A NIR-Based Study of Desorption Kinetics during Continuous Spin Freeze-Drying

The pharmaceutical industry is progressing toward the development of more continuous manufacturing techniques. At the same time, the industry is striving toward more process understanding and improved process control, which requires the implementation of process analytical technology tools (PAT). For the purpose of drying biopharmaceuticals, a continuous spin freeze-drying technology for unit doses was developed, which is based on creating thin layers of product by spinning the solution during the freezing step. Drying is performed under vacuum using infrared heaters to provide energy for the sublimation process. This approach reduces drying times by more than 90% compared to conventional batch freeze-drying. In this work, a new methodology is presented using near-infrared (NIR) spectroscopy to study the desorption kinetics during the secondary drying step of the continuous spin freeze-drying process. An inline PLS-based NIR calibration model to predict the residual moisture content of a standard formulation (i.e., 10% sucrose) was constructed and validated. This model was then used to evaluate the effect of different process parameters on the desorption rate. Product temperature, which was controlled by a PID feedback mechanism of the IR heaters, had the highest positive impact on the drying rate during secondary drying. Using a higher cooling rate during spin freezing was found to significantly increase the desorption rate as well. A higher filling volume had a smaller negative effect on the drying rate while the chamber pressure during drying was found to have no significant effect in the range between 10 and 30 Pa.

Preparation and selectivity evaluation of grafted temperature-responsive imprinted composite polyvinylidene fluoride resin membranes for selective adsorption of ReO4−

Purpose A novel grafted temperature-responsive ReO4− Imprinted composite membranes (Re-ICMs) was successfully prepared by using polyvinylidene fluoride (PVDF) resin membranes as substrates, this study aimed to separate and purify ReO effectively. Design/methodology/approach Re-ICMs were synthesized by PVDF resin membranes as the substrate, acrylic acid (AA), acrylamide (AM), ethylene glycol dimethacrylate (EGDMA) were functional monomers. The morphology and structure of Re-ICMs were characterized by scanning electron microscope and Fourier transform infrared spectroscopy. Findings The maximum adsorption capacity toward ReO4− was 0.1,163 mmol/g and the separation decree had relation to MnO4− was 19.3. The optimal operation conditions were studied detailedly and the results as follows: the molar ratios of AA, AM, EGDMA, ascorbic acid, NH4ReO4, were 0.8, 0.96, 0.02, 0.003 and 0.006. The optimal time and temperature were 20 h and 40°C, respectively. The Langmuir and pseudo-second-order models were fit these adsorption characteristics well. Practical implications Rhenium (Re) is mainly used to chemical petroleum and make superalloys for jet engine parts. This study was representing a technology in separate and purify of Re, which provided a method for the development of the petroleum and aviation industry. Originality/value This contribution provided a novel method to separate ReO4− from MnO4−. The maximum adsorption capacity was 0.1163 mmol/g at 35°C and the adsorption equilibrium time was within 2 h. Meanwhile, the adsorption selectivity rate ReO4−/MnO4− was 19.3 and the desorption rate was 78.3%. Controlling the adsorption experiment at 35°C and desorption experiment at 25°C in aqueous solution, it could remain 61.3% of the initial adsorption capacity with the adsorption selectivity rate of 13.3 by 10 adsorption/desorption cycles, a slight decrease, varied from 78.3% to 65.3%, in desorption rate was observed.

Experimental Study on Desorption Characteristics of Anthracite in Positive Pressure Environments

In order to investigate the desorption characteristics of methane adsorption in coal under positive pressure conditions, methane adsorption and successive desorption experiments of anthracite coal under positive pressure conditions were conducted on the developed experimental equipment, and the experimental data were analyzed. In the process of desorption of coal samples with the same adsorption equilibrium pressure and the same pressure drop gradient, the phase desorption rate decreased with the increase of pressure, and the positive pressure environment had a significant inhibitory effect on the desorption of methane in coal.

Ice mantles on dust grains: dramatic variation of thickness with grain size

ABSTRACT We compute the desorption rate of icy mantles on dust grains as a function of the size and composition of both the grain and the mantle. We combine existing models of cosmic ray (CR)-related desorption phenomena with a model of CR transport to accurately calculate the desorption rates in dark regions of molecular clouds. We show that different desorption mechanisms dominate for grains of different sizes and in different regions of the cloud. We then use these calculations to investigate a simple model of the growth of mantles, given a distribution of grain sizes. We find that modest variations of the desorption rate with grain size lead to a strong dependence of mantle thickness on grain size. Furthermore, we show that freeze-out is almost complete in the absence of an external ultraviolet (UV) field, even when photodesorption from CR-produced UV is taken into consideration. Even at gas densities of $10^4\, {\rm cm^{-3}}$, less than 30 per cent of the CO remain in the gas phase after 3 × 105 yr for standard values of the CR ionization rate.

Study of Cadmium Desorption Kinetics from Riverine Sediments

In natural streams, the majority of heavy metal ions are generally associated ‎with ‎sediment particles. Under some environmental conditions, these metal ions may release from ‎the ‎sediment particles.‎ In such conditions, the desorption rate of heavy metals is very important for decision-makers of ‎water quality assessment. In this study, the effect of cadmium desorption ‎from the river bed ‎sediments has been ‎experimentally investigated. Artificially contaminated sediments were used ‎for performing batch desorption ‎experiments. The experiments were conducted by adding 1 gr of contaminated ‎sediment (D50 = 0.53 mm) with a known concentration and shaking until observing a ‎roughly ‎constant cadmium concentration in the solution. It was concluded that the cadmium ions were strongly bond to the river bed sediment; meanwhile, at the ‎equilibrium time, up to about 7 to 29 percent of cadmium ions were ‎released from the‎ artificially contaminated sediments. The experiments were followed by ‎two agitation rates of 100 and 200 rpm. It was revealed that by increasing the flow turbulence, the amount ‎of desorbed cadmium is slightly increased. Besides, the desorption kinetics was evaluated using eight models of Zero-, first-, second-, third-order, ‎parabolic diffusion, double parabolic diffusion, two constant rate, and simple Elovich. The results of the evaluation showed that simple Elovich (with R2 = 0.991), double parabolic diffusion (with R2 = 0.9882), two constant rate (with R2 = 0.983) and parabolic diffusion models (with R2 = 0.846) have respectively the best performance in calculation of Cd desorption rate from the sediments.

Experimental Performance of a Membrane Desorber Operating under Simulated Warm Weather Condensation Temperatures

In absorption systems using the aqueous lithium bromide mixture, the Coefficient of Performance is affected by the desorber. The main function of this component is to separate the refrigerant fluid from the working mixture. In conventional boiling desorbers, constant heat flux and vacuum pressure conditions are necessary to carry out the desorption process, and usually, the absorbers are heavy and bulky; thus, they are not suitable in compact systems. In this study, a membrane desorber was evaluated, operating at atmospheric pressure conditions with a water/lithium bromide solution with a concentration of 49.6% w/w. The effects of the solution temperature, solution mass flow, and condensation temperature on the desorption rate were analyzed. The maximum desorption rate value was 6.1 kg/m2h with the following operation conditions: the solution temperature at 95.2 °C, the solution mass flow at 4.00 × 10−2 kg/s, and the cooling water temperature at 30.1 °C. On the other hand, the minimum value was 1.1 kg/m2h with the solution temperature at 80.2 °C, the solution mass flow at 2.50 × 10−2 kg/s, and the cooling water temperature at 45.1 °C. The thermal energy efficiency, defined as the ratio between the thermal energy used to evaporate the refrigerant fluid with respect to the total thermal energy entering the membrane desorber, varied from 0.08 to 0.30. According to the results, a high solution mass flow, a high solution temperature, and a low condensation temperature lead to an increase in the desorption rate; however, a low solution mass flow enhanced the thermal energy efficiency. The proposed membrane desorber could replace a conventional boiling desorber, especially in absorption cooling systems that operate at high condensation temperatures as in warm weather regions.