Nuclear Magnetic Resonance Investigation of the Fractionation of Water–Ethanol Mixtures with Cellulose and Its Cross-Linked Biopolymer Forms

Cellulose (CE) was cross-linked with epichlorohydrin (EPI) at variable compositions, and the fractionation properties were investigated in binary water–ethanol (W–E) solutions, including the pure solvent systems. The relative uptake of each solvent was measured using quantitative ¹H nuclear magnetic resonance (qNMR) spectroscopy. This study highlights the utility of qNMR as a rapid screening method for estimation of solvent selective fractionation in binary mixtures. The uptake properties of CE–EPI cross-linked polymers with ethanol and water were well-described using the Sips isotherm model. Modeling shows that the monolayer surface coverage (<i>Q</i>_m) of ethanol and water onto the polymer materials covers a range (1.13–2.44 g/g) of values with heterogeneous adsorption behavior, in agreement with the Sips exponential fitting parameter (<i>n</i>_s ≠ 1). The CE–EPI adsorbents display unique fractionation with water and ethanol from binary solutions, as evidenced by the relative selectivity (<i>R</i>_selectivity) value in binary W–E solvent systems. The <i>R</i>_selectivity [<i>Q</i>_m(W)/<i>Q</i>_m(E)] values at saturative conditions varied (from 1.10 to 2.03) and further illustrate that CE materials display molecular selective solvent fractionation in binary W–E solutions. This study provides a greater molecular level understanding for the adsorptive uptake properties of CE that are relevant to developing CE-based adsorbent technology for the fractionation of biofuels and related chemical separations

NMR Investigation of the Fractionation of Water–Ethanol Mixtures with Starch and Its Cross-Linked Forms

The development of low-cost materials and efficient methods for the fractionation of water and ethanol in binary mixtures is of great interest for food processing and biofuels production. Herein, we report a systematic study of a series of linear and branched starch-based biopolymers along with their modified forms via cross-linking with epichlorohydrin (EPI) at variable EPI composition. The fractionation properties of these adsorbent materials were studied in binary ethanol–water solutions and compared against those of neat solvents. ¹H NMR spectroscopy was used to assess the binary solvent composition for the study of isotherms for the respective solvent components. The monolayer adsorption capacity (<i>Q</i>_m) for starch and its cross-linked forms varied from 0.01 to 2.70 g·g^–1 for water and ethanol in binary mixtures according to the Sips isotherm model. The fractionation selectivity [<i>R</i>_selectivity; <i>Q</i>_m(W)/<i>Q</i>_m(E)] of starch-EPI adsorbents for water (W) and ethanol (E) in binary mixtures ranges from 3.8 to 80. At saturative conditions in binary W–E mixtures, the <i>R</i>_selectivity isotherm parameter reveals unique solvent-selective uptake that depends on the amylose versus amylopectin composition and the EPI content of these cross-linked materials. The unique water uptake properties of starch and its cross-linked forms illustrate the role of textural properties and relative hydrophobic character of the polymer network based on the selective adsorption properties. Starch and its modified forms represent a promising class of adsorbent materials and a sustainable technology for the adsorptive-based fractionation of W–E binary mixtures

Renewable Starch Carriers with Switchable Adsorption Properties

This Research Article describes a systematic study on the structure and sorption properties of Carnation-based starch-particles (SPs) by various techniques. Structural characterization of the SPs utilized spectroscopy (¹H NMR and FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The sorption properties of the SPs were characterized by solvent swelling and uptake isotherms with cationic adsorbates at equilibrium and kinetic conditions. The surface area (SA; ∼3–588 m²/g) of the SPs was estimated using nitrogen gas and dye adsorption isotherm methods, where the range in SA was related to solvent swelling effects on the textural properties. The SPs contain lipid constituents according to results obtained by ¹H NMR spectroscopy, DSC, and confocal laser microscopy (CLM) with iodine staining. The unique solvent swelling properties of the SPs reveal greater swelling in water over ethanol. SPs display preferential equilibrium uptake of methylene blue (MB; <i>Q</i>_m ≈ 716 mg/g) over cetylpyridinium bromide (CPB; <i>Q</i>_m ≈ 292 mg/g). The uptake of MB was reduced by an order of magnitude (<i>Q</i>_m ≈ 67 mg/g) when the SPs were doped with CPB, further revealing the role of competitive adsorption and similar binding modes for MB and CPB. The doping of SPs with CPB provide a facile approach for alteration of the surface functional properties such as the hydrophile–lipophile character, surface charge, and hydration properties of the SPs. Evidence of monolayer and multilayer adsorption of CPB onto SPs lead to switchable adsorption properties where such amphiphile surface patterning can be harnessed to yield materials with unique controlled-release properties for diverse chemical systems according to tunable surface charge using self-assembly

Miscanthus Biomass for the Sustainable Fractionation of Ethanol–Water Mixtures

Miscanthus is a rich source of lignocellulosic biomass with low mineral content suitable for applications that range from biofuel production to value-added biomass-derived products including a sustainable biosorbent. Herein, Miscanthus and its modified forms were used for the fractionation of water (W) and ethanol (E) mixtures that were analyzed by an <i>in situ</i> analytical method, referred to as quantitative NMR (qNMR) spectroscopy. Miscanthus was pretreated by hydrolysis and subsequent grinding to yield materials with variable biopolymer content (cellulose and lignins) and particle size. The Miscanthus materials were evaluated as sorbents in binary water–ethanol (W-E) mixtures. The maximum biomass adsorption capacity (<i>Q</i>_m; g g^–1) with water (<i>Q</i>_m,W) and ethanol (<i>Q</i>_m,E) fractions were determined by the best-fit Sips model parameters listed in parentheses: raw Miscanthus biomass (<i>Q</i>_m,W = 8.93 and <i>Q</i>_m,E = 4.15) and pretreated Miscanthus biomass (<i>Q</i>_m,W = 4.73 and <i>Q</i>_m,E = 3.22, g g^–1). The fractionation properties of Miscanthus and its biopolymer constituents show molecular selectivity [<i>R</i>_selectivity = <i>Q</i>_m,W/<i>Q</i>_m,E] between W and E. The <i>R</i>_selectivity values are given in parentheses, as follows: untreated Miscanthus (3:1), pretreated Miscanthus (1.5:1), and lignins (1:5.4). The pretreated Miscanthus was prepared by acid and base hydrolysis for the removal of hemicellulose and lignins, respectively, leading to cellulose enrichment. The raw and pretreated Miscanthus have preferential water uptake properties that relate to the relative biopolymer composition. To test the reusability and regeneration of Miscanthus, the biosorbent was tested over four adsorption–desorption cycles. This work contributes to a greater understanding of chemical treatment effects on biomass adsorption properties and evaluation of the adsorptive contributions of biopolymer components for the fractionation of water–ethanol mixtures

Starch Particles, Energy Harvesting, and the “Goldilocks Effect”

This study reports on the unique water vapor adsorption properties of biomass-derived starch particles (SPs). SPs offer an alternative desiccant for air-to-air energy exchangers in heating, ventilation, and air conditioning systems because of their remarkable adsorption–desorption performance. SP₁₅ has a particle diameter (<i>d</i>_p) of 15 μm with a surface area (SA) of 2.89 m²/g and a pore width (<i>P</i>_w) of 80 Å. Microporous starch particles (SP₁₅) were compared with high amylose starch (HAS₁₅; SA = 0.56 m²/g, <i>d</i>_p = 15 μm, <i>P</i>_w = 46 Å) and silica gel (SG₁₃; SA = 478 m²/g, <i>d</i>_p = 13 μm, <i>P</i>_w = 62 Å). Transient water vapor tests were performed using a customized small-scale energy exchanger coated with SP₁₅, HAS₁₅, and SG₁₃. The water swelling (%) for SP₁₅ was ca. 2 orders of magnitude greater with markedly higher (ca. three- and six-fold) water vapor uptake compared to HAS₁₅ and SG₁₃, respectively. At similar desiccant coating levels on the energy exchanger, the latent effectiveness of the SP₁₅ system was much improved (4–31%) over the HAS₁₅ and SG₁₃ systems at controlled operating conditions. SP₁₅ is a unique desiccant material with high affinity for water vapor and superior adsorption properties where ca. 98% regeneration was achieved under mild conditions. Therefore, SPs display unique adsorption–desorption properties, herein referred to as the “Goldilocks effect”. This contribution reports on the utility of SPs as promising desiccant coatings in air-to-air energy exchangers for ventilation systems or as advanced materials for potential water/energy harvesting applications