Real-time application and modelling of the NOx-sorption reaction on a particulate calcium carbonate surface-flow filter exposed to combustion exhaust.

Of major interest, especially in city environments, and increasingly inside vehicles or industrial plants, is the drive to reduce human exposure to nitrogen oxides (NOx). This trend has drawn increasing attention to filtration, which has developed remarkably owing to the capabilities of recently developed mathematical models and novel filter concepts. This paper reports on the study of the kinetic modelling of adsorption of nitrogen dioxide (NO2), collected from the tailpipe of a diesel engine, reacting to calcium nitrate salt (Ca(NO3)2) on a surface flow filter consisting of a coating of fine ground limestone or marble (CaCO3) in combination with micro-nanofibrillated cellulose (MNFC) acting as binder and humectant applied onto a multiply recycled newsprint substrate. The coating and substrate are both porous, but on different pore size scales, with the coating having significantly lower permeability. To maximise gas-coating contact, therefore, the coating deposition is pixelated, achieved by pin coating. An axially dispersed gaseous plug flow model (dispersion model) was used to simulate the transport within the coating pore network structure, following earlier flow modelling studies, and a kinetic reaction model was used to examine NO2 to NO3- conversion in correlation with experimental results. Modelling results indicate a 60.38% conversion of exposed NO2 gas to Ca(NO3)2 under the specific conditions applied, with an absolute relative error between the predicted and experimentally estimated value being 0.81%. The model additionally enabled a prediction of effects of changing parameters over a limited perturbation range, thus assisting in predicting filter element consumption, with attention given to the active component CaCO3 surface as a function of particle size in relation to the gas contact exchange, promoting the reaction over time. It is intended that the Ca(NO3)2 formed from the reaction can go on to be used as a value-added fertiliser, thus contributing to circular economy.

Biodegradable Cellulose/Polycaprolactone/Keratin/Calcium Carbonate Mulch Films Prepared in Imidazolium-Based Ionic Liquid.

Ionic liquid 1-butyl-3-methylimidazolium chloride [BMIM][Cl] was used to prepare cellulose (CELL), cellulose/polycaprolactone (CELL/PCL), cellulose/polycaprolactone/keratin (CELL/PCL/KER), and cellulose/polycaprolactone/keratin/ground calcium carbonate (CELL/PCL/KER/GCC) biodegradable mulch films. Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) spectroscopy, optical microscopy, and Field-Emission Scanning Electron Microscopy (FE-SEM) were used to verify the films' surface chemistry and morphology. Mulch film made of only cellulose regenerated from ionic liquid solution exhibited the highest tensile strength (75.3 ± 2.1 MPa) and modulus of elasticity of 944.4 ± 2.0 MPa. Among samples containing PCL, CELL/PCL/KER/GCC is characterized by the highest tensile strength (15.8 ± 0.4 MPa) and modulus of elasticity (687.5 ± 16.6 MPa). The film's breaking strain decreased for all samples containing PCL upon the addition of KER and KER/GCC. The melting temperature of pure PCL is 62.3 °C, whereas that of CELL/PCL film has a slight tendency for melting point depression (61.0 °C), which is a characteristic of partially miscible polymer blends. Furthermore, Differential Scanning Calorimetry (DSC) analysis revealed that the addition of KER or KER/GCC to CELL/PCL films resulted in an increment in melting temperature from 61.0 to 62.6 and 68.9 °C and an improvement in sample crystallinity by 2.2 and 3.0 times, respectively. The light transmittance of all studied samples was greater than 60%. The reported method for mulch film preparation is green and recyclable ([BMIM][Cl] can be recovered), and the inclusion of KER derived by extraction from waste chicken feathers enables conversion to organic biofertilizer. The findings of this study contribute to sustainable agriculture by providing nutrients that enhance the growth rate of plants, and hence food production, while reducing environmental pressure. The addition of GCC furthermore provides a source of Ca2+ for plant micronutrition and a supplementary control of soil pH.

Micro Nanofibrillated Cellulose as Functional Additive Supporting Processability of Surface-Active Mineral Suspensions: Exemplified by Pixel Coating of an NOx-Sorbent Layer.

Unlike established coating formulations, functional particulate coatings often demand the omission of polymer dispersant so as to retain surface functionality. This results in heterogeneous complex rheology. We take an example from a novel development for an NOx mitigation surface flow filter system, in which ground calcium carbonate (GCC), applied in a coating, reacts with NO2 releasing CO2. Inclusion of mesoporous ancillary mineral acts to capture the CO2. The coating is applied as droplets to maximize gas-contact dynamic by forming a pixelated 2D array using a coating device consisting of protruding pins, which are loaded by submersion in the aqueous coating color such that the adhering droplets are transferred onto the substrate. The flow is driven by surface meniscus wetting causing lateral spread and bulk pore permeation. Filamentation occurs during the retraction of the pins. Stress-related viscoelastic and induced dilatancy in the suspension containing the ancillary mesoporous mineral disrupts processability. Adopting shear, oscillation and extensional rheometric methods, we show that the inclusion of an ancillary mineral that alone absorbs water, e.g., perlite (a naturally occurring porous volcanic glass), is rheologically preferable to one that in addition to absorbing water also immobilizes it on the mineral surface, e.g., sepiolite. When including micro-nanofibrillated cellulose (MNFC), critical for maintaining moisture to support NO2 sorption, it is observed that it acts also as a flow modifier, enabling uniform coating transfer to be achieved, thus eliminating any possible detrimental effect on mineral surface activity by avoiding the use of soluble polymeric dispersant.

Modification of CaCO3 and CaCO3 pin-coated cellulose paper under supercritical carbon dioxide-ethanol mixture for enhanced NO2 capture.

In this work, we examine two modifications of fine-ground calcium carbonate material (GCC) in order to enhanced sorption of NO2 and subsequent reaction properties toward NO2-/NO3- formation by firstly exposing the GCC to supercritical (sc) CO2 in order to increase particle surface area, a choice specifically made to avoid altering the surface chemistry, and secondly considering the potential advantage of using a surface coupling agent toward NO2. The modification by the coupling agent amino silane (AMEO silane) was applied in a supercritical CO2-ethanol mixture. The samples were characterised before and after modification by field emission scanning electron microscopy (FESEM), specific surface area determination (BET nitrogen adsorption), ATR-FTIR spectroscopy and ion chromatography to reveal the effects of the surface modification(s) on the morphology, surface textural properties and sorption versus reaction properties with NO2. The performance of the treated sorbents for NO2 capture was evaluated at room temperature. Results show that reactivity of NO2 with GCC was observed to increase as a function of increased surface area resulting from scCO2 exposure, but that the presence of AMEO silane on the surface, while enhancing initial adsorption of NO2 was seen subsequently to act to block reactivity. Thus, judicious use of coupling agent can provide desired rapid initial adsorption of the gas, but the goal of long-term CaCO3-consuming reactivity, so as to prolong the uptake of NO2 beyond surface saturation alone, is achieved by increasing surface area while retaining chemical-free exposed CaCO3 surface.

Iso- and Anisotropic Etching of Micro Nanofibrillated Cellulose Films by Sequential Oxygen and Nitrogen Gas Plasma Exposure for Tunable Wettability on Crystalline and Amorphous Regions.

The surface of cellulose films, obtained from micro nanofibrillated cellulose produced with different enzymatic pretreatment digestion times of refined pulp, was exposed to gas plasma, resulting in a range of surface chemical and morphological changes affecting the mechanical and surface interactional properties. The action of separate and dual exposure to oxygen and nitrogen cold dielectric barrier discharge plasma was studied with respect to the generation of roughness (confocal laser and atomic force microscopy), nanostructural and chemical changes on the cellulose film surface, and their combined effect on wettability. Elemental analysis showed that with longer enzymatic pretreatment time the wetting response was sensitive to the chemical and morphological changes induced by both plasma gases, but distinctly oxygen plasma was seen to induce much greater morphological change while nitrogen plasma contributed more to chemical modification of the film surface. In this novel study, it is shown that exposure to oxygen plasma, subsequently followed by exposure to nitrogen plasma, leads first to an increase in wetting, and second to more hydrophobic behaviour, thus improving, for example, suitability for printing using polar functional inks or providing film barrier properties, respectively.

Coupled Effects of Fibril Width, Residual and Mechanically Liberated Lignin on the Flow, Viscoelasticity, and Dewatering of Cellulosic Nanomaterials.

The rheological behavior of aqueous suspensions of lignocellulose nanofibrils (LCNFs) is investigated systematically by considering the coupled effect of residual lignin and LCNF morphology. The LCNF was obtained by high-energy fluidization of TEMPO-oxidized mechanical fibers, followed by size fractionation (fibril widths of ∼5, ∼9, and ∼18 nm). The nanofibril width and the corresponding fibril-fibril interactions are strongly influenced by the presence and distribution of lignin in the respective fractions, either retained on the fibril surface or as free structures present in the finest size fraction. All samples containing lignin display dilatancy, typifying gel suspensions with aggregated hydrophobic particles. Fine fractionated samples display strong gel behavior. The coarse fractionated sample, by contrast, shows a greater tendency to flocculate via entanglement and displays less gel-like characteristics; hence, it dewaters more freely.

From colloidal spheres to nanofibrils: extensional flow properties of mineral pigment and mixtures with micro and nanofibrils under progressive double layer suppression.

Suspensions of mineral pigment and cellulose fibrillar derivatives are materials regularly found in the forest products industries, particularly in paper and board production. Many manufacturing processes, including forming and coating employ flow geometries incorporating extensional flow. Traditionally, colloidal mineral pigment suspensions have been considered to show little to no non-linear behaviour in extensional viscosity. Additionally, recently, nanofibrillar materials, such as microfibrillar (MFC) and nanofibrillar cellulose (NFC), collectively termed MNFC, have been confirmed by their failure to follow the Cox-Merz rule to behave more as particulate material rather than showing polymeric rheological properties when dispersed in water. Such suspensions and their mixtures are currently intensively investigated to enable them to generate likely enhanced composite material properties. The processes frequently involve exposure to increasing levels of ionic strength, coming either from the weak solubility of pigments, such as calcium carbonate, or retained salts arising from the feed fibre source processing. By taking the simple case of polyacrylate stabilised calcium carbonate suspension and comparing the extensional viscosity as a function of post extension capillary-induced Hencky strain on a CaBER extensional rheometer over a range of increasing salt concentration, it has been shown that the regime of constriction changes as the classic DLVO double layer is progressively suppressed. This change is seen to lead to a characteristic double (bimodal) measured viscosity response for flocculated systems. With this novel characteristic established, more complex mixed suspensions of calcium carbonate, clay and MNFC have been studied, and the effects of fibrils versus flocculation identified and where possible separated. This technique is suggested to enable a better understanding of the origin of viscoelasticity in these important emerging water-based suspensions.