Research Note pubs.acs.org/IECR
Cyclodextrin Inhibits Calcium Carbonate Crystallization and Scaling Venous Derakhshanian and Sujit Banerjee* Institute of Paper Science and Technology, School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, 500 Tenth St. NW, Atlanta, Georgia 30332-0620, United States ABSTRACT: β-Cyclodextrin inhibits calcium carbonate crystallization and also reduces the degree of scaling on stainless steel surfaces. The rate of crystallization is not affected. The size of the calcium carbonate crystals is reduced by the cyclodextrin. Under the conditions used, the cyclodextrin was effective at concentrations between 5 ppm and 100 ppm.
■
INTRODUCTION Calcium scaling is an expensive recurring problem in industries that use large volumes of water. Antiscalants presently used are typically phosphorus-containing compounds,1−4 although proteins5 and other agents have been proposed. In this paper, we introduce β-cyclodextrin (β-CD) as a new cost-effective antiscalant. Cyclodextrins (CDs) are torus-shaped cyclic oligomers consisting of 6 (α), 7 (β), or 8 (γ) glucose units with α-1,4-linkages. The structure of β-CD is illustrated in Figure 1. CDs have a hydrophobic cavity that has been
concentrated solutions were too high to measure accurately; those from weaker solutions were too low. Nevertheless, the same trends were observed with these mixtures. The total suspended solids (TSS) in water was measured after filtering 100 mL of solution through a 1.2-μm glass fiber filter, which was dried at 105 °C for 1 h. Softwood black liquor was obtained from the MeadWestvaco mill at Evadale, TX. Stainless coupons (3.2 cm × 2.9 cm, ∼20 g) were immersed for 2 min in the liquor (control) and in liquor containing 100 ppmv β-CD. The liquor volume was 300 mL in both cases. The coupons were air-dried overnight and the weight gain recorded. A second experiment was run according to the above procedure, but with the samples heated to 120 °C for 2 h in a bomb. The coupons were air-dried as before, but were then weighed and contacted with aluminum oxide sandpaper (from 3M, 336U, frit grain 100) weighted with a 100-g load of the same area as the coupon. The weighted sandpaper was dragged over 10 s twice on each face of the coupon. The coupons were reweighed and the weight loss from sanding determined.
■
RESULTS AND DISCUSSION Turbidity was used as a screening tool to determine the effectiveness of β-CD in inhibiting CaCO3 crystallization. Dose−response curves are provided in Figure 2. Turbidity profiles of β-CD concentrations between 5 ppm and 100 ppm were all similar to those for 5 and 100 ppm and are omitted for the sake of clarity. The profile at 1 ppm β-CD was the same as that of the control, which indicated that this dose was too small to have an effect. Profiles at concentrations of β-CD at 200 or 300 ppm (not shown) were also the same as the control. Hence, β-CD is only effective at the 5−100 ppm range. The benefit of the CD is lost at higher dosage. This type of reversal has been noted in other β-CD applications, e.g., in sludge dewatering and in the detackification of adhesives.8,9 In these applications, the CD is applied in conjunction with a cationic polymer and the diameter of the polymer is affected by the CD.10 The mechanism responsible for reversal in the present CaCO3 application is not known.
Figure 1. Structure of β-cyclodextrin.
exploited in numerous applications ranging from odor control to sludge dewatering.6−8 They can also complex with cations.6 We reasoned that if a CD is able to form a sufficiently strong complex with the Ca ion, it could potentially reduce calcium carbonate deposition and inhibit scale formation. β-CD is relatively inexpensive and typically made from cornstarch; it is nontoxic and is FDA approved for direct food use. As such, it could offer a viable green alternative to commercial antiscalants.
■
MATERIALS AND METHODS Turbidity was measured with an Orbeco-Hellige 965 turbidimeter. Sodium carbonate (250 ppm as Na) and calcium chloride (75 ppm as Ca) were mixed and the turbidity read immediately and for 15 min thereafter. Turbidities from more© 2012 American Chemical Society
Received: Revised: Accepted: Published: 4463
January 27, 2012 March 5, 2012 March 8, 2012 March 9, 2012 dx.doi.org/10.1021/ie300245q | Ind. Eng. Chem. Res. 2012, 51, 4463−4465
Industrial & Engineering Chemistry Research
Research Note
Figure 2. Turbidity reduction as a function of β-cyclodextrin dose. The error bars are from duplicate determinations.
Figure 4. Relationship between turbidity and suspended mass of CaCO3.
A concentration of 50 ppm was chosen as a representative value at which the β-CD is effective. Results of parallel measurements of turbidity and TSS are illustrated in Figure 3.
contains mainly lignin along with inorganic pulping chemicals. It is concentrated in multiple effect evaporators and then fired in a recovery boiler to reclaim energy. Evaporator scaling is a common problem. Two experiments were done in order to determine the effect of β-CD on scaling. First, a stainless steel coupon was immersed in BL (with and without 100 ppm βCD) for 2 min at room temperature. The weight gained by the dried coupon was 140 ± 35 mg for the control and 60 ± 3 mg for the CD-treated sample. In a second experiment, the sample containing the steel coupon was heated to 120 °C and the amount of the deposits measured as above. Some of the deposits were then scraped off with sandpaper and the amount lost was measured. This approach measured the strength of attachment of the deposits and was adapted from an application on the deposition of adhesives on surfaces.9 The weight loss incurred upon sanding was 57 ± 8 and 133 ± 16 mg, with and without the presence of β-CD, respectively. Clearly, the CD decreases the amount deposited and also increases the ease of removal of the deposits. While the material deposited was not identified in this study, the deposits are principally sodium and calcium salts.11 The effectiveness of the CD in a complex mixture such as BL is remarkable because commercial antiscalants often lose their effectiveness in environments containing dissolved polymeric species, because of competitive effects. The nature of the interaction between CD and calcium is likely to be complex. Nicolis et al.12 reported that calcium was located outside the β-CD ring, whereas Reale et al.13 showed that first-group alkali cations form inclusion complexes with βCD. β-CD can also complex with cationic polymers by dispersing the charge.10 Regardless of the mechanism, our principal finding is that the β-CD complexes with calcium strongly enough to inhibit crystallization. In conclusion, we have shown that β-CD can inhibit both the crystallization of calcium carbonate from solution and the attachment of scale on stainless steel surfaces. While we have only studied simple CDs in this preliminary work, we note that CDs have been derivatized for specific applications and it is possible that a derivatized CD might prove more effective, albeit at a higher cost.
Figure 3. Reduction of turbidity and suspended mass of CaCO3 in the presence of β-cyclodextrin. The error bars are from duplicate determinations.
Turbidity also depends upon crystal size, and β-CD could affect turbidity by changing the amount of solids in suspension or the particle size, or both. The Figure 3 data are replotted in Figure 4 as turbidity vs mass at increasing times. While both lines have the same slope indicating the same rate of crystallization, the line with the CD is offset along the abscissa. The crystals formed in the presence of the CD give rise to higher turbidity from the same mass, indicating that these crystals are smaller. Hence, the CD reduces both the degree of crystallization and the size of the crystals involved. While only results from β-CD are presented here, α- and γ-CD gave very similar results. Because β-CD is cheaper, further work was not pursued with the other CDs. In an application potentially important to the paper industry, the effect of β-CD on deposits from black liquor (BL) was investigated. BL is the solution derived from kraft pulping and 4464
dx.doi.org/10.1021/ie300245q | Ind. Eng. Chem. Res. 2012, 51, 4463−4465
Industrial & Engineering Chemistry Research
■
Research Note
AUTHOR INFORMATION
Corresponding Author
*Tel.: (404)894-9709. Fax: (404)894-4778. E-mail: sb@gatech. edu. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by the Department of Energy (under Contract No. DE-FC36-04GO14308) and Air Products Corporation.
■
REFERENCES
(1) Sawada, K. The mechanisms of crystallization and transformation of calcium carbonates. Pure Appl. Chem. 1997, 69, 921−928. (2) Reddy, M. M. Crystallization of calcium carbonate in the presence of trace concentrations of phosphorus-containing anions. J. Cryst. Growth 1977, 41, 287−295. (3) Amjad, Z.; Kleptsanis, G.; Koutsoukos, P. G. Precipitation and crystal growth of calcium carbonate in the presence of acrylic acid copolymers. Presented at the 15th International Symposium on Industrial Crystallization, Sorrento, Italy, September 2002. (4) Hamed, O. A.; Al-Sofi, M. A. K.; Mustafa, G. M.; Dalvi, A. G. The performance of different anti-scalants in multi-stage flash distillers. Desalination 2007, 204, 385−402. (5) Heinemann, F.; Gummich, M.; Radmacher, M.; Fritz, M. Modification of CaCO3 precipitation rates by water-soluble nacre proteins. Mater. Sci. Eng., C 2011, 31, 99−105. (6) Szejtli, J. Introduction and general overview of cyclodextrin chemistry. Chem. Rev. 1998, 98, 1743−1753. (7) Buschmann, H.-J.; Schollmeyer, E. Applications of cyclodextrins in cosmetic products: a review. J. Cosmetic Sci. 2002, 53, 185−191. (8) Hartong, B. H.; Abu-Daabes, M.; Le, T.; Saidan, M.; Banerjee, S. Sludge dewatering with cyclodextrins. Water Res. 2007, 41, 1201− 1206. (9) Banerjee, S.; Le, T.; Haynes, R. D.; Bradbury, J. E. Solubilizing and detackifying stickies with β-cyclodextrin. BioRes. 2012, 7, 1533− 1539. (10) Wang, Y.; Banerjee, S. Cyclodextrins modify the properties of cationic polyacrylamides. J. Colloid Interface Sci. 2009, 339, 325−329. (11) Severtson, S. J.; Duggirala, P. Y.; Carter, P. W.; Reed, P. E. Mechanism and chemical control of CaCO3 scaling in the kraft process. Tappi J. 1999, 82 (6), 167−174. (12) Nicolis, I.; Coleman, A. W.; Charpin, P.; De Rango, C. First sphere coordination of divalent metal cations by cyclodextrin: structure of the β-cyclodextrin-calcium chloride-water compound. Acta Crystallogr., Sect. B: Struct. Sci. 1996, B52, 122−130. (13) Reale, S.; Teixido, E.; de Angelis, F. Study of alkali metal cations binding selectivity of β-cyclodextrin by ESI-MS. Annal. Chim. (Rome, Italy) 2005, 95, 375−381.
4465
dx.doi.org/10.1021/ie300245q | Ind. Eng. Chem. Res. 2012, 51, 4463−4465
