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RAPID ONLINE ANALYSIS FOR SODIUM CYANIDE PRODUCTION

IP.com Disclosure Number: IPCOM000212142D
Publication Date: 2011-Nov-01
Document File: 3 page(s) / 492K

Publishing Venue

The IP.com Prior Art Database

Abstract

Here we disclose the use of a rapid online spectroscopic method to monitor and control sodium cyanide production from caustic and hydrogen cyanide. The method, in this implementation, is near-infrared spectroscopy with a fiber-optically coupled immersion probe inserted directly into the process.

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Title: “Rapid online analysis for sodium cyanide production”.

Summary

Here we disclose the use of a rapid online spectroscopic method to monitor and control sodium cyanide production from caustic and hydrogen cyanide.  The method, in this implementation, is near-infrared spectroscopy with a fiber-optically coupled immersion probe inserted directly into the process.

1. Introduction

At a high level, the batch process for NaCN production follows these steps:

            Step 1) add water

            Step 2) add NaOH  until desired NaOH concentration is achieved

            Step 3) add HCN until NaOH concentration is depleted sufficiently.

            Step 4) empty reactor

The reaction happening is NaOH + HCN à NaCN +H2O.  A first analysis of the caustic concentration is performed at the end of Step 2 and a second analysis is made of the final NaCN and residual NaOH concentrations at the end of Step 3.

Figure 1: A) Schematic of the NaCN production process

3. Experimental

3.1 Technology

There are several options for online analysis that could be used.  Of the options online NIR is the simplest and most suitable to the given application.  It is a Diode Array near infrared (NIR) transmission spectroscopic technique which is detailed here, though a mid-infrared attenuated total reflectance, Raman spectroscopy technique or an online titration system should also be feasible. The higher resolution of a FTNIR system could also be applied.  It was also determined that the Diode Array system would be more suitable than a filter photometer because it allows for more complex chemometric modeling which is required by this application to account for temperature variations and subtle concentration and spectral variations.  A filter photometer could also be applied with careful filter selection and sacrifice of measurement precision.

Example NIR spectra of NaCN and NaOH solutions at varying concentrations with a 5mm transmission pathlength are shown in Figure 2.  The reference for these spectra was acquired in air.  This demonstrates that there is spectral variation in the NIR which can be utilized for the building of quantitative prediction of the NaOH and NaCN concentrations.

Figure 2: Demonstrated spectral variation of NaCN and NaOH solutions

3.2 Setup

The NIR spectrometer and computer can be located in a general purpose area with fiber optic cables delivering the light to and from the 5 mm pathlength immersion pro...