Influence mechanism of excipients on drug crystallization: experimental investigation and model analysis and prediction

The influence of temperature, stirring speed, and excipients on crystal growth kinetics of mesalazine and allopurinol was investigated through experiment and chemical potential gradient model. The results indicated that the Diffusion-Surface Reaction model (DSR (1,2)) showed good performance in modeling API crystal growth kinetics within the ARDs of 4%. Excipients played a crucial role in inhibiting crystal growth in all the systems. It can not only improve the API solubility, but also reduce the crystal growth rate. By comparing diffusion rate and surface-reaction rate constant within the DSR (1,2) model, it was found that the controlling step of mesalazine crystallization was surface-reaction. Allopurinol crystallization was dominated by both surface-reaction and diffusion. Meanwhile, the crystal growth kinetics of mesalazine and allopurinol were predicted successfully with the ARDs of 2.53% and 4.78%. This work provided a mechanistic understanding of polymer influence on the inhibition of API crystal growth.

Estimation Method of Biomass Energy Reserves in China: A Case Study of Corn Straw

Nowadays, biomass resources are the best choice to replace fossil resources. Energy development in biomass is mainly through pyrolysis of biomass. At present, no one has estimated how much biomass energy there is for a country. In this article, taking corn as an example, China as the production country, the potential biomass resources in China are speculated, in which Lignocellulose is the main experimental biomass and pyrolyzed to obtain biomass energy. The most common method of biomass energy conversion is isothermal conversion. The first-order reaction model is used for kinetic analysis of the conversion. The sample is subjected to powder falling pyrolysis at 480 degrees. In order to overcome the regional differences in China, the data of 30 degrees north latitude are used. Finally, the reaction time and the total amount of biomass energy available for development and utilization in China in 2020 are obtained.

Fractal–Fractional Michaelis–Menten Enzymatic Reaction Model via Different Kernels

In this paper, three new models of fractal–fractional Michaelis–Menten enzymatic reaction (FFMMER) are studied. We present these models based on three different kernels, namely, power law, exponential decay, and Mittag-Leffler kernels. We construct three schema of successive approximations according to the theory of fractional calculus and with the help of Lagrange polynomials. The approximate solutions are compared with the resulting numerical solutions using the finite difference method (FDM). Because the approximate solutions in the classical case of the three models are very close to each other and almost matches, it is sufficient to compare one model, and the results were good. We investigate the effects of the fractal order and fractional order for all models. All calculations were performed using Mathematica software.

Anaerobic Treatment for Palm Oil Mill Effluent Using Covered In-the Ground Anaerobic Reactor (CIGAR)

Wastewater from crude palm oil mills contains high organic matter, which potentially produces biogas through anaerobic digestion processes. The design and operation of an anaerobic bioreactor require a good understanding of the reaction kinetic in the bioreactor. This study aimed to evaluate the biogas production from POME and to determine the kinetic parameters of microbial growth and the substrate utilization rates in a CIGAR. An experiment was conducted using a 5-m3 bioreactor with a working volume of 4.4 m3. Wastewater from the Bekri palm oil mill was stored in a 5-m3 tank. After stabilization, the wastewater was loaded into the reactor at a rate of 100 to 250 L/d, corresponding to a COD loading rate of 1.373-3.097 kg·m-3.d-1, and an HRT of 18-44 days. Monod, Contois, Moser, and Shuler kinetic models were evaluated. The results showed that the Shuler model performed best for microbial activities, while the first order reaction model performed best for the substrate utilization kinetic. The maximum specific growth rate (μmax) for the Shuler model was 0.052 d-1 and the saturation constant (Kso) was 0.119. The maximum substrate utilization rate constant (ks) was 2.183 d-1 and biomass yield (Yx/s) 0.024 kg/kg. The maximum average efficiency of anaerobic degradation (34.4%) occurred at a feeding rate of 100 L/d with methane yield of 0.120 Nm3/kg of removed COD. This value is relatively low compared to the maximum potential of 0.350 Nm3/kg CODr.