Fabrication of ceramic nanofiltration membrane for chloride ion separation (gas condensate case study)

Master thesis in the field of chemical nanoengineering

Abstract

Ceramic nanofiltration membrane for chloride ion separation (Case study: gas condensate)

In this research, the separation of chloride ion using double-layer alumina-titania nanofiltration membrane has been investigated. For this purpose, first, the alumina-titania double-layer membrane is made based on alpha-alumina membrane support. Pressing method was used to make the retainer, and sol-gel and immersion methods were used for layering on the retainer. Then, membrane efficiency for chlorine removal by vertical flow and cross flow membrane filtration devices has been investigated at laboratory temperature. Filtration tests have been performed for different values ??of pressure, pH and concentration of salt solution, the results have been examined and compared. Vertical flow and cross flow membrane filtration devices have been used, respectively, using nitrogen gas and a piston pump of different pressures in order to check the penetration and transfer of solutions inside the membrane. Scanning electron microscopy, X-ray diffraction and nitrogen absorption/desorption have been used to characterize the membranes calcined at 600 degrees Celsius. The crystal structures obtained from the characterization include brookite phase of titanium oxide, gamma phase of aluminum oxide and combined phase of aluminum oxide-titanium. Also, the average membrane pore size is 1.6 nm. The results of the filtration tests show that the membrane made by having two layers with different isoelectric points shows a very good performance in the entire pH range under investigation. The rate of chlorine excretion is dependent on pH, so that the rate of excretion is higher in the pH of the acidic region than in the alkaline region. By increasing the concentration of sodium chloride solution, the amount of chlorine removal decreased due to the increase in the thickness of the electric double layer, and also the results show that with the increase in pressure, the amount of chlorine removal increases.

Introduction

Gas condensates [1] hydrocarbon liquids are very light crude oil compounds that result from pressure and temperature changes in the gas produced from gas fields, after being transferred to surface separators. they become Gas condensates are typically graded from colorless liquids to light-colored liquids with shades of red, green, or blue. Gas condensates have a high AIP in the range of 40 to 60 and are very valuable from a commercial point of view[1].

The Middle East region is considered as one of the poles of gas condensate production in the world, and the largest contribution in this field is from Iran and Qatar. Gas condensate is one of the important sources for the production of gasoline and mid-distillation fuels. Also, based on the 127th principle of the law of the Islamic Republic of Iran on the implementation of the law on the development of public transportation and fuel consumption management - approved in 2016 - the Ministry of Petroleum was obliged to implement the plan to produce gasoline from gas condensate faster. Therefore, according to the current conditions of the country, producing more gasoline is one of the most important concerns of the country. On the other hand, units that use gas condensate as feed have reactors and catalysts that suffer poisoning and corrosion due to the presence of chlorine ions. As a result of poisoning of catalysts and corrosion of devices, the efficiency and effectiveness decrease and costs increase. Various methods such as pH stabilization and creating a film of corrosion inhibitors [2] and corrosion resistant coatings [3] have been carried out to reduce corrosion. But these methods only increase corrosion resistance and do not remove corrosive chlorine ions from condensate. One of the best methods to reduce chlorine ions in gas condensate is the use of nanofiltration ceramic membranes[2]. Nanofiltration ceramic membranes are considered as one of the successful tools for separation due to their mechanical, chemical and temperature characteristics. Therefore, the purpose of this thesis is to separate chlorine ions using alumina-titania nanofiltration membranes. For this purpose, double-layer membranes were first made using pressing, sol-gel and immersion methods.. Then, using membrane filtration devices, the performance of these membranes was investigated in order to separate chlorine ions at ambient temperature. Also, the effects of different pH, concentration and pressure parameters were investigated.

1-2- Equilibrium separation and speed controller separation

Generally, the separation processes of fluid mixtures can be divided into two categories: equilibrium separation and speed controller separation. Common separation processes such as evaporation, distillation, extraction, adsorption and adsorption, which are also used in industry, are based on equilibrium distribution. A primary phase, which consists of a mixture of components to be separated, is placed in direct contact with a secondary phase. After a certain period of time, thermodynamic equilibrium is established between the two phases. This means that both phases have the same temperature and all components have the same potential in the two phases. Although the analytical concentrations of a component may be different in two phases, for example, a component can be rich in one phase, but its amount in the other phase is very low. So basically, phase balance does not mean equality of one component in two phases. Now, if the two phases are separated by a suitable device, the enriched component can usually be recovered by establishing a new equilibrium at a different pressure or temperature. This method can be repeated to obtain a phase in which there is one of the components with the desired purity.

On the other hand, if the separation is caused by the difference in the transfer rate through some mediums and is influenced by the driving force of the difference in pressure, temperature, concentration or electric field, the separation process is called rate controlling. Membrane is such a medium that separates one phase from another. Figure 1-1 shows a picture of a vibrating cell membrane. The membrane is placed on a rigid support plate with high porosity between two upper and lower chambers. The incoming feed, which includes components A and B, enters the upper chamber and flows over the membrane. Part of the feed flow is transferred to the lower chamber. With a suitable membrane, only component A can pass through the membrane (permeant[3]), while component B will remain in the upper compartment. (Remainder[4]). Either A or B can be the desired product. In other words, depending on the conditions, it will be a penetrant or residual product. The stirrer is used to improve the mass transfer rate [4].

(Images are available in the main file)

Membrane separation processes are rapidly expanding in many emerging and existing applications. Among these fields are chemical engineering [5-7], petrochemical industry [10-8], environment [13-11], biotechnology [14 and 15], pharmaceutical [16], water treatment [17 and 18], food industry [19], beverage [20 and 21] and dairy [22], paper and pulp production [23], textile industry [24 and 25]. and electronic [26] and metallurgical [26 and 27] industries.

In recent years, membranes and membrane separation methods have grown and expanded from laboratory scale to industrial processes. Today, the membrane is used to produce drinking water from sea water using reverse osmosis, cleaning and recycling valuable substances from the effluent from industrial factories by electrodialysis and nanofiltration, treating industrial effluents using filtration processes (microfiltration, ultrafiltration and nanofiltration) and membrane bioreactor processes, separating macromolecule solutions in the pharmaceutical and food industries by ultrafiltration, removing urea and other toxic substances from the blood system with the help of Dialysis, separation of gases in order to produce nitrogen, sweetening of natural gas and recycling of valuable gases are used in petrochemical processes.

The most important characteristic of membranes is their ability to control the rate of permeation of various chemical elements and compounds. In many cases, membrane processes are faster and more effective than conventional separation methods. With membranes, the separation is usually done at room temperature. Therefore, the separation of temperature-sensitive solutions is done without any chemical change. The importance of this issue is clear in the pharmaceutical and biotechnology industries, where products are sensitive to temperature. The most important component of a membrane system is the membrane [28].