Acid number

The acid number is a measure of the acidity of a product and is used as a guide in the quality control of resid or asphalt properties. Since a variety of oxidation products contribute to the acid number, and the organic acids vary widely in service properties, so the test is not sufficiently accurate to predict the precise behavior of asphalt in service. 

The saponification number expresses the amount of base that will react with 1 g of a sample when heated in a specific manner. Since certain elements are sometimes added to asphalt and also consume alkali and acids, the results obtained indicate the effect of these extraneous materials in addition to the saponifiable material present. In the test method (ASTM D94 IP 136), a known weight of the sample is dissolved in methyl ethyl ketone or a mixture of suitable solvents, and the mixture is heated with a known amount of standard alcoholic potassium hydroxide for between 30 and 90 minutes at 80°C (176°F). The excess alkali is titrated with standard hydrochloric acid and the saponification number is calculated. 

The acid number is defined as the number of milligrams of potassium hydroxide required to neutralize the acid groups present in 1 g of the polyol. It is determined by dissolving the sample in a 1 1 mixture of benzene and alcohol and titrating this solution with standard alcoholic potassium hydroxide using phenolphthalein as indicator. A blank titration is also run using no polyol. 

Vi = volume (in ml) of potassium hydroxide solution required for titration of sample  

Note polyols for the production of solid polyurethane elastomers should have acid numbers less than 3. 

About 40 g sample is weighed into a 250 ml Erlenmeyer flask. 50 ml of acid number solvent is added by dispensing burette, stirring using a magnetic stirrer until the sample is completely in solution. Five drops of phenolphthalein indicator are added and the solution titrated with OTn alcoholic KOH to the first faint-pink end-point. A blank is determined in the same way, omitting the sample. 

To conclude, the common physico-chemical characteristics of oligo-polyols for polyurethanes determined by standard analytical methods are hydroxyl number, hydroxyl percentage, primary hydroxyl content, molecular weight, equivalent weight, molecular weight distribution, viscosity, specific gravity, acidity and colour (See Chapters 3.1-3.11). 

Of course, some oligo-polyols have specific and particular characteristics and these special characteristics will be presented in detail for each group of oligo-polyol. For example  

Summarising, no matter what their chemical structure, oligo-polyols have some general and common characteristics such as  

As was mentioned previously, for practical reasons, the oligo-polyols are divided in the present book into two important groups oligo-polyols for elastic polyurethanes and oligo-polyols for rigid polyurethanes. 

The main oligo-polyol types described in detail in the present book are presented in 

45 g (0.06 mol) of adipic acid, 21.3 g (0.075 mol) of oleic acid, 22 g (0.15 mol) of phthalic anhydride, and 52.5 g (0.39 mol) of anhydrous 1,1,1-tris-(hydroxymethyl)pro-pane are placed into the apparatus as described under a) and the air is displaced by evacuation and filling with nitrogen.The mixture is slowly heated under a stream of ni-trogen at 120 °C the contents of the flask have melted and the stirrer can be started. The internal temperature is raised to 190 °C over a period of 2 h as soon as the temperature at the top of the column drops below 70 °C,the pump is attached and the apparatus slowly evacuated to 40 torr over the course of 2 h. At this pressure and an internal temperature of 190 °C,the mixture is stirred for a further 8 h.The pump is then switched off and the product allowed to cool under nitrogen.The highly branched polyester, which remains as a viscous liquid, has an acid number of 2 and an OH number of 350 it can be used directly for the preparation of a rigid polyurethane foam (see Example 5-29). Addition of 5 ppm SnClj as catalyst reduces the reaction time by 10%. 

1-2 g of the polyester are dissolved by warming with 50 ml of acetone and, after cooling, are titrated as quickly as possible with 0.1 M alcoholic potassium hydroxide using phenolphthalein as indicator, until the red color remains for a second.The alkali requirement of the solvent is determined in a blank experimentThe acid number is given by the weight of KOH in mg, required to neutralize 1 g of substance  

Twenty-five grams of a plasticizer is placed in 125 ml Erlenmeyer flask and 50 ml alcohol is added to dissolve the sample If the sample is not completely soluble, 50 ml of equal amounts of alcohol and acetone are used. This sample is titrated with 0.0 IN NaOH or KOH in the presence of bromothymol blue used as an indicator. 

ISO standard uses a similar method of titration but phenolphthalein is used as an indicator and 0.1 N NaOH is used as a titrating agent. The results are expressed as acidity, which is a percentage of phthalic acid. 

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Fig. 3. Fluman LH, FSH, and TSH a suburnt [69431-84-1]. Amino acid numbering is relative to maximum homology between species (48). Note the 4 amino acid deletion in human a suburnt between positions 6 and 9. Consensus glycosylation sites are at Asn-56 and 82. GHO = carbohydrate chain.

Fig. 2. Piimaiy structure of bPRL, bPL, oPL, and bGH. Amino acid numbers are relative to maximum homology among hormones (12).

Naphthenic acid corrosion has been a problem ia petroleum-refining operations siace the early 1900s. Naphthenic acid corrosion data have been reported for various materials of constmction (16), and correlations have been found relating corrosion rates to temperature and total acid number (17). Refineries processing highly naphthenic cmdes must use steel alloys 316 stainless steel [11107-04-3] is the material of choice. Conversely, naphthenic acid derivatives find use as corrosion inhibitors ia oil-weU and petroleum refinery appHcations. 

Naphthenic acids occur ia a wide boiling range of cmde oil fractions, with acid content increa sing with boiling point to a maximum ia the gas oil fraction (ca 325°C). Jet fuel, kerosene, and diesel fractions are the source of most commercial naphthenic acid. The acid number of the naphthenic acids decreases as heavier petroleum fractions are isolated, ranging from 255 mg KOH/g for acids recovered from kerosene and 170 from diesel, to 108 from heavy fuel oil (19). The amount of unsaturation as indicated by iodine number also increases in the high molecular weight acids recovered from heavier distillation cuts. 

Analytical and Test Methods. The acid number of terephthahc acid discussed above is a titration of a sample dissolved in pyridine, using a sodium or potassium hydroxide titrant. However, specifications on certain impurities are so strict that this test caimot, as a practical matter, be failed. Its use has been discontinued by some manufacturers. 

Phthahc resins are usually processed to an acid number of 25—35, yielding a polymer with an average of 1800—2000. The solution viscosity of the polymer is usually followed to ascertain the polymer end point. The resin is cooled to 150°C and hydroquinone stabilizer (150 ppm) is added to prevent premature gelation during the subsequent blending process with styrene at 80°C. The final polymer solution is cooled to 25°C before a final quaUty check and dmmming out for shipment. 

The tendency of aliphatic ethers toward oxidation requires the use of antioxidants such as hindered phenoHcs (eg, BHT), secondary aromatic amines, and phosphites. This is especially tme in polyether polyols used in making polyurethanes (PUR) because they may become discolored and the increase in acid number affects PUR production. The antioxidants also reduce oxidation during PUR production where the temperature could reach 230°C. A number of new antioxidant products and combinations have become available (115,120,124—139) (see Antioxidants). 

Acidic contaminants are poisonous to the alcoholysis catalysts and must be avoided. If the oil has a high acid number, or there are high acidity residues left in the reactor from the previous batch, such as sublimed phthaUc anhydride condensed under the dome of the reactor, the reaction can be severely retarded. A longer batch time or additional amount of catalyst is then required. Both are undesirable. 

Process Control. The progress of the alkyd reaction is usually monitored by periodical deterrninations of the acid number and the solution viscosity of samples taken from the reactor. The frequency of sampling is commonly every half-hour. Deterrnined values are plotted against time on semi-1 ogarithmic coordinates, as shown in Figure 4. 

Rosin is compatible with many materials because of its polar functionaUty, cycloaUphatic stmcture, and its low molecular weight. It has an acid number of ca 165 and a saponification number of ca 170. It is soluble in aUphatic, aromatic, and chlorinated hydrocarbons, as well as esters and ethers. Because of its solubiUty and compatibiUty characteristics, it is useful for modifying the properties of many polymers. 

IManila Copal. The Manilas are collected in Indonesia and the Philippines. They are soluble in alcohols and ketones, and insoluble in hydrocarbons and esters. The resins soften between 81—90°C and have acid numbers of 110—141. Principal uses are in coatings and varnishes. 

Pontia.na.k. This resin is a copal and is similar to the alcohol-soluble Manilas. It is partially fossilized, so it melts at a higher temperature. Softening points range from 99—135°C, and acid numbers from about 112—120. Pontianak [9000-14-0] is used in specialty coatings and adhesives. 

East India. Resins. The East India resins are related to the dammars, although they are older and harder. They are not obtained by tapping trees, but are collected where they are found, principally in Indonesia. Because they are semifossil resins, their softening points are high, ranging from about 110—130°C. The East India resins [9000-16-2] have low (20—30) acid numbers. They are soluble only in aryl hydrocarbons and hydrogenated aUphatic hydrocarbons, and are used primarily in coatings. 

Gum Elemi. This resin, tapped from trees in the Philippines, contains a higher concentration of essential oils than other natural resins. It is a soft, sticky, plastic material that can be deformed manually. Gum elemi [9000-75-3] contains 20—25% essential oils, 13—19% acids, 30—35% resenes (condensed decarboxylated resin acids), and 20—25% terpenic resinols (condensed terpene alcohols). It has an acid number of 20—35 and a saponification number of 20—40. Gum elemi is a film-forming plasticizing resin used in lacquers. 

Sandarac. This resin, which originates in Morocco, is a polar, acidic, hard resin with a softening point of 100—130°C, an acid number of 117—155, and a saponification number of 145—157. Sandarac [9000-57-1] is soluble in alcohols and insoluble in aryl and aUphatic hydrocarbons. It is used in varnishes and lacquers for coating paper, wood, and metal. 

Mastic. Most commercial mastic [61789-92-2] is collected on the Greek island of Chios, near the Turkish coast. It is a soft resin with a softening point of 55°C. It has an acid number of 50—70 and a saponification number of 62—90. It is soluble in alcohols and aryl hydrocarbons. Mastic is used in wood coatings, lacquers, adhesives, and printing inks. 

Composition. Shellac is primarily a mixture of aUphatic polyhydroxy acids in the form of lactones and esters. It has an acid number of ca 70, a saponification number of ca 230, a hydroxyl number of ca 260, and an iodine number of ca 15. Its average molecular weight is ca 1000. Shellac is a complex mixture, but some of its constituents have been identified. Aleuritic acid, an optically inactive 9,10,16-trihydroxypalmitic acid, has been isolated by saponification. Related carboxyflc acids such as 16-hydroxy- and 9,10-dihydroxypalmitic acids, also have been identified after saponification. These acids may not be primary products of hydrolysis, but may have been produced by the treatment. Studies show that shellac contains carboxyflc acids with long methylene chains, unsaturated esters, probably an aliphatic aldehyde, a saturated aliphatic ester, a primary alcohol, and isolated or unconjugated double bonds. 

A second field evaluation of the ASP process has been initiated in Wyoming. Additionally, an ASP field project has been designed for the Peoples Repubhc of China. The appHcability of the ASP process to a variety of reservoirs has yet to be fully determined. AppHcation of alkali and alkali polymer flooding has been limited to cmde oils having discernible acid numbers, wherein the alkali produced cmde oil soaps which in combination with alkali resulted in providing low interfacial tensions. The ASP process appears to be suitable for cmde oils with nil acid numbers (177), and hence should have broad apphcabdity. 

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