Gluconic Acid Powder CAS 526-95-4

This method uses the oxidation of microorganisms to synthesize gluconicacidaqsoln from glucose, which can be divided into fungal fermentation, bacterial fermentation, fungal fermentation, immobilized cell and immobilized enzyme fermentation. At present, Aspergillus niger fermentation, immobilized cells and immobilized enzymes are widely used. It is a method developed in the 1960s. The immobilization methods of enzymes (cells) can be roughly divided into four types: adsorption method, covalent coupling method, cross-linking method and embedding method.

Adsorption method: enzyme immobilization is achieved through the interaction of secondary bonds between the carrier surface and the enzyme surface.

Covalent coupling method: It combines the active side chain group of the enzyme with the functional group of the carrier through covalent bonds, so as to achieve the function of immobilizing the enzyme. This method of immobilizing the enzyme shows good stability, and is conducive to the continuous use of the enzyme.

Cross linking method: It refers to the use of bifunctional or multifunctional group reagents to cross link and bridge enzyme molecules, which is easy to inactivate.

The embedding methods include grid embedding, microencapsulated embedding and liposome embedding. The embedding method can obtain higher enzyme activity because the enzyme itself does not participate in the chemical binding reaction; However, the diffusion of immobilized cells and immobilized enzymes is limited, so the oxygen consumption is huge, and the improvement of oxygen transfer rate is a big problem.

Therefore, the design and synthesis of novel enzyme immobilization materials with excellent performance and the development of simple and practical immobilization methods are one of the focuses of immobilized enzyme research at present. In recent years, biocatalysis has also been developed to produce gluconicacidaqsoln. This method uses membranes to filter out the reaction product acid, and transfers the acid from the reaction solution in time, reducing the inhibition of reaction product (acid) on catalyst (bacteria). Compared with traditional methods, the recycling of bacteria increases the content of bacteria, thereby increasing the yield.

At present, most of our country uses fermentation to produce calcium gluconate, and then uses calcium gluconate to synthesize gluconicacidaqsoln through ion exchange, evaporation and concentration, and crystallization.

The biological fermentation method requires many processes such as culture, screening and sterilization, and has strict requirements on temperature, many by-products, and a long cycle. In addition, the purity of gluconicacidaqsoln products is affected due to the addition of impurities such as cells during the production of gluconicacidaqsoln, so its development urgently needs to solve many technical problems.

There are two mechanisms of homogeneous chemical oxidation: one is to limit the oxidation capacity of oxidants (such as sodium hypochlorite and hydrogen peroxide) by adjusting the reaction conditions to strong alkaline conditions, so as to oxidize the aldehyde group of glucose to carboxyl group; The second is the Cannizarro mechanism proposed by Ashida et al. for the conversion of glucose to gluconicacidaqsoln when adding hydrogen ion acceptors (some ketones, alkenes and oxygen are suitable hydrogen ion acceptors in the presence of Raney Ni). Hydrogen peroxide and sodium hypochlorite were used as oxidants respectively, and the yields were 70% and 90%, respectively. The industrial pilot test was realized.

However, the homogeneous chemical oxidation method needs to strictly control the content of the active components of the catalyst in the reaction solution, which is dependent on temperature and pH value of the solution. There are many intermediate steps, many by-products, and it is difficult to separate the products. Moreover, the salt used as the catalyst is difficult to regenerate, and the yield is low. The reaction time is long and the environment is seriously polluted.

In terms of electrolysis methods, the synthesis of gluconicacidaqsoln by electrolytic oxidation can be divided into direct electrolytic synthesis, indirect electrolytic synthesis and "paired electrolysis" synthesis. In this method, a certain amount of glucose solution is added into the electrolytic cell, and then an appropriate electrolyte is added. The glucose is electrolyzed and oxidized under certain temperature, voltage and constant current density. The reaction principle is to obtain an appropriate "oxidation medium" by electrolysis, and then use this "oxidation medium" to oxidize glucose to generate gluconicacidaqsoln.

For example, the indirect electrolytic synthesis method is to use the medium in the reduced state to generate the medium in the oxidation state at the anode. The glucose reacts with the generated medium in the oxidation state to generate gluconicacidaqsoln, and the medium returns to the original reduced state. Both direct electrolytic synthesis and indirect electrolytic synthesis react in the anode area, while the "paired electrolytic synthesis" method reacts in both the cathode and anode areas at the same time, so the electrolytic efficiency is relatively high.

The electrolytic oxidation of gluconicacidaqsoln has been industrialized abroad, but it is still in the experimental stage at home. Ruthenium is plated on titanium as the working electrode. The current density is 0.18A/m, the glucose concentration is 0.02 mol/L, the reaction temperature is 50 ℃, and the medium concentration is 0.2 mol/L.

Under this condition, the current efficiency (theoretical power consumption per unit mole of gluconicacidaqsoln generated/actual power consumption per unit mole of gluconicacidaqsoln generated) can reach 76.50%, and the data of parallel test is good, which is expected to realize industrial pilot test. Although the electrochemical oxidation method overcomes the disadvantages of biological fermentation method and homogeneous chemical oxidation method, such as many by-products and processes, it consumes large energy in industrial production, and the conditions are difficult to control, so it is rarely used in industrial production.

The preparation of gluconicacidaqsoln by heterogeneous catalytic oxidation is to oxidize glucose to acid by adding solid phase catalyst of supported metal into the liquid glucose solution, and then using O as oxidant.

At present, domestic research is still in the laboratory stage. Some studies introduced the synthesis route and process flow of catalytic oxidation of gluconicacidaqsoln. Based on the analysis of the test results, a pilot study of the product was carried out. Studied Pd The results of Co/C catalyst, XPS and BET show that the addition of c0 changes the structure of the catalyst and is beneficial to the reduction of Pd, thus improving the conversion and selectivity of the reaction (the conversion of glucose reaches 92% and the selectivity of the catalyst is 94%).

The heterogeneous catalytic oxidation method can synthesize gluconic acid powder in only one step, and the reaction conditions are mild (atmospheric pressure, close to room temperature), the yield is high, the by-products are few, the product is easy to separate, and the catalyst can be recycled. It is an environmentally friendly method to synthesize gluconicacidaqsoln. However, the stability study of Pd metal catalyst still needs some time to get a good solution. Although Au catalyst makes up for the shortcomings of Pd catalyst, it still needs some research for industrial application.