CS210733B1 - A method for producing 2-furaldehyde - Google Patents

Abstract

The invention solves the problem of pressureless continuous production of 2-furaldehyde for the processing of pentoses and oligopentoses from industrial solutions, sulfite leachates from the processing of hardwoods, waste solutions of pentoses, corn cobs, straw, bagasse and other similar raw materials, with the creation of optimal conditions for the formation of 2-furaldehyde and the maximum limitation of the conditions of its decomposition, by the fact that the process is carried out in a reactor with a mechanically fluidized layer of granular material heated to the reaction temperature, onto the surface of which an aqueous solution of pentoses and oligopentoses with a catalyst is sprayed by nozzles. The fluid state of the inorganic sorted granular material is induced mechanically, by vibrations with simultaneous heat supply. The resulting 2-furaldehyde vapors together with water vapors are quickly removed for condensation and the resulting 2-furaldehyde product is isolated from the condensate by rectification.

Description

1. 210733

BACKGROUND OF THE INVENTION The present invention relates to a two-step continuous process for the preparation of 2-furaldehyde from a pre-hydrolysate. from partial hydrolysates of plant materials containing pentosanes, possibly from other pentoses and oligopentoses containing solutions such as e.g. aqueous pre-hydrolysates from beech chips, which are produced during the production of cellulose, sulphite extracts from the processing of deciduous woody plants, waste pentose solutions from the production of crystalline sugars and others.

The prior art processes for the production of 2-furaldehyde are predominantly single-stage, in which pentosane hydrolysis and pentose dehydration are carried out in pressurized devices (at a pressure of 0.7 to 1.8 MPa), with the addition of a catalyst (mostly mineral acids), or even without its feeding, in the latter case, as the catalyst in the process, acetic acid and formic acid are released. There are discontinuous and continuously operating devices. Podlá čsl. U.S. Patent No. T20,136 discloses a pressureless continuous process for the production of 2-furaldehyde utilizing fluidized bed technology, wherein pentosane-containing particulate granules can be processed which meet the requirements of the fluidized-bed process. crumbs of corn cobs. Many prior art processes for the production of 2-furaldehyde have a number of disadvantages. For example, in the case of pressurized one-step processes: - 2-furaldehyde extracts do not reach even 50% of the theory calculated on the pentosane content - the pressure equipment is demanding on the construction material, it requires especially the solution of the dispensing and emptying of the solid material into the pressure equipment and is capital intensive, - the demand for thermal energy is high, - the concentration of 2-furaldehyde in the condensates is relatively low and therefore a considerable amount of thermal energy is required to isolate 2-furaldehyde from the solutions, - lignocellulosic waste is considerable wet and its use is not satisfactorily addressed.

Although the pressureless fluid process has a number of advantages, such as, for example, less structural material requirements, since the device is non-pressurized, the concentration of 2-furaldehyde in the condensates is substantially higher, yielding a dry lignocellulosic residue whose combustion yields the necessary heat for the entire process. and the yield of 2-furaldehyde is at the pressure level. However, this pressureless method also has some disadvantages. It can only process loose-grained plant material; fine drift from the unsorted raw material along with 2-furaldehyde condensates enters some parts of the equipment, limiting the continualization of the production process. Other drawbacks include, for example, ducted condensation of 2-furaldehyde in a stream of inert flue gases, or that, when dispensing granular material into the apparatus, there is also air oxygen that breaks down 2-furaldehyde, which reduces its extracts.

SUMMARY OF THE INVENTION The present invention is solved by the present invention in which bottle-hydrolyzable pentosans are hydrolyzed with dilute mineral acids by known mineral acids to form mono- and oligosaccharides, and the mineral acid solution used for partial hydrolysis is dehydrated to 2-furaldehyde according to the invention in a second step. wherein the fluid state of the inorganic sorted granular material is induced mechanically and its surface heated to the reaction temperature is sprayed with an aqueous solution of pentoses and oligo-pentoses with the catalyst and wherein the resulting 2-furaldehyde vapors together with the water vapor are rapidly removed to condense. The granular material - the carrier is brought into the fluidized state by vibrations. The temperature required for the reactions to proceed to the fluidized bed of the granular support is brought through the corrugated trays, heat pipes or other heat transfer surface. For dehydration, pentoses and oligopentoses from industrial solutions may be used. beech yeast predhydrol yzate production, sulphite leachate from processed woods, pentose waste solutions from the production of crystalline D-xylol from deciduous woods, maize crops, grass, bagasse and others, which is also one of the many advantages of the invention.

Claims (1)

210733 For dehydration of pentoses and oligopentoses, the conditions for the formation of 2-furaldehyde are optimally formed in the reaction medium and the conditions of its decomposition are maximally reduced by the fact that the process is carried out in a reactor with a mechanically fluidized bed of granular organic material heated to the reaction temperature. by which the aqueous solution of pentoses and oligopentoses with the catalyst is atomized by the nozzles and the resulting 2-furaldehyde vapors, water vapor and other thermal decomposition products are rapidly removed from the reaction vessel for condensation. In this way, the inlet of atmospheric oxygen into the reaction space is avoided, the process takes place in an environment of water vapor and the resulting carbon dioxide, which ensures a rapid removal of the 2-furaldehyde vapor to condensation. The actual fluidization of the granular inorganic material - the carrier - is carried out mechanically. The required amount of heat can be fed through the fins or heat pipes, respectively the heat transfer surface. EXAMPLE In a laboratory-type apparatus with a mesh size of 200 x 300 mm and a high stagnation layer of 40 mm, a silicone pellet having an average grain size of 0.5 mm was used as a support. Fluidization of the granular support layer was performed with an electrodynamic vibrator placed on the bottom the wall of the apparatus. The apparatus was attached to the pedestal by means of rubber shock absorbers. The heat transfer to the granular material layer was carried out by electric heating bodies. With simultaneous vibration and heat, the carrier was heated to 220 ° C. The pentosan prehydrolysate solution, which was obtained by steaming hydrolysis of beech sawdust with 1% sulfuric acid and neutralizing it to a dry matter content of 50% organic matter, was sprayed onto the surface of the preheated carrier by means of a spray nozzle. The resulting vapor mixture was evacuated to rapid condensation. A 2-furaldehyde in the rectification column was isolated from the condensate. The amount of crude 2-uraldehyde bole by 26% calculated on the dry matter after subtraction of the acid content. OBJECT OF THE INVENTION A process for the production of 2-furaldehyde by a two-step, pressureless continuous process at atmospheric pressure using a catalyst at temperatures of 160-240 ° C in a fluidized-bed reactor of granular material, wherein in the first stage hydrolyzed pentosans are hydrolyzed with dilute mineral acids to form mono and oligosaccharides, characterized in that the resulting mineral acid solution used for partial hydrolysis is subjected to dehydration in the second stage to 2-furaldehyde, where the fluent state of the inorganic graded granular material is induced by mechanical vibration with simultaneous heat input and heated to the surface to the reaction temperature, an aqueous solution of pentoses and oligopentoses is sprayed with the nozzles, whereby the resulting 2-furaldehyde vapors, together with the water vapor, are accelerated to condense and the final product 2-furaldehyde is isolated from the condensate by rectification. 'Severografia, n. P., Plant 7, Most