PROCESS FOR ENZYMATIC HYDROLYSIS FROM A MIXTURE OF PRE-TREATED SUBSTRATES OF DIFFERENT POROSITIES

Abstract

The present invention relates to a process for enzymatic hydrolysis in which, under agitation, pre-treated lignocellulosic substrates are brought into contact with water and with enzymes such that the mixture has a content of dry matter of between 12 and 35% by weight, said process being characterised in that a mixture is used of at least two pre-treated lignocellulosic substrates with different porosities, at least one of the substrates being a substrate said to be of low porosity having a porosity of less than 60% of the volume and the other substrate a substrate said to be of high porosity having a porosity greater than or equal to 60% of the volume, and said substrate of low porosity being present in a quantity of at least 30% by weight in relation to the total weight of said mixture.

Claims

1. Process for enzymatic hydrolysis in which, under agitation, pre-treated lignocellulosic substrates are brought into contact with water and with enzymes such that the mixture has a content of dry matter of between 12 and 35% by weight, said process being characterised in that a mixture is used of at least two pre-treated lignocellulosic substrates with different porosities, at least one of the substrates being a substrate said to be of low porosity having a porosity of less than 60% of the volume and the other substrate a substrate said to be of high porosity having a porosity greater than or equal to 60% of the volume, and said substrate of low porosity being present in a quantity of at least 30% by weight in relation to the total weight of said mixture.

2. Process according to claim 1 in which the substrate of low porosity is present in a quantity of between 30 and 50% by weight in relation to the total weight of said mixture.

3. Process according to claim 1 in which the substrate of low porosity is present in a quantity of between 40 and 50% by weight in relation to the total weight of said mixture.

4. Process according to claim 1 in which the substrate said to be of low porosity has a porosity of less than 58% of the volume.

5. Process according to claim 1 in which the substrate said to be of low porosity has an apparent density of greater than 680 kg/m3.

6. Process according to claim 1 in which the substrate said to be of low porosity is miscanthus.

7. Process according to claim 1 in which the substrate said to be of high porosity has a porosity of greater than 65% of the volume.

8. Process according to claim 1 in which the substrate said to be of high porosity has an apparent density of between 530 and 680 kg/m.sup.3.

9. Process according to claim 1 in which the substrate said to be of high porosity is wheat straw.

10. Process according to claim 1 in which the pre-treated lignocellulosic substrates are brought into contact at a content of dry matter of between 18 and 24% by weight.

11. Process according to claim 1 in which the process takes place at a temperature of between 40 and 60 C., at a pH of between 4 and 6, and at atmospheric pressure.

12. Process according to claim 1 in which said process is implemented in a sequentially fed reactor during which no racking of the contents of the reactor is carried out.

13. Process according to claim 1 in which said process is implemented in a batch reactor.

14. Process according to claim 1 in which said process is followed by a fermentation step in the presence of an alcohol-producing microorganism.

15. Process according to claim 1 in which said process is carried out in the presence of an alcohol-producing microorganism according to a process of simultaneous saccharification and fermentation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] FIG. 1 represents the results of the enzymatic hydrolysis tests of the Examples.

[0089] Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

[0090] In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

[0091] The entire disclosures of all applications, patents and publications, cited herein and of corresponding French application No. 17/59.032, filed Sep. 28, 2017, are incorporated by reference herein.

EXAMPLES

[0092] The substrates used for the test examples are pre-treated wheat straw and miscanthus, respectively. Table 1 summarises the physical and chemical characteristics of the pre-treated wheat straw and miscanthus. The pre-treated substrates generally have a dry matter of between 40 and 60% by weight, said dry matter in the table referring to the pre-treated substrate as is. Batch tests on a substrate of high porosity (wheat straw), on a substrate of low porosity (miscanthus) and on a combination of the two at different ratios were carried out (Table 2). All the tests were performed at a content of dry matter of 20% by weight in the mixture of the process.

[0093] The performances in the tests were assessed taking into account the three factors of: (i) mixing time, (ii) energy consumption by the mixture and (iii) the concentration of glucose contained in the reaction mixture at the end of the enzymatic hydrolysis.

[0094] The results show that the rheological behaviour during the enzymatic hydrolysis depends on the substrates used to feed the reactor (FIG. 1): the torque is higher for wheat straw than for miscanthus. Wheat straw (test S-B) recorded a considerable reduction in the torque values between the start and the end of the tests. In fact, the torque required for a good mixing of the reaction medium drops from 0.64 Nm to 0.22 Nm for the S-B test. Furthermore, the torque in the case of the miscanthus test (test M-B) drops from 0.09 to 0.045 Nm (FIG. 1).

[0095] The value of the torque is closely correlated to the energy consumption for the mixing. As a consequence, test S-B required more than 32.5 kJ, whereas test M-B required between 5 and 7 kJ, with an energy reduction of nearly 80%. The mixing time, which is an indicator of the rheological performances in the reactor, was more than 50 s for the wheat straw compared to just 17 s for the miscanthus.

[0096] The concentration of glucose was similar for all the tests: between 19 and 21 g/L.

[0097] The differing rheological and energy values for the two substrates can be explained by the viscosity. The reaction medium composed of 20% by weight of dry matter of wheat straw (test S-B) was highly viscous, with an apparent viscosity of 420.13.1 cP. Conversely, the miscanthus (test M-B) had a gentle fluid-dynamic behaviour with low viscosity values 79.404.05 cP at 20% by weight of dry matter. This difference is due to a different physical structure of the two substrates. Table 1 shows that the wheat straw has a higher degree of porosity than the miscanthus (73% of the volume and 52% of the volume, respectively). The rheological behaviour can then be explained by an impregnation of water that is much higher for the particles with greater porosity (wheat straw).

[0098] Moreover, batch tests (Table 2) were carried out on mixtures of wheat straw and miscanthus at different concentrations. As expected, the reduction in the concentration of wheat straw in the mixture allowed a reduction of the mixing time and the energy consumptions. In test SM-80:20, the viscosity was still highly influenced by the presence of wheat straw. However, when the content of miscanthus present in the reaction mixture reaches 30% by weight (test SM-70:30), the viscosity of the mixture falls and its behaviour is similar to that observed during test M-B.

[0099] The reduction in torque values as a result of the increase in the miscanthus content in the reaction mixture is of major significance for the energy consumption. Test SM-80:20 required 30.5 kJ for the mixing, similar to test S-B, but the total energy consumption falls to around 8 kJ for test SM-70:30. This value is very close to the 5.8 kJ recorded with test M-B. A synergy effect can therefore be seen in terms of the fall in viscosity. In fact, the effect of the water impregnation by the substrates of high porosity is cancelled out by the substrates of low porosity when the concentration of substrates of low porosity is at least 30% by weight in said mixture.

TABLE-US-00001 TABLE 1 Description of the wheat straw and miscanthus Miscanthus Wheat straw Dry matter of the pre-treated substrate 47.73 144 46.06 1.90 (% by weight) Apparent density (kg/m.sup.3) 722.54 12.14 607.46 18.76 Porosity (% of the volume) 52.00 2.60 73.00 3.65

TABLE-US-00002 TABLE 2 Abbreviations and description of the tests. Abbreviation Description of the tests S-B Batch test with wheat straw M-B Batch test with miscanthus SM-80:20 Batch test with a mixture composed of 80% by weight of wheat straw and 20% by weight of miscanthus SM-70:30 Batch test with a mixture composed of 70% by weight of wheat straw and 30% by weight of miscanthus SM-50:50 Batch test with a mixture composed of 50% by weight of wheat straw and 50% by weight of miscanthus SM-30:70 Batch test of a mixture composed of 30% by weight of wheat straw and 70% by weight of miscanthus

[0100] The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

[0101] From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.