Using the stem of the khakshir plant in removing colored pollution from water environments and investigating the effect of adsorbent performance on the nano scale on removal

Chemical Engineering Master's Thesis

Abstract

In this research, the optimal absorption conditions for cationic dyes have been investigated and the removal of brilliant green dye [1] by the natural adsorbent of khakshir has been investigated. First, the effective conditions in the amount of brilliant green removal by the khakshir stem adsorbent were researched, then using the top-down method (one of the methods of preparing nanomaterials), the size of the adsorbent parts used was converted into nano particles (nanogel) and used as adsorbent. After the color removal operation, the adsorption capacity of the adsorbent in both micro and nano dimensions was investigated and compared. Absorbent particles were evaluated by Fourier Transform Infrared (FTIR), Scanning Electron Microscope (SEM) and Scanning Electron Microscope (TEM). In order to increase the efficiency of the process, the attention of the work was focused on the mass transfer resistances, and by using the ultrafine disc mill, the mass transfer resistance was eliminated when the adsorbed substance reaches the active sites from the surface of the adsorbent. The adsorption process was investigated using Freundlich, Langmuir and Mackin isotherms, and the Langmuir isotherm among the investigated inter-isotherms described the adsorption process with both forms of adsorbent well. Also, adsorption kinetics was also investigated for surface absorption in this research, which included pseudo-first-order, second-order, Bengham, and intraparticle penetration models, which resulted in following the second-order model. The results of this research determined that the absorption action is better at pH=5, the optimal contact time for the khakshir adsorbent was 25 minutes for the micro dimensions and 4 minutes for the nanogel dimensions, and the amount of the adsorbent dose in the micro and nano form was not different and it was 3 gr/lit for the micro dimensions and 30 gr/lit for the nanogel form, the optimal concentration for removal was also found to be 20 ppm and 25 ppm. The amount of color removal for the nanogel shape was very good and about 98%, and for the micro size, the removal percentage was about 89%.

Key words: adsorption isotherm, agricultural waste, cheap adsorbent, surface absorption, color removal, nanogel.

1-1 Introduction

In the last few years, sustainable development and attention to the future generation have made researchers work on methods to reduce environmental damage and reduce the spread of pollution. style="direction: rtl;">Colors are an important class of contaminants that can be detected by the human eye. Although it should be avoided in precious water sources, however, different technologies and processes are used to solve this problem. However, among the various methods for color removal, surface absorption has taken a prominent position. The demand for efficient and low-cost methods for adsorption is growing and has increased the importance of cheap adsorbents[1] to replace expensive adsorbents[1]. Comprehensive reviews of the literature of past works show that cheap adsorbents should be available and show high adsorption capacity. In the past works, the optimal conditions of absorption and the type of absorbed material and the conditions of suitable environments for absorption and the ability to convert the desired adsorbent into activated carbon have been discussed [1]. Textile industries are responsible for the release of various colors into natural water sources, the reason for which can be seen in the lack of efficiency in dyeing techniques. More than 15% of the dyes may enter the water directly when using reactive dyes [2].

In the surface absorption operation, a component is transferred from the gas or liquid phase to the solid surface. Among the applications of this process, we can mention the decolorization of sugar syrup, the purification of industrial or edible oils, and the removal of pollutants from the air or other gas mixtures. Figure 1-1. The cluster diagram shows the general distribution of polluting substances.

(Images and diagrams are available in the main file)

The term surface adsorption is used to describe the fact that the concentration of adsorbed molecules on the contact surface of a solid is greater than that of a gas or solution phase. Adsorption on a solid surface is due to the attraction of atoms or molecules on its solid surface. Various physical and chemical forces are effective in the process of surface adsorption, and its amount depends on the nature of the absorbed substance and the absorbing body, and for this reason, for example, a substance that is present in a mixture can be separated [3, 4].

A few examples that are stated below will represent the general nature of separations and show its main applications. In the case of gas separations from the absorption process, dry air and other gases are used in dehumidification, deodorization and separation of impurities from industrial gases such as carbon dioxide, recovery of valuable solvents from their dilute solution with air or other gases, and separation of a mixture of gaseous hydrocarbons such as a mixture of methane, ethylene, ethane, propylene and propane[5].

Liquid separation processes include dehumidification of gasoline, decolorization of petroleum products and aqueous sugar solutions, deodorization and deflavoring of water, and separation of aromatic and paraffin hydrocarbons, each of which has a wide application in the industry and is used according to the case and conditions of the work scope. In addition to the mentioned cases, dye absorption is among the desired processes in various industries, and works have also been done to increase the color transfer from the soluble phase to cellulose, among the applications of this process in the production of colored paper and textile industries, we can mention [6]. And the uneven distribution of raw materials between the phase absorbed on the solid surface and the fluid mass causes separation[7]. The adsorption is used for the removal of a particular basic dye from an aqueous solution, known as Brilliant Green (BG), by means of a natural agricultural waste material. The natural agricultural waste used in this work was Descronia Sophia. Then the top-down methods are used for absorbent to convert in Nano scale (Nano gel). After removing process, adsorbents capability in both micro and nano scale was studied. Adsorbent particles were evaluated by means of Fourier transform infrared device analysis (FTIR), scanning electron microscopy (SEM) and Transmission Electron Microscope (TEM). To increase the efficiency of adsorption, the attention was focused on mass transfer resistances by super disk milling machine. The mass transfer resistance in transferring the absorbent from the surface of the adsorbent to active sites was eliminated. Equilibrium isotherms for the adsorption of BG on DS and Nano gel of DS were analyzed by Freundlich, Langmuir and Temkin isotherm models using non-linear regression technique. Langmuir isotherm was found to best represent the data for BG adsorption on all the adsorbents. To describe the adsorption mechanism, kinetic models such as pseudo-first order, pseudo-second order and the intra particle diffusion were applied. The pseudo-second-order diffusion model showed good fit for data. Maximum dye removal for both shape of adsorbents was at pH=5 and the best contact time in first shape of DS (micro) is 25 min and for Nano gel was 4 min, dosage of adsorbents in micro form of adsorbent was 0.3gr.lit-1 and for Nano gel form was 3gr.lit-1. The optimum dye concentration for first form of adsorbent was 20ppm and for Nano gel form of adsorbent was 25ppm. For Nano gel form of adsorbent, the removal efficiency for Nano gel form of adsorbent was about 98% and for micro scale reached to 89%.

Keywords: Cationic Dye, Agriculture Waste, Low Cost Adsorbent, Adsorption, Dye Removal, Nano Gel.