ZSM-5 zeolites with wood lignin oxidized or not

Abstract

The present invention relates to a process for preparing a zeolite ZSM-5 presenting a Si/Al molar ratio comprised between 2 and 8, preferably between 3 and 8, comprising the following steps: a) mixing at least one silicon source, at least one aluminum source, at least one organic template and at least one aqueous solvent, in order to obtain a synthesis mixture in solution or gel form; b) ageing the mixture obtained in step a) at a temperature of between 20? C. and 200? C. during at least 30 minutes; and d) crystallizing the resulting mixture during at least 24 hours, wherein a step c) of adding wood lignin or oxidized wood lignin to the mixture is performed after step a) or after step b). It also relates to a zeolite which is obtainable by such a process, and to its use.

Claims

1. Process for preparing a zeolite ZSM-5 exhibiting a Si/Al molar ratio comprised between 2 and 8, preferably between 3 and 8, comprising the following steps: a) mixing at least one silicon source, at least one aluminum source, at least one organic template and at least one aqueous solvent, in order to obtain a synthesis mixture in solution or gel form; b) ageing the mixture obtained in step a) at a temperature of between 20? C. and 200? C. during at least 30 minutes; and d) crystallizing the resulting mixture during at least 24 hours, wherein a step c) of adding wood lignin or oxidized wood lignin to the mixture is performed after step a) or after step b).

2. Process according to claim 1, wherein it further comprises a step e) of separating the solid obtained in step d) by means of centrifugation, filtration or evaporation of the solvent.

3. Process according to claim 1, wherein it comprises the following steps: a) mixing at least one silicon source, at least one aluminum source, at least one organic template and at least one aqueous solvent, in order to obtain a synthesis mixture in solution or gel form; b) ageing the mixture obtained in step a) at a temperature of between 20? C. and 200? C. during at least 30 minutes; c) adding wood lignin or oxidized wood lignin to the mixture of step b) ; and d) crystallizing the mixture of step c) during at least 24 hours.

4. Process according to claim 1, wherein it comprises the following steps: a) mixing at least one silicon source, at least one aluminum source, at least one organic template and at least one aqueous solvent, in order to obtain a synthesis mixture in solution or gel form; c) adding wood lignin or oxidized wood lignin to the mixture of step a); b) ageing the mixture obtained in step c) at a temperature of between 20? C. and 200? C. during at least 30 minutes; and d) crystallizing the mixture of step b) during at least 24 hours.

5. Process according to claim 1, wherein the silicon source is chosen from tetraethylorthosilicate (TEOS) (C.sub.8H.sub.20O.sub.4Si), colloidal silica, disodium metasilicate (Na.sub.2O.sub.3Si) and their mixtures.

6. Process according to claim 1, wherein the aluminum source is chosen from sodium aluminate (NaAlO.sub.2), aluminum isopropoxide (C.sub.9H.sub.21AlO.sub.3), aluminum sulfate (Al.sub.2O.sub.12S.sub.3) and their mixtures, and/or wherein the organic template is chosen from tetrapropyl ammonium hydroxide (TPAOH) (C.sub.12H.sub.29NO), tetramethyl ammonium hydroxide (TMAOH) (C.sub.4H.sub.13NO), tetramethyl ammonium bromide (C.sub.4H.sub.12BrN), tetrapropyl ammonium bromide (C.sub.12H.sub.28BrN) and their mixtures.

7. Process according to claim 1, wherein step a) comprises the following sub-steps: a1) mixing at least one aluminum source with at least one organic template in at least one aqueous solvent, in order to obtain a mixture; a2) adding at least one silicon source, and preferably at least one salt, more preferably at least sodium chloride, into the mixture of step a1), in order to obtain the synthesis mixture in solution or gel form, preferably the molar ratio of the silicon source to the salt, preferably sodium chloride, is of at least 2.20, preferably between 2.20 and 3, preferably between 2.20 and 2.80, preferably between 2.20 and 2.50.

8. Process according to claim 1, wherein the wood lignin presents at least one, preferably all, of the following features: it presents an ash content of between 3% to 10%, preferably from 5% to 8% by weight of the total weight of the dry wood lignin; it presents a residual carbohydrate content of between 5% to 20%, preferably from 8% to 20%, preferably from 10% to 15% by weight of the total weight of the wood lignin; some parts of the wood lignin are extracted in at least one organic solvent, which may be polar or apolar, preferably the organic solvent is chosen from hexane, chloroform and acetone, wherein an amount of 3% to 10% by weight of the total weight of the wood lignin is extracted in hexane, preferably an amount of 4% to 8% by weight; an amount of 3% to 10% by weight of the total weight of the wood lignin is extracted in chloroform, preferably an amount of 4% to 8% by weight; and an amount of 1% to 10% by weight of the total weight of the wood lignin is extracted in acetone, preferably an amount of 1.5% to 5% by weight; and/or it presents a Klason lignin content of between 50% to 95%, preferably from 50% to 90%, preferably from 50% to 80%, preferably from 60% to 70% by weight of the total weight of the wood lignin; and/or it presents a sulfur atomic content of between 0.8 at % to 8 at %, preferably from 3 at % to 6 at % by weight of the total weight of the dry wood lignin it presents a carbon atomic content of between 35 at % to 55 at %, preferably from 37 at % to 51 at % by weight of the total weight of the dry wood lignin; and/or it presents a hydrogen atomic content of between 3.8 at % to 6.5 at %, preferably from 4 at % to 6.2 at % by weight of the total weight of the dry wood lignin; and/or it comprises a nitrogen atomic content of between 0.1 at % to 0.5 at % by weight of the total weight of the dry wood lignin.

9. Process according to claim 1, wherein the wood lignin is oxidized and is obtained by a chemical treatment, preferably an alkali treatment of the wood lignin, preferably the oxidation is performed by mixing the wood lignin with an alkali solution, and may be heated, typically at a temperature of 70? C. to 100? C., preferably of 80? C. to 90? C., typically for at least 1 h.

10. Process according to claim 1, wherein the ageing of step b) is performed during at least 1 h, preferably at least 1 h30, preferably between 1 h and 5 h.

11. Process according to claim 1, wherein the zeolite ZSM-5 presents a Si/Al molar ratio comprised between 3 and 7.6, preferably between 3 and 7, preferably between 3 and 4.

12. Zeolite ZSM-5 presenting a Si/Al molar ratio comprised between 2 and 8, preferably between 3 and 8, which is obtainable by the process according to claim 1.

13. Zeolite ZSM-5 according to claim 12, which presents: a specific surface area of between 150 m.sup.2/g and 250 m.sup.2/g, preferably between 180 m.sup.2/g and 220 m.sup.2/g, and a total pore volume of between 0.01 cm.sup.3/g and 0.5 cm.sup.3/g, preferably between 0.05 cm.sup.3/g and 0.2 cm.sup.3/g, wherein the microporous volume is 70% of the total pore volume, as measured by N.sub.2 adsorption-desorption.

14. Zeolite ZSM-5 according to claim 12, wherein it is in the form of crystals presenting an oblong shape with a length and a width, the length being greater than the width, for example at least 2 times greater; preferably the crystals have a length of from 10 ?m to 30 ?m, preferably of from 15 ?m to 25 ?m.

15. Use of a zeolite ZSM-5 according to claim 12, in at least one of the following applications: as a catalyst, especially in hydrocarbon conversions, preferably Fluid Catalytic Cracking such as methanol to olefins conversion or n-hexane cracking; for adsorbing or desorbing liquids and/or gases, such as water treatment or industrial gases treatment; for selective separations of gas or liquid mixtures, i.e. as molecular sieves; as detergents; for treating pesticides, organic chlorine or hydrocarbons-loaded effluents; for remediating heavy metals contained in soils or waters; for purifying soils or waters from radioactive elements, such as cesium; or as a seed in an industrial process for preparing ZSM-5 zeolites presenting a Si/Al molar ratio comprised between 2 and 8, preferably between 3 and 8.

Description

Example 1: Synthesis of ZSM-5 Zeolite Incorporating Wood Lignin

Lignins

[0115] Several batch of lignins have been tested: alkali lignin (low sulfonate content, Sigma Aldrich: 46.5 at % C and 4.9 at % H) (also called kraft alkali lignin), wood lignin (from the Kirov plant, city of Kirov, Russia, hereafter wood lignin), oxidized wood lignin and walnut shells (ecoshell).

[0116] However, the wood lignin with the following composition (Table 1) was selected to produce high Al-containing ZSM-5 zeolite:

TABLE-US-00001 TABLE 1 Composition of wood lignin sample Residual Extractive substances, % Ash carbohydrate Chlo- Klason content, content, Full Hexane roform Acetone lignin, % % content extract extract extract % 6.9 13.5 14.3 5.9 6.0 2.4 65.3

[0117] This wood lignin was dried at room temperature and sieved until particle size was of 0.5 mm.

Detailed Analysis of the Wood Lignin (i.e. From the Kirov Plant, City of Kirov, Russia as Mentioned Before)

Extractive Substances Analysis

[0118] Lignin extraction was performed in Soxhlet extractor in series of n-hexane, chloroform and acetone extractions. The extracted substances were dried on a rotary vacuum evaporator at a temperature 40? C.

[0119] The obtained extracted substances were analyzed by GS-MS (Agilent G 1530A in tandem with mass selective detector Agilent HP 5973, capillary column HP-5 25 m?0.2 mm with a liquid phase of 5% phenylmethylsiloxane).

The Relative Component Composition of Wood Lignin Extracted Substances

[0120] Analysis of the extracted components composition showed the presence of fatty (C.sub.16-C.sub.24) acids and resin acids (dehydroabietic and abietic acids; but also 7-oxodehydroabietic acid methyl ester) and sterol components (campasterol, sistosterol, sitostanol but also cholesterol).

Elementary Composition Analysis

[0121] Analysis of wood lignin elementary composition was performed on the machine elementar vario EL.

[0122] The results are shown in the table below.

TABLE-US-00002 TABLE 2 Elemental composition of hydrolysis lignin O C H O N S 47.24 4.34 30.72 0.15 0.87

Functional Group Analysis

[0123] Content of methoxy groups in wood lignin was determined by ZeiselVieb?ckSchwappach method (G. Zakis, Functional Analysis of Lignins and Their Derivatives, 1994). Hydroxy groups content was determined by methylation with dimethylsulfate followed by methoxyl groups analysis.

[0124] The results are shown in table 3.

TABLE-US-00003 TABLE 3 Functional group content in hydrolysis lignin Methoxyl groups, % Hydroxyl groups, % 10.64 5.84

FTIR Analyses

[0125] FTIR analyses of wood lignin were carried out in a reflectance mode using a Nicolet? iS? 50 FT-IR Spectrometer (Thermo Nicolet Corp. Madison, WI, USA) equipped with a build in diamond ATR unit. The region between 4000 and 400 cm.sup.?1 with a resolution of 4 cm.sup.?1 and 66 scans was recorded (data not shown).

[0126] The characteristic vibration bands of lignin complex matter corresponding to CH deformation in guaiacyl units, aromatics stretching were observed at 1182 cm.sup.?1 and 1602 cm.sup.?1, respectively.

Preparation of Oxidized Lignin

[0127] The oxidation procedure of the wood lignin of Table 1 was performed as follows: [0128] i) At first, dissolution of wood lignin in a round-bottomed 3-neck flask with a volume of 1 L, equipped with a thermometer, a propeller stirrer and a reflux condenser. [0129] ii) The alkali solution (3.6 g of NaOH in 0.5 L of water, thus 0.18 M) is then placed in the flask, and, through the side-neck, small portions of lignin in amount of 20 g are added under vigorous stirring. The temperature in the flask is preferably raised to 85? C. let under stirring for at least 1 h. [0130] iii) The solution is cooled to room temperature and approximately 0.5 L of solution of oxidized lignin is obtained at a concentration of 40 g/L. [0131] iv) The solvent is then evaporated and the dark brown solid recovered.

Detailed Analysis of the Oxidized Wood Lignin Thus Obtained

.SUP.13.C NMR Analysis

[0132] NMR-analysis of wood lignin was performed on a spectrometer Bruker MSL400. Frequency 100.6 MHz, 7 mm zirconium rotor rotates at a frequency of 8 kHz, the pulse width of H.sup.1 and C.sup.13 was 90?, pulse delay of 4 s, contact time 1.5 ms, the number of pulses being 5000.

[0133] Solid-state .sup.13C NMR analysis allows to quantify structural units contained in lignin (C.sub.Ar-O, C.sub.Ar-C, C.sub.Ar-H) (E. A. Capanema, M. Y. Balakshin, J. F. Kadla, A comprehensive approach for quantitative lignin characterization by NMR Spectroscopy. J. Agric. Food Chem. 2004, 52, 1850).

[0134] The relative content of carbon atoms with various substituents in phenylpropane units of lignin was estimated in relation to 6 carbon atoms of aryl structure. The results are shown in the table 4 below.

TABLE-US-00004 TABLE 4 Quantitative estimation of structural elements in hydrolyzed lignin as revealed by .sup.13C NMR in relation to 6 carbon atoms of aryl structure Structural Integrated Fragment structure element region, ppm Relative content [00003] ?C.sub.Ar-O? 162-136 1.8 [00004] ?C.sub.Ar-C? 136-125 1.9 [00005] ?C.sub.Ar-H? 125-106 2.3

Preparation of the ZSM-5 Zeolites

[0135] Three types of ZSM-5 zeolites were prepared.

[0136] For this purpose, 0.12 g of NaAlO2 was mixed with 17.7 mL of tetrapropylammonium hydroxide (TPAOH) in 41 mL of distilled water. Then, 0.353 g of NaCl and 3.1 mL of tetraethylorthosilicate (TEOS) were dissolved in the previous solution. Ageing was performed during 2 h at room temperature.

[0137] Thereafter, different amounts of the oxidized lignin (obtained as described above) were added, and crystallization occurred during 48 h at 170? C.

[0138] The amounts of oxidized lignin are: 100 mg, 300 mg or 500 mg.

[0139] Thus, respectively, the corresponding zeolites are called z_100LO, z_300L0 and z_500LO.

[0140] It is noticed that during the preparation of the synthesis gel, oxidized lignin was added after mixing all the other reactants. It is important to mention that even at low mass (100 mg), this compound only partially dissolved in the solution.

Structural Properties

[0141] The diffraction patterns of the samples prepared with different quantities of oxidized lignin after calcination step exhibited the sole presence of MFI structure, which indicates the total combustion of the biomass. Moreover, the addition of oxidized lignin did neither lead to a loss in crystallinity nor contribute to the appearance of a new crystalline phase. N.sub.2 adsorption-desorption measurements reported typical type I isotherm related to microporous materials for the three samples. Specific surface areas (S.sub.BET) of around 200 m.sup.2/g and total pore volume of around 0.1 cm.sup.3/g was obtained, where the microporous volume is 70% of the latter (Table 5), confirming that z_xLO possess predominantly a microporous structure. In stark contrast, Gomes et al (Microporous and Mesoporous Mater. 254 (2017) 28-36), reported a type IV isotherm, thus indicating the presence of mesopores in the zeolite while using wood lignin in the synthesis of ZSM-5 zeolite. The pore distribution profiles obtained by the BJH method (i.e. Barrett-Joyner-Halenda method, which is a standard method for measuring pore volume and pore size distribution of solid materials) further confirm the sole presence of micropores in z_xLO materials.

TABLE-US-00005 TABLE 5 Specific surface area (S.sub.BET), external surface area (S.sub.ext), total pore volume (V.sub.pore) and microporous volume (V.sub.micro) obtained by N.sub.2 adsorption-desorption Sample S.sub.BET (m.sup.2/g) S.sub.ext (m.sup.2/g) V.sub.pore (cm.sup.3/g) V.sub.micro (cm.sup.3/g) z_100LO 200 55.9 0.108 0.071 z_300LO 201 60.1 0.105 0.069 z_500LO 195 54.7 0.102 0.069

[0142] The microstructure of the samples was analyzed by SEM.

[0143] z_100LO exhibits the characteristic coffin-shaped crystals associated to ZSM-5 zeolite type. Interestingly, the addition of oxidized lignin leads to the formation of crystals of dimensions around 20 ?m presenting the oblong shape of a peanut. The increase of the biomass quantity increases also the appearance of these peculiar crystals, until a homogeneity is observed for z_500LO. Observing in more details, these peanuts are nothing more than an agglomeration of rectangular filaments that consists in nanocrystals with the shape of French fries. It seems that these filaments grow from a central point of the agglomerate that can be the starting matter for those elongated crystals growth. Once again, the same was observed for Si/Al=8 of Pereira et al. (ZSM-5 SAR8 of Biomass-mediated ZSM-5 zeolite synthesis: when self-assembly allows to cross the Si/Al lower limit, Chemical Science, 2018, 9, 6532-6539), although the crystals exhibited a spherical form. Gomes et al. (Microporous and Mesoporous Mater. 254 (2017) 28-36) also reported a different crystals morphology with high surface roughness formed by the assembly of sub-units which allowed to produce a ZSM-5 material with mesopores (4 nm) and exhibiting a high specific surface area of 450 m.sup.2/g.

[0144] The mapping of the elements of z_500LO was also performed by EDX coupled to SEM (not represented), and it was detected the presence of sole Si, Al and O elements, confirming the previous assumption of total removal of oxidized lignin. Surprisingly, it was determined a Si/Al ratio of 4, being the lowest ever reported for the ZSM-5 zeolite. Likewise, it was determined that z_100LO has a Si/Al ratio of 8, and z_300L0 a Si/Al ratio of 6.

[0145] FIG. 2 represents a SEM image of z_500LO zeolite crystals, which exhibit an unusual oblong shape, named peanut-shape morphology.

[0146] In order to confirm these results, solid-state NMR was performed. This technique relies on the detection of relevant basic nuclei on the zeolite framework by their natural isotopes (natural abundance in parentheses): .sup.29Si (4.7%), .sup.27Al (>99.9%), and .sup.17O (0.04%). The resonance lined obtained for .sup.29Si are usually narrow and, due to their important role as framework element (besides .sup.27Al), these nuclei have been widely used in solid-state NMR studies of micro- and mesoporous materials for structural investigations. The most important application of .sup.29Si NMR is due to the relationship between the .sup.29Si chemical shift sensitivity and the degree of condensation of the SiO tetrahedra, that is the number and type of tetrahedrally coordinated atoms connected to a given SiO.sub.4 unit Si(nAl), with n=0, 1, 2, 3 or 4. The chemical shift ranges from ?80 to ?115 ppm, with the high-field shift signal for Si(0Al). Here, n indicates the number of Al atoms sharing oxygens with the SiO.sub.4 tetrahedron under consideration.

[0147] Differences in the chemical shift between Si(nAl) and Si(n+1Al) are about 5-6 ppm. In this way, the spectra obtained can be used to calculate the framework Si/Al ratio from the NMR signal intensities (I) according to equation 1.

[00001]$\begin{array}{cc}{\left(\frac{\mathrm{Si}}{\mathrm{Al}}\right)}_{\mathrm{NMR}}=\frac{{.Math.}_{n=0}^4{I}_{\mathrm{Si}\left(\mathrm{nAl}\right)}}{{.Math.}_{n=0}^{4}0.25{\mathrm{nI}}_{\mathrm{Si}\left(\mathrm{nAl}\right)}}=\frac{0.1+0.05+0.2+0.55+0.1}{0.2?\left(4?0.1+3?0.05+2?0.2+0.55\right)}=2.67=3& \left(1\right)\end{array}$

[0148] This seems to imply that the presence of oxidized lignin allows the stabilization of the aluminosilicate structure, allowing the lowest Si/Al ratio (SAR) ever reported.

[0149] .sup.27Al NMR spectra reveal a small existence of extra-framework Al (about 0 ppm) besides the lattice aluminum (tetrahedrally coordinated Al at about 40-65 ppm), which can be negligible and admit a real Si/Al ratio of 3 in the z_500LO framework.

[0150] Br?nsted and Lewis acid sites of z_500LO were discriminately measured by FTIR of adsorbed pyridine. The spectrum is similar to the one exhibited by conventional samples with bands at the same wavenumber. By integration of the peaks at 1544 and 1455 cm.sup.?1 after desorption at 150? C., it was obtained 285 and 14.6 ?mol/g for Br?nsted and Lewis acid sites, respectively. Moreover, the Al concentration was determined to be 1444 ?mol/g. Normally, the total concentration of acid sites (Br?nsted+Lewis) should be equal to the concentration of Al in the zeolites. Unfortunately, this is not the case. It might have been an error in Al quantification or a non-negligible fraction of acid sites that are not accessible to pyridine. Nonetheless, high Al content in the aluminosilicate structure directly increases the Bronsted acidity, while Al zoning or extra-framework aluminum species (EFAl) is related to Lewis acid sites. The low value of the latter seems to indicate the nearly absence of these species, as verified by .sup.27Al MAS NMR.

[0151] OH DRIFT spectrum of z_500LO showed three bands at: (i) 3745 cm.sup.?1 characteristic of isolated SiOH with very low intensity compared with commercial zeolites; (ii) 3670 cm.sup.?1 characteristic of extra-framework aluminum AlOH of equally low intensity; and (iii) 3620 cm.sup.?1 characteristic of zeolite framework with high intensity. Once again, these results suggest the presence of very small quantity of EFAl species.

Catalytic Performance in the Methanol-to-Hydrocarbons Reaction

[0152] In the previous section, it was presented the in depth characterization of z_500LO. It is expected that such low Si/Al ratio may lead to interesting catalytic performance in the MTH reaction. The catalyst lifetime was compared to the commercial CBV3020E (Zeolyst company), along with the coke analysis.

[0153] The sample z_500LO exhibited lower capacity to maintain the full conversion of methanol and dimethyl ether than CBV3020E, however its deactivation rate showed to be slower. This may be attributed to the crystal size of the two samples. The commercial zeolite exhibits nanocrystals, which induces shorter diffusion paths for the exit of the reactant/products molecules being able to keep the active sites clean for a longer time. On the other side, once the coke precursors start to poison those sites, the conversion quickly diminishes. In the case of z_500LO, the crystals exhibited an oblong micrometric size, hindering the exit of molecules that slowly deactivate the catalyst. This may be confirmed by the coke analysis that showed lower coke content at 600? C. than CBV3020E. Indeed, this temperature seems non-sufficient to remove all the coke present in z_500LO as there is still a decrease in the mass up to the end of the experiment. This is related to the size of the molecules, which suggest that as bigger as the molecules are, more energy is needed to provide to decompose them. By staying for a longer time in contact with the active sites, coke precursors are able to further react.

[0154] Regarding the products selectivity (Table 6), z_500LO exhibited higher olefins selectivity than CBV3020E, especially towards ethylene and butylene isomers. On the other side, there was a similar formation of compounds with 5 carbons or more for both samples. This is a surprising result as higher aluminum content is associated with higher active sites and, consequently, higher selectivity towards heavier products. It seems that the crystals morphology plays here an important role in the catalytic performance beside the acidity.

TABLE-US-00006 TABLE 6 Selectivity in ethylene (C.sub.2H.sub.4), propylene (C.sub.3H.sub.6), butylene isomers (C.sub.4H.sub.8) and compounds with 5 carbons or more (including aromatics - C.sub.5+) after 1 h on stream of the samples (commercial CBV3020E and z_500LO of the invention) Samples % S.sub.C2H4 % S.sub.C3H6 % S.sub.C4H8 % S.sub.C5+ CBV3020E 3 26 9 30 z_500LO 15 28 13 32

[0155] Hence, it is shown that the incorporation of oxidized lignin in ZSM-5 zeolite synthesis is successful. In depth characterization assessed for one of the samples possessing the lowest Si/Al ratio ever reported, maintaining the sole presence of MFI microporous and crystalline structure.

[0156] The catalytic performance of this new material led to an increased light olefins selectivity and longer catalyst lifetime, which may lead to potential industrial applications.

[0157] FIG. 3 presents the results of methanol conversion (in %) over z_500L0 obtained at 450? C. and WHSV (weight hourly space velocity) =1.1 h -1 , as a function of time on stream (TOS). Selectivities towards the different products are indicated in Table 6.

Catalytic Performance of z_500LO of the Invention in the Methanol-to-Hydrocarbons Reaction as Compared to Prior Art Zeolites

[0158] Surprisingly, the catalytic performance achieved in the methanol conversion into hydrocarbons by z_500LO catalyst according to the invention appears clearly different from the ones obtained with the prior art biomass-templated zeolites, that is: [0159] the prior art ZSM-5 zeolite with a high Si/Al ratio obtained with wood lignin as disclosed in FIG. 5(a) of Pereira et al, 2016 (Influence of Biomass Residues on the Metastability of Zeolite Structures, Nanoscience and Nanotechnology Letters, Vol.8, 1-7, 2016); and [0160] the prior art ZSM-5 zeolite with a Si/Al ratio of 7.6 obtained with washed alkaline hydrolysis of biomass extracted from sugar cane bagasse (zeolite ZSM-5-a as disclosed in Pereira et al, 2018, Biomass-mediated ZSM-5 zeolite synthesis: when self-assembly allows to cross the Si/Al lower limit, Chemical Science, 2018, 9, 6532-6539). Said zeolite ZSM-5-a does not contain any wood lignin.

[0161] Indeed, the catalyst stability (life-time) is seriously improved with respect to its counterparts despite the presence of numerous acid sites, due to the high Al-loading in the zeolite frame.

[0162] In addition, the selectivity towards ethylene and butylenes is favored for the z_500LO catalyst of the invention, typically Methanol-To-Olefins (MTO) behavior, whilst a clear Methanol-To-Gasoline (MTG) was observed for the former prior art zeolites, which showed up to 60% selectivity towards C.sub.5+ hydrocarbons fraction produced.

[0163] The stability of these zeolites submitted to high temperatures, steam presence or further regeneration in air, has been successfully evaluated: the zeolite of the invention (z_500LO) is the most stable.

Catalytic Performance in the Cracking of N-Hexane (So Called ?-Test)

[0164] The high cracking rate of n-hexane achieved at 500? C. over the prior art ZSM-5-a zeolite disclosed in Pereira et al, 2018 mentioned above (Biomass-mediated ZSM-5 zeolite synthesis: when self-assembly allows to cross the Si/Al lower limit, Chemical Science, 2018, 9, 6532-6539) was measured according to the protocol described in said publication.

[0165] Briefly, n-hexane cracking experiments were performed in a high-throughput unit (Vinci Technologies). Eight tubular quartz reactors assembled in parallel to each other (187 mm in length and 6 mm internal diameter) were used. After cationic exchange (80? C. for 4 h with a 1 M NH.sub.4NO.sub.3 aqueous solution, repeated three-times) and calcination 5 h at 500? C. in air, ZSM-5 zeolite was activated under nitrogen at 500? C. for 2 h prior to catalytic evaluation at the same temperature, then the flow was shifted to an 11% volumic of n-hexane in nitrogen (60 mL/min). The products were injected on line after 3, 17 and 32 min on stream using a GC-2010 Shimadzu chromatograph. The set-up details as well as chromatographic conditions were already reported in A. J. Maia, B. Louis, Y. L. Lam and M. M. Pereira, J. Catal., 2010, 269, 103. The activity was presented as the average result obtained at 3, 17 and 32 min on stream (in the absence of significant deactivation).

[0166] The high initial cracking rate of n-hexane at 500? C. over the prior art ZSM-5-a zeolite was equal to 3856 ?mol.gcat.sup.?1.min.sup.?1 with a ratio propylene/propane=0.88.

[0167] Preliminary tests performed over the z_500LO zeolite of the invention under the same conditions led to a drastic improvement with respect to commercial ZSM-5 zeolite (Petrobras, Si/Al=25): the initial reaction rate was three-times superior for z_500LO over Petrobras zeolite. The selectivity towards propylene was also superior for z_500LO whatever the degree of conversion (verified up to 40%). Finally, outstanding ratios propylene/propane>2.5 were obtained with z_500LO.

Example 2: Synthesis of ZSM-5 Zeolites According to the Invention With Different Lignins and Characterization

1. Synthesis of ZSM-5 Zeolites With Different Lignins (Si/Al Molar Ratio=10 in the Gel)

[0168] Two lignin-assisted ZSM-5 zeolite synthesis recipes were prepared according the hydrothermal method with the following molar ratios: [0169] (i) ZSM-5 type A: NaAlO.sub.2:TEOS:TPAOH:NaCl:H.sub.2O=1:10:13:4.4:3000 (molar ratio TEOS:NaCl of 10:4.4, i.e. around 2.27), or [0170] (ii) ZSM-5 type B: NaAlO.sub.2:TEOS:TPAOH:NaCl:H.sub.2O=1:9.6:14.1:4.3:2307 (molar ratio TEOS:NaCl of 9.6:4.3, i.e. around 2.23).

[0171] Specifically for synthesis (i) (ZSM-5 type A), 0.125 g sodium aluminate anhydrous (NaAlO.sub.2) and 0.375g sodium chloride (NaCl) were added in a 500 mL Erlenmeyer flask containing 30 mL of distilled water. Then, 19.1 mL tetrapropylammonium hydroxide (TPAOH, Sigma-Aldrich, 20% in weight in water) was mixed to the solution under stirring. Then, 30 mL of deionized water was added to the solution, followed by the addition of 3.5 mL tetraethylorthosilicate (TEOS, 99%) dropwise to the solution under vigorous stirring (ca. 600 rpm). Finally, 0.3 g lignin powder was poured in the solution. Ageing and homogenization of the mixture were performed during 2 h, at room temperature. The gel was then transferred to a Teflon-lined stainless-steel autoclave (60 mL effective volume) and placed in an oven at 170? C. for 7 days (crystallization).

[0172] After the crystallization, the solution was filtered and washed with distilled water until pH 7 and dried at 110? C. overnight. The obtained powder was calcined at 550? C. for 15 h in air to remove the structure directing agent and to obtain Na-ZSM-5 zeolite. The obtained white powder was ion-exchanged three times with 30 mL NH.sub.4NO.sub.3 aqueous solution (1 M) per 0.2 g of ZSM-5 at 80? C. under stirring for 1 h. The solution was then filtered and washed with deionized water followed by drying at 110? C. in an oven. The ammonium zeolite-form was calcined in air at 550? C. for 15 h to produce acidic H-ZSM-5 zeolite.

[0173] For synthesis (ii) (ZSM-5 type B), the same steps were used, with the molar ratios indicated for (ii). 0.3 g of lignin powder was also used.

[0174] The lignin powder indicated in the above synthesis is as defined in section 2 below.

[0175] It is worthy to mention here that the two ZSM-5 A and B-types were obtained with different recipes than the one reported by Gomes et al (Microporous and Mesoporous Mater. 254 (2017) 28-36) using lignin originated from the city of Kirov. Indeed, a nearly three-times higher sodium chloride and silica source were used in said former study (in the study of Gomes et al, the molar ratio TEOS:NaCl is 27:13, i.e. around 2.08).

2. Characterization of Lionin Samples

2.1. Used Lignins

[0176] 8 lignins were used:

[0177] 4 types of lignins (lignosulfonates) were provided by Borregaard (Norway) having different molecular weights (MW) and different sulfur contents (S), as follows: [0178] DP-22664: >90% polymer (<10% water); density 650 kg/m.sup.3; low MW; low S-content; 50.4 at % C; 4.6 at % H; [0179] DP-22665: >90% polymer; medium MW; high S-content; 38.3 at % C; 4.1 at % H; [0180] DP-22666: >90% polymer (<10% water); density 500-630 kg/m.sup.3; high MW; medium S-content; 48.4 at % C; 5.0 at % H; and [0181] DP-22667: >90% polymer (<10% water); density 650 kg/m.sup.3; medium MW; medium S-content; 41.9 at % C; 4.6 at % H.

[0182] The 4 following lignin sources were also used, and their content was characterized as follows: [0183] Kraft alkali lignin (low sulfonate content, Aldrich, as indicated in Example 1): 46.5 at % C and 4.9 at % H; [0184] walnut shell (eco-shell, as indicated in Example 1): 47.5 at % C ; 6.1 at % H ; 0.2 at % N; [0185] lignin from the Kirov plant (city of Kirov, Russia, as indicated in Example 1; HL); and [0186] oxidized lignin (OHL) of the lignin from the Kirov plant: 56.9 at % C and 5.1 at % H. The oxidation procedure of the HL lignin for obtaining the OHL lignin is described below.

2.2. Oxidation Procedure of the HL Lignin for Obtaining the OHL

[0187] There are three possible procedures:

[0188] The first procedure for HL oxidation into OHL has been reported by Evstigneyev et al. (E. I. Evstigneyev, O. S.Yuzikhin, A. A.Gurinov, A. Y. Ivanov, T. O. Artamonova, M. A. Khodorkovskiy, E. A.Bessonova, A. V.Vasilyev, J. Wood Chem.Technol.36 (2016) 259).

[0189] It comprises an alkali treatment: specifically, HL dissolution was carried out in a 1 L round-bottomed three-necked flask equipped with a thermometer, a propeller stirrer and a reflux condenser, on a mantle heater. The alkali solution (3.6 g of NaOH in 0.5 L of water) was placed in a flask and 20 g of HL were added in small portions under vigorous stirring. The temperature in the flask was then raised to 85? C. and stirring was continued for 1 h. Finally 0.5 L of OHL solution (pH 9.5) was cooled and obtained with a concentration of 40 g/L.

[0190] The second procedure comprises a treatment with molecular oxygen and has been adapted from Rahimi et al. (Nature 515 (2014) 249-252): HL has been oxidized into OHL using molecular oxygen and then further treated with a mixture of formic acid and sodium formate. A soluble fraction of low molecular weight soluble aromatics of 61% in weight was obtained, whilst 30% of non-soluble oligomeric species were formed, as described in the scheme hereunder:

##STR00006##

[0191] Finally, the third possible procedure for oxidizing HL may be performed by hydrogen peroxide (H.sub.2O.sub.2) in the presence of sulfuric acid to yield OHL.

2.3. Compositions of the HL and the OHL

[0192] The methods used for determining the composition of HL and OHL samples were the followings: [0193] (i) Klason lignin (non-soluble residue) and acid-soluble lignin were determined according to the methods reported by Dence (C. W. Dence, The determination of lignin. In Methods in Lignin Chemistry; Lin, S. Y.;Dence, C. W., Eds.; Springer-Verlag: Berlin, 1992; 33-61). [0194] (ii) Carbohydrates contents were determined by photocolorimetry using the phenol-sulfuric acid method (E. I. Evstigneyev, Russian J. Bioorg. Chem. 43 (2017) 732). [0195] (iii) The quantity of methoxy groups (determined by the reaction between lignins and hydroiodic acid) and the total ash content were determined according to Zakis (G. F. Zakis, Functional Analysis of Lignins and their Derivatives. Atlanta, GA: TAPPI Press, 1994). [0196] (iv) Carboxyl and phenolic groups were analyzed by conventional methods slightly modified for lignin analysis (E. I. Evstigneyev, Russian J. Appl. Chem. 86 (2013) 258).

[0197] The chemical composition and properties of HL and OHL (OHL obtained according to the first procedure described in section 2.2.) are given in Table 7:

TABLE-US-00007 TABLE 7 Characterization of HL and OHL (obtained according to the first procedure), content, mass % Klason Carbo- Lignin lignin hydrates OMe COOH OH.sub.phen C?O Ash HL 89.5 (0.3).sup.a 6.8 12.0 4.5 3.0 4.2 3.4 OHL 87.4 (2.7).sup.a 5.1 5.5 10.3 2.1 5.1 1.0 Note: .sup.acontent of acid-soluble lignin is given under brackets

[0198] The structure of OHL obtained by the third procedure (H.sub.2O.sub.2) was studied by solid-state .sup.13C NMR spectroscopy (data not shown). It is shown that aromatic rings of HL have been oxidized into muconic acid type structures, which correspond to muconic acid structures of formula (II) mentioned in the description.

[0199] The successful oxidation procedure is further confirmed by the IR data which assessed the presence of the characteristic C?O unconjugated stretching vibration at 1713 cm.sup.?1 only appeared in the oxidized lignin, corresponding to the formation of muconic acid groups on HL aromatic rings.

2.4. ZSM-5 Zeolites Nomenclature

[0200] The following nomenclature is used: [0201] ZSM-5 zeolites of type A or B (see section 1 (i) and (ii) above) are obtained. They include different lignins (as indicated in section 2.1 above). [0202] ZSM-5 type A obtained with DP-22664 are called ZSM-5 type A DP-22664. [0203] ZSM-5 type A obtained with DP-22665 are called ZSM-5 type A DP-22665. [0204] ZSM-5 type A obtained with DP-22666 are called ZSM-5 type A DP-22666. [0205] ZSM-5 type A obtained with DP-22667 are called ZSM-5 type A DP-22667. [0206] ZSM-5 type A obtained with walnut shells are called ZSM-5 type A walnut shell. [0207] ZSM-5 type B obtained with OHL (the oxidized lignin of the lignin from the Kirov plant) are called ZSM-5 type B OHL. For this zeolite, 0.3 g of OHL (300 mg) was used, but similar experiments were made using 0.1 g (100 mg) or 0.5 g (500 mg) of OHL.

3. Characterization of Selected ZSM-5 Zeolite Samples

[0208] a) ZSM-5 type A DP-22664 to ZSM-5 type A DP-22667 (which are ZSM-5 with Si/Al molar ratio of 3-4):

[0209] The presence of the following elements has been assessed by EDX in calcined and exchanged material in its H-form: Oxygen 74.9 wt %; Sodium 0.1 wt %; Aluminium 6.5 wt %; Silicon 18.5 w t%. This corresponds to a bulk Si/Al=3 for this material prepared according to type A (recipe (i) in section 1, data not shown).

[0210] The chemical composition of lignin appears to impact the Si/Al ratio of the obtained ZSM-5 material. To reach the lowest ratio, it is preferred to have a lignin composition with: [0211] high S-content; and [0212] medium Molecular Weight (MW).

[0213] In other words, to reach the lowest Si/Al molar ratio, it is preferred to use a lignin composition similar to the one of DP-22665. [0214] b) ZSM-5 type B OHL (which are ZSM-5 with Si/Al molar ratio of 3-8):

[0215] EDX mapping confirms a highly homogeneous distribution of Al and Si atoms throughout the crystal. An average Si/Al value of 3.5 could be measured using 500 mg of OHL during the synthesis protocol (see Table 8 below). While diminishing the quantity of OHL to 300 mg and 100 mg, a significant raise in the Si/Al molar ratio to 6 and 8 could be observed, respectively.

TABLE-US-00008 TABLE 8 Characterization of ZSM-5 type B OHL (with 500 mg of OHL) Element Weight % Atomic % Net Int. Error % Al content 9.5 6.8 185.2 6.6 9.4 6.7 180.1 6.5 8.6 6.6 348.8 4.5 Si content 31.3 21.6 500.3 6.2 30.6 21.0 482.2 6.2 38.8 28.4 1346.5 4.5

[0216] Thus, one can observe that the higher amount of OHL is added, the lowest Si/Al is achieved. Pictures of these 3 zeolites (i.e. with 100 mg, 300 mg or 500 mg of OHL) all show homogenous crystals (data not shown).

[0217] For ZSM-5 type B OHL with 500 mg of OHL, in spite of the sole presence of MR structure in the XRD pattern (data not shown), it appears that some peaks cannot be indexed using conventional orthorhombic unit cell (Pnma space group); the latter peaks are super lattice reflections due to Al ordering. A careful inspection of the XRD pattern shows that those extra-reflections appear as shoulders at slightly smaller 2? angles than the main peaks, thus forming doublets in those peaks. As already reported in Pereira et al (M. M. Pereira, E. S. Gomes, A. V. Silva, A. B. Pinar, M. G. Willinger, S. Shanmugam, C. Chizallet, G. Laugel, P. Losch, B. Louis, Biomass-mediated ZSM-5 zeolite synthesis: when self-assembly allows to cross the Si/Al lower limit, Chem. Sci. 9 (2018) 6532-6539), the presence of a second unit cell with larger dimensions (due to more Al insertion in the framework) could be assessed. Besides, pyridine adsorption measurements confirmed the nearly absence of the vibration at 1455 cm.sup.?1 corresponding to Lewis acid sites. The ratio between the bands at 1546 cm.sup.?1 (Br?nsted acid sites) and 1455 cm.sup.?1 (Lewis acid sites) could be estimated to 20, thus confirming the full introduction of Al-atoms within the zeolite frame. [0218] c) ZSM-5 type A walnut shell (which are ZSM-5 with Si/Al molar ratio of 6-7):

[0219] The use of walnut shells allowed achieving ZSM-5 zeolite crystal spheroids having approximately a diameter of 6 ?m. Numerous nano-sized elongated sub-units form these spheres. According to EDX analysis, a bulk Si/Al=6.6 could be assessed (see Table 9).

TABLE-US-00009 TABLE 9 Characterization of ZSM-5 type A walnut shell Element Weight % Atomic % Net Int. Error % C content 3.3 5.4 267.0 9.9 O content 52.1 63.5 10051.1 5.1 Al content 5.7 4.1 698.5 4.9 Si content 38.9 27.0 4070.1 4.5 [0220] d) Thermal analysis of ZSM-5 zeolites prepared with different lignins:

[0221] Thermogravimetric analysis of non-calcined ZSM-5 samples (i.e. ZSM-5 type A DP-22665 to ZSM-5 type A DP-22667) has been performed to evaluate the organic matter content present within the ZSM-5 zeolites. It clearly appears that a larger weight loss was observed between 400? C. and 450? C. in ZSM-5 zeolites type A DP-22665 to DP-22667, as compared to the reference zeolite prepared in the absence of lignin (data not shown).

[0222] This indicates the presence of supplementary organic matter, being between 2% and 4% in weight, originating from the lignosulfonate to the normal presence of TPA.sup.+ template cations.

Example 3: Synthesis of ZSM-5 Zeolites With Different Ligins Having a Si/Al=14 in the Gel According to the Invention

[0223] The ZSM-5 zeolite was synthesized by using the following initial composition of the gel: [0224] (iii) 1 NaAlO.sub.2:13 NaCl:14 TEOS:3 TPAOH:3718 H.sub.2O.

[0225] Sodium chloride (0.760 g, Janssen Chimica, P. A.), tetrapropylammonium hydroxide (TPAOH, 6.0 g, Sigma-Aldrich, 1 M in H.sub.2O), sodium aluminate (NaAlO.sub.2, 0.080 g, Sigma-Aldrich) and distilled water were mixed until a clear solution was obtained. Then, TEOS 2.8 g, Sigma-Aldrich, 99%) and lignin DP-22665 (mentioned in part 2 of Example 2) (0.6 g) were added to the solution. After, the synthesis gel was aged for 1.5 h at room temperature under stirring. The synthesis gel was set inside a Teflon-lined autoclave (40 mL) and the zeolite crystallization performed under static condition at 170? C. for 24 h. After cooling down, the solid was recovered by filtration and washed until neutral pH. The final solid was calcined at 600? C. for 5 h under air.

[0226] In order to obtain the zeolite acid form, two successive exchanges using 2 M NH.sub.4NO.sub.3 aqueous solution at 80? C. for 1 h (1g of zeolite per 50 mL of solution) were performed. The ammonium form was converted into the protonic form by calcination at 450? C. for 4 h under air.

[0227] The same procedure has been conducted but the quantity of TPAOH was reduced down to 1, according to (iv) 1 NaAlO.sub.2:13 NaCl:14 TEOS:1 TPAOH:3718 H.sub.2O. It has been verified by XRD (not shown) that a crystalline ZSM-5 pure structure could still be obtained while reducing the quantity of organic template (TPAOH) by 20% to 80%, preferably between 60% and 70%. The presence of lignin may compensate the presence of TPAOH at least to some extent.

[0228] The mass ratio between lignin and NaAlO.sub.2 (mass ratio lignin/NaAlO.sub.2) was varied between 2 and 15 in the synthesis recipe, preferably between 3 and 8.

[0229] ZSM-5 zeolites according to the invention were obtained, which have in both cases (i.e. (iii) and (iv)) a Si/Al ratio of 6?1.