Lignocellulose Liquefaction to Biocrude: A Tutorial Review

Lignocellulose Biomass Liquefaction: Process and Applications Development as Polyurethane Foams

One of the main strategies for sustainable human society progress is the development of efficient strategies to limit waste production and maximize renewable resource utilization. In this context, this review highlights the opportunity to transform vegetable biomass residues into valuable commercial products. Biomass conversion entails the depolymerization of lignocellulosic biomass towards biopolyols and the synthesis and characterization of the valuable products obtained by using them. The influence of the reaction parameters in both acid and basic catalysis is highlighted, respectively the influence of microwaves on the liquefaction reaction versus conventional heating. Following the depolymerization reaction, polyols are employed to produce polyurethane foams. As a special characteristic, the addition of flame-retardant properties was emphasized. Another interesting topic is the biodegradability of these products, considering the negative consequences that waste accumulation has on the environment.

Oxidative Conversion of Glucose to Formic Acid as a Renewable Hydrogen Source Using an Abundant Solid Base Catalyst

Formic acid is one of the most desirable liquid hydrogen carriers. The selective production of formic acid from monosaccharides in water under mild reaction conditions using solid catalysts was investigated. Calcium oxide, an abundant solid base catalyst available from seashell or limestone by thermal decomposition, was found to be the most active of the simple oxides tested, with formic acid yields of 50 % and 66 % from glucose and xylose, respectively, in 1.4 % H2 O2 aqueous solution at 343 K for 30 min. The main reaction pathway is a sequential formation of formic acid from glucose by C-C bond cleavage involving aldehyde groups in the acyclic form. The reaction also involves base-catalyzed aldose-ketose isomerization and retroaldol reaction, resulting in the formation of fructose and trioses including glyceraldehyde and dihydroxyacetone. These intermediates were further decomposed into formic acid or glycolic acid. The catalytic activity remained unchanged for further reuse by a simple post-calcination.

Debottlenecking a Pulp Mill by Producing Biofuels from Black Liquor in Three Steps

By extracting lignin, pulp production can be increased without heavy investments in a new recovery boiler, the typical bottleneck of a pulp mill. The extraction is performed by using 0.20 and 0.15 weight equivalents of CO2 and H2 SO4 respectively. Herein, we describe lignin esterification with fatty acids using benign reagents to generate a lignin ester mixable with gas oils. The esterification is accomplished by activating the fatty acid and lignin with acetic anhydride which can be regenerated from the acetic acid recycled in this reaction. The resulting mass balance ratio is fatty acid/lignin/acetic acid (2 : 1 : 0.1). This lignin ester can be hydroprocessed to generate hydrocarbons in gasoline, aviation, and diesel range. A 300-hour continuous production of fuel was accomplished. By recirculating reagents from both the esterification step and applying a water gas shift reaction on off-gases from the hydroprocessing, a favorable overall mass balance is realized.

A Perspective on Biofuels Use and CCS for GHG Mitigation in the Marine Sector

The greenhouse gas (GHG) emissions of the marine sector were around 2.6% of world GHG emissions in 2015 and are expected to increase 50%–250% to 2050 under a “business as usual” scenario, making the decarbonization of this fossil fuel-intensive sector an urgent priority. Biofuels, which come in various forms, are one of the most promising options to replace existing marine fuels for accomplishing this in the short to medium term. Some unique challenges, however, impede biofuels penetration in the shipping sector, including the low cost of the existing fuels, the extensive present-day refueling infrastructure, and the exclusion of the sector from the Paris climate agreement. To address this, it is necessary to first identify those biofuels best suited for deployment as marine fuel. In this work, the long list of possible biofuel candidates has been narrowed down to four high-potential options—bio-methanol, bio-dimethyl ether, bio-liquefied natural gas, and bio-oil. These options are further evaluated based on six criteria—cost, potential availability, present technology status, GHG mitigation potential, infrastructure compatibility, and carbon capture and storage (CCS) compatibility—via both an extensive literature review and stakeholder discussions. These four candidates turn out to be relatively evenly matched overall, but each possesses certain strengths and shortcomings that could favor that fuel under specific circumstances, such as if compatibility with existing shipping infrastructure or with CCS deployment become pivotal requirements. Furthermore, we pay particular attention to the possibility of integrating deployment of these biofuels with CCS to further reduce marine sector emissions. It is shown that this aspect is presently not on the radar of the industry stakeholders but is likely to grow in importance as CCS acceptability increases in the broader green energy sector.

BAILs mediated Catalytic Thermo Liquefaction (CTL) process to convert municipal solid waste into carbon densified liquid (CTL-Oil)

Continual increase in municipal solid waste (MSW) posing global environmental challenge which directed focus towards the waste to energy to achieve dual goal of waste minimization and energy generation. The present manuscript introducing Bronsted acid ionic liquids (BAILs) mediated Catalytic Thermo Liquefaction (CTL) process for conversion of MSW into carbon densified liquid (CTL-Oil) which can be used for multiple energy and fuel applications. BAILs with different counter ions were synthesized and tested for CTL of wet organic biodegradable MSW. The exploration of BAILs provides significant benefits in terms of operating conditions (120 °C, 90 min) with zero char and gases. Of the synthesized catalysts [Benz-SO₃HIm]⁺[H₂PO₄]^-,[Benz-SO₃Him]⁺[HSO₄]^-_,[Benz-SO₃HIm]⁺[TsO]^-and [BenzSO₃HIm]⁺[TfO]^-, BAIL with [HSO₄]^-counter ion showed a profound effect on CTL. The intensified CTL process resulted in > 85% MSW conversion with > 80% yield of CTL-Oil without any char and gas formation. Use of BAILs assisted the ease of dissolution and hydrolysis of biomass to produce CTL-Oil via hydrolysis, condensation, cyclization and dehydration reactions. The plausible mechanism for CTL has been proposed. The physicochemical analysis of CTL-Oil was conducted by using elemental analysis, Bomb calorimeter, GC-MS and ATR-FTIR. It was found that the CTL-Oil was rich source of C (48-55%), H (6-8%), O (30-41%) containing compounds such as long-chain hydrocarbons, carboxylic acids, heterocyclic compounds, aldehydes, ketones and esters, etc. Furthermore, the calorific value of CTL-Oil was found to be 20-23 MJ/kg, thus it can be explored for multiple energy and fuel applications. However, the CTL process also adds several environmental and process economic benefits over the conventional waste liquefaction/disposal processes.

Selective removal of lignin to enhance the process of preparing fermentable sugars and platform chemicals from lignocellulosic biomass

The economic dependency on fossil fuels and the resulting effects on climate and environment have put more focus on finding alternative renewable sources (e.g. lignocellulose) for the production of fuels and chemicals. Nevertheless, the yield and quality of fermentable sugar and platform chemical produced by directly degradation of lignocellulose are severely restricted owing to the presence of lignin and its derivatives. Therefore, the present study was aimed to selective removal of lignin to enhance the process of preparing fermentable sugars and platform chemicals from lignocellulosic biomass. The results showed that the highest degree of delignification was 92.01%. Reducing sugar obtained by enzymatic hydrolysis of lignocellulose was suitable for L-lactic acid fermentation without appreciable inhibition. The highest cellulose digestibility and yield of 5-HMF were 90.67% and 61.02%, respectively. SO₄^2-/ZrO₂ could be reused at least 5 times without appreciable loss of catalytic performance, which shows an industrial application prospects in biorefinery.

Fully Recyclable Bio-Based Thermoplastic Materials from Liquefied Wood

A novel, low-cost, and fully recyclable thermoplastic material is produced from liquefied lignocellulosic biomass and natural fibers. The matrix, which is the heavy fraction of the liquefaction product, is characterized in terms of molecular weight distribution, density, viscosity, softening point and tensile strength. It is possible to increase the mechanical strength of the matrix by a factor of up to 100 by reinforcing it with flax fibers. Specifically, the tensile strength increased from 0.4 MPa for the non-reinforced matrix, to 55 MPa for the matrix/flax composite with a fiber content of 20 wt %. These values are comparable to conventional thermoplastics, such as poly(methyl methacrylate), polyvinyl chloride, or polystyrene.

Catalytic Transfer Hydrogenation of Biomass-Derived Substrates to Value-Added Chemicals on Dual-Function Catalysts: Opportunities and Challenges

Aqueous-phase hydrodeoxygenation (APH) of bioderived feedstocks into useful chemical building blocks is one the most important processes for biomass conversion. However, several technological challenges, such as elevated reaction temperature (220-280 °C), high H₂ pressure (4-10 MPa), uncontrollable side reactions, and intensive capital investment, have resulted in a bottleneck for the further development of existing APH processes. Catalytic transfer hydrogenation (CTH) under much milder conditions with non-fossil-based H₂ has attracted extensive interest as a result of several advantageous features, including high atom efficiency (≈100 %), low energy intensity, and green H₂ obtained from renewable sources. Typically, CTH can be categorized as internal H₂ transfer (sacrificing small amounts of feedstocks for H₂ generation) and external H₂ transfer from H₂ donors (e.g., alcohols, formic acid). Although the last decade has witnessed a few successful applications of conventional APH technologies, CTH is still relatively new for biomass conversion. Very limited attempts have been made in both academia and industry. Understanding the fundamentals for precise control of catalyst structures is key for tunable dual functionality to combine simultaneous H₂ generation and hydrogenation. Therefore, this Review focuses on the rational design of dual-functionalized catalysts for synchronous H₂ generation and hydrogenation of bio-feedstocks into value-added chemicals through CTH technologies. Most recent studies, published from 2015 to 2018, on the transformation of selected model compounds, including glycerol, xylitol, sorbitol, levulinic acid, hydroxymethylfurfural, furfural, cresol, phenol, and guaiacol, are critically reviewed herein. The relationship between the nanostructures of heterogeneous catalysts and the catalytic activity and selectivity for C-O, C-H, C-C, and O-H bond cleavage are discussed to provide insights into future designs for the atom-economical conversion of biomass into fuels and chemicals.