New Predictive Models for COD from All Stages in Full ECF Bleaching Sequences
This paper proposes new mathematical models for the prediction of chemical oxygen demand (COD) from different stages in full ECF bleaching sequences and discusses several important issues related to model development and interpretation. The effects of different process conditions, like pH, chemical charge, initial Kappa number, carryover, temperature etc., on the formation of COD from the different chlorine dioxide stages (Do, D1, D2) and extraction stages (E, EO, EP, EOP) were studied and corresponding models were developed for softwood and hardwood pulps. The models, based on results obtained from the extensive studies of the kinetics, stoichiometry, and effluent properties of the chlorine dioxide stages and extraction stages in the ECF bleaching of pulp, were tested for accuracy on a vast range of data both from literature and laboratory experiments. The kinetics, stoichiometry and effluent properties have not previously been considered together for optimization and would be of considerable use in bleach plant optimization as well as in process control of different stages. This study will also help in understanding the need for modifications of the conventional conditions in both the chlorine dioxide and the extraction stages to obtain the best mix between a low formation of COD and high bleaching efficiency.
Modified cooking and oxygen bleaching for improved production economy and reduced effluent load
Combinations of modified cooking, oxygen bleaching and final bleaching in three stages, (C+ D)(EO)D, were compared in a laboratory investigation with conventional cookine. oxveen bleaching and final -. .bleaching in five and three stages, (C+D)(E~)DED and (C + D)(EO)D. Modified cooking to kappa number 28 followed by oxygen bleaching to kappa number 12 gives the lowest production costs w~th unchanged pulp quality. The production costs (capital costs included) are about USD 9 per tonne of pulp lower for the modified alternative than for conventional cooking to kappa number 30, oxygen bleaching to kappa number 16 and final bleaching in five stages. Compared to the reference alternative, a kappa number of 12 after the oxygen stage means a reduction in the bleach plant effluents of TOCl by 25%. of COD by 20% and of color by 40%. A combination of modified cooking and oxygen bleaching can thus become a favorable process alternative, reducing the environmental impact.
Recent progress in engineering near-infrared persistent luminescence nanoprobes for time-resolved biosensing/bioimaging
Persistent luminescence nanoprobes (PLNPs) can remain luminescent after ceasing excitation. Due to the ultra-long decay time of persistent luminescence (PersL), autofluorescence interference can be efficiently eliminated by collecting PersL signal after autofluorescence decays completely, thus the imaging contrast and sensing sensitivity can be significantly improved. Since near-infrared (NIR) light shows reduced scattering and absorption coefficient in penetrating biological organs or tissues, near-infrared persistent luminescence nanoprobes (NIR PLNPs) possess deep tissue penetration and offer a bright prospect in the areas of in vivo biosensing/bioimaging. In this review, we firstly summarize the design of different types of NIR PLNPs for biosensing/bioimaging, such as transition metal ions-doped NIR PLNPs, lanthanide ions-doped NIR PLNPs, organic molecules-based NIR PLNPs, and semiconducting polymer self-assembled NIR PLNPs. Notably, organic molecules-based NIR PLNPs and semiconductor self-assembled NIR PLNPs, for the first time, were introduced to the review of PLNPs. Secondly, the effects of different types of charge carriers on NIR PersL and luminescence decay of NIR PLNPs are significantly emphasized so as to build up an in-depth understanding of their luminescence mechanism. It includes the regulation of valence band and conduction band of different host materials, alteration of defect types, depth and concentration changes caused by ion doping, effective radiation transitions and energy transfer generated by different luminescence centers. Given the design and potential of NIR PLNPs as long-lived luminescent materials, the current challenges and future perspective in this rapidly growing field are also discussed.