Succinoglycan - American Chemical Society

Chapter 8

Succinoglycan A New Biopolymer for the Oil Field 1

Downloaded by EMORY UNIV on August 12, 2015 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch008

Anthony J. Clarke-Sturman, Dirk den Ottelander, and Phillip L. Sturla Shell Research Ltd., Sittingbourne Research Centre, Sittingbourne, Kent, ME9 8AG, United Kingdom

Succinoglycan, a microbially produced polysaccharide with an eight sugar repeating unit, has s i m i l a r properties to xanthan, and has been successfully used i n well completion f l u i d s i n the North Sea, where an apparently unique property -- p a r t i a l l y reversible v i s c o s i t y collapse, at a temperature, Tm, determined by the brine composition, was considered advantageous. This v i s c o s i t y collapse i s associated with a structural order-disorder t r a n s i t i o n , which i n sea water occurs at around 75°C. (A similar t r a n s i t i o n , normally at a higher temperature, occurs i n xanthan.) In calcium bromide brines, the Tm values of both succinoglycan and xanthan fall, leading to v i s c o s i t y loss as both biopolymers are more r e a d i l y degraded i n the disordered state. S t a b i l i t y of both biopolymers can be improved by using brines based on potassium formate rather than calcium halides.

The o i l price r i s e s i n the 1970s stimulated interest i n Enhanced O i l Recovery (EOR), and f a i r l y rapidly the biopolymer xanthan, the e x t r a c e l l u l a r polysaccharide from the bacterium Xanthomonas campestris. an organism which normally resides on cabbage leaves, was i d e n t i f i e d as a leading contender as a v i s c o s i f i e r f o r polymer enhanced water flooding. Xanthan, used i n EOR t r i a l s i n the USA, and s t i l l being considered elsewhere, has found a niche i n d r i l l i n g f l u i d s , which, together with other o i l f i e l d uses, accounts for some 2000 tons per year. Xanthan solutions have several useful properties; they display a highly pseudoplastic rheology, are tolerant to s a l t , and have good thermal s t a b i l i t y . There was we f e l t , however, some scope f o r improvement. Current address: Shell International Petroleum Company, PAC/31, Shell Centre, London, SE1 7NA, United Kingdom 0097-6156/89A)396-0157$06.00A) © 1989 American Chemical Society In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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"Shell" and Biotechnology. Xanthan is manufactured by fermentation, a biotechnological process. How could "Shell", an o i l company, be interested i n such processes? The Royal Dutch/Shell Group i s , however, no newcomer to biotechnology. The Milstead Laboratory of Chemical Enzymology was set up i n 1962 and was headed by Professor John Cornforth, who went on to win the 1975 Nobel p r i z e for Chemistry shortly after he r e t i r e d . In 1970 a fermentation laboratory was b u i l t on the same s i t e . The f i r s t large scale process studied was the conversion of natural gas to 'single c e l l p r o t e i n for animal feed. Although technically successful, the project was f i n a l l y defeated by a combination of high o i l , (and gas), prices and cheap soya beans. It did, however, leave us with a strong background i n fermentation technology and microbial physiology. Work on the fermentation of microbial polysaccharides started i n the mid 1970's, with the aim of producing improved polymers. Many thousands of samples were screened for microorganisms which produced viscous polymers. Out of over 2000 such 'slime producing* organisms i s o l a t e d , only one, i d e n t i f i e d as a Pseudomonas species, now NCIB 11592, seemed to produce a polymer with interesting new properties.


1

Succinoglycan. I n i t i a l l y i d e n t i f i e d advantages of this polymer, succinoglycan, were that aqueous solutions of i t were more viscous than solutions containing an equal concentrations of xanthan, and that the polymer tolerated higher concentrations of s a l t , i n the sense that solutions passed more r e a d i l y through microporous f i l t e r s . These properties made the polymer of potential interest for EOR. An interesting c h a r a c t e r i s t i c , however, was that at a p a r t i c u l a r temperature, often around 70 C i n sea water for example, the v i s c o s i t y would collapse, to be p a r t i a l l y recovered on cooling. Experimental Polysaccharides. Many strains of bacteria produce succinoglycan (1). The Rhizobia. p a r t i c u l a r l y , grow very slowly, and the rate of polymer production i s low. Much effort was spent obtaining a s t r a i n which produced succinoglycan at a high rate and of good quality (2.3). An organism was selected and a fermentation process developed at laboratory scale. The process has been scaled up successfully and operated at 220 cubic metre scale. Succinoglycan i s now available commercially, i n Europe, under the trademark S h e l l f l o - S and as i t is a concentrated solution rather than a powder, i t readily disperses i n brines commonly used i n the oilfield. Shellflo-XA, a proprietary grade of xanthan and cellobond X-100 a hydroxyethylcellulose (HEC) were used for comparative purposes. Chemical analysis. Succinoglycan, p u r i f i e d by m i c r o - f i l t r a t i o n and d i a l y s i s , was hydrolysed i n 0.5M sulphuric acid at a concentration of approximately 5mg/ml for 16 hours at 95°C. Sugars and acids were determined by HPLC using Biorad HPX-87 columns. No pretreatment was required for acids analysis - detection was by measurement of UV

In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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CLARKE-STURMANETAL.

Succinoglycan

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absorption at 206nm. Sugars analysis required the n e u t r a l i z a t i o n of the solution with barium carbonate - detection was by r e f r a c t i v e index measurement. T y p i c a l l y over 95% of the carbon i n the o r i g i n a l sample, which was determined by microanalysis, was recovered i n the sugars and acids. Hakomori methylation analysis, and preparation and GLC^gf the PAAN derivatives (4), were used to determine the linkages. C NMR of p a r t i a l l y hydrolysed samples confirmed the octasaccharide repeat u n i t , the beta linkages and the presence of the carboxylic acids. Rheological measurements. Routine v i s c o s i t y measurements were made with a Wells-Brookfield micro-cone and plate viscometer, or a Brookfield LVT(D) viscometer with UL adapter. Viscosity-temperature p r o f i l e s were obtained using the l a t t e r coupled v i a an insulated heating jacket to a Haake F3C c i r c u l a t o r and PG100 temperature programmer or microcomputer and suitable interface. Signals from the viscometer and a suitably placed thermocouple were recorded on an X-Y recorder, or captured d i r e c t l y by an HP laboratory data system. A number of other viscometers were also used, including Haake CV100 and RV3 models. The l a t t e r was coupled with a D40/300 measuring head and o i l bath c i r c u l a t o r for measurements above 100 C. Back pressures up to 4 bar were used and measurements made up to about 160°C. Hydrolysis rate measurements. Hydrolysis rates were examined by mixing polymer solutions with hydrochloric a c i d , i n apparatus previously described (5). Solutions of polymer and acid are mixed r a p i d l y , and the torque on a rotating PTFE coated fork, attached to a Brookfield LVTD viscometer, recorded as a function of time. Decreases i n v i s c o s i t y were approximated to f i r s t - o r d e r , and h a l f - l i v e s for v i s c o s i t y loss calculated. Results and Discussion Composition and Structure. Chemical analysis of the polymer from our f i r s t s t r a i n (NCIB 11592) indicated that i t was a polysaccharide containing the sugars, glucose and galactose, and the carboxylic acids - - succinic and pyruvic - - i n the approximate r a t i o s 7:1:1:1. A s i m i l a r polymer had been discovered some years e a r l i e r by Harada and h i s coworkers i n Japan (6), produced by an organism which grew on ethylene glycol as sole carbon source. Almost simultaneous with our discoveries (2), the structure of succinoglycan, as the polymer was c a l l e d , was published (7) (Figure 1). Like a l l polymers, succinoglycan, i s not a single polymer but a family. Succinoglycan i s the e x t r a c e l l u l a r water-soluble polysaccharide produced by a number of Agrobacterium. Rhizobium. and related species of s o i l b a c t e r i a . A l l have octasaccharide repeating units (Figure 1) with tetra-glucose units i n side chains attached to tetrasaccharide main-chain repeating u n i t s , each containing a single galactose sugar. Pyruvic acid is bound as pyruvate k e t a l on the terminus of each side chain, and succinic acid i s bound as mono-ester, at an unknown position or positions, as are acetate groups which are found i n some s t r a i n s .


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We have examined succinoglycans from a number of bacteria. The polymers from d i f f e r e n t organisms have d i f f e r e n t proportions of acid substituents (Table 1). They also have s l i g h t l y d i f f e r e n t physical properties, p a r t i c u l a r l y v i s c o s i t y (Figure 2). In some cases i t may be useful to select a polymer with p a r t i c u l a r c h a r a c t e r i s t i c s .


Rheology. The v i s c o s i t y of d i l u t e solutions r i s e s rapidly with concentration (Figure 3). The rheology i s , of course, pseudoplastic: the apparent v i s c o s i t y f a l l s with increasing shear rate. The v i s c o s i t y of concentrated solutions, the commercial product for example, i s , however, lower than might be expected from extrapolation of low concentration data. This i s because, i n common with many s t i f f or r i g i d molecules such as surfactants, a l i q u i d c r y s t a l l i n e phase i s present. In succinoglycan the mesophase appears at concentrations greater than about 0.5 per cent w/v. Comparison of Xanthan and Succinoglycan. The physical properties of succinoglycan and i t s solutions are similar to those of xanthan. Both polysaccharide molecules are r e l a t i v e l y s t i f f , s t i f f e r even than simple c e l l u l o s i c s such as HEC, and have a molecular masses i n excess of two m i l l i o n . Recent work by Rinaudo and coworkers (Personal communication) and Crecenzi and colleagues (Int. J . B i o l . Macromol., submitted) has shown that succinoglycan molecules are also s t i f f e r than those of xanthan. This greater s t i f f n e s s i s one reason why solutions of succinoglycan are more viscous than xanthan solutions of equal concentration. The s t i f f e r the molecule, for a given molecular length, the larger the volume of solution that i s swept out as the molecules rotate, and the greater the interaction with neighbouring polymer molecules. Such interactions begin to occur at quite low concentrations, much less than 1 g/1. I f the interactions are ' s t i c k y , that i s , there i s a long contact time, entanglement can occur leading to higher v i s c o s i t i e s and ultimately a gel. Entanglement and weak gel formation are c h a r a c t e r i s t i c of some o i l f i e l d polysaccharides such as guar and starch, but are present only weakly, i f at a l l , i n both xanthan and succinoglycan solutions. Solutions of xanthan and succinoglycan are thus able to pass through porous media such as rock, while guar and starch cannot because of t h e i r g e l - l i k e nature. Hence the d i f f e r e n t uses of these polymers i n the o i l f i e l d . 1

Order-disorder Transition. In common with xanthan, succinoglycan exhibits an order-disorder t r a n s i t i o n , which i n xanthan has been characterized by a number of techniques, including o p t i c a l rotation and birefringence measurements (8). V i s c o s i t y measurements, as a function of temperature, can show the t r a n s i t i o n i n xanthan (9), although the v i s c o s i t y change i s often small as the xanthan backbone i s c e l l u l o s e and s t i l l quite s t i f f . In contrast, however, the v i s c o s i t y change i n succinoglycan solutions i s dramatic (Figure 4). Effect of Temperature. The f a l l i n v i s c o s i t y usually occurs over a small temperature range, and to a l e v e l close to that of the solvent i t s e l f . The recovery of v i s c o s i t y on cooling i s p a r t i a l (Figure 5)


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CLARKE-STURMAN ET AL. Succinoglycan Table 1. Composition of Succinoglycan from Different Strains Glucose

Pseudomonas sp. NCIB IS592


Pseudomonas sp. NCIB 11264 Rhizobium meliloti

K24

Rhizobium meliloti

DSM 30136

igrobecterium

radiobacter

NCIB 8149

Agrobacterium

radiobacter

NCIB 9042

Agrobacterium

tumefaciens

DSM 30208

Galactose

1.02 0.94 1.00 1.05 1.05 0.94 0.97

7 7 7 7 7 7 7

Pyruvate

Acetate

Succinate

0.96 0.91 1.00 1.02 0.98 1.00 0.89

Succinoglycan - American Chemical Society

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