In this chapter, practical engineering strategies for recyclable magnetic materials for biomass conversion are discussed, starting with the syntheses and chemical functionalization of magnetic nanoparticles and nanoscopic materials. Nanoscale magnetic materials are attractive for the design of various catalytic systems because of their large surface-to-volume ratio, temperature stability and easy (magneto-)recovery. The applications discussed here are focused on transforming lignocellulosic biomass to sugars (and subsequent biofuel), as well as biobased chemicals. Lignocellulosic biomass can be broken down with a catalytic biomass pretreatment followed by fractionation. Tailored magnetic nanocatalysts can be used in both processes. An alternative strategy for generating low-molecular-weight sugars from lignocellulosic biomass is the use of enzymes (e.g. catalase) on magnetic beads. An attribute of all systems discussed is that they can be recycled magnetically, thus decreasing the required costs of “green materials”.

Spherical carbon molecular sieves (CMS) have selective adsorptive properties which are suitable for separation and purification of gas mixtures. Precise methods of characterization are needed to understand the performance of CMS in separation processes. To this end, the pore size distribution (PSD) of four carbon molecular sieves were evaluated experimentally using immersion calorimetry and complemented with gas adsorption measurements at cryogenic temperatures for N-2, O-2 and Ar, and at 273 K for CO2. Theoretical pore size distributions were estimated using two-dimensional non-local Density Functional Theory (2D-NLDFT) models. Calorimetry results showed that B and C samples had a narrow pore size distribution with pores below 0.7 nm. Meanwhile, the pore size distributions calculated from O-2 and Ar adsorption isotherms, gave an apex in the 0.5-0.6 nm region for all the carbons together with a growing development of porosity at around 0.8 nm and above for carbons A and D. The agreement observed between experiments and theory confirmed the validity of the theoretical 2D-NLDFT models to anticipate the PSD. Carbon C with pores exclusively below 0.7 nm separated CO2 and CH4 while carbon D with pores in the supermicroporous region separated propane and propylene chromatographically. (C) 2019 The Authors. Published by Elsevier Ltd.

A morphological study of lignin-bound anthracite briquettes was carried out to understand the mechanisms that hold together anthracite fines and silicon grains at elevated temperatures and high abrasion conditions. Lab-scale briquettes were prepared from anthracite fines, lignin, collagen, silicon, and other additives; and then pyrolyzed at 800 degrees C, 1400 degrees C and 1600 degrees C under nitrogen atmosphere to simulate the conditions inside a foundry cupola. The pyrolyzed samples were analyzed by reflected light microscopy, electron microscopy and x-ray diffraction. These analyses gave information on the transformations that lignin-bound anthracite briquettes may undergo in a cupola furnace. Lignin and collagen melted and formed an amorphous carbon phase that linked anthracite and silicon grains. Silicon carbide (SiC) nanowires coated in silicon oxide were formed at 1400 degrees C, and at 1600 degrees C most of the silicon was converted to SiC. Silicon carbide nanowires filled the interstitial voids left by volatilization of lignin and collagen. These findings support the idea that lignin and collagen hold anthracite fines at low temperature regimes. Silicon carbide nanowires contribute to briquette strength at high temperature conditions, acting as reinforcing filler and prevent collapse of the lignin-collagen matrix surrounding the anthracite grains. (C) 2018 Elsevier Ltd. All rights reserved.

In this chapter, practical engineering strategies for recyclable magnetic materials for biomass conversion are discussed, starting with the synthesis and chemical functionalization of magnetic nanoparticles and nanoscopic materials. Nanoscale magnetic materials are attractive for the design of various catalytic systems because of their large surfaces, temperature-stability and easy (magneto-)recovery. The applications discussed here are focused on transforming lignocellulosic biomass to sugars (and subsequent biofuel), as well as feedstock chemicals. The breaking down of lignocellulosic biomass can be achieved by subsequent biomass pretreatment and fractionation. Tailored magnetic nanocatalysts can be used in both processes. An alternative strategy for generating low molecular sugars from lignocellulosic biomass is the use of enzymes (e.g. catalase) on magnetic beads. It is an attribute of all systems discussed that they can be recycled magnetically, thus decreasing the required costs of “green materials”.

Sustainable biomaterial binders were developed from lignin and collagen to replace the conventional petroleum pitch and coal tar pitch binders that have been used when making specialty graphites and graphite electrodes. The team prepared lab-scale graphite electrodes by first creating green composites, by hot-pressing together the lignin, collagen, petroleum coke, and other additives, followed by carbonization and graphitization. Response Surface Methodology (RSM) experimental design was employed, based on Box-Behnken Design (BBD). This was employed to optimize the recipes and processing protocols for the green composite hot-pressing of 3.5 cm diameter x 19 cm long cylinder specimens. Relative to density, the apparent optimum conditions occurred with 13.0% lignin, 3.6% collagen, 27.4% petroleum coke fines, and the balance of petroleum coke particles plus some additives. The green hot-pressing protocol employed 30 MPa pressure at 400 degrees C for 2 h. Baking peaked at 800 degrees C, ramped up and down over 13 days. This baked product hosted an apparent density of 1.67 g/mL, and exhibited 6.2% puffing. Another baked product hosted 1.56 g/mL and 1.67% puffing. After the baked product was graphitized, we achieved an apparent density of 1.51 g/mL and resistance of 25-30 mu Omega m. These results approached the specifications for specialty graphites. (C) 2016 Elsevier Ltd. All rights reserved.

Functionalization of silica surfaces using organo-silanes is highly sensitive to reaction conditions.Silica-coated nanoparticles were functionalized with propyl-sulfonic acid groups (PS) under different synthesis conditions including, various solvents (Ethanol, methanol, acetonitrile, and toluene), water content in the reaction media (0% to 50%), 3-mercaptopropyl-trimethoxysilane concentration (MPTMS) (0.5% to 10%), and reaction time (6 to 16 h).Size of the PS-nanoparticles was determined by TEM and varied from 3.5 to 20.3 nm with sulfur load.Elemental analysis revealed sulfur contents from 0.8% to 22%.FTIR analysis showed increased C-H band intensities with increasing sulfur content of PS-nanoparticles.Although PS-nanoparticles with sulfur loads under 3% did not improve the hydrolysis of cellobiose, PS acid-functionalized nanoparticles with about 6% S achieved 96.0% cellobiose conversion.The control experiment, without catalyst, converted 32.8% of the initial cellobiose.PS-nanoparticles with (6% -8% S) were obtained using (0.5%) silane concentration and 15 -16 h reaction time in ethanol.

Propyl-sulfonic (PS) acid-functionalized nanoparticles were synthesized, characterized and evaluated as catalysts for pretreatment of corn stover. Silica coated nanoparticles were functionalized with 0.5% mercaptopropyltrimethoxysilane (MPTMS) at neutral pH in a mixture of water and ethanol. Sulfur contents of the acid functionalized nanoparticles, measured in a CHNS analyzer, varied from 6%-10%, and the acid load ranged from 0.040 to 0.066 mmol H+/g. A Box-Behnken design was employed to calculate the minimum number experiments required to obtain an estimate of the surface response for temperature, catalyst load, and %S content of the catalyst. Pretreatment of corn stover was carried out at three temperature levels 160, 180, and 200°C for 1 h. Three levels of catalyst load were used 0.1, 0.2, and 0.3 g of catalyst per gram of biomass. Hydro-thermolysis controls were carried at each temperature level. The catalyst load did not have an effect on the glucose yield at 160°C, and the average glucose yield obtained at this temperature was 59.0%. The glucose yield was linearly correlated to the catalyst load during pretreatment at 180°C, and a maximum glucose yield of 90% was reached when using 0.2 g of PS nanoparticles that had a total sulfur content of 6.1%. Complete hydrolysis of glucose was reached at 200°C but the average xylose yield was 4.6%, and about 20.2% of the combined glucose and xylose were lost as hydroxymethylfurfural and furfural. Results showed that acid-functionalized nanoparticles can be potential catalysts for the pretreatment of biomass for its later conversion to ethanol.

Superparamagnetic iron oxide nanoparticles were functionalized with a quasi-monolayer of 11-sulfoundecanoic acid and 10-phosphono-1-decanesulfonic acid ligands to create separable solid acid catalysts. The ligands are bound through carboxylate or phosphonate bonds to the magnetite core. The ligand-core bonding surface is separated by a hydrocarbon linker from an outer surface with exposed sulfonic acid groups. The more tightly packed monolayer of the phosphonate ligand corresponded to a higher sulfonic acid loading by weight, a reduced agglomeration of particles, a greater tendency to remain suspended in solution in the presence of an external magnetic field, and a higher catalytic activity per sulfonic acid group. The particles were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), potentiometric titration, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), inductively coupled plasma optical emission spectrometry (ICP-OES), and dynamic light scattering (DLS). In sucrose catalysis reactions, the phosphonic-sulfonic nanoparticles (PSNPs) were seen to be incompletely recovered by an external magnetic field, while the carboxylic-sulfonic nanoparticles (CSNPs) showed a trend of increasing activity over the first four recycle runs. The activity of the acid-functionatized nanoparticles was compared to the traditional solid acid catalyst Amberlyst-15 for the hydrolysis of starch in aqueous solution. Catalytic activity for starch hydrolysis was in the order PSNPs > CSNPs > Amberlyst-15. Monolayer acid functionalization of iron oxides presents a novel strategy for the development of recyclable solid acid catalysts.

Perfluoroalkylsufonic (PFS) and alkylsufonic (AS) acid-functionalized magnetic nanoparticles were synthesized and characterized, then evaluated for their ability to hydrolyze hemicelluloses. The magnetic core was made of cobalt spinel ferrite and was coated with silica to protect it from oxidation. The silanol groups allowed surface chemical modification of the nanoparticles with the PFS and AS acid functionalities. Thermogravimetric analysis gave a total organic load of 12.6% and 32.5% (w/w) for AS and PFS nanoparticles, respectively. The surface sulfur content was calculated from XPS analysis as 1.37% and 1.93% for PFS and AS nanoparticles, respectively. Wheat straw samples were treated with the acid-functionalized nanoparticles at two different conditions: 80℃ for 24 h and 160℃ for 2 h. These experiments aimed to hydrolyze wheat straw hemicelluloses to soluble oligosaccharides. PFS nanoparticles solubilized significantly higher amounts of hemicelluloses (24.0% ± 1.1%) than their alkyl-sulfonic counterparts (9.1% ± 1.7%) at 80℃, whereas the hydrothermolysis control solubilized 7.7% ± 0.8% of the original hemicelluloses in the sample. At 160℃, PFS and AS nanoparticles gave significantly higher amounts of oligosaccharides (46.3% ± 0.4% and 45 ± 1.2%, respectively) than the control (35.0% ± 1.8%). The hemicelluloses conversion at 160?C reached 66.3% ± 0.9% using PFS nanoparticles and 61.0% ± 1.2% using AS nanoparticles compared with the control experiment, which solubilized 50.9% ± 1.7% of hemicelluloses in the biomass.

Photoperiod-sensitive sorghum, as a competitive biomass for ethanol production, was investigated to develop an integrated process for improving ethanol yield. Response surface methodology was employed to study the relationship between pretreatment variables (including temperature, sulfuric acid concentration, and reaction time) and cellulose recovery, as well as efficiency of enzymatic hydrolysis (EEH) in the solid part. Recovery yield decreased and EEH increased as the pretreatment temperature, acidic concentration, and reaction time increased. A model was successfully developed to predict total glucose yield with a maximum value of 82.2%. Conditions of co-fermentation were also optimized, and the optimal ethanol yield was obtained with constant-temperature simultaneous saccharification and fermentation at 38°C. Acetate buffer at a concentration of 50mM was found helpful for increasing efficiency of enzymatic hydrolysis, as well as ethanol yield. The maximum ethanol yield was 0.21g ethanol per dry mass at the conditions of 38°C, 0.05g yeast/L, and 50mM acetate buffer. A complete cellulose balance was provided for the whole process.

Mineral acids have been used effectively for the pretreatment of cellulosic biomass to improve sugar recovery and promote its conversion to ethanol; however, substantial capital investment is required to enable separation of the acid, and corrosion-resistant materials are necessary. Disposal and neutralization costs are also concerns because they can decrease the economic feasibility of the process. In this work, three acid-functionalized nanoparticles were synthesized for pretreatment and hydrolysis of lignocellulosic biomass. Silica-protected cobalt spinel ferrite nanoparticles were functionalized with perfluoroalkylsulfonic acid (PFS), alkylsulfonic acid (AS), and butylcarboxylic acid (BCOOH) groups. These nanoparticles were magnetically separated from the reaction media and reused. TEM images showed that the average diameter was 2 nm for both PFS and BCOOH nanoparticles and 7 nm for AS nanoparticles. FTIR confirmed the presence of sulfonic and carboxylic acid functional groups. Ion exchange titration measurements yielded 0.9, 1.7, and 0.2 mmol H + /g of catalyst for PFS, AS, and BCOOH nanoparticles, respectively. Elemental analysis results indicated that PFS and AS nanoparticles had 3.1 and 4.9% sulfur, respectively. Cellobiose hydrolysis was used as a model reaction to evaluate the performance of acid-functionalized magnetic nanoparticles for breaking β-(1→4) glycosidic bonds. Cellobiose conversion of 78% was achieved when using AS nanoparticles as the catalyst at 175°C for 1 h, which was significantly higher than the conversion for the control experiment (52%). AS nanoparticles retained more than 60% of their sulfonic acids groups after the first run, and 65 and 60% conversions were obtained for the second and third runs, respectively.

Acid catalysts have been successfully used for the pretreatment of cellulosic biomass to improve the sugar recovery and its later conversion to ethanol. However, the use of acid requires considerable equipment investment as well as disposing of the residues. Acid-functionalized nanoparticles were synthesized for pretreatment and hydrolysis of lignocellulosic biomass to increase conversion efficiency at mild conditions. The advantage of using functionalized metal nanoparticles is not only the acidic properties to catalyze hydrolysis and being small enough to be able to penetrate into the lignocellulosic structure, but also being easily separable from products using a strong magnetic field. Cobalt spinel ferrite magnetic nanoparticles were synthesized using a microemulsion method and then covered with a layer of silica to protect them from oxidation. The silanol groups of the silica serve as the support of the sulfonic acid groups that were later attached to the surface of the nanoparticles. TEM images and FTIR methods were used to characterize the properties of acid-functionalized nanoparticles in terms of nanoparticle size, presence of sulfonic acid functional groups, and pH as an indicator of acid sites present. Citric acid functionalized magnetite nanoparticles were also evaluated. Cellulose powder was treated with the acid supported nanoparticles at 80C for 24 h to hydrolyze cellulose to sugars. Further hydrolysis of the liquid fraction was carried out to account for the amount of solubilized polysaccharides. HPLC was used to evaluate the amount of sugar obtained in the aqueous solution. The analysis of carbohydrates in the liquid fraction of the post-hydrolysis revealed a significant amount of monosaccharides compared to hydrothermolysis. The acid functionalized nanoparticles may have broken down the non soluble polysaccharides to its oligomeric components.