CS277299B6 - A method for producing 2-furaldehyde from pentose solutions - Google Patents

Abstract

The solution concerns the production of furaldehyde from pentose solutions by isothermal dehydration. The essence of the solution is that the pentose solution with the catalyst is heated to boiling temperature, under a pressure of 480 to 800 kPa for 30 to 120 s, is subjected to isothermal dehydration in a turbulent flow regime with a residence time of the reaction solution in the range of 3 to 8 min. and then the reaction mixture is expanded, while the resulting fural vapors are led to the rectification in the form of a steam injection, while the fural contained in the liquid phase of the reaction solution is swept by superheated water vapor and an inert gas and is led to condensation

Description

1 CS 277299 B6

The invention relates to a process for the preparation of 2-furaldehyde from pentose solutions by isothermal dehydration. At present, there are many ways to produce 2-furaldehyde in industrial practice. They are single-stage methods in which pentahydrate sahydrolysis and pentose dehydration are carried out in one device and two-stage, where hydrolysis and dehydration are separated. For other reasons, methods of making 2-furaldehyde can be judged to be either pressurized or non-pressurized, with or without addition of catalysts, continuously, semi-continuously, and discontinuously. All of the above methods have advantages but also drawbacks. In single-stage pressure processes, lignocellulose is considerably reduced and, in addition to lignin, contains a significant amount of 2-furaldehyde condensation products, which greatly limits the use of lignocellulose for feed purposes.

Pressure methods also have the disadvantage that they are difficult to control. The main problem-generating element in these modes is the feedstock feeders into the reactor, as well as the reactors from the reactor. The rotary or sliding portions of these devices are subjected to high pressures, temperatures, and frictional action of the particulate matter of the plant material, and thus to excessive loading, and most often constitutes a narrow point of reliable operation of the industrial device.

The discontinuous devices are labor intensive and at the same time the quality of the lignocellulose obtained detracts from its further processing. The advantages of the two-stage process for the processing of secondary agricultural raw materials are that after partial hydrolysis of the pentoxanes with dilute acids and subsequent extraction with water, a pentose solution is obtained and the lignocellulose is suitable for further processing of pulp feed and organomineral fertilizer.

In the two-stage process for the production of 2-furaldehyde, the dehydration problems of pentoses to 2-furaldehyde are not satisfactorily solved. The results of the experiments confirmed that the rate of 2-furaldehyde formation is much higher than that of the distilled 2-furaldehyde from the reaction solution. This increases its concentration in the reaction solution and the reaction is continued by forming 2-furaldehyde polycondensates by precipitating these compounds from the solution in the form of a relatively good filterable particulate material, thereby reducing the yield of 2-furaldehyde.

The present invention is solved by the invention, the invention being solved by the invention, which heats the boiling point solution with the catalyst to a boiling point at a pressure of 480 to 800 kPa for 30 to 120 s, and is subjected to isothermal dehydration under a turbulent flow regime at the reaction solution. in the range of 3-8 min, and then the reaction mixture is expanded, whereby the fural vapors formed in the form of a steam spray are rectified, while the furalized liquid phase of the reaction solution is passed through overheated steam or inert gas to condense. and CS 277299 B6 2

The liquid portion of the reconstituted solution after dehydration can be subjected to the process several times until a solution containing unreacted xylose is obtained.

According to the invention, a one-pass yield of 10% is achieved by theory. The advantage of the solution lies in the rapid heating under high pressure by the subsequent expansion of the reaction mixture and the rapid removal of the formed fibrous vapors from the reaction solution, which prevents further reaction. The advantage of the solution is also the rectified flow of pentose solution mixed with the catalyst into the turbulence and the next flow. Example 1

According to the invention, 2-furaldehyde was obtained, wherein a pentose solution with a D-xylose concentration of 5%, mixed with a 10% sulfuric acid-based catalyst, was conveyed by a plunger high-pressure pump through a heat exchanger tube in which the sarea solution was simultaneously heated at a temperature of 160 ° C, where the thermally insulated reactor vessel was flown in which a thermometer and a manometer were built. The vessel was used to level the pumping of the positive displacement pump. The reaction flow rate was 15 liters per hour, the residence time in the reactor was 5 minutes at 160 ° C and 600 kPa. The reacted pentose solution from the reactor pressure space expanded through the expander valve of the cyclone, where loosened fural vapors which were discharged into the collection vessel were separated. The device capacity was 5 to 30 1 for an hour. The xylose-related yield of 2-furaldehyde was 9.8%. It was conducted in such a way that the furaldehyde formed was not drained from the vapor phase, but the expanded vapors were condensed and remained in the collection tank of the reacted solution.

Since the residuals of the reaction solution contain a small amount of 2-furaldehyde, the remainder of the reaction solution is subjected to steaming. The inert gases CO2 and N2 have also been tested. Example 2

According to the invention, 2-furaldehyde was obtained, wherein the pentose solution at a concentration of 5 wt. D-xylose mixed with a 10% hydrochloric acid catalyst with a heat exchanger tube / internal diameter of 10 mm / 1 m / s in which the reaction solution was heated to 120 ° C. It flowed into an isothermal channel reactor whose cross-section was close to the cross-section of the tube of the heat exchanger to maintain the flow conditions of flow in the reactor. The reactor was allowed to stand for 10 min, the reactor temperature was 120 ° C. The reacted pentose solution from the pressurized space expanded through the expansion cap to the cyclone, where fural vapors were released and narrated. The yield of furaldehyde on D-xylose was 11.6%. The reacted reaction solution was re-heated and dehydrated with the above apparatus to give an additional 8.9% of furaldehyde. Repeatedly, the total recovery of furaldehyde will be repeated

Claims (1)

33.6% calculated for pentose, i. E. 52% related to the theoretical yield of furaldehyde. EXAMPLE 3 Furaldehyde of a dehydration-pententose solution containing 3 wt. D-xylose and 12% sulfuric acid. The solution thus prepared was subjected to rapid heating in a channel exchanger at a turbulent flow of solution in a 10x10 mm channel. Heating time 120 s. The solution was fed by a plunger pump at a pressure of 800 kPa to a flow reactor, with isothermal dehydration at the turbulent flow of the channel for 8 min at 800 kPa. The reacted solution was subjected to expansion, the vapors released for rectification, and the furaldehyde-containing liquid portion was passed through an overheated water vapor (130 ° C, 0.1 MPa). The fural couples were conducted by narration. Furaldehyde yield 21% relative to D-xylose (32.8% to theoretical furaldehyde) after one pass. The procedure was repeated three times and a yield of 44.5% on D-xylose (69.5% on theoretical furaldehyde) was obtained. PATENT REQUIREMENTS A process for producing 2-furaldehyde from pentose solutions by isothermal dehydration, wherein the pentose solution with the catalyst is heated to boiling under a pressure of 480 to 800 kPa for 30 to 120 hours, subjected to an isothermal dehydration of the flow-flowing mode at the reaction time and then the reaction mixture is expanded, while the resulting fural vapor is rectified as a vapor spray while the fural contained in the liquid phase reaction solution is passed through superheated steam or inert gas to condense. End of document