractionating HTL biocrude on the basis of polarity. A non-polar co-solvent such as n-heptane produces an enhanced product fraction more suitable for hydrotreating than the mixed product obtained without co-solvent.

Yields of oil products from thermochemical biomass conversion processes

Thermochemical biomass conversion processes, including mainly pyrolysis, liquefaction and supercritical fluid extraction, were applied non-catalytically and catalytically to obtain the maximum fuels from biomass. Different solvents and their mixtures were used in simple and supercritical extractions. Basic catalysts, such as NaOH, Na 2CO 3 and K 2CO 3, were used in catalytic conversion experiments. The experiments were performed within the 498–820 K range.

98/01946 Yields of oil products from thermochemical biomass conversion processes : Demirbas, A. Energy Convers. Mgmt, 1998, 39, (7), 685–690

98/01946 Yields of oil products from thermochemical biomass conversion processes : Demirbas, A. Energy Convers. Mgmt, 1998, 39, (7), 685–690