An industrial ammonia synthesis reactor was studied in order to optimize its operational conditions by means of increasing overall ammonia production. A heterogeneous, one-dimensional model and a two-dimensional rigorous model were utilized to evaluate the process behavior. The simulation results of the two models were compared with data from an industrial ammonia plant. The one-dimensional model was found to be adequate for optimization purposes. Applying the Genetic Algorithm (GA) as a powerful method for complex problems, the model was employed to optimize the reactor performance in varying its quench flows. The optimal temperature profile along the fixed bed reactor was studied by changing independent variables including the quench temperature and the quench flow rates. Optimization results show that the optimum quench temperature is about 615°K and that the optimum quench flows can enhance ammonia production rate by 3.3%.

This work investigates the effects of different design parameters such as hemp content in the skins (10-40% wt.), layer thickness (1 and 2 mm), and foaming agent content in the core (0% wt., 0.6% wt. and 1.2% wt.) on the flexural properties of three layer sandwich panels of hemp and high density polyethylene produced by compression molding. The results show that hemp content was the most significant parameter for the flexural properties of these panels. In addition, it was found that specific modulus and strength (per unit weight) were 30% and 36% higher when using a foam core, respectively.

This paper presents an experimental investigation of the impact behaviour of three layer sandwich structures made of high density polyethylene (HDPE) and hemp, with and without a foam core. Low-velocity falling weight and Charpy impact tests were performed to investigate the influence of hemp content, skin thickness and core density. The strength, load, absorbed energy, and deflection histories were recorded and analysed and the damaged specimens were inspected to determine the failure patterns. Based on the Charpy impact results, the structures with foam core had higher energy absorption capabilities compared to their counterparts without foam core. In addition, based on the falling weight impact results the energy dissipation properties of sandwich structures without foam core were superior to the structures with foam core. This property was also greatly influenced by skin fibre content, skin thickness and structure configuration.

Abstract. It is well known that for polymer composites based on natural fibers, the addition of a coupling agent is necessary to improve fiber dispersion and adhesion with the matrix. Nevertheless, an optimum content must be found which is related to the total surface area created between the fibers and the matrix. But in most cases reported in the literature, a single property (like tensile strength or flexural modulus) is used to determine this optimum value. In this work, high density polyethylene (HDPE) was reinforced with hemp fibers as a typical system. In particular, the addition of a coupling agent based on maleated polyethylene (MAPE) was studied to determine its optimum content. To better detect the specific effect of the selected coupling agent, reinforcement content was limited to 10% wt., while the MAPE content was controlled at different levels (0, 5, 7, 9 and 11% wt. based on total hemp content). Compounding was performed in a twin-screw extruder and the samples were produced by compression molding. From the composites obtained, a complete set of characterization in terms of morphology (SEM), mechanical properties (tension, flexion, and impact), and density (pycnometry) was made. From all the results obtained, it can be shown that 9% wt. MAPE is the optimum content maximizing all the mechanical properties. These results indicate that any physical property can be used to determine the optimum coupling agent content.