Acid corrosion weak acids


Carbonic acid. Carbonic acid (as do most weak acids) produces smoother attack than stronger acids. Pitting and surface roughness on carbon steel increase as the amount of dissolved oxygen increases (Figs. 7.11 and 7.12). In regions of condensation, grooving frequently occurs (Figs. 7.13 through 7.15). Grooves are caused by the flow of acidic condensate across surfaces. Friable, light-colored corrosion products containing carbonate are often present and sometimes form during cooling. Similar products may surround leaks and failure sites. Carbonate-containing material effervesces strongly when exposed to mineral acids.  [c.170]

The evolution of hydrogen from the acid molecule can also occur in slightly dissociated weak acids such as HjCOj and HjS. In the case of only slightly dissociated weak acids, such as HjCOj and HjS, production of hydrogen can also occur from the acid molecules. In this case, the acid concentration rather than the pH value is a measure of the aggressiveness of the corrosion. In the same way, hydrogen can be evolved from HjO  [c.36]

In sulfuric acid production involving heat recovery and recovery of waste sulfuric acid, acids of various concentrations at high temperatures can be dealt with. Corrosion damage has been observed, for example, in sulfuric acid coolers, which seriously impairs the availability of such installations. The use of anodic protection can prevent such damage.  [c.478]

Organic Carboxylic Acids — (RCOOH) are usually weak acids but can be very corrosive to skin. However, The substitution of Cl atoms on the carbon next to the carboxylic carbon produces a stronger acid. Thus, trichloroacetic acid is almost a strong acid whereas acetic acid is a weak one.  [c.169]

The elements of this group are relatively electropositive but less so than those of Group 3. If heated to high temperatures they react directly with most non-metals, particularly oxygen, hydrogen (reversibly), and, in the case of titanium, nitrogen (Ti actually bums in N2). When finely divided the metals are pyrophoric and for this reason care is necessary when machining them to avoid the production of fine waste chips. In spite of this inherent reactivity, the most noticeable feature of these metals in the massive form at room temperature is their outstanding resistance to corrosion, which is due to the formation of a dense, adherent, self-healing oxide film. This is particularly striking in the case of zirconium. With the exception of hydrofluoric acid (which is the best solvent, probably because of the formation of soluble fluoro complexes) mineral acids have little effect unless hot. Even when hot, aqueous alkalis do not attack the metals. The presence of oxidizing agents such as nitric acid frequently reduces the reactivity of the metals by ensuring the retention of the protective oxide film.  [c.958]

Waters of pH less than 6 may be expected to be corrosive, but, because any weak acids present in the solution may not be fully ionised, it does not follow that water of pH greater than 7 will not be corrosive. Mine waters are particularly corrosive to cast iron, often to such an extent as to preclude its use with them, because of their relatively high acid content, derived from the hydrolysis of ferric salts of the strong acids, mainly sulphate, and because the ferric ion can act as a powerful cathodic depolariser.  [c.589]

Sulphates, silicates, carbonates, colloids and certain organic compounds act as inhibitors if evenly distributed, and sodium silicate has been used as such in certain media. Nitrates tend to promote corrosion, especially in acid soil waters, due to cathodic de-polarisation and to the formation of soluble nitrates. Alkaline soils can cause serious corrosion with the formation of alkali plumbites which decompose to give (red) lead monoxide. Organic acids and carbon dioxide from rotting vegetable matter or manure also have a strong corrosive action. This is probably the explanation of phenol corrosion , which is not caused by phenol, but thought to be caused by decomposition of jute or hessian in applied protective layers.  [c.730]

The US Bureau of Mines found the chemical and galvanic corrosion behaviour of both the TZM and Mo-30W alloy to be generally equal or superior to that of unalloyed molybdenum in many aqueous solutions of acids, bases and salts. Notable exceptions occurred in 6-1 % nitric acid where both alloys corroded appreciably faster than molybdenum. In mercuric chloride solutions the TZM alloy was susceptible to a type of crevice corrosion which was not due to differential aeration. The alloys were usually not adversely affected by contact with dissimilar metals in galvanic couple experiments, but the dissimilar metals sometimes corroded galvanically. Both alloys were resistant to synthetic sea water spray at 60°C.  [c.848]

There are usually several aqueous waste streams arising from both water generated by the oxidation reactions and wash water. The principal hydrocarbon constituents of these aqueous wastes are the C —C mono- and dibasic acids, but also present are butanol [71-36-3] pentanol [71-41-0] S-hydroxycaproic acid [1191-25-9] and various lactones and diols (71,72). The spent caustic streams contain similar components in addition to the caustic values. These streams can be burned for recovery of sodium carbonate or sold direcdy as a by-product for use in the paper industry. The most concentrated waste stream is one often called stiU bottoms, heavy ends, or nonvolatile residue. It comes from the final distillation column in which the KA oil is steam-stripped overhead. The tails stream from this column contains most of the nonvolatile by-products, as well as metals and residues from the catalysts and from corrosion. Both the metals and acid content may be high enough to dictate that this stream be classified as a hazardous waste. It usually is burned and the energy used to generate steam (73). Much effort has gone into recovering valuable materials from it over the years, including adipic acid, which may be present in as much as 3—4% of the cyclohexane oxidized (74). It has potential as a feedstock in the production of monobasic acids, polyester polyols, butanediol, and maleic acid (75,76). The frequency of fugitive emissions from cyclohexane oxidation plants has been reviewed (77).  [c.241]

Vapors emitted from the materials of closed storage and exhibit cases have been a frequent source of pollution problems. Oak wood, which in the past was often used for the constmction of such cases, emits a significant amount of organic acid vapors, including formic and acetic acids, which have caused corrosion of metal objects, as well as shell and mineral specimens in natural history collections. Plywood and particle board, especially those with a urea—formaldehyde adhesive, similarly often emit appreciable amounts of corrosive vapors. Sealing of these materials has proven to be not sufficiently rehable to prevent the problem, and generally thek use for these purposes is not considered acceptable practice.  [c.429]

The treatment of spent lye consists of a series of operations designed to remove nearly all of the organic impurities (6,7). The spent lye commonly is treated with mineral or fatty acids to reduce the content of free caustic and soda ash and to reduce the pH to 4.6—4.8 (8). Sulfates are to be avoided since they are associated with foaming and heat exchanger fouling during subsequent refining. After cooling, the soHd soap is skimmed, and an acid and a coagulant are added, followed by filtration. Addition of caustic soda removes the balance of coagulant in solution and adjusts the pH to a point at which the hquor is least corrosive to subsequent process treatment. Spent lyes from modem Hquid-Hquid countercurrent extraction used with continuous saponification systems require tittle treatment other than reduction of free alkali by neutralization with hydrochloric acid. The dilute glycerol is now ready for concentration to 80% soap lye cmde glycerol.  [c.347]

Hafnium is a highly reactive metal. The reaction with air at room temperature is self-limited by the adherent, highly impervious oxide film which is formed. This film provides oxidation stabiUty at room temperature and resistance to corrosion by aqueous solutions of mineral acids, salts, or caustics. Thicker oxide films are formed at higher temperature, but slowly enough that forging or hot rolling of hafnium ingots is conducted in air at a temperature between 900 and 1000°C, with subsequent removal of surface scale by sandblasting and then a nitric—hydrofluoric acid pickling. High surface area hafnium powder or porous sponge metal ignites quite easily in air. Clean hafnium metal ignites spontaneously in oxygen of about 2 MPa (300 psi).  [c.440]

At proper pH in aqueous media, malic acid forms complexes or chelates with metal ions (see Chelating agents). These chelating reactions are useful in industrial processes requiring elimination or control of metal-ion catalysis (eg, of oxidation), removal of corrosion products (eg, mst), lowering of metal oxidation potentials (electroplating), etc. The chelating properties of malic acid vary with different metal cations, ionic strength, pH, etc, and in many cases approximate those of other hydroxy carboxylic acids (28). Formation constants for malic acid chelates with various metal ions are as follows Ca, 1.8 Cu, 3.4 Mg, 2.2 and Zn, 2.8. Malic acid forms a weak buffer from approximately pH 3.0 to 6.0 (Fig. 3).  [c.522]

Cation exchangers are regenerated with mineral acids when used in the form. Sulfuric acid [8014-95-7] is preferred over hydrochloric acid [7647-01-0], HCl, in many countries because it is less expensive and less corrosive. However, the use of hydrochloric acid is the best method of overcoming precipitation problems in installations which deionize water with high concentrations of barium or calcium compared to other cations. A 4% acid concentration is common, although sulfuric acid regenerations may start as low as 0.8—1% to minimize calcium sulfate [7718-18-9] precipitation.  [c.384]

Lead shows excellent resistance to phosphoric and sulfuric acid in almost all concentrations and at elevated temperatures, as well as to sulfide, sulfite, and sulfate solutions. The corrosion film is insoluble lead sulfate which rapidly reforms if it is damaged. Lead is also resistant to chlorides, fluorides, and bromates at low concentrations and low temperatures. However, because lead is soluble in nitric and acetic acids, it is not resistant to these acids.  [c.63]

The unique features of molecular sieves are demonstrated in the removal of water from natural gas streams containing high percentages of acid gases, eg, H2S and CO2. Other dry-bed adsorbents degrade in highly acidic environments. However, acid-resistant molecular sieves have been developed which maintain dehydration capacities over long periods of on-stream use. They also are used to dehydrate gas streams containing corrosive components such as chlorine, sulfur dioxide, and hydrogen chloride.  [c.456]

Nickel—Molybdenum. Molybdenum in soHd solution with nickel strengthens the latter metal and improves its corrosion resistance, eg, in the HASTELLOY aHoys. HASTELLOY aHoy B-2 is noted for its superior resistance to corrosion by hydrochloric acid at aH concentrations up to the boiling point by other nonoxidizing acids, such as sulfuric and phosphoric and by hot hydrogen chloride gas. Other nickel—molybdenum aHoys contain chromium, which improves the resistance to corrosion and, especiaHy, to oxidation. The Ni—Cr—Mo HASTELLOY aHoy C-22, which also contains cobalt and tungsten, is resistant to a wide range of chemical process environments, including strong oxidizing acids, organic and inorganic media, chlorine, and brine. HASTELLOY aHoy C-276 also has exceHent resistance to corrosion by oxidizing environments, oxidizing acids, chloride solutions, and other acids and salts.  [c.6]

The reactor coolant pH is controlled using lithium-7 hydroxide [72255-97-17, LiOH. Reactor coolant pH at 300°C, as a function of boric acid and lithium hydroxide concentrations, is shown in Figure 3 (4). A pure boric acid solution is only slightly more acidic than pure water, 5.6 at 300°C, because of the relatively low ionisation of boric acid at operating primary temperatures (see Boron COMPOUNDS). Thus the presence of lithium hydroxide, which has a much higher ionisation, increases the pH ca 1—2 units above that of pure water at operating temperatures. This leads to a reduction in corrosion rates of system materials (see Hydrogen-ION activity).  [c.191]

Metal Treatment. The oxaUc acid process for anodising aluminum (67,68) was developed in Japan. OxaUc acid is used as an electrolyte, and the thin aluminum oxide layer forms on the surface of alurninum. The coatings are hard, abrasion- and corrosion-resistant. In addition to oxaUc acid, inorganic oxalate salts are also used in coloring anodic coatings (qv). OxaUc acid is a constituent of cleaners that are used for automotive radiators, boilers, and steel plates before phosphating. Many of its industrial cleaning appHcations are based on its acidity and reducing power which promote dissolution of mst and formation of oxalate coatings on steel (qv). As a chelating agent, oxaUc acid forms water-soluble complexes on metal surfaces during cleaning and rinsing.  [c.462]

Four columns are needed to produce the desired products. Considering the Sharp Distillation Sequencing heuristics, heuristic (/) does not apply, as there is more than one product in this mixture. Fatty acids are moderately corrosive, but none is particularly more so than the others, so heuristic (2) does not apply. The most volatile product, the caproic and capryflc mixture, is a small (10 mol %) fraction of the feed, so heuristic (3) does not apply. The least volatile product, the oleic—stearic acids, is 27% of the feed, but is not nearly as large as the capric—lauric acid product, so heuristic (4) does not apply. The spht between lauric and myristic acids is closest to equimolar (55 45) and is easy. Therefore, by heuristic (5) it should be performed first. The boiling point list implies that the distillate of the first column contains caproic, capryflc, capric, and lauric acids. This stream requires only one further separation, which by heuristic (/) is between the caproic—capryflc acids and capric—lauric acids.  [c.445]

Vitreous siUca is relatively inert to attack from most acids for temperatures up to 100°C. The weight loss data in acid solutions are summarized in Table 3. The main exceptions are phosphoric acid, which causes some corrosion above approximately 150°C, and hydrofluoric acid, which reacts readily at room temperature (91). This latter dissolution proceeds as follows  [c.501]

Sulfur is not considered corrosive to the usual constmction materials. Dry, molten sulfur is handled satisfactorily in mild steel or cast-iron equipment. However, acid-generating impurities, which may be introduced in handling and storage, create corrosive conditions. The exposure of sulfur to moisture and air causes the formation of acids which attack many metals. To combat such corrosion difficulties, protective coatings of organic compounds, cement, or sprayed resistant metals are often appHed to exposed steel surfaces, including pipe and equipment used in handling Hquid sulfur, and to stmctural members that come in contact with soHd sulfur. Also practical in some appHcations is the use of resistant metal alloys, particularly those of aluminum and stainless steel. Naturalization of the generated acids by the addition of basic chemicals is sometimes employed.  [c.117]

Tin is amphoteric and reacts with strong acids and strong bases, but is relatively resistant to nearly neutral solutions. Distihed water has no effect on tin. Oxygen greatly accelerates corrosion in aqueous solutions. In the absence of oxygen, the high over-potential of tin (0.75 V) causes a film of hydrogen to be retained on the surface which retards acid attack. The metal is normally covered with a thin protective oxide film which thickens with increasing temperature.  [c.57]

The acid wash test consists of shaking a mixture of 96% sulfuric acid with benzene and comparing the color of the (lower) acid layer with a set of color standards. Other quaUtative tests include those for SO2 and H2S determination. The copper strip corrosion test indicates the presence of acidic or corrosive sulfur impurities. The test for thiophene is colorimetric.  [c.46]

Hydrogenations can be carried out in batch reactors, in continuous slurry reactors, or in fixed-bed reactors. The material of constmetion is usually 316 L stainless steel because of its better corrosion resistance to fatty acids. The hydrogenation reaction is exothermic and provisions must be made for the effective removal or control of the heat a reduction of one IV per g of C g fatty acid releases 7.1 J (1.7 cal), which raises the temperature 1.58°C. This heat of hydrogenation is used to raise the temperature of the fatty acid to the desired reaction temperature and is maintained with cooling water to control the reaction.  [c.91]

A.cid Soak Cleaners. Benefits ia processiag steel usiag acid soak cleaners iaclude the abdity to both clean and demst ia the same tank. Acid soak cleaners, which are less popular, more expensive, and more corrosive than alkaline cleaners, have found use ia some lines whea platiag oa aluminum alloys and copper alloys. Formulations for acidic soak cleaners have not shown high sod-load capacity, and are used for relatively clean stock. More common formulas are based on phosphoric acid mixtures with surfactants and organic emulsifying agents. Acid soak cleaners for aluminum may contain nitric acid mixtures. Excellent rinsing is required after these to prevent any carryover iato sensitive platiag solutioas.  [c.149]

Acid There are several definitions for acid. The Arrhenius definition is a substance that ionizes in water to product ions. The Bronsted definition is a substance that is a proton (H ) donor. This does not require the substances to be in aqueous (water) solution. The Lewis definition is a substance that can accept a pair of electrons. This does not require a proton or aqueous solution. There are several other definitions as well. An acidic solution is defined as one that has a pH less than 7.0. The following are examples of strong acids, meaning that they completely dissociate into ions and form in aqueous (water) solution. For example HCl - + Cl. All of these will cause severe burns upon skin contact Perchloric acid (HCIO4), Hydroiodic acid (HI), Hydrobromic acid (HBr), Hydrochloric acid (HCl), Sulfuric acid (H2SO4), and Nitric acid (HNO3). Weak acids do not dissociate completely into ions. Examples of these include acetic acid (a 5% solution of acetic acid in water is called vinegar), formic acid, ammonium cation, and water itself. The strength of acids can be measured using the pH scale. The lower the pH, the greater the acidity of a solution. Just because an acid is weak does not mean that it can t be harmful. For example, HF, hydrofluoric acid, is a weak acid. When you spill it on your hand it doesn t burn, but over the course of hours it migrates to the bones in your fingers and then begins to dissolve them from the inside out (a painful process amputation can be required). Some common properties of acids are (1) They have a sour taste. For example, citric acid in lemons and vinegar are both sour (2) They can react with metals such as magnesium, zinc, or iron to corrode them and produce explosive hydrogen gas. Do not store acids in metal containers (3) Solutions of acids can conduct electricity. It is important to know the pH of substances because they may be corrosive or react with incompatible materials. For example, acids and bases should not be stored or used near each other as their accidental combination could generate a huge amount of heat and energy, possibly resulting in an explosion. pH is also important to know in case you spill the material on your skin or eyes. Whenever a substance enters the eye, flush with water for 15 minutes and get prompt medical attention.  [c.515]

Nickel has excellent corrosion-resistance properties. Nickel and nickel alloys are useful in reducing environments and under some oxidising conditions in which a passive oxide film is developed. In general, nickel is very resistant to corrosion in marine and industrial atmospheres, in distilled and natural waters, and in flowing seawater. Nickel has excellent resistance to corrosion by caustic soda and other alkaHes. In nonoxidizing acids, nickel does not readily discharge hydrogen. Hence, nickel has fairly good resistance to sulfuric acid, hydrochloricacid, organic acids, and other acids, but has poor resistance to strongly oxidizing acids such as nitric acid. Nickel has excellent resistance to neutral and alkaline salt solutions. Nonoxidizing acid salts are moderately corrosive, and oxidizing acid salts and oxidizing alkaline salts generally are corrosive to nickel. Nickel also is resistant to corrosion by chlorine, hydrogen chloride, fluorine, and molten salts.  [c.5]

Acid strength depends on the tendency of the acid to dissociate into a hydrogen ion and counter ion. Weak acids, such as carbonic and organics, dissociate only slightly compared to strong mineral acids such as sulfuric, hydrochloric, and nitric. Since dissociation is incomplete in weak acids at a constant pH, more hydrogen ion is available to attack the iron oxide. Hydrogen ions consumed in corrosion cannot be replaced in strong acid solutions since dissociation of these acids is almost complete. In weak acid solutions, however, more hydrogen ions can be produced by dissociation as the hydrogen ions in solution are consumed during corrosion.  [c.160]

Crude oils differ appreciably in their properties according to origin and the ratio of the different components in the mixture. Lighter crudes generally yield more valuable light and middle distillates and are sold at higher prices. Crudes containing a high percent of impurities, such as sulfur compounds, are less desirable than low-sulfur crudes because of their corrosivity and the extra treating cost. Corrosivity of crude oils is a function of many parameters among which are the type of sulfur compounds and their decomposition temperatures, the total acid number, the type of carboxylic and naphthenic acids in the crude and their decomposition temperatures. It was found that naphthenic acids begin to decompose at 600°F. Refinery experience has shown that above 750°F there is no naphthenic acid corrosion. The subject has been reviewed by Kane and Cayard. ° For a refiner, it is necessary to establish certain criteria to relate one crude to another to be able to assess crude quality and choose the best processing scheme. The following are some of the important tests used to determine the properties of crude oils.  [c.19]

Stainless steels are iron-based alloys, which contain at least 11 per cent chromium. Hundreds of grades of stainless steel are available with alloying elements including nickel, molybdenum, manganese and copper. Stainless steels are not electrochemically inert, but are protected by a thin layer of oxide. This passive layer is unstable in oxidizing and reducing environments. If lost completely, the underlying steel corrodes rapidly in corrosive (particularly acidic) environments. Where the oxide is lost locally, pitting, crevice corrosion or stress corrosion cracking can proceed at rates of several millimeters per year. Chemical species including the halide ions assist in the breakdown of the passive film in even mild conditions such as neutral sodium chloride solution. For satisfactory service, stainless steels should be passivated continuously (or intermittently, see Section 53.3.5) with a suitable oxidizing species. The redox potential of an environment is of prime importance in the selection of a stainless steel. In reducing conditions, the protective oxide cannot form, and general corrosion takes place in strongly oxidizing conditions, pitting corrosion is possible.  [c.905]

Less well studied than the effects of the Thiobacilli are corrosion reactions due to the formation of acids from the oxidation of organic materials. These may include the products of microbial attack on protective coatings such as hesssian sacking and bitumen coatings used for iron pipes initiated by the cellulose-decomposing bacteria. Paper and synthetic rubber coatings for insulation cables may also be attacked. Under strongly aerobic conditions CO2 is the end product of the oxidation of the organic material, and lead carbonate has been detected as a corrosion product of lead-coated underground cables. Under semi-anaerobic conditions organic acids accumulate and these may lead to simple acid corrosion or alternatively may accelerate corrosion by chelation of passive layers on metal. Besides bacteria, moulds and yeasts may accumulate organic acids even under aerobic conditions and in some cases may synthesise complex secondary metabolites some of which, although only weakly acid, are powerful chelating agents. These may be of special significance when microbial slimes accumulate on metal surfaces, as relatively high concentrations of potentially corrosive products may be trapped in them, and corrosion pits result. It is possible that massive pitting in aluminium fuel tanks in aircraft may originate in this way .  [c.395]

The salts of the perfluorinated acids are not corrosive, so one is in a better position to discuss toxicity not related to corrosivity. The toxicity of the salts varies depending on the exact stmcture. The ammonium salt of perfluorooctanoic acid is nonirritating to the skin and moderately irritating to the eyes. Its oral toxicity is rated at moderate the LD q is 540 mg per kg of body weight (52). There has been some concern in the past that ammonium perfluorooctanoate was teratogenic. More recent results indicate that it is neither embryotoxic nor teratogenic (52,53). It was not found to be mutagenic in either the Ames assay or one employing Saccharomjces cerevisiae D4 yeast (52). It also did not cause cell transformation in a mammalian cell transformation assay (53). Although ammonium perfluorooctanoate was fed to albino rats for two years, no compound-induced carcinogenicity was found in the study. There were statistically significant compound-related benign testicular tumors (52,53). Prolonged or repeated exposure can cause liver damage which results in jaundice or tenderness of the upper abdomen (53). The dust from the ammonium salts of the perfluorinated acids is irritating to breathe and should only be handled in a weU-ventilated area or preferably a hood.  [c.312]

Reaction with Nitrogen Nucleophiles. The acid-cataly2ed reaction of primary, secondary, and tertiary amines with ethyleneknine yields asymmetrically substituted ethylenediamines (71). Steric effects dominate basicity in the relative reactivity of various amines in the ring-opening reaction with ethyleneknine (72). The use of carbon dioxide as catalyst in the aminoethylation of aUphatic amines, for which a patent appHcation has been filed (73), has two advantages. Fkst, the corrosive salts produced when mineral acids are used as catalysts (74,75) are no longer formed, and second, the reaction proceeds with good yields under atmospheric pressure.  [c.4]

Several different acids can be used for anodizing. Phosphoric acid is employed primarily to produce a very porous film. During the anodizing step, the phosphoric acid attacks the growing anodic film, etching a portion of it away. The resulting film can be used as a paint base or adhesive bonding preparation having exceUent adhesion properties. Chromic acid is used when high corrosion and abrasion resistance is needed. Most aircraft parts receive this type of anodic coating because any residual acid does not corrode the metal. The anodic film has a distinctive dull green color when chromic acid is employed. OxaHc acid is rarely used but produces a very hard, wear-resistant coating. The anodic film has a grayish yeUow color. Some movable aluminum engine parts receive this type of anodizing. SulfophthaHc acid, otherwise known as duranodic or integral coloring, is used to produce a decorative anodic film ranging in color from bronze to black. This process was used extensively from 1950 to 1970 for the color of window and building fascia parts. This process consumes large amounts of electricity, however, and has become too expensive to use. Sulfuric acid is the most widely used acid for anodizing. It produces a hard, clear anodic film which can be subsequently colored using inorganic or organic coloring solutions. Sulfuric acid anodizing is used for both wear-resistant coatings and decorative purposes.  [c.224]

Naphthenic acids are generally obtained by caustic extraction of petroleum distillates boiling between 200 and 370°C. A continuous process has been developed for removing naphthenic acids from refinery streams by caustic washing (22). Caustic extraction also removes other acidic components of the petroleum fraction, including phenol and cresols (cresyhc acid), mercaptans, and thiophenols. In addition to reducing corrosion in the refinery, the caustic wash is necessary to improve the burning quaUties, storage stabiUty, and odor of the finished kerosene and diesel fuels. The petroleum fractions are extracted with dilute (2—10%) sodium hydroxide since the sodium naphthenate salts are emulsifying agents. Stronger caustic strengths increase the solubihty of hydrocarbon oils (unsaponiftables) in the sodium naphthenate. The Fiber-Film contacting process patented by Merichem reduces emulsification and caustic carryover during removal of naphthenic acid from petroleum fractions and achieves low acid number specifications in a single stage (23,24). Noncaustic processes for recovery of naphthenic acids from petroleum distillates, including ammonia (qv) (25), triethylene glycol (26),  [c.510]

The corrosion resistance of niobium and its high electrical conductivity and ductihty make it a valuable stmctural material for chemical and metallurgical appHcations. The heat-transfer coefficient of niobium is more than twice that of titanium and three times higher than zirconium and stainless steels. Niobium is corrosion-resistant to most media, with the exception of hydrofluoric acid and hot concentrated hydrochloric and sulfuric acids. The pickling solution for removal of normal surface oxides is one part nitric acid, one part sulfuric acid, two parts hydrofluoric acid, and four parts water (by volume) (see Metal surface treatments). Niobium also shows good corrosion resistance to sulftdizing atmospheres of low oxygen potential, which maybe used in the production of substitute natural gas from sulfur-containing materials (67). Liquid sodium, potassium, sodium—potassium alloys, or lithium have htfle effect on niobium up to 1000°C, and its resistance to many other Hquid metals is good.  [c.26]

Synthesis. The outline of LCP synthesis has already been discussed nearly aH are made by the acidolysis route. The in situ acetylation polymerization route, which starts from the free hydroxy compounds and carboxyHc acids rather than preformed acetylated monomers, is increasingly used because larger polymer batches can be made in the same reactor vessel. Polymerizations can be mn batchwise or continuously and the volatile acetic acid is removed by distiHation under vacuum in the conventional way. Because of the corrosive nature of this by-product, the reactors must be made of a corrosion-resistant aHoy. Stainless steel is generaHy adequate but some manufacturers prefer to use HasteHoy. Several unique problems arise in LCP polymerization due to the extreme shear sensitivity of the LCP melt. One concerns agitator design it is possible under certain circumstances for the whole batch to revolve with the agitator shaft as a quasi-soHdlump, due to the high rate of shear thinning at the waHs of the reactor. Under such conditions no  [c.306]

The reaction of aniline with formaldehyde can be carried out in a single reactor (Fig. 2). However, most commercial processes probably use multiple reactors, which provide greater control of the MDA isomer distribution and oligomeric content of the final product (17—20). Use of hydrochloric acid and high reaction temperatures necessitates the use of corrosion resistant metallurgy. Normally the acid is first mixed with excess aniline, which causes an exotherm. Formaldehyde is then added, with efficient agitation and at low temperatures (<50°C), to the aniline—aniline hydrochloride solution. The reaction is usually staged to control the condensation and rearrangement steps. The final reaction temperatures are normally 80—120°C. After completion of reaction, the acidic PMDA is treated with aqueous sodium hydroxide to neutrali2e the excess acid. A large amount of salt is formed during this step thus the plants must be located near an oudet capable of handling the generated salt water (normally a seacoast). Processes that recycle the acid and eliminate the salt disposal problem have been patented (21,22). The organic layer is then washed with water and stripped to remove unreacted aniline and water. The unreacted aniline is recycled back to the beginning of the reaction. The product may be purified to isolate pure 4,4 -MDA, packaged for shipment, or treated with phosgene to produce the corresponding isocyanate. The 4,4 -MDA is normally sold in flaked or granular form in lined steel dmms. Depending on the MDA content, PMDA is sold as a waxy soHd or a yellow to brown viscous supercooled Hquid in steel dmms.  [c.249]

A Hquid-phase variation of the direct hydration was developed by Tokuyama Soda (78). The disadvantages of the gas-phase processes are largely avoided by employing a weakly acidic aqueous catalyst solution of a siHcotungstate (82). Preheated propylene, water, and recycled aqueous catalyst solution are pressurized and fed into a reaction chamber where they react in the Hquid state at 270°C and 20.3 MPa (200 atm) and form aqueous isopropyl alcohol. Propylene conversions of 60—70% per pass are obtained, and selectivity to isopropyl alcohol is 98—99 mol % of converted propylene. The catalyst is recycled and requites Htde replenishment compared to other processes. Corrosion and environmental problems are also minimized because the catalyst is a weak acid and because the system is completely closed. On account of the low gas recycle ratio, regular commercial propylene of 95% purity can be used as feedstock.  [c.109]

Many of these chemicals ate recovered as by-products of the pulping operation, eg, taU oU (qv) and turpentine (see Terpenoids). Some cause problems in pulping or bleaching, eg, the heartwood phenols react with lignin during acid sulfite pulping mote rapidly than the pulping chemicals do and inhibit the lignin solubilization reaction. Condensed lignins and phenoHcs ate dark or form colored salts with metal ions. These compounds ate not easily bleached and consume excess bleaching chemical. In alkaline pulping, the fatty acids and their glycerides form sodium soaps, thereby causing foam problems that reduce washing and evaporator efficiency (see Soap). Western ted cedar contains a group of tropolones, eg, thujic acid (5,5-dimethyl-1,3,6-cyc1oheptatriene-1-carboxylic acid), which necessitates the use of special corrosion-resistant alloys in the digester. High rosin-containing species, eg, pine, cause problems in the production of mechanical pulps such as gtoundwood and thermomechanical pulps owing to the tacky nature of the rosin. Such materials cause problems during paper production and form impurities in paper products.  [c.248]

Continuous high pressure splitting was developed by Colgate-Emery and by Procter Gamble (6,7). Temperatures of 240—270°C are preferred, giving pressures of 4.8—5.2 MPa (700—750 psig). The splitting is carried out in a cylindrical-shaped tower, 18.3—24.4 m high and 0.51—1.22 m in diameter of 316 L stainless steel or 316 L cladding on carbon steel. Splitting coconut oil requires better corrosion resistance because of the shorter-chain fatty acids present. Corrosion-resistant linings such as Carpenter 20 Cb or Incoloy 825 can be utili2ed. The tower is operated with countercurrent flow, with water being introduced into the top part of the tower and fat at the bottom of the tower. The tower contains disengaging 2ones where fatty acids are collected at the top of the tower and aqueous glycerol (sweet water) at the bottom (Fig. 1). Heat is conserved by the use of heat exchangers that cool the existing fatty acid while heating the incoming water (steam) the exiting sweet water is cooled by the entering fat, which in turn is heated in the exchanger. Make-up heat is apphed to the center of the tower (the hydrolysis section containing the continuous fat phase) using internal steam coils, electric heating, or direct superheated steam. The pressure in the tower is controlled by a backpressure valve in the fatty acid discharge line, whereas the fat/sweet water interface is controlled by the rate of sweet water discharged. About 98—98.5% spHt is usually obtained. The sweet water contains 10—15% glycerol and is purified in a series of steps involving removal of any dissolved salts, fat, and oil impurities, and then concentration by evaporation of water and/or distillation (8). In some continuous high pressure splitting units, approximately 0.05% of ZnO catalyst is used to speed the reaction rates and raise conversion to >99.0%.  [c.90]

Chloramines and bromamines react with moisture releasing potentially corrosive, toxic, and explosive gases and should be stored under dry conditions at moderate temperatures, segregated from incompatible materials. Since they are highly reactive they should not be mixed with other materials such as acids, bases, reducing agents, oxidizing agents, organic compounds, ammonium compounds, etc, since vigorous reactions can occur, accompanied by fire and even explosions, Hberating large amounts of heat and potentially toxic gases. A/-Halamines are irritating to the skin, eyes, and mucous membranes. However, they are nonirritating under use conditions in dilute aqueous solution. Acute oral toxicities, LD q (mg/kg, rat) are TCCA 490, SDCC 735, and BCDMH 600 (184). Residual cyanuric acid from use of chloroisocyanurates has low toxicity. Monochloramine has been shown to be a weak mutagen and its use in drinking water is under review by the EPA (33,185).  [c.459]

Starch (qv) and cellulose (qv) are both polymers of glucose, but cellulose is much more difficult to hydrolyze to the sugar. Its stmcture is more crystalline which protects the internal bonds from hydrolysis, and cellulose in plants is protected by lignin (qv), a polyphenoHc material that forms a seal around the cellulose for further protection against hydrolysis (210). CeUulosic wastes also contain substantial amounts of hemiceUulose (qv), which is a polymer of pentoses. The aqueous mineral acids used to hydrolyze the ceUulose to glucose destroy much of the sugars, particularly the pentoses, in the process. Nevertheless, a 1978 study claimed that forests could theoreticaUy provide 50% of the oil and gas used by U.S. utUities, replacing 20% of annual fossil fuel consumption (211). None of this has taken place, but research has continued. A new process utilizing low temperature hydrolysis to separate ceUulose from paper has been Ucensed, with plans to constmct a plant in Germany (212). The process uses electro dialysis rather than diffusion dialysis to recover hydrochloric acid for reuse. Other new ways of reducing the cost of converting ceUulosic wastes from wood, newspapers, and municipal garbage into glucose include the use of less corrosive acids and reduced hydrolysis time. One way of making ceUulose wastes more susceptible to hydrolysis is by subjecting them to a short burst of high energy electron beam radiation (213). Hydropulping of ceUulose feedstocks foUowed by a 10 ]ls burst from a 3 X 10 -eV electron-beam accelerator is claimed to reduce the time of hydrolysis by dilute acid from hours to seconds.  [c.409]

Eh values less than 6 will tend to be corrosive as a result of the excess ydrogen ions. On the other hand, raising the pH above 9 will cause some of the metal ions to precipitate as carbonates or as hydroxides at higher pH levels. Alkahnity is important in keeping pH values at the right levels. Bicarbonate alkahnity is the primaiy buffer in waste-waters. It is important to have adequate alkahnity to neutrahze the acid waste components as well as those formed by partial metabolism of organics. Many neutral organics such as carbohydrates, aldehydes, ketones, and alcohols are biodegraded through organic acids which must be neutralized by the available alkahnity. If alkalinity is inadequate, sodium carbonate is a better form to add than hme. Lime tends to be hard to control accurately and results in high pH levels and precipitation of the calcium which forms part of the kahnitv. In a few instances, sodium bicarbonate may be the best source of alkahnity.  [c.2212]


See pages that mention the term Acid corrosion weak acids : [c.2789]    [c.51]    [c.289]    [c.321]    [c.362]    [c.45]   
The Nalco Guide to Cooling Water System Failure Analysis (1993) -- [ c.170 ]