AN-PAN-1063
2023-09
Inline analysis of borate and sulfate solutions with Raman spectroscopy
Summary
Boron is a semimetal found in the form of borax (sodium tetraborate) and other oxides in nature [1]. Boric acid (H3BO3) is derived from borax and is used in several industrial applications such as glass manufacturing, electronics, detergents, food preservatives, and more [2].
Boric acid can be produced from borax through various processes. Sulfuric acid is mainly used during borax synthesis since it is considered to have minimal environmental impact.
In 2021, the boric acid market was estimated at US$ 706.52 million and is expected to reach US$ 1,169.89 million by 2030 [3]. As the market grows, so does the need for a more cost-efficient and environmentally friendly production process.
This Process Application Note shows the excellent performance of the PTRam, the single-channel Raman instrument for process development from Metrohm Process Analytics, while measuring boric acid and sodium sulfate solutions inline at low concentrations (<100 mg/L).
Introduction
There are several ways to manufacture boric acid from borax. Some of these processes use strong acids like nitric acid or chloric acid, however, production costs using these chemicals are high due to equipment wear. Out of these acids, sulfuric acid is primarily used (Reaction 1) since it is considered to have the smallest environmental footprint.
Maximizing production efficiency and reducing costs in a boric acid refinery is possible by monitoring and controlling the sodium sulfate (Na2SO4) chemistry in the crystallization stage (Figure 1). If the reagent concentrations are outside of the set limits, chemical dosage is not controlled, waste increases, and production costs are higher.
Gravimetric analysis is traditionally used for quantifying desired constituents of mixed chemicals or solutions by weight after separation [5]. This conventional method can monitor H3BO3 [6] and Na2SO4 concentrations [7]. However, practical challenges arise through laborious sample preparation methods and manual data analysis. Additionally, gravimetric analysis does not provide users with real-time process information.
For optimal boric acid production, multiple parameters must be monitored in a safer, more efficient, and faster manner. This is possible via inline process analysis with reagent-free spectroscopy (e.g., Raman).
Metrohm Process Analytics offers the PTRam Process Analyzer (Figure 2) which enables direct comparison of «real-time» spectral data from the process to a reference method (e.g., titration). This allows operators to create a simple, yet indispensable calibration model used to produce quantitative results during the boric acid manufacturing process.
Application
Laser used: 785 nm. Samples of H3BO3 and Na2SO4 single salt and mixed salt solutions were taken for this study. Only a minimal number of reference measurements were required for calibration and modeling.
One of the many functions of Raman spectroscopy is its use for material identification. Most materials can be identified by their Raman signature, as they exhibit sharp, distinctive peaks serving as a molecular fingerprint. The spectrum contains information not only regarding sample composition, but also about the concentrations of its constituents, which are directly proportional to the intensity of the spectrum. Because of the spectral differences, Raman analyzers are known to be capable of identification and confirmation of chemical substances used in a variety of industries (e.g., semiconductors, food, pharmaceuticals, etc.).
Results
In this application study, the boric acid salt and sodium sulfate salt exhibit intense Raman bands at 880 cm-1 and 993 cm-1, respectively (Figure 3). The limits of detection (LODs) for H3BO3 and Na2SO4 solutions are 15 mg/L (15 mg/L BO3 3-) and 10 mg/L (7 mg/L SO4 2-) (Table 1). This clearly demonstrates the ability of inline Raman spectroscopy for accurate quantitative analysis at low analyte concentrations.
Table 1. LOD (limit of detection in mg/L) of H3BO3 and Na2SO4 solutions with inline Raman spectroscopy.
Parameters | Factors | Concentration range (mg/L) | SEP† | LODst‡ | LODio* |
---|---|---|---|---|---|
H3BO3 solution | 2 | 0–80 | 4.6 | 15.2 | 14.5 |
Na2SO4 solution | 2 | 0–80 | 3.1 | 10.2 | 6.9 |
H3BO3 in 1 g/L Na2SO4 | 2 | 0–80 | 10.1 | 33.3 | 31.6 |
Na2SO4 in 5 g/L H3BO3 | 2 | 0–80 | 3.5 | 1.6 | 7.8 |
Conclusion
In conclusion, the use of Raman spectroscopy for inline analysis of borate and sulfate solutions presents significant advantages in the context of boric acid production. As the boric acid market expands, the demand for efficient and eco-friendly production intensifies. Inline analysis, facilitated by reagent-free spectroscopy techniques such as Raman, enables real-time monitoring of process parameters, as demonstrated by the PTRam Process Analyzer. By identifying distinctive molecular signatures and offering accurate quantitative results, Raman spectroscopy presents a robust approach for optimizing boric acid production, addressing challenges associated with traditional methods.
Benefits for Raman in process
- Increased product throughput, reproducibility, production rates, and profitability.
- Gain insight into chemical reactions occurring in the manufacturing process.
References
- Boron | Properties, Uses, & Facts | Britannica. https://www.britannica.com/science/boron-chemical-element (accessed 2023-08-21).
- Boron Mining: Sources And Major Producers | Borates Today. https://borates.today/boron-mining-sources-and-major-producers/ (accessed 2023-08-21).
- Boric Acid Market Size to Worth Around US$ 1,169.89 Million by 2030. https://www.precedenceresearch.com/boric-acid-market (accessed 2022-07-22).
- Mergen, A.; Demirhan, M. H.; Bilen, M. Processing of Boric Acid from Borax by a Wet Chemical Method. Adv. Powder Technol. 2003, 14 (3), 279–293. https://doi.org/10.1163/15685520360685947.
- Gravimetric analysis | Definition, Steps, Types, & Facts | Britannica. https://www.britannica.com/science/gravimetric-analysis (accessed 2023-08-21).
- Childs, M. P. Quantification of Boric Acid Concentration and Losses Due to Vaporization in the PASTA Facility., Texas A&M University, 2016.
- Sodium Sulphate for Industrial Use — Determination of Sulphates Content — Calculation Method and Barium Sulphate Gravimetric Method, July 1975.