Modeling and simulation of marine SCR system based on Modelica

With the increasing awareness of global marine environmental protection, the emission of ship exhaust pollutants is strictly restricted. Selective catalytic reduction (SCR) technology is the mainstream technology to reduce ship NOx emission and make it meet IMO tier III regulations. A SCR reaction kinetic model based on Modelica language was established by Dymola software to predict the denitration efficiency, ammonia slip rate, and other parameters of SCR system. According to the functional structure of marine SCR system, the SCR system model is divided into urea injection module, mixer module, and SCR reactor module. The model was verified by SCR system bench test of WD10 diesel engine, which proved that the model can preferably reflect the actual situation. Using the established model, the effects of temperature, flow rate, NH3/NOx Stoichiometric Ratio (NSR), and cell density on the denitration performance of SCR system were analyzed. The results showed that the exhaust gas temperature and NSR have a great influence on the denitration efficiency. The injection amount of urea solution in marine SCR system should be based on the exhaust gas temperature and exhaust flow rate.

Fabrication Of Carbon Aerogels From Coir For Oil Adsorption

Coir, known as coconut fibers, are an abundant cellulosic source in Vietnam, which are mostly discarded when copra and coconut water are taken, causing environmental pollution and waste of potential biomass. In this research, carbon aerogels from chemically pretreated coir were successfully synthesized via simple sol-gel process with NaOH-urea solution, economical freeze-drying, and carbonization. The samples, including pretreated coir, coir aerogels, and carbon aerogels, are characterized using FTIR spectroscopy, SEM, XRD spectroscopy, and TGA. The carbon aerogels exhibit low density (0.034–0.047 g/cm3), high porosity (97.63–98.32 %), and comparable motor oil sorption capacity (22.71 g/g). The properties of carbon aerogels are compared with those of coir aerogels, indicating such better values than those of coir aerogels. Coir-derived carbon aerogels is a potential replacement for the hydrophobically-coated cellulose aerogels in term of treating oil spills.

Effect of Sodium Hydroxide/Urea/Deionised Water Solution Ratio on the Solubility of Oil Palm Empty Fruit Bunches Extracted Biocellulose

Biocellulose extracted from oil palm empty fruit bunches (OPEFB) is attracting increased research interest in versatile applications as an alternative material to synthetic cellulose. Normally, biocellulose needs to undergo dissolution prior its applications. Among all explored solvents to dissolve biocellulose, aqueous sodium hydroxide (NaOH)/urea solution is gaining increased attention. OPEFB biocellulose solubility in NaOH/urea/deionised (DI) water solution has not been fully studied by researchers. This study aimed to investigate the solubility of OPEFB biocellulose in NaOH/urea/DI water solution by manipulating the NaOH/urea/DI water solution ratio and weight percentage of OPEFB biocellulose. Results indicated that increasing the NaOH/urea/DI water solution ratio increased the solubility of OPEFB biocellulose. Further increased NaOH/urea/DI water solution ratio resulted in decreased solubility. Meanwhile, increased OPEFB biocellulose weight percentage decreased the solubility of OPEFB biocellulose in NaOH/urea/DI water solution. The highest solubility of 70.89%±1.85% was exhibited by 7% NaOH/12% urea/81% DI water (w/w) solution and 1 w/v% OPEFB biocellulose. This study on OPEFB biocellulose solubility in NaOH/urea/DI water solution can promote cost-effective and wide utilisation of the abundantly available OPEFB for the synthesis of cellulose fibres, films, and hydrogels in the textile, packaging, and biomedical industries.

The Relationship between Crystal Structure and Mechanical Performance for Fabrication of Regenerated Cellulose Film through Coagulation Conditions

Cellulose films regenerated from aqueous alkali–urea solution possess different properties depending on coagulation conditions. However, the correlation between coagulant species and properties of regenerated cellulose (RC) films has not been clarified yet. In this study, RC films were prepared from cellulose nanofiber (CNF) and microcrystalline cellulose (MCC) under several coagulation conditions. Cellulose dissolved in aqueous LiOH–urea solution was regenerated using various solvents at ambient temperature to investigate the effects of their dielectric constant on the properties of RC film. The crystal structure, mechanical properties, and surface morphology of prepared RC films were analyzed using X-ray diffraction (XRD), tensile tester, and atomic probe microscopy (AFM), respectively. It is revealed that the preferential orientation of (110) and (020) crystal planes, which are formed by inter- and intramolecular hydrogen bonding in cellulose crystal regions, changed depending on coagulant species. Furthermore, we found out that tensile strength, elongation at break, and crystal structure properties of RC films strongly correlate to the dielectric constant of solvents used for the coagulation process. This work, therefore, would be able to provide an indicator to control the mechanical performance of RC film depending on its application and to develop detailed researches on controlling the crystal structure of cellulose.

Melting and Heat Transfer Characteristics of Urea Water Solution According to a Heating Module’s Operating Conditions in a Frozen Urea Tank

The urea-selective catalytic reduction (SCR) system, a nitrogen oxide reduction device for diesel vehicles, is a catalytic system that uses urea water solution (UWS) as a reducing agent. This system has a relatively wide range of operating temperatures. However, the freezing point of the reducing urea solution used in this system is −11 °C. When the ambient temperature dips below this freezing point in winter, the solution may freeze. Therefore, it is important to understand the melting characteristics of frozen UWS in relation to the operating conditions of the heating device to supply the minimum amount of aqueous solution required by the system in the initial stage of normal operation and startup of the urea–SCR system. In this study, we artificially froze a liquid solution by placing it along with a heating module in an acrylic chamber to simulate a urea solution tank. Two types of heating modules (P120 and P160) consisting of two heating elements and heat transfer bodies were used to melt the frozen solution. The melting characteristics of the frozen solution were observed, for example, changes in the temperature distribution around the heating module and the cross-sectional melting shape with the passage of time since the start of the power supply to the heating module. The shape of melting around the heating module differed depending on the level of UWS relative to the heater inside the urea tank. In case 1, it melted in a wide shape with an open top, and in case 2, it melted in a closed shape. This shape change was attributed to the formation of internal gaseous space due to volume reduction during melting and the heat transfer characteristics of the fluid and solid substances.

A Novel Application of Cellulose Aerogel Composites From Pineapple Leaf Fibers And Cotton Waste: Removal of Dyes and Oil In Wastewater

In a world where demands for freshwater are ever-growing, wastewater remediation becomes a global concern. Especially, water, which is contaminated by oil, dyes, poses challenges to the management of water resources. The development of innovative processes for wastewater treatment is still a major obstacle. With regard to its fast removal rate and environmental compatibility, cellulose aerogel composites are recently considered as a potential contributor for water remediation. In this study, cellulose aerogel composites are fabricated using the sol-gel method from two-agroindustrial wastes: pineapple leaf fibers and cotton waste fibers in alkali-urea solution followed by freeze-drying. The prepared cellulose aerogel composites are extremely lightweight with a low density (0.053−0.069 g.cm−3) and high porosity of nearly 95%. It is worth noting that the mechanical strength of the cellulose aerogel composites is remarkably improved with their Young’s modulus increasing by 5-9 times compared to that of the previous aerogel composites using polyvinyl alcohol as a binder. The as-synthesized aerogel composites are directly applied to adsorb cationic methylene blue and exhibit a maximum adsorption uptake of 34.01 g.g-1. The methyltrimethoxysilane-coated cellulose aerogel composites also show their ability to deal with oil pollution with a maximum oil adsorption capacity of 15.8 g.g−1 within only 20 sec. Besides the oil removal, our developed cellulose aerogel composites have demonstrated their capability in treating dye-contaminated wastewater for the first time based on their evidenced ability to eliminate methylene blue.

An Effect of pH on Radiation Assisted Modification of Oxygen-Rich Activated Carbon by Urea

Activated carbons (ACs) are a versatile group of adsorbents for water pollution control, especially organic dyes. Harsh chemicals and high temperatures are required for the activation process of ACs, which becomes a significant concern due to their toxicity and harmful effects on human health and the environment. Gamma irradiation, an alternative green technique, is a promising strategy for pretreatment and escalates the nitrogen or oxygen functional group of ACs. The current study provides the modification of ACs by the gamma irradiation in the various pH (5-11) of urea solution. The modified ACs were characterized by scanning electron microscopy (SEM), nitrogen gas adsorption-desorption analysts (BET), temperature program desorption (TPD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray diffraction spectroscopy (XRD). The point of zero charges and dye adsorption capacities were determined. This finding demonstrates that the ACs can be modified by gamma irradiation at 25 kGy in the urea solution media. The degree of graphitization enhanced significantly at pH 11(AC-pH11). The oxygen-rich functional groups created by radiation assists could enhance the electrostatic attraction between acid gases or cationic dyes. AC-pH11 also was able to adsorb methylene blue (160.73 ± 1.70 mg/g) greater than methyl orange (127.57 ± 2.22 mg/g).

Hydrophobic association and solvation of neopentane in Urea, TMAO and Urea-TMAO solution

A detailed knowledge on hydrophobic association and solvation is crucial in understanding the con-formational stability of proteins and polymers in osmolyte solutions. Using Molecular Dynamics simulations, we found the hydrophobic association using neopentane molecules is greater in mixed urea-TMAO-water solution in comparison to that in 8 M urea solution, in 4 M TMAO solution and in neat water. The neopentane association in urea solution is greater than that in TMAO solution or neat water. We find the association is even less in TMAO solution than pure water. From free ener-gy calculations, it is revealed that the neopentane sized cavity creation in mixed urea-TMAO-water is most unfavorable and that causes the highest hydrophobic association. The cavity formation in urea solution is either more unfavorable or comparable to that in TMAO solution. Importantly, it is found that the population of neopentane-neopentane contact pair and the free energy contribution for cavity formation step in TMAO solution are very sensitive towards the choice of TMAO force-fields. A careful construction of TMAO force-fields is important for studying hydrophobic associa-tion. Interestingly it is observed that the total solute-solvent dispersion interaction energy contribu-tion is always most favorable in mixed urea-TMAO-water. The magnitude of this interaction energy is greater in urea solution relative to TMAO solution for two different force-fields of TMAO, whereas the lowest value is obtained in pure water. It is revealed that the extent of the overall hy-drophobic association in osmolyte solutions is mainly governed by the cavity creation step and it nullifies the contribution comes from the solute-solvent interaction contribution.