FR2604728A1 - Process for saccharification of wood-cellulose materials and plant for making use of the process - Google Patents

Abstract

The process is characterised in that the milled cellulosic material is conveyed to a reactor 1 fed with hydrochloric acid in 42% aqueous solution; the hydrolysed mass, partially separated from the hydrochloric acid recycled to the reactor 1, is conveyed to a filtration equipment 9 for separating lignin from the sugar solution; the sugar liquid separated from the lignin is conveyed to a concentrating apparatus 10 where the content of sugars and other substances in solution is raised and the content of residual hydrochloric acid is reduced; the recovered hydrochloric acid is recycled to the reactor 1. The solution depleted in hydrochloric acid is then conveyed into storage vessels 11 where the posthydrolysis stage takes place. The glucose thus formed is afterwards conveyed to fermentation while the separated lignin can be employed as fuel.

Description

 The present invention relates to a process for the saccharification of woody-cellulosic materials for the production of fermentable sugars and to an installation for the implementation of the process.

 The best known of the cellulose hydrolysis processes using concentrated hydrochloric acid is the Bergius process dating back to around 1920.

 It is known that this process was exclusively applied to woody materials in parts of reduced dimensions and was carried out by an attack with hydrochloric acid in aqueous solution at 42% at room temperature and pressure, passing the acid solution through the mass woody. However, by this process neither straw nor other tiny products could be treated, since a uniform flow of acid solution could not have been established. Preferential flow routes would have been created and therefore part of the mass to be treated would not have been attacked.

 The sugars obtained by hydrolysis were mother polZ to be transformed into monomers by heating at 1200C for 20 minutes. This led to the need to act under pressure, which involved the risk of a significant demolition of the glucose that had formed.

 Although this process promised much more interesting theoretical results than the other processes (for example the Schoeller process), it did not have practical dissemination because an essential condition for the process to be economically advantageous was the need to recovering hydrochloric acid both from the point of view of the cost of the reagent and from the point of view of the difficulties that the presence of a very high percentage of hydrochloric acid would have created throughout the cycle and finally on the discharge waters.

 More recently, other processes for the saccharification of cellulose have been developed, tending to overcome the drawbacks and limitations of the Bergius process.

 Among these is the Battelle process, which is the subject of European patents nO 81.810246.9 and nO 81.201182.3.

 Briefly, this process provided for two distinct stages: a first stage of separation of the cellulose, using a solvent (phenol + hydrochloric acid), of the pentose solution and of the lignin solution in phenol; a second stage of hydrolysis of the "cleaned" cellulose by treatment with gaseous hydrochloric acid.

 This process, however, was quite complicated and very expensive.

 From the point of view of the preparation, it also presented great difficulties due to the high viscosity of the treated material (partially formed from tiny woody-cellulosic material and partially from complex sugars) which made it almost impossible to circulate in the installation.

 Having noted the difficulties of practical implementation of this process, the applicant for this patent returns to the origins of the process, again taking into consideration the Bergius process and applying to the same process a fundamental variant which related to the developments which had occurred in the saccharifere sector, in analogy with what had been planned - at the time by Bergius, to apply them to straw (and other similar products) which represents the material able to guarantee its availability also in the very distant future and therefore allowing to take into account very high investment costs.

 As planned by Bergius, a 42% hydrochloric acid solution, cooled to a temperature below 200C, was used, in which the quantity of straw necessary gradually and sufficient to create a solid ratio compared to the mass equal to 20-25%.

 During the step of introducing the straw into the liquid, hydrochloric acid gas was also blown in order to acidify the part of water contained in the straw (12-15% of the total) and therefore maintain constant in the liquid the concentration of hydrochloric acid at 42%. After about four hours, the completed hydrolysis operation was considered and the loss of hydrochloric acid was stripped in the laboratory.

 The results were satisfactory due to the fact that a yield of fermentable sugar was obtained on the order of 90% of theoretical.

 Starting from this point, a pilot project was then developed to check the validity of the process, also outside the laboratory. It was anticipated that the pilot plant would essentially consist of a mixing reactor into which initially 42% hydrochloric acid solution, straw and gaseous hydrochloric acid had been introduced. The hydrochloric acid, after the stripping operation, was recovered and recycled to the reactor.

 At the end of the process, a concentrate had to be obtained in which the sugar solution should have reached total values of the order of 30% and residual hydrochloric acid values of approximately 6%. It was expected that the product thus obtained was diluted 1 to 1, which made it possible to obtain a product having approximately 15% of total sugars and 3% of hydrochloric acid. The sugars present should have consisted of pentose (about a third) and polymer sugars (two thirds). The last operation should have treated this mass by heating to 900C for three hours in order to transform the polymer sugars into monomer sugars (post-hydrolysis).

 After carrying out these operations, fermentation could begin, after neutralization with calcium hydrate until there was a residual acidity in the mass to be fermented equal to a pH = 4.

 During the experimental stage in a pilot installation, however, we encountered many difficulties, due to the presence of lignin.

 The essential aim of the present invention is therefore that of overcoming the drawbacks encountered in the processes of known type by the development of a new process for the saccharification of woody-cellulosic materials and in particular of straw or other residues. agricultural products to produce iron-sugars which operates at a low temperature to reduce the destruction of the glucose in formation produced by heat, and in which the hydrolyzed mass has a low viscosity so that it can circulate easily during different stages of the process.

 Another object of the invention is to develop a process which makes it possible to obtain high concentrations of sugar and consequently reduced percentages of hydrochloric acid.

 Yet another object of the invention is to provide an installation for the implementation of the method mentioned above.

 These and other objects are achieved by the invention with reference, the main characteristics of which are described in the claims which follow.

 It should be noted that the step of filtering and drying the degassed sugar product provided according to the present invention, allowing the elimination of lignin from the hydrolyzed, offers the possibility of sending a concentration of sugar-free solution to the concentration. suspended substances.

 This type of sugar solution can be concentrated to values of 85 Brix, which results in a reduction of the hydrochloric acid content below 6%.

 The main advantages of this system are: - significant reduction in the loss of hydrochloric acid; - possibility of making sugar solutions intended to give, after fermentation, hydro-alcoholic solutions up to 10% alcohol (in the specific case in which the sugar obtained is used for the production of dehydrated alcohol, c (i.e. usable as fuel). In this regard it is obvious that there is a great saving of energy if one distils hydroalcoholic solutions at 100 compared to hydroalcoholic solutions at 20 C.

 Still with regard to the transformation of sugar into alcohol, another important energy saving occurs by the concentration of the discharge water from the distillation columns. This concentration is required for ecological reasons and also and above all in consideration of the fact that the dry substance contained in the said discharge waters after the concentration represents a remarkable contribution to the energy balance as a fuel. It is therefore obvious that, even if the concentration of landfill waters is taken into account, the energy costs of concentration are relatively low if solutions with a high Brix can be sent to the concentration.

 Other characteristics and advantages of the present invention will emerge more clearly from the detailed description of the process made with reference to an installation illustrated with a simple non-limiting example in the appended drawing which represents a simplified overall diagram of a installation for implementing the method according to the present invention.

 In a mixing reactor 1 is continuously introduced, through a hopper 2, woody-cellulosic material cut into small pieces (formed for example of crushed straw reduced into pieces of the order of 2-.5 mm) and at the same time a 42% hydrochloric acid solution is introduced through a mixer 3. In reactor 1 takes place the mixing of the material with the acid solution under atmospheric pressure conditions and at the temperature of about 200C and according to a ratio of one part of material per 4-6 parts of acid solution.

 In order to optimize the hydrolysis reaction, part of the product is recycled to reactor 1 through the mixer 3 after cooling in a refrigerator 4 which keeps the temperature in reactor 1 at around 200C. Then we put the product on a break. in tanks 5 and 6 provided with agitator so that the complete reaction can take place. The hydrolyzed product is sent to a pre-evaporator 7 where it is heated to about 700C under atmospheric pressure conditions, distilling 40-50% of hydrochloric acid. The pre-evaporator 7 is associated with an expansion tank 8 from the head from which gaseous hydrochloric acid is extracted, mixed with steam at a concentration of approximately 92% of gas. This mixture is recycled to reactor 1 through the mixer 3. At the base of the expansion tank 8, the partially degassed sugar product having an acid residue of approximately 50% relative to the original quantity is extracted.

 The sugar product is then filtered so as to separate the lignin from the liquid part.

This filtering takes place in a multi-stage filtering group 9 by washing with water in countercurrent.

In more detail, the multi-stage filtering group of 9 is composed of a battery of vacuum filters B,
D, F and H arranged in series and intercalated by mixers A, C, E and G. Each stage includes a mixer (for example C) and a filter (D) placed downstream of the mixer (C). Each mixer is supplied either with product to be filtered (which is then sent to the next filter) or with filtered liquid coming from the filter of the next stage.

 In mixer A it is the sugar product which is fed, while in mixer G of the last stage water is introduced for the backwashing of the product.

 This system of filtering and washing in series makes it possible to provide, on the one hand, a sugar solution free of suspended matter and, on the other hand, a mass of liquid free of acid and sugars. The acid and sugars are in fact transferred, because they are soluble in water, in the liquid sent to the next step of concentration.

 It should be noted that the quantity of water required for this operation is quite limited, that is to say not more than 10 - 15% of the total mass.

 The emptied lignin can be recovered and, after pressing and drying, used for example as fuel.

The sugar liquid is conveyed, from the filtering step described above, to a concentrator
rion under vacuum pushes 10 to multiple effect where the recovery of hydrochloric acid (in aqueous solution) takes place, this acid being recycled to the reactor 1 through the mixer 3, also taking place the separation of a mass ( concentrate) which has a sugar and other substance content in solution of approximately 85 Brix and a residual hydrochloric acid content of approximately 6%.

 According to what has been shown in the appended diagram, the concentrator 10 comprises a series of evaporators 20-24, associated with expansion tanks 25-29, in which the concentration takes place by successive evaporations in high vacuum conditions, using low temperature steam from the heads of said expansion tanks 25-28.

 In the first evaporator 20 the heat is instead supplied in the traditional way.

 After concentration, the total sugars present in the concentrate are formed of polymers and pentose, in addition to glucose. For the transformation of the polymers into monomers, the concentrated sugar liquid is sent to a subsequent reactor 11 where, at the temperature of 900 ° C. for a permanence time of approximately 2 hours, the post-hydrolysis takes place (transformation in an acid medium of the polymer sugars into glucose).

 Before post-hydrolysis, the mass is diluted by the introduction of water into the mixer 12 in order to bring the fermentable sugars, or which will become fermentable, to 20% (and the concentration of residual hydrochloric acid to approximately 3%), with a view to obtaining, after fermentation (if provided), hydro-alcoholic liquids with the highest possible alcohol content (10%).

 When the complete polymer reversion has been obtained after the post-hydrolysis, the sugar liquid is neutralized until pH = 4 is obtained using calcium hydrate, this value being necessary to allow good fermentation.

 The invention achieves the aims.

 Obviously, the invention is susceptible of numerous modifications and variants without going beyond the protection framework thereof.

 It should in particular be emphasized that the filtering system described above can be implemented not only by using vacuum filters in series, but also by using press filters or other types.

 In addition, all the details can be replaced by technically equivalent elements and the elements making up the installation as well as the process parameters can be varied as required.

Claims (8)

R E V E N D I C A T I O N S 1. - Process for the saccharification of woody-cellulosic materials by hydrolysis with concentrated hydrochloric acid, characterized in that it comprises the following stages: a) a mixture of the woody-cellulosic material is carried out with a 42% solution % hydrochloric acid under conditions of atmospheric pressure and at a temperature of about 20 "C and according to a ratio of one part of material per 4-6 parts of acid solution; b) the hydrolysed product is subjected to a break so that the complete reaction can take place; c) pre-evaporation is carried out under atmospheric pressure conditions and at a temperature of about 700C, distilling 40 t 50% of the hydrochloric acid which is brought into the process and extracting a partially degassed sugar product; d) filtering said partially degassed sugar product so as to separate the lignin from the liquid part; e) concentrating the sugar liquid separated from the lignin and o n recovers the hydrochloric acid which is brought back into the process and at the same time the content of hydrochloric acid in the mass is reduced to a level useful for the next step; f) heating is carried out at approximately 900C for approximately two hours of the concentrated sugar liquid for the trams formation in acid medium (post-hydrolysis) of the polymeric sugars into glucose. 2) Method according to claim 1, characterized in that said filtering of the partially degassed sugar product is obtained by a series of inter-calibrated filters by mixtures and backwashing with water. 3. Method according to claim 2, characterized in that said filtering takes place according to the principle of vacuum filtration. 4. Method according to claim 1, characterized in that said concentration of the sugar liquid separated from the lignin is carried out by a series of successive evaporations under conditions of high vacuum using steam at low temperature. 5. Method according to claim 1, characterized in that the mass, after the concentration step has a content of sugars and other substances in solution equal to approximately 85 Brix and a content of residual hydrochloric acid equal to approximately 6%. 6. Method according to claim 1, characterized in that said woody-cellulosic material is formed of crushed straw reduced into pieces of the order of 2 t 5 mm. 7. Installation for implementing the method according to claims 1 to 6, characterized in that it comprises: - a reactor (1) for hydrolyzing the cellulose, supplied with woody-cellulosic material through a hopper (2) and a 42% solution of hydrochloric acid through a mixer (3), being further provided for recycling to the reactor (1) through said mixer (3) after cooling of said recycling product in a refrigerator (4); - at least one pause tank (5,6J disposed downstream of said reactor (1); - a subsequent pre-evaporator (7) associated with an expansion tank (8), from the head of which hydrochloric acid is extracted gaseous mixed with steam at a concentration of about 92% gas, said mixture being recycled to the reactor (1) through said mixer (3), and from which the partially extracted sugar product is extracted degassed; - a subsequent multi-stage filtering group (9) where the lignin is separated from the sugar liquid by washing with water in countercurrent; - a subsequent vacuum concentrator (10) to multiple effect where the hydrochloric acid is separated in aqueous solution which is recycled to the reactor (1) through said mixer (3) and from a mass in which the content of sugars and other substances in solution is approximately 85 Brix and the residual hydrochloric acid content is approximately 6%; - s A subsequent post-hydrolysis reactor (11) which receives said mass after it has been diluted with water to reduce the concentration of residual hydrochloric acid to around 3%. 8. Installation according to claim 7, characterized in that said multi-stage filtering group (9) consists of a battery of vacuum filters (B, D, F and H) arranged in series and interposed by mixers ( A, C, E and G), where each stage comprises a mixer and a filter placed downstream of said mixer, each mixer being supplied either with product to be filtered or with filtered liquid coming from the filter of the next stage, into the mixer of the last stage (G) water being introduced to backwash the product to be filtered.