Ying Zheng

A review of plastic waste biodegradation.

ABSTRACT With more and more plastics being employed in human lives and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegradation of plastic wastes has assumed increasing importance in the last few years. This review looks at the technological advancement made in the development of more easily biodegradable plastics and the biodegradation of conventional plastics by microorganisms. Additives, such as pro-oxidants and starch, are applied in synthetic materials to modify and make plastics biodegradable. Recent research has shown that thermoplastics derived from polyolefins, traditionally considered resistant to biodegradation in ambient environment, are biodegraded following photo-degradation and chemical degradation. Thermoset plastics, such as aliphatic polyester and polyester polyurethane, are easily attacked by microorganisms directly because of the potential hydrolytic cleavage of ester or urethane bonds in their structures. Some microorganisms have been isolated to utilize polyurethane as a sole source of carbon and nitrogen source. Aliphatic-aromatic copolyesters have active commercial applications because of their good mechanical properties and biodegradability. Reviewing published and ongoing studies on plastic biodegradation, this paper attempts to make conclusions on potentially viable methods to reduce impacts of plastic waste on the environment.

Overall pressure balance and system stability in a liquid-solid circulating fluidized bed

Abstract A pressure balance analysis has been carried out, along with a dimensionless empirical correlation for the solids holdup in the riser and a semi-empirical equation for the pressure drop across the non-mechanical control valve derived in this work, to successfully predict the stable operating conditions and explain the origin of the unstable operation phenomena of the liquid–solid circulating fluidized bed. The effects of the total and auxiliary liquid velocity, the solids inventory and the unit geometry on the stable operation range are discussed. Furthermore, this work also reveals the importance of unit structure in improving the performance of the liquid–solid circulating fluidized bed systems.

The onset velocity of a liquid–solid circulating fluidized bed

Abstract The critical transition velocity, Ucr, previously defined by Liang et al. [W.-G. Liang, S.-L. Zhang, J.-X. Zhu, Y. Jin, Z.-Q. Yu and Z.-W. Wang, Flow characteristics of the liquid–solid circulating fluidized bed, Powder Technol., 90 (1997) 95–102.] to demarcate the liquid–solid conventional and circulating fluidization regimes, was found to vary with the total solids inventory and the solids feeding system. In this work, an onset velocity for circulating fluidization regime, Ucf, is proposed to give the lowest Ucr value and to provide a convenient demarcation velocity that is independent of system geometry. This liquid velocity is obtained by measuring the time required to empty all particles in a batch operated fluidized bed under different liquid velocities. This method can be used for a wide range of particles and involves less influence of the operating conditions such as the solids inventory and the solids feeding system. Compared to the critical transition velocity, this newly defined onset velocity is a more intrinsic parameter, only dependent on the liquid and particle properties. Based on the experimental results obtained in this work and other published results, the influence of particle properties and equipment setup on the onset velocity is also discussed.

Selective Deoxygenation of Biomass‐Derived Bio‐oils within Hydrogen‐Modest Environments: A Review and New Insights

Abstract Research development of processes for refining bio‐oils is becoming increasingly popular. One issue that these processes possess is their high requirement for H2 gas. In response, researchers must develop catalysts that perform deoxygenation while minimizing H2 consumption—selective deoxygenation. Unlike traditional deoxygenation processes, selective deoxygenation reactions and catalysts represent an information gap that, prior to this publication, has yet to be reviewed. This review addresses the gap by providing both a summary of recent research developments and insight into future developments of new catalytic materials. Bifunctional catalysts containing a combination of oxophilicity and an active metal phase appear to be the most beneficial for selective deoxygenation processes in a H2‐modest environment. It is important that catalysts have a supply of disassociated hydrogen, because without such, activity and stability will suffer. The authors recommend to maximize the use of internally available hydrogen in bio‐fuel, which may be the only viable approach for deoxygenation if external H2 gas is limited. This would be possible through the development of catalysts that promote both the water–gas‐shift and deoxygenation reactions.

Hydrotreatment of lignocellulosic biomass derived oil using a sulfided NiMo/γ-Al2O3 catalyst

Bio-oils derived from lignocellulosic materials have poor properties for use as fuels and cannot be blended with transportation fuels. Hydrotreating is an effective method for eliminating contaminants and saturating double bonds. This article is one of the few that report the hydrotreatment of a biomass-derived oil over a sulfided NiMo/γ-Al2O3 catalyst and the deactivation of the catalyst. The results confirm that hydrotreatment is an effective technology for improving the quality of bio-oil. The total acid number of the upgraded bio-oil decreased from 23 mg KOH g−1 (raw bio-oil) to 2 mg KOH g−1. Oxygenated functional groups are removed, light liquid products are generated and carbon double bonds are saturated. The catalyst can become deactivated at a high operating temperature due to severe coke deposition. The deactivated catalyst was studied by using multiple analytical methods such as TEM, XRD, BET and TPO to study the deactivation pathways.

The role of oxygen functional groups in the adsorption of heteroaromatic nitrogen compounds.

A wood-based activated carbon (AC) was oxidized using different oxidants. The resultant adsorbents were applied to adsorb nitrogen (N) containing compounds that appeared in light cycled oil. Appropriate oxidation treatment can increase oxygen functional groups on the surface of AC without much damage to its pore structure. Oxygen functional groups play a key role in enhancing adsorptive selectivity of carbons. Lactone groups can facilitate the selective removal of 1-ring N compounds. Phenolic groups, total CO2-releasing groups and total O groups show an improvement in the adsorption of 2-ring N compounds. Aldehyde groups favor the adsorption of 3-ring and 4-ring N compounds. However, excessive oxidation can result in the collapse of pore structure and closure of pore channels. For instance, the carbon oxidized by a mixture of concentrated H2SO4 and HNO3 has an extremely low adsorption performance.

Chemical dispersion of oil with mineral fines in a low temperature environment

The increasing risks of potential oil spills in the arctic regions, which are characterized by low temperatures, are a big challenge. The traditional dispersant method has shown limited effectiveness in oil cleanup. This work studied the role of mineral fines in the formation of oil-mineral aggregates (OMAs) at low temperature (0-4 °C) environment. The loading amount of minerals and dispersant with different dispersant and oil types were investigated under a full factorial design. The shapes and sizes of OMAs were analyzed. Results showed that the behavior of OMA formation differs when dispersant and mineral fines are used individually or together. Both the experimental and microscopic results also showed the existence of optimal dispersant to oil ratios and mineral to oil ratios. In general, poor oil removal performance was observed for more viscous oil. Corexit 9500 performed better than Corexit 9527 with various oils, in terms of oil dispersion and OMA formation.

Surface Dissolution and the Development of Scallops

Abstract Flow-assisted corrosion (FAC) is a significant problem with carbon steel components exposed to rapidly moving water or water/steam mixtures. Such components often develop distinctive patterns of surface damage called scalloping, so to gain further insight into FAC it is of interest to understand the formation and significance of scallops. Experiments were carried out on the dissolution of pipes made of plaster of Paris (CaSO4.½H2O) to study the evolution of scalloping patterns as well as to explore the link between scalloping and hydrodynamics and scalloping and dissolution rate. The conductivity and pH of water flowing through the test sections were recorded and posttest examination was carried out. Scallops were observed along the plaster surface at the end of the tests. Their characteristics are strongly related to the flow rate; scallop size decreases with increasing flow rate whereas surface density of scallops increases with increasing flow rate. Imperfections such as voids on embedded particles seem necessary for scallops to develop at all.

Co-promotion of fluorine and boron on NiMo/Al2O3 for hydrotreating light cycle oil

A hydrotreating catalyst, NiMo/Al2O3, was modified with different amounts of fluorine (F) and boron (B) through the pore-saturated impregnation method. The resulting catalysts were characterized by BET, pyridine-IR, XPS, and TEM techniques. Incorporation of fluorine and boron led to the variations in the catalyst acidity and the dispersion of active metals, causing direct impacts on the hydrotreating activities of the catalysts. The hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) activities of the catalysts were examined in an autoclave reactor using real light cycle oil as feed. The HDS activity decreased in the order NiMo/F,B-Al(5.0) > NiMo/F,B-Al(7.0) > NiMo/F,B-Al(3.5), indicating the existence of an optimum amount of F and B.

Development of a Magnetically Recyclable Molybdenum Disulfide Catalyst for Direct Hydrodesulfurization

Superparamagnetic MoS2/SiO2/Fe3O4 catalysts that consist of magnetite as the core, silica as the covering layer, and molybdenum sulfide as the top layer were prepared in easy steps. Two different surfactants (anionic and cationic) were used to assist with the synthesis of two of the samples, and one sample was prepared without surfactant. The surfactant was found to have a significant effect on the properties and activity of the final catalysts. Hydrodesulfurization (HDS) tests of the catalysts show higher activity for the cationic‐surfactant‐assisted catalyst. Between the direct desulfurization (DDS) and hydrogenation pathways for the prepared catalysts, the DDS pathway was found to be dominant for the HDS of dibenzothiophene. As a result of the magnetic properties of this catalyst, it can be separated easily from the reaction media by a magnetic field applied externally and reused, which makes it an ideal choice for slurry reactors that process heavy and extra‐heavy crude oil.