Process for producing ascorbic acid in presence of sulfite

Abstract

The present invention comprises the use of sulfite additives to reduce discoloration of L-ascorbic acid produced from acid or aqueous solutions of 2-keto-L-gulonic acid. In one aspect, the present invention comprises a continuous process for producing L-ascorbic acid from an aqueous solution of 2-keto-L-gulonic acid. The use of sulfite additives reduces product stream color and improves product recovery by binding to high molecular weight reaction by-products. In a continuous process, the reaction stream is separated from residual sulfite and sulfite-bound by-products products to produce a product stream enriched in aqueous ascorbic acid for recovery, and an enriched 2-keto-L-gulonic acid stream which is recycled to the reactor. The in situ use of sulfite additives during the reaction increases the overall yield of L-ascorbic ascorbic acid, with no loss in selectivity of the synthesis.

Description

[0001] This application claims priority from US Provisional Application Nos. 60 / 257,991, filed December 22, 2000, and 60 / 314,999, filed August 24, 2001. The disclosures of these provisional applications are hereby incorporated by reference. This invention was made with United States Government support under Cooperative Research Agreement No. 70NANB5H1138 funded by the National Institute of Standards and Technology's Advanced Technology Program. The US Government has certain rights in this invention. Field of invention:

[0002] The present invention relates to a method for producing ascorbic acid. In particular, the present invention relates to the use of sulfite species in the synthesis of ascorbic acid to reduce the color of ascorbic acid and improve product recovery. The present invention also describes a continuous process for the preparation of L-ascorbic acid from an aqueous solution of 2-keto-L-gulonic acid by an aqueous cyclization process in the presence of a sulfit...

Examples

Embodiment 1

[0107] Examples 1-3: Examples 1-3 (Table 1) illustrate the effect of bisulfite additive concentration on the conversion of 2-keto-L-gulonic acid to ascorbic acid and the selectivity of the reaction. In Example 1, four samples were heated at 120°C for 2 hours, and each sample contained a 10 wt% solution of 2-keto-L-gulonic acid (based on anhydride) without any sulfite, on ice After cooling in a bath, analysis of 2-keto-L-gulonic acid and ascorbic acid was performed by high performance liquid chromatography (HPLC). In Examples 2 and 3, four sodium bisulfite (NaHSO 3 ) or 0.13wt% sodium bisulfite (NaHSO 3 ) in a 10 wt% solution of 2-keto-L-gulonic acid (anhydride based) was treated as described in Example 1. The average percent conversion of 2-keto-L-gulonic acid and percent selectivity to ascorbic acid for the four samples used in each example were calculated and listed in Table 1. It can be seen that increasing sulfite does not decrease selectivity, and in fact increases sel...

Embodiment 9-23

[0115] Examples 9-23: Examples 9-23 illustrate the percent selectivity and solution color of the concentration of sulfurous acid for the conversion of 2-keto-L-gulonic acid to ascorbic acid relative to the Reference Example in which no sulfurous acid was added. influences. The reactions were carried out continuously in 1 / 8" O.D. x 50' long (30 mL volume) Teflon tubular reactors at temperatures of 120, 150 and 180°C under a total pressure of 165 psig The contact time for a continuous reactor system is equal to the reactor volume divided by the volume flow rate of the feed, and is similar to the reaction time in batch experiments.

[0116] The results are shown in Table 3. The reduced color of the sulfurous acid-treated solution was measured by absorbance at 450 nm. In all cases, an increase in color was observed upon conversion and was expressed as an absolute increase in absorbance. The difference in absorbance of the feed and product solutions can be expressed by comparing...

Embodiment 24

[0117] Example 24: Example 24 illustrates the separation of a solution comprising a mixture of sulfurous acid, 2-keto-L-gulonic acid and L-ascorbic acid by ion exclusion in a pulse test. A feed mixture of 0.2 column bed volumes was injected into the column packed with ion exclusion resin, the mixture was composed of 15% 2-keto-L-gulonic acid, 15% L-ascorbic acid and sulfurous acid (5.4 wt%) composition. The feed mixture was eluted with water. refer to Figure 5 , showing the peak-to-peak distances of sulfur species (S), 2-keto-L-gulonic acid (KLG) and L-ascorbic acid (AsA). Indicates that the sulfur species, 2-keto-L-gulonic acid and L-ascorbic acid peaks can be distinguished by 0.1 bed volume. This spacing in the pulse test demonstrates the feasibility of separating the L-ascorbate sulfur species, 2-keto-L-gulonic acid, in the SMB setup.

[0001] This application claims priority from US Provisional Application Nos. 60 / 257,991, filed December 22, 2000, and 60 / 314,999, filed August 24, 2001. The disclosures of these provisional applications are hereby incorporated by reference. This invention was made with United States Government support under Cooperative Research Agreement No. 70NANB5H1138 funded by the National Institute of Standards and Technology's Advanced Technology Program. The US Government has certain rights in this invention. Field of invention:

[0002] The present invention relates to a method for producing ascorbic acid. In particular, the present invention relates to the use of sulfite species in the synthesis of ascorbic acid to reduce the color of ascorbic acid and improve product recovery. The present invention also describes a continuous process for the preparation of L-ascorbic acid from an aqueous solution of 2-keto-L-gulonic acid by an aqueous cyclization process in the presence of a sulfit...

Examples

Embodiment 1

[0107] Examples 1-3: Examples 1-3 (Table 1) illustrate the effect of bisulfite additive concentration on the conversion of 2-keto-L-gulonic acid to ascorbic acid and the selectivity of the reaction. In Example 1, four samples were heated at 120°C for 2 hours, and each sample contained a 10 wt% solution of 2-keto-L-gulonic acid (based on anhydride) without any sulfite, on ice After cooling in a bath, analysis of 2-keto-L-gulonic acid and ascorbic acid was performed by high performance liquid chromatography (HPLC). In Examples 2 and 3, four sodium bisulfite (NaHSO 3 ) or 0.13wt% sodium bisulfite (NaHSO 3 ) in a 10 wt% solution of 2-keto-L-gulonic acid (anhydride based) was treated as described in Example 1. The average percent conversion of 2-keto-L-gulonic acid and percent selectivity to ascorbic acid for the four samples used in each example were calculated and listed in Table 1. It can be seen that increasing sulfite does not decrease selectivity, and in fact increases sel...

Embodiment 9-23

[0115] Examples 9-23: Examples 9-23 illustrate the percent selectivity and solution color of the concentration of sulfurous acid for the conversion of 2-keto-L-gulonic acid to ascorbic acid relative to the Reference Example in which no sulfurous acid was added. influences. The reactions were carried out continuously in 1 / 8" O.D. x 50' long (30 mL volume) Teflon tubular reactors at temperatures of 120, 150 and 180°C under a total pressure of 165 psig The contact time for a continuous reactor system is equal to the reactor volume divided by the volume flow rate of the feed, and is similar to the reaction time in batch experiments.

[0116] The results are shown in Table 3. The reduced color of the sulfurous acid-treated solution was measured by absorbance at 450 nm. In all cases, an increase in color was observed upon conversion and was expressed as an absolute increase in absorbance. The difference in absorbance of the feed and product solutions can be expressed by comparing...

Embodiment 24

[0117] Example 24: Example 24 illustrates the separation of a solution comprising a mixture of sulfurous acid, 2-keto-L-gulonic acid and L-ascorbic acid by ion exclusion in a pulse test. A feed mixture of 0.2 column bed volumes was injected into the column packed with ion exclusion resin, the mixture was composed of 15% 2-keto-L-gulonic acid, 15% L-ascorbic acid and sulfurous acid (5.4 wt%) composition. The feed mixture was eluted with water. refer to Figure 5 , showing the peak-to-peak distances of sulfur species (S), 2-keto-L-gulonic acid (KLG) and L-ascorbic acid (AsA). Indicates that the sulfur species, 2-keto-L-gulonic acid and L-ascorbic acid peaks can be distinguished by 0.1 bed volume. This spacing in the pulse test demonstrates the feasibility of separating the L-ascorbate sulfur species, 2-keto-L-gulonic acid, in the SMB setup.

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