Modeling of chloride ion removal from gas condensate using nanofiltration

Master thesis in chemical nanoengineering

Abstract

Modeling of chloride ion removal from gas condensate using nanofiltration

Chloride ions in gas condensate can cause severe corrosion of equipment and pipes. Therefore, it is necessary to remove it from the condensate flow. The aim of this work is the mathematical modeling of the nanofiltration process for the separation of chloride ions from gas condensate. For this purpose, spatial load models, hollow fiber membrane modeling, neural networks, Enfis and the nearest neighbor method have been used and investigated. The space charge model was used for the membrane system on a laboratory scale, and the result showed a large amount of chloride separation from gas condensate. In the investigation of hollow fibers, first the output of the model was compared with the laboratory data, and this modeling was done very accurately and led to the prediction of appropriate separation. Separation varies according to fluid flow rate. In the next stage of the work, neural networks were used, which can be used for complex mathematical models and large amounts of calculations. It is noteworthy that artificial neural networks can improve the problem of low accuracy of other models. Finally, Enfis and the nearest neighbor method have been used to study chloride separation from gas condensate. To compare laboratory data and modeling results, changes in pressure, concentration and pH have been investigated. A good agreement between the experimental data and the modeling results in the theoretical studies was obtained. Therefore, the high accuracy of the results of the modeling process and the flexibility of the model provide the ability to generalize it to similar processes. Basic

1-1- Introduction

Filtration is a process during which the solute is physically separated by passing through a semi-permeable medium or barrier. Membrane processes are advanced filtration processes that take advantage of the separation properties of porous polymer or inorganic layers and are used in a wide range of industrial processes to separate biomolecules, colloids, ions, solvents, and gases. In the IUPAC definition, nanofiltration is a membrane-based, pressure-driven separation process, in which particles and molecules smaller than 2 nm are separated [1]. Membranes can be used in most separation processes and complement chemical processes such as distillation, extraction and absorption, or be a good substitute for them. rtl;">possibility of performing separation operations at ambient temperature

easy access to all separated phases

separation operations by equipment with low weight and volume

simple installation and operation

minimum need for control, inspection, maintenance

no need to use chemicals for separation and as a result the absence of environmental issues

In the past, the most common use of microfiltration in the beverage industry was cold commercial sterilization for pharmaceutical purposes and the supply of pure water in semiconductor processes. Until 1960, despite the understanding of the basic principles of modern membranes, there were no important industries in this field, until gradually by removing some of their disadvantages such as high price, slow and time-consuming processes, non-selectivity, etc. Membranes made their way from the laboratory to industry.Membranes can be classified in several ways [2,3]:

1-1-2- Classification of membranes

Classification based on the constituent material:

Organic polymers, inorganic materials (oxides, ceramics and metals), matrices Hybrid or composite materials

Classification based on the cross-sectional area of ??the membrane:

Isotropic (symmetric), heterogeneous (asymmetric), two or multilayer, thin layer hybrid matrix composite

Classification based on the preparation method:

Polymer phase separation , sol-gel process, surface reaction, stretching, extrusion, engraving

Classification based on the shape of the membrane:

Sheet, hollow fiber and hollow capsule

The basis of membrane processes is the passage of materials through a sieve, which is done by a thrust force. This drift in membrane processes is divided into four categories and includes:

a) pressure difference: in membrane processes of microfiltration, ultrafiltration, nanofiltration and reverse osmosis

b) electric potential difference: such as electrodialysis and membrane electrolysis

c) temperature difference

d) concentration difference

In the membrane processes of microfiltration, ultrafiltration, nanofiltration and reverse osmosis, the driving force is the pressure difference, but in other membrane processes, as mentioned, this driving force can be different. The range of application and dimensions of microfiltration, ultrafiltration, nanofiltration and reverse osmosis membranes are different.

In a filtration process, two phases that are not in thermodynamic equilibrium with each other are separated by a semipermeable membrane. The mentioned membrane acts like a physical barrier or barrier and controls the passage or non-passage of substances from one phase to another. Reverse osmosis is used for desalination of aqueous solutions, production of very pure water and in food and milk industries. Since very small particles are forcibly trapped during the reverse osmosis process, very small openings (less than one nanometer) and high pressures (more than 40 bar) are required to perform this process.

Ultrafiltration process is used to separate particles between 1 and 100 nanometers (polymers, proteins, viruses, etc.) [5, 4]. In ultrafiltration, the openings of the membrane are larger than the openings of reverse osmosis membranes and low pressures (less than 20 bar) are needed. In the last two decades, significant efforts have been made to achieve improvements in the field of producing membranes that have properties between the two mentioned processes, i.e. high pressure (similar to the reverse osmosis process) and low pressure (such as the ultrafiltration process), which results in the production of nanofiltration. Today, nanofiltration has found an important place in various industries and has filled the gap between reverse osmosis and ultrafiltration. The size of the pores in nanomembranes is between reverse osmosis and ultrafiltration membranes (in the range of 2 nm or smaller), and therefore particles with a diameter intermediate between reverse osmosis and ultrafiltration are separated by a sieving mechanism. In addition to these materials used in the construction of nanomembranes, they are charged and the particles are separated under an electrostatic repulsion mechanism [6]. For this reason, it is called a nanofilter [7]. Nanofiltration works in the range between ultrafiltration [2] and reverse osmosis [3]. It removes organic molecules with a molecular weight of more than 200 to 400. Soluble salts are also rejected in amounts of 20 to 98%. Salts that have monovalent anions (such as sodium chloride or calcium chloride) are excreted in about 20 to 80 percent. If salts with polyvalent anions (such as magnesium sulfate) are removed more than 90 to 98% [9, 8].

Usually, the separation of monovalent, divalent salts and non-ionic solutes with a molecular weight of less than 2000 g/mol is the main factor in choosing new membranes with properties and characteristics between reverse osmosis membranes and It is ultrafiltration.