Xanthan for

Several new exopolysaccharides such as welan and rhamsan produced by Alcaltngettes spp may supercede xanthan for some industrial applications. These are based on the same repeat tetrasaccharide backbone of glucose, glucuronic acid, glucose and rhamnose but differ in the substituents rhamsan has a disaccharide side chain and welan a monosaccharide. Both are stable at high temperature and have excellent pseudoplastic properties. 

Your company, a major oil producer, is concerned about the rapid decline in productivity of its Canyon Reef Reservoir in Kent County, Texas. Your Oil Production Department, which holds some patents on producing xanthan biopolymers, is considering forming a joint venture with a food company for developing and operating a fermentation facility to produce the 20 million annual pounds of polymer needed captively for a polymer flood of Canyon Reef Merchant sales of xanthan for food uses by the partner would also be considered if economically desirable. 

Management has asked you to determine whether xanthan might be produced at a sufficiently low price to make the proposed EOR operation competitive with the importation of foreign crudes over the next decade. Your Senior Vice President has also asked whether selling xanthan for current food uses would help to launch the new business at an earlier date than that compatible with EOR market economics. 

Philips, J.C., J.W. Miller, W.C. Wemau, B E. Tate, and M.H. Auerbach, A New High-Pyruvate Xanthan for Enhanced Oil Recovery, Society of Petroleum Engineers, SPENo. 10617 (1982). 

Addition to purified and diluted solutions of xanthan. For this study, it was necessary to prepare a non-aggregated xanthan solution which was obtained by extensive ultrafiltration of a commercial xanthan sample which was initially non-aggregated. The absence of aggregation was confirmed by the Huggins constant which was 0.4 and the intrinsic viscosity which was 6.7 m kg. This corresponds to a molecular weight of 4.8x10 daltons. This xanthan solution was adjusted at a polymer concentration of 0.4 g.l"l in a protein-rich solution such as com steep liquor (CSL). Before use, the com steep solution was centrifuged and only the clear supernatant was added to the xanthan solution. The solvent was 0.1 M sodium chloride and the ratio of protein to xanthan was 10% (w/w). 

In order to model polymer transport phenomena of this type, where polydispersity effects are important, it is not adequate to consider the polymer as a single component of concentration, c, as has been done so far in this chapter. The polymer itself is made up of many components which are different only in their size (although the Mark-Houwink parameters that apply for the polymer will be esentially the same for each of the polymer subcomponents). Thus it is necessary to use a multicomponent representation of the polymer molecular weight distribution in order to model the polymer behaviour adequately in such experiments. Brown and Sorbie (1989) have adopted this approach in order to model the Chauveteau-Lecourtier results quantitatively. They used a multicomponent representation of the MWD based on a Wesslau distribution function (Rodriguez, 1983, p. 134) with 26 discrete fractions being used to represent the xanthan. For this case, a set of convection-dispersion equations including dispersion and surface exclusion... 

Concentrations above 0.3% form a gel with borate which is reversible upon the subsequent addition of mannitol (a sequestrant for borate) or of acid. Usefiil combinations are formed with carrageenan (63) and xanthan gum (64) and agar. In many appHcations, it is used in combination with these gums at considerable cost savings. 

Xanthan gum dissolves in acids and bases, and under certain conditions, the viscosity remains stable for several months. Xanthan gum has exceUent StabiHty and compatibUity with high concentrations of many salts, eg, 15% solutions of sodium chloride and 25% solutions of calcium chloride (79). 

Uses. The unique properties of xanthan gum make it suitable for many appHcations for the food, pharmaceutical, and agricultural industries (79). 

Welan has similar properties to xanthan gum except that it has increased viscosity at low shear rates and improved thermal stabiUty and compatibihty with calcium at alkaline pH (90). The increased thermal stabiUty has led to its use as a drilling mud viscosifter especially for high temperature weUs. The excellent compatibihty with calcium at high pH has resulted in its use in a variety of specialized cement and concrete appHcations. 

Applications. The high heat tolerance and good salt compatibiUty of welan gum indicate its potential for use as an additive in several aspects of oil and natural gas recovery. Welan also has suspension properties superior to xanthan gum, which is desirable in oil-field drilling operations and hydraulic fracturing projects. It is compatible with ethylene glycol, and a welan—ethylene glycol composition that forms a viscous material useful in the formulation of insulating materials has been described (244). 

Xanthan gum [11138-66-2] is an anionic heteropolysaccharide produced by several species of bacteria in the genus Aanthomonas A. campestris NRRL B-1459 produces the biopolymer with the most desirable physical properties and is used for commercial production of xanthan gum (see Gums). This strain was identified in the 1950s as part of a program to develop microbial polysaccharides derived from fermentations utilizing com sugar (333,334). The primary... 

Low molecular weight (1000—5000) polyacrylates and copolymers of acryflc acid and AMPS are used as dispersants for weighted water-base muds (64). These materials, 40—50% of which is the active polymer, are usually provided in a Hquid form. They are particularly useful where high temperatures are encountered or in muds, which derive most of their viscosity from fine drill soHds, and polymers such as xanthan gum and polyacrylamide. Another high temperature polymer, a sulfonated styrene maleic—anhydride copolymer, is provided in powdered form (65,66). AH of these materials are used in relatively low (ca 0.2—0.7 kg/m (0.5—2 lb /bbl)) concentrations in the mud. 

For products intended to remain stable dispersions for an extended period, a particle size of 2 p.m or less is desirable. A thickening agent is usuaUy added after the reaction has been completed and the mixture is cooled in order to prevent settling and agglomeration. Examples of thickeners are guar gum, xanthan gum, and hydroxyethylceUulose. The final products are generaUy between 40 and 50% soUds, with a viscosity of 1500 5000 mPa-s(=cP). 

Microcrystalline ceUuloses ate marketed under the trade name Avicel. The physical characteristics of microcrystalline ceUuloses differ markedly from those of the original ceUulose. The ftee-flowiag powders have particle sizes as smaU as 0.2—10 p.m. Avicel ceUuloses coated with xanthan gum, guar gum, or carboxy-methylceUulose to modify and stabilize their properties are also available. The Avicel products are promoted for use ia low calorie whipped toppiags andiciags andia fat-reduced salad dressiags and frozen desserts (see Fat substitutes). 

Bacterial Cellulose. Development of a new strain of Acetobacter may lead to economical production of another novel ceUulose. CeUulon fiber has a very fine fiber diameter and therefore a much larger surface area, which makes it physicaUy distinct from wood ceUulose. Its physical properties mote closely resemble those of the microcrystalline ceUuloses thus it feels smooth ia the mouth, has a high water-binding capacity, and provides viscous aqueous dispersions at low concentration. It iateracts synergisticaUy with xanthan and CMC for enhanced viscosity and stabUity. 

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