Inhibitors filming

Filming amine chemistry in the refinery includes amides, diamides and imidazoline salts. Each type is known to be effective in selected environments. The amino group is the important functional and salt-forming species. For readily handled commercial products, the amide intermediate is reacted with an imidazohne salt to enhance solubility in carrier solvents and to decrease gelling or phase separation. However, both groups are effective inhibitors. 

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Filming inhibitors are characterized by possessing a polar, electron dense head and a nonpolar, oil-soluble tail. Examples of compounds which have these... 

Care should be taken when using a corrosion inhibitor in an existing system which has not received corrosion inhibitor treatment in the past or in any system containing rust. When applied, a filming inhibitor will loosen and remove existing rust. The rust will travel with the fuel and accumulate on filters or in areas of low turbulence within a fuel system. New metal surfaces will be exposed upon removal of the rust and can further corrode if not protected. 

Aluminum alloys are susceptible to underdeposit corrosion. Stainless steels are also susceptible to underdeposit corrosion as well as deep pitting. Anodic, cathodic, and filming inhibitors are used to mitigate corrosion (40). 

Upstream oil production uses inhibitors for oil drilling operations as well as permanent production tubulars and pipelines, where two-phase and three-phase production streams are treated with filming inhibitors. The amount used ( 153 million) in production is dependent on the amount of water produced with the oil. The economics of such a system is calculated as cost per barrel of oil or water produced. This has been estimated in the lower 48 states to range from 0.02 per barrel of oil produced to 0.23 per barrel of oil produced, depending on factors such as temperature, corrosive gases present, and operating procedures. 

Inhibitors are used in severe and harsh environments encountered in rotary cookers and hydrostatic sterilizers. The medium consists of hot water, steam, and cooling water. A single approach to this problem may not provide the solution. A combination of anodic, cathodic, and filming inhibitors was selected for corrosion prevention depending on the water composition and equipment material. 

Electrochemical inhibitors retard or prevent the anodic and/or cathodic partial reactions (i.e they influence the reaction at the metal/corrosive medium interface). Chemical inhibitors can react both with the material and form protective coatings and with the medium itself or its constituents and thus diminish its aggressiveness. Physical inhibitors form adsorption layers on the metal surface, which block the corrosion reaction. Inhibitors that influence the electrochemical electrode reactions are subdivided according to their mode of action and site of action in the area of the metal/ medium phase boundary, with the subdivision being between interface inhibitors, electrolyte film inhibitors, membrane inhibitors, and passivators. 

For many years it was believed that inhibitors adsorb on the metal surface, and test methods were developed to examine the filming behavior" of inhibitors. It had been shown early that such filming inhibitors need an iron sulfide film to be effective. Later the same was shown for iron carbonate systems. 

Inhibitors are chemicals that react with a metallic surface, or the environment this surface is exposed to, giving the surface a certain level of protection. Inhibitors often work by adsorbing themselves on the metalhc surface, protecting the metalhc surface by forming a film. Inhibitors are normally distributed from a solution or dispersion. Some are included in a protective coating formulation. Inhibitors slow corrosion processes by... 

Areas downstream of welds, minor huckhng of the line, low spots, and solids deposits can increase shear stress and turbulence, which may aggravate corrosion. Low spots cause slugs of hquid at intervals. Turbulence removes protective scale, aggravates abrasion and erosion if sohds are present, and may affect inhibitor performance by removing the film. Inhibitors must be able to withstand the shear stresses. 

If a chemical string is not feasible, batch treatments using persistent film inhibitors may be used. The inhibitor is designed to form a tough film that is not too soluble in the production stream so it will last for a sufficient time between treatments. The batch may be displaced with liquids, gas, or nitrogen. Squeeze inhibitors must be designed to be stable in the formation, and not cause severe emulsion problems. The adsorption characteristics should be controlled for proper feedback of the inhibitor. Pumped wells, can be treated by continuous addition or batching down the annulus. 

The most important type of inhibitor to the oil industry is the filming inhibitors. One end of the inhibitor molecule is adsorbed onto the metal surface. The non-polar tail of the inhibitor molecule is oriented in a direction generally vertical to the metal surface. It is believed that the hydrocarbon (non-polar) tails mesh with each other in a sort of zipper effect to form a tight film that repels aqueous fluids, estabhshing a barrier to the chemical and electrochemical attack of fluids on the base metal. A secondary effect is the physical adsorption of hydrocarbon molecules from the process fluids by the hydrocarbon tails of the adsorbed inhibitor molecules. This increases both the thickness and effectiveness of the hydrophobic barrier to corrosion. 

Based on the above explanation, it may be understood why such inhibitors are generally more effective in the presence of an oil phase. In fact, it is often difficult to use filming inhibitors effectively and economically in its absence. 

Filming inhibitors are available in a wide variety of formulations and solubility characteristics. The question of whether to use an oil-soluble or a water-soluble inhibitor is somewhat arbitrary. Some operators prefer to use a water-soluble or water-dispersible inhibitor when the water to oil ratio of the producing well is greater than one. Other operators hold an opposing view, preferring to build a high concentration of oil-soluble inhibitor in the lesser phase. In practice, both methods have been... 

Refineries and petrochemical processes employ a variety of film-forming inhibitors under varying conditions. Due to the function of this type of inhibitor, they are generally more effective in the presence of an oil phase. In fact, it is often difficult to use filming inhibitors effectively and economically in the absence of an oil phase. Inhibitors are available with a wide range of solubihties and other physical properties. The concentrations at which they are used generally is about 10 ppm based on the hydrocarbon phase, so the economics are generally quite favorable. 

The use of neutralizing amines for acid corrosion in refinery processing is an example of alteration of the environment. The use of filming amines may be thought of as a combination of enviroiunent alteration and a protective barrier, for example, the absorbed inhibitor film supplemented by the sorbed oil film. Chemical treatments employing neutralizers and/or filming inhibitors should be screened in the laboratory and tested in the plant to verify laboratory indications. Such tests are no more error-proof than those on metals or coatings. 

Corrosion prevention by chemicals is not ordinarily practical in refinery work for acids that are either concentrated or strong. However, dilute acid streams often may be rendered non-corrosive by use of inexpensive neutralizers and/or filming inhibitors. Examples include the mixed condensate composed of water and hydrocarbon liquids from dehydrogenation of ethyl benzene to styrene in the presence of steam, various acidic wash streams, etc. 

There is some disagreement as to the desirable feeding point for film-forming inhibitors. All inhibitor suppliers say that the materials can be fed directly to the steam and condensate systems. Some suppliers recommend adding the inhibitor to the feed water or directly to the boiler and say that the inhibitor will evaporate with the steam and condensate in a thin, continuous film. However, most of the commercially available filming inhibitors are formulated produets, each component having a somewhat different volatihty (and solubility) and, therefore, the preferred point of addition should be the steam header. 

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