ABSTRACT
Foam are substances that are been formed when pockets of gases are trapped in a liquid or solid. Foam stabilizations are caused by van der waals force between molecules, there are conditions required for foaming to occur. Foams have different applications that are been utilised in their different forms. Defoamers are substances that hinders the formation of foam in liquids. The purpose of the defoaming test is to check the performance of silicone defoamer as an antifoaming agent after meeting some certain criteria. They are different method that can be used to test for defoamers which include the bartsch method, ross-miles test, automated shake test (AST) and foam rise method. The foam rise method was used to carry out this investigation. The foam sample used for this research was crude oil foam
Defoamers used for this experiment were improvised with solvents and silicone. Silicone was mixed with`each of the solvents in different proportions. During the experiment, physical properties of the components and defoamers were determined with measuring instruments and visual examinations. Different parameters were used to rate the defoamer’s performance. Charts in which the parameters were used to compare the defoamers were depicted.
From the figures(charts) shown, the defoamer which could be preferable for use in checkmating crude oil foam was defoamer E.
CHAPTER ONE
INTRODUCTION
1.1 Background of Study
Foam is a substance that is formed when pocket of gases is trapped in a liquid or solid. In most foams the volume of gas is relatively large with thin films of liquid or solid separating the regions of gas. (Tarek 2015)
Essentially, solids foams are divided into open-cell and closed-cell foams. In the case of closed cell foam the gas forms discrete pockets, each completely surrounded by a solid material. In the open-cell foam, the gas pockets are connected to each other. A bath sponge falls under the division of open-cell foam. Water can easily flow through the entire structure leaving the entire structure, displacing the air. A camping mat is an example of closed-cell foam; in this case the gas pockets are sealed from each other so the mat can soak up water. (Tarek 2015)
In some ways leavened bread can be considered to be a foam, as the yeast cause the bread to rise by the appearance of tiny bubbles of gas in the dough. Ideally the dough is a closed cell foam in which the gas pockets do not connect with each other. When the dough is cut gas is released in the bubbles that are cut, the gas remaining in the dough cannot escape. However, if the dough is allowed to rise too far, it becomes an open-cell foam in which the gas pockets are been connected with each other. If the dough is cut or the surface is broken, a large volume of gas can escape which causes the dough to collapse. The open structure of an over risen dough is easy to observe; the dough contains gas space filled with threads of the flour/water paste, unlike other foams of discrete gas bubble. (Tarek 2015)
1.1.1 Structure of foams
In several cases a foam is considered to be a multi-scale system. One scale is the bubble type. Real-life foams are typically disordered and have a variety of bubble sizes. At larger sizes, the study of idealized foams is closely linked to the mathematical problems of minimal surfaces and three-dimensional tessellations, also called honeycombs.
For a scale which is lower than the bubble one, the thickness of the film for dry enough foams can be considered as a network of interconnected films called lamellae. Ideally the lamellae are connected by three films and radiate at 120 degrees outward from the connection points known as plateau borders. An even lower scale can be found in the liquid-air interface which occurs at the surface of the film. The interface is stabilized by a layer of amphiphilic structure most times which are often made of surfactants, particles-pickering emulsion or more complex associations (Tarek 2015)
1.1.2 Foaming and foam stability
For foam to be produced there are several conditions required which are:
- Mechanical work
- Surface active components(surfactants) that reduce surface tension
- The formation of foam faster than its breakdown
To create foam work (W) is needed to increase the surface area (ΔA):
W= (1.1.2.1)
Where is the surface tension.
One of the ways by which foam is created is through the process of dispersion, where a large amount of gas is mixed with a liquid. A specific method of dispersion involves injecting a gas through a hole in a solid into a liquid. If this process come to a completion slowly, then one bubble can be emitted from the orifice at a time as shown in the diagram below. (en.wikipedia.org)
Fig 1.1: Rising bubble from orifice
Source:en.wikipedia.org/wiki/foam
Stabilization of foams is caused by van der waals forces between molecules in the foam, electrical double layers are created by dipolar surfactants and the marangoni effects acts as a restoring force to the lamellas.
Marangoni effect is the flow of fluid caused by a gradient in surface tension.
There are destabilizing effects which can break foam down they include:
- Gravitation: it causes drainage of liquid to the foam base,
- Osmotic pressure: it causes drainage from the lamellas to the Plateau borders due to internal concentration differences in the foam, while
- Laplace pressure: it causes diffusion of gas from small to large bubbles due to pressure difference. Films can break under disjoining pressure,
- These effects can lead to rearrangement of the foam structure at scales larger than the bubbles, which may be individual or collective.
- Application of foams
1.Liquid foams
Liquid foams can be used in retardant foam, such as those that are been used to extinguish fires especially fires like oil fires.
The unique property of gas-liquid foam with very high specific surface area are been exploited in the chemical processes of froth flotation and foam fractionation (Tarek 2015).
Froth floatation is the process of selectively separating hydrophobic materials from hydrophilic materials. Foam fractionation is a chemical process in which hydrophobic molecules are preferentially separated from a liquid solution using rising foam columns. (en.wikipedia.org)
- Solid foams
Solid foams form an important class of lightweight cellular engineering materials. These foams can be classified into two types based on the structure of the pore which are open-cell-structured foams (also known as reticulated foams) and closed –cell foam.
Open-cell structure has pores that are connected to each other and form an interconnected network that is relatively soft. Open-cell foams fill with whatever they are been surrounded with. If they are filled with air, a relatively good insulator is the result, but if the cells are filled with water, the insulation property will be reduced. Foam rubber is a type of open cell foam (Tarek 2015)
Closed-cell foams do not have pores that are interconnected. The compressive strength of the closed-cell foams is higher due to their structures. However, closed cell foams are also denser generally, it requires more material, and as a result they are more expensive to produce. The closed-cells can be filled with specialized gas to provide improved insulation. The closed cell foams do have higher dimensional stability, low moisture absorption coefficients, and higher strength compared to open-cell-structured foams. Every type of foam is useful as an essential material; sandwich-structured composite materials (Tarek 2015).
During the early 20th century, various types of specially manufactured solid foams came into use. the low density of these foams have made them good enough as thermal insulators and flotation devices, and the lightness and compressibility which they have makes them ideal as packing materials and stuffings (Tarek 2015).
- Syntactic foam
Syntactic foams are closed-cell foams which have hollow particles embedded in a matrix material. The spheres can be made from several materials, including ceramic, glass and polymers. The advantage of syntactic foams is that they have a very high strength-to-weight ratio, making them more ideal materials for many applications in the case of deep sea and space applications. A particular syntactic foam employs shape memory polymer as its matrix, enabling the foam to take on the characteristics of shape memory resins and composite materials i.e. it can be reshaped when it is been heated above a certain temperature and cooled. Shape memory foams have a lot of possible applications like dynamic structural support, flexible foam core, and expandable foam fill (Tarek 2015).
- Integral skin foam
Another term for this foam is “self-skin foam”. It is type of foam that have high density skin and low density core. They can be in an “open-mould process”. In the open-mould process, two reactive components are mixed and poured into an open mould; the mould is then closed and the mixture is allowed to expand and cure. Arm rests, baby seats, soles of shoe, and mattresses are produced from this process. The closed-mould process popularly known as reaction injection moulding(RIM), injects mixed components into a closed mould under high pressure condition. (Tarek 2015)
- Crude oil foam
Petroleum-based foams are one of the most important and abundant types of non-aqueous foams. Furthermore, the complexity of the continuous phase in these foams is higher than in other non-aqueous foams. This is due to the fact that the composition of crude oil varies greatly depending on the well location and age. Crude oil is a naturally occurring liquid, mineral oil consisting of a variety of organic compounds, mainly saturated and aromatic hydrocarbons, but also more complex compounds such as resins and asphaltenes. The oil industry characterizes the quality of the oil using its API gravity:
(1.1.4.1)
A crude with an API gravity less than 10º is denser than water and corresponds to a bitumen, and a crude with an API gravity higher than 31º is a light crude oil. Crude oils with API gravities between 20 and 45ºare called conventional oils and those with API levels lower than 20º are called heavy oils. Foams can be encountered in any stage of oil recovering and processing and they can be desirable or a nuisance. For example, oil foams can be useful has drilling fluids or gas blocking agents during extraction from porous media, but undesirable during gas/oil or oil/ water separation and during refining. An additional complexity of petroleum foams, apart from oil composition, is that they usually contain water, particles (sand, clay, corrosion products, paraffin crystals, precipitated asphaltenes, etc.) or even additives introduced during the oil extraction phase (surfactants commonly used as bactericides, anti-corrosion, anti-oxidant, emulsion breaker, asphaltene dispersant, antiscale, etc.). These factors produce petroleum foams that may exhibit several different types of behaviour. When working with crude-oil foams, it is important to understand certain terminologies such as:
– live oil: it refers to oil saturated with dissolved gases;
– dead oil: it refers to oil without dissolved gases;
– foamy oil: it is a heavy crude oil that produces stable dispersed bubbles under moderate depressurization and stable foam under severe depressurization.
In a reservoir, a thermodynamic equilibrium naturally exists between the lightest hydrocarbons (methane, ethane, etc.) dissolved in the oil and the denser liquid phase. The amount of dissolved gas in the so-called “live oil” is proportional to the temperature and pressure in the system and given by Henry’s law. During live oil extraction, depressurization occurs between the reservoir and the wellhead. The live oil then becomes supersaturated and the system expels the excess dissolved gas, inducing nucleation and growth of bubbles within the liquid oil phase, modifying its composition as well as its flow properties. In the case of light oils, bubbles coalesce very quickly and a slug flow can appear as large volumes of gas exit the well. However, in the case of heavy oils, bubbles remain dispersed within the oil, leading to a system that resembles “chocolate mousse” and typically referred to as a “foamy oil phenomenon”, even though if a more appropriate term should be “bubbly oil”, as the gas volume fraction is typically found to be between 5 and 40%. This phenomenon appears during higher production rates than expected by reservoir modelling. While the foamy-oil flow encountered in many Nigerian, Canadian and Venezuelan heavy-oil reservoirs during production under solution gas drive presents several advantages, both in terms of higher-than-expected well productivity and high primary recovery factor, this phenomenon leads to major drawbacks on surface facilities, especially during gas/oil separation (Blaquez et al., 2014)
1.1.4.1 Factors contributing to crude oil foam formation
The amount of foam that a system can create, the stability of the foam and, even, the capacity to create gas/ liquid films depend on the characteristics of the gas dissolved. Gases that do not have an affinity for the crude oil tend to form unstable foams. However, if the gas is soluble in the oil, foams can be formed and the extent will depend on the pressure and temperature of the system. The initial Gas to Oil Ratio (GOR) in the crude oil determines the quantity of gas that can be released, which is related to the foam formation. It also bears on foam stability by the number of bubbles and their size distribution. The composition of the crude oil is equally important to the eventual foaming properties. There are several constituents that can promote the formation of foam and/or stabilize it once it is generated. For example, Callaghan et al. (1985) have found that short-chain carboxylic acids and phenols with a molecular mass lower than 400 are responsible for foam production. Other authors evoke asphaltenes and resins as the primary cause of foam. Poindexter et al (2002) identified several parameters that are important for controlling the foaming behaviour of crude-oils, which include bulk viscosity and density, oil-gas surface tension, asphaltenes and resins content and their molecular weight. Viscosity plays an important role in any foam (aqueous or non-aqueous) because it is directly related to the drainage of interstitial fluid in the foam. In addition to lowering the drainage rate, high viscosity systems can also lower the rate of gas diffusion between bubbles (Ostwald ripening) and both effects tend to promote foam stability. In fact, Poindexter et al. (2002) indicate that crude oils with bulk viscosities lower than 150 cP at 37.8ºC produce little or no foam. On the other hand, Fraga et al. (2011) have evaluated high viscosity oils and found that these oils did not generate foams even when they contain high levels of stabilizing species. As with aqueous foam, the surface properties of liquid-gas interface in crude-oil foam are also important. In particular, it has been found that the surface rheological behaviour plays an important role in stabilizing the thin-liquid films in the foam. The presence of other phases apart from oil and gas, such as water or solids, can also influence the foam behaviour and stability. Along these lines Marcano et al. (2009) have studied the stability of foams formed from diesel oil and fatty acids surfactants (to simulate Venezuelan crude oils) with dispersed water. They found that it is possible to create stable foam by adding water at concentrations higher than 2%. They suggest that when water is present in the system, the bubbles formed will be surrounded by water and dispersed in the oil, originating an air/water/oil dispersed system stabilized by the mixture of surfactants, the low molecular weight surfactants being adsorbed at the air/water interface, and the high molecular weight surfactants being adsorbed at the water/oil interface. In their review on foamy oil flow, Sheng et al. (1999) indicate that the presence of water has no measurable effect on the nucleation of bubbles, hence on bubble frequency but it has an influence on the rheological behaviour of the mixtures. Abivin et al. (2009) have compared the rheological behaviour of a multiphase dispersed system, namely gas bubbles and water droplets embedded in a heavy crude oil, to the one of a system containing only bubbles. They found that the bubbly emulsion is less viscous than the original emulsion. This phenomenon was attributed to the elongation of the gas bubbles, which is facilitated by the high viscosity of the water-in-oil emulsion. As already mentioned, the presence of solid particles at the interface (sand, aggregates, salts, etc.) can stabilize foam. Furthermore, foam creation and stability can also be enhanced in solid porous media. Sheng et al. (1997) indicate that higher stability foam can be achieved in a porous media than that in a bulk vessel. This effect is a consequence of the wetting behaviour of the media and its subsequent influence on the capillary pressure imposed on the thin foam films (Blacquez et al., 2014).
1.1.5 Defoaming
To understand defoaming, it is necessary to understand how foam becomes stabilized in the first place. Foam is stabilized when the so-called Marangoni effect comes into play. This, in turn, is based on the “Gibb’s elasticity.” A foam lamella is elastic because the surface tension changes with change in surface area of the gas bubble. In a foam lamella, the surfactant molecules tend to concentrate at the bottom. This gives rise to a gradient in surface tension, which causes surfactant molecules in the lamella to be drawn upward; as they do so, they carry liquid with them. This “wet” or “dynamic” foam is vulnerable to attack by chemical antifoam agents. One example of this is champagne bubbles which are rapidly destroyed by the alcohol in the champagne. (www.wacker.com)
Foam, is a serious problem in the chemical industry especially in the case of biochemical processes. Many biological substances easily create foam on agitation and aeration. Foam is a problem because the liquid flow is altered and transfer of oxygen is blocked from air thereby preventing microbial respiration in aerobic fermentation processes. For this reason, antifoaming agents, like silicone oils, are added to prevent these problems. The addition of chemicals as an antifoaming agent is known as chemical method. Chemical methods of foam control are not always desired because of the problems of contamination and reduction of mass transfer that they may cause especially in food and pharmaceutical industries, where the product quality is of great importance. In order to prevent foam formation, in such cases mechanical methods are mostly dominant over chemical ones.(Tarek 2015)
1.2 Statement of Problem
The most noticeable form of foam is foam floating on the stock surface. This is the case with crude oil formation. It is easy to monitor and relatively easy to handle. Surface foam may cause problems with liquid levels resulting in overflow and carryover. This might reduce the process efficiency and availability of process equipment.
1.3 Aims and Objectives
The aim was to produce defoamer using solvents such as diesel, kerosene, naphtha and palm kernel oil and their blends with silicone and check for their effectiveness in controlling crude oil foam formation.
The objective involves combining each of the solvent with silicone to produce defoamers.
1.4 Significance of the Work
The purpose of this research is to proffer solution that will control foaming in the crude oil flow station using defoamers.
1.5 Scope of Research
In this research, defoamers was produced using four different solvents as well as their blends in combination with silicone. Foamy fluid used was the crude oil emulsion. The foam was formed under static conditions. Tests were carried out to determine the effectiveness of each defoamer in resolving the foaming tendency of the crude oil emulsion/ foamy fluid. Properties such as the specific gravity, turbidity, and pH of the defoamer products were also determined.
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