ES2904254A1 - Adsorbent Zn/MN recovered from the Base Espinela for the elimination of sulfur in gasification processes (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Adsorbent Zn/MN recovered from spinel base for the elimination of sulfur into gasification processes. The present invention discloses the use of an adsorbent recovered from spinelet base with ZN formula0.15 or2,15 or ZN0.25 MN2,75 or4, which works in a temperature range of between 300ºC and 500ºC, for sulfur removal in Gasification processes such as those of coal, biomass and residues. This adsorbent has been obtained from alkaline batteries and recycled Zn/C batteries. Therefore, the present invention could be of interest to the industry that produces gaseous fuels from biomass and residues, also for the biotechnology industry that produces energy and value chemicals added from waste and biomass. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

Recovered spinel-based Zn/Mn adsorbent for sulfur removal in gasification processes

The present invention discloses the use of a recovered spinel-based adsorbent with formula Zno,85Mn2,i5O4 or Zno,25Mn2,75O4, which works in a temperature range between 300 °C and 500 °C, for the elimination of sulfur in gasification processes such as coal, biomass and waste gasification processes. Said adsorbent has been obtained from alkaline batteries and recycled Zn/C batteries.

Therefore, the present invention could be of interest to the industry that produces gaseous fuels from biomass and waste, as well as to the biotechnological industry that produces energy and value-added chemical products from waste and biomass.

STATE OF ART

The removal of reduced sulfur species in gasification processes has been a problem since the 1990s. At that time, this problem was associated with the gasification of coal and the need to comply with the environmental limits of emissions in the combustion of gas synthesis in boilers, engines and turbines and to prevent corrosion. Recently, the focus has been on achieving a complete reduction of sulfur in biomass and waste gasification processes given the role that synthesis gas and biogas play as predecessors of value-added products such as biofuels or chemical products. Sulfur removal is also today associated with the prevention of sulfur poisoning of sulfur sensitive catalysts when upgrading syngas or biogas to biomethane. Particularly, for synthesis gas, technologies that use regenerable adsorbents that work in the temperature range of 300 - 500°C are desirable to improve the integration process.

Many types of materials have been used to test H2S removal, such as: zeolites, activated carbon, iron-based materials and different oxides. It is widely known that zinc oxide adsorbents and their derivatives are highly effective in removing hydrogen sulfide, and experimental studies have shown that its concentration can be reduced to ppmv levels. However, it is also known that the Zinc oxide tends to be reduced to elemental zinc in a reducing environment, lowering its desulfurization capacity. In an effort to remove this limitation, Ko et al. [Ko, T.-H., H. Chu, and Y.-J. Liou, A study of Zn-Mn based sorbent for the high-temperature removal of H2S from coal-derived gas. Journal of Hazardous Materials, 2007. 147(1): p. 334-341] identified a positive effect in the presence of manganese, pointing out that manganese oxide could inhibit the evaporation of zinc in reducing atmospheres, and improve the capacity of the adsorbent to retain sulfur compounds. Consequently, manganese-based adsorbents have attracted the attention of different research groups, which have collected the advantages of using manganese oxides in desulfurization processes in their work:

• Herszage et al [Herszage, J and M. dos Santos Alfonso; Mechanism of Hydrogen sulphide oxidation by Manganese (IV) Oxide in Aqueous Solutions, Langmuir,2003, 19(23), p: 9684-9692] describe the benefits obtained from using Mn oxides in desulfurization processes, but these studies were focused on aqueous solutions.

• Other works include the use of supported manganese-based adsorbents, for example using AhO3 [Chytil, S., et al., Performance of Mn-based H2S sorbents in dry, reducing atmosphere - Manganese oxide support effects. Fuel, 2017. 196: p.

124-133.], MCM [Jie, M., et al., Semi-Coke-Supported Mixed Metal Oxides for Hydrogen Sulfide Removal at High Temperatures. Environmental Engineering Science, 2011. 29(7): p. 611-616.] or SiO2 [Ko, T.-H., et al., Performance of ZnMn2O4/SiO2 sorbent for high temperature H2S removal from hot coal gas. CSR Advances, 2017. 7(57): p. 35795-35804.], however, its usefulness for removing sulfur depends on the preparation of the adsorbent and the effect of the support.

Therefore, it is necessary to develop new sustainable and more efficient adsorbents for the effective removal of sulfur in gasification processes, particularly in coal, biomass and waste gasification processes.

DESCRIPTION OF THE INVENTION

The first aspect of the invention refers to the use of a recovered spinel-based adsorbent with formula Zn0.85Mn2.15O4 or Zn0.25Mn2.75O4 that works in a temperature range between 300 °C and 500 °C, for the elimination of sulfur in gasification processes, preferably in coal, biomass and waste gasification processes.

Spinel-based adsorbents with the formula Zno,85Mn2,i5O4 or Zno,25Mn2,75O4 show excellent behavior and can be used for almost any gasification gas. Said spinel-based adsorbents with formula Zn0.85Mn2.i5O4 or Zn0.25Mn2.75O4 have shown higher efficiency and higher sulfur retention than commercial adsorbents with ZnO as base (Z-Sorb-III).

Note that the adsorbent works surprisingly well in a gas with a concentration of 9000ppm H2S. This assures us that, in the presence of lower concentrations, for example, equal to or less than 1000 ppm or less, the recovered spinel-based adsorbents with formula Zn0.85Mn2.15O4 or Zn0.25Mn2.75O4 of the present invention perform much better.

In a preferred embodiment of the invention, the adsorbent is obtained from alkaline batteries and recycled Zn/C batteries. The use of energy accumulators (batteries) is essential in our daily lives, but from an environmental point of view it is essential to properly dispose of these products after use and to recover and reuse the valuable components used in their manufacture, in this case zinc and manganese that are part of the anode and cathode of batteries and accumulators. Recovering adsorbents from alkaline batteries and recycled Zn/C batteries implies a reduction in the consumption of raw materials, since they are obtained from recycled batteries, also contributing to a reduction in waste and their sustainable management.

The adsorbent is recovered from alkaline batteries and Zn/C batteries. It is composed of a mixture of Zn and Mn oxides with the formula Zn0.85Mn2.15O4 or Zn0.25Mn2.75O4, with tetragonal symmetry and a space group I41/amd that corresponds to the spinel structure. Crystalline structure and composition play a very important role in adsorbents used to remove sulfur in coal, biomass and waste gasification processes. Working temperatures in a temperature range between 300 °C and 500 °C play a crucial role in the sulfur retention mechanisms that consist of the formation of sulfides and other minor sulfur species.

The procedure for obtaining spinel-based adsorbents with the formula Zn0.85Mn2.i5O4 or Zn0.25Mn2.75O4 from alkaline batteries and recycled Zn/C batteries comprises the following stages:

a) Obtain the black mass from a recycled alkaline battery and/or a recycled Zn/C battery;

b) Acid leaching of the black mass obtained in step (a) at room temperature preferably using H2O, H2O2 and HCl in a 1:1:2 ratio;

c) Precipitate the liquid obtained in step (b) at a pH between 12 and preferably using NaOH.

The first stage, stage (a) of the process refers to obtaining the black mass from an alkaline cell and/or a recycled Zn/C battery. In the present invention, the term "black mass" refers to the inorganic solid obtained in the battery disassembly stages and the contained electrolytes, where graphite and manganese and zinc oxides form the anode and cathode of the batteries. The main Battery components are manganese dioxide (positive electrode), zinc (negative electrode), the electrolyte (KOH or ZnCl2 NH4CO, and steel (the battery cover). These residues cause some concern in society as they can have negative effects in public health and the environment, mainly due to its high content of heavy metals.The starting point to obtain the black mass is the mechanical separation that aims to separate electrodes, steel, paper and plastic through cutting and grinding stages , magnetic separation, dimensional separation (screening), Eddy Current Separation (ECS) and grinding of the dust fraction.

Stage (b) of the process refers to the leaching in a constant acidic medium and of the black mass obtained in stage (a) at room temperature. The resulting solids are removed by filtration. The term "room temperature" refers herein to a range between 17°C and 27°C.

Preferably the acid medium used in step (b) is an acid solution of H2O, H2O2 and HCl in a 1:1:2 ratio, for example an acid solution of 25% v/v of water, 25% v/v of H2O2 and 50% HCl of 35% purity. A lower percentage of H2O2 does not adequately dissolve Mn and a higher percentage increases foams during the dissolution process and causes overflow in the reactor. The leaching in an acid medium of stage (b) is continued with the precipitation of the liquid obtained in stage (b) at a pH between 12 and 14. Stage (c) refers to a selective alkaline precipitation (stage (c )) using an alkaline medium. Preferably the alkaline medium used in step (c) is a solution of NaOH or KOH, preferably NaOH. Preferred concentrations for alkaline media are greater than 6M.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this invention pertains. Methods and materials similar or equivalent to those described herein may be used in the practice of the present invention. Throughout the description and claims, the word "comprising" and its variants are not intended to exclude other technical characteristics, additives, components or steps. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided for illustrative purposes and are not intended to limit the present invention.

BREBE DESCRIPTION OF THE DRAWINGS

FIG. 1: Breakdown curves (10 bar, 400°C and SV=3500h-1) of recovered oxides BMO1, BMO2, BMO3, BMO4 and Z-Sorb III

FIG.2: XRD diffractograms for (a) fresh sample and (b) used samples of recovered oxides BMO1, BMO2, BMO3, BMO4

FIG. 3: TEM images for (a) BMO1, (b) BMO2, (c) BMO3, (d) BMO4 fresh samples

FIG.4: TEM-EDS analysis for (a) BMO1, (b) BMO2, (c) BMO3, (d) BMO4 fresh samples

FIG. 5: TEM images for (a) BMO1, (b) BMO2, (c) BMO3, (d) BMO4 used samples

FIG.6: TEM-EDS analysis for (a) BMO1, (b) BMO2, (c) BMO3, (d) BMO4 used samples

EXAMPLES

Materials

In this document, different samples recovered from recycled batteries have been studied to investigate their suitability as absorbent for sulfur removal applicable to the cleaning of synthesis gas for its subsequent conversion into value-added products such as fuels or chemicals.

The samples studied are binary metal oxides and have been identified with the BMOX nomenclature where X ranges from 1 to 4.

The recovered oxides BMOX (X=1-4) investigated were obtained following a procedure that consists of acid leaching from black mass, a common residue generated by spent alkaline batteries, and subsequent selective precipitation of the resulting solution. First, different amounts of the black mass are leached in 250 ml of milliQ water, 250 ml of H2O2 (Panreac®) and 500 ml of HCL (Panreac®) at room temperature for 1 hour. After this, to obtain the different BMOX binary oxides (X=1-4), the mixtures were filtered and the collected liquids were precipitated with 6 M NaOH until reaching a pH between 12 and 14. To obtain the binary oxides Zn0.85Mn2. 15O4 and Zn0.25Mn2.75O4 leached 100 g and 200 g of black mass, respectively.

Characterization of materials

Physical and chemical characterization of all samples. was performed before and after the desulfurization tests. X-ray fluorescence analysis (XRF). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) provided relevant information on the structure and composition of the samples. while the analysis with the transmission electron microscope (TEM) was used to obtain relevant information on the distribution of the active phases on the surface of the samples.

The mineralogical composition of the samples was first determined by X-ray fluorescence (XRF) analysis using a PANalyticalAxios dispersive spectrometer (4 kW) and structural characterization was carried out with X-ray diffraction (XRD) analysis using a Siemens D5000 diffractometer (Cu Ka radiation). The collected data were refined by the Rietveld method using version 4.2 of the TOPAS analytical program (Bruker ASX).

To analyze the surface of the samples obtained, X-ray photoelectron spectroscopy (XPS) has been used. Spectra of all samples were recorded using a Fisons MT500 spectrometer equipped with a hemispherical electron analyzer (CLAM2) and a non-monochromatic MgKa X-ray source working at 300W. Binding energies were calibrated for the C 1s peak at 285.0 eV. Atomic coefficients were calculated from the reported peak intensity coefficients and sensitivity atomic factors.

Table 1 below details the composition of the investigated samples in terms of main components determined by X-ray diffraction (XRF).

Table 1: Elemental components of the studied samples

to commercial

b Recovered from batteries

A sample of commercial adsorbent Z-Sorb-III has been added to Table 1 for comparison.

In table 1 it can be seen that the active species in the recovered samples BMO1, BMO2, BMO3 and BMO4 consist mainly of Mn and Zn with a low content of Ni (<1%), while in the sample Z-Sorb-III the majority component is Zn with a Ni content greater than 7%. In addition, in table 1 it can be seen that all the samples BMO1, BMO2, BMO3 and BMO4 have a spinel structure.

Experimental procedure

All samples were supplied in powder form and were prepared by first crushing them in an agate mortar and then pelletizing them to sizes ranging between 0.5-1mm using a Specat 15T manual hydraulic press.

Sample analyzes were carried out in a laboratory-scale microactivity reactor, which is an automated computerized laboratory system for the study of catalysts and adsorbents, equipped with three independent mass flow controllers to produce the appropriate gas mixture. up to 4.5 Nl/min of maximum gas flow and where reactions can be studied at up to 600 °C and 30 bar pressure. Both the reactor (9.2 mm internal diameter and 300 mm long) and the system pipes and fittings are made of Hastelloy C, to avoid corrosion problems due to 1H2S.

In the experiments, between 2 and 3 grams of each sample were used, once pelletized, and desulfurization tests were carried out at 10 bar pressure and 400°C, using as feeding a mixture of gases with 0.9% H2S in N2 and a space velocity of 3500 h-1 to simulate a desulfurization process of a biomass gasification gas with steam. The inlet and outlet gases were analyzed with a Varian CP4900 gas chromatograph, equipped with two columns, a Porapack and a molecular sieve with two thermal conductivity detectors.

To facilitate the comparison of the samples studied, the theoretical values of sulfur adsorption capacity (S0) and adsorption time (te) were calculated for each of the samples based on reaction stoichiometrics (reactions 1, 2, 3) and the amount of individual active oxides present in each sample:

ZnO H2S ^ ZnS H2O

NiO H2S ^ NiS H2O

MnO H2S ^ MnS H2O

For the theoretical calculation of the adsorption capacity of each sample, So, the contribution of each of the three individual active species ZnO, MnO, NiO has been added using the following equation [1]:

The actual amount of sulfur captured by the adsorbent (St(g)), assuming that all the sulfur is retained by the adsorbent and that no sulfur escapes in the gas stream at the reactor outlet until a breakthrough time ts is reached given, it has been calculated with the equation [2]:

Where:

MWs is the molecular mass of S,

P is the absolute pressure under sulfidation conditions,

Fgas is the volumetric flow rate of gas at process conditions,

And ^h 2 ^s represents the mole fraction of H2S in the input,

Rg is the universal gas constant and

T is the absolute temperature under sulfidation conditions.

The theoretical adsorption time, to, has been calculated as the quotient between the theoretical amount of sulfur S that each sample can adsorb, based on its composition, and the mass flow of sulfur used in each experiment (g/min) according to this formula [3]:

As can be seen, the theoretical time depends on the initial concentration of hydrogen sulfide, the sulfidation pressure and temperature, as well as the gas flow, and will vary depending on the experimental conditions. These parameters are used to compare the efficiency of all investigated samples.

Table 2 shows the theoretical values S0 and t0 calculated for all the samples studied. Table 2: Theoretical sulfur adsorption capacity and time of the studied samples.

to Commercial

b Recovered from batteries

The experimental sulfur retention capacity was obtained with the same procedure for all the samples: First, the operating conditions were reached using N2 as inert gas. When stable operating conditions were reached (400 °C and 10 bar), a mixture consisting of 0.9% H2S in N2 was passed through the reactor. In all experiments, the composition of the outlet gas was analyzed continuously, including the heating and cooling stages, thus obtaining rupture curves until the outlet gas reached a concentration of 0.1% v/v H2S.

To evaluate the performance of the samples in terms of sulfur removal capacity, the efficiency (%) is used according to the formula

[4] Efficiency= St/S0 *100

Finally, all the samples were characterized by XRD, XPS and XRF to identify the main sulfur compounds formed and potential changes in the structure of the adsorbents during the desulfurization process. The results will be displayed below.

Results

Breakdown curves: sulfur adsorption capacity

All experiments were carried out under the same operating conditions (Pressure = 10 bar, Temperature = 400 °C, and space velocity SV = 3500 h-1). Figure 1 shows the breakthrough curves of all investigated recovered samples BMO1, BMO2, BMO3, BMO4, where the breakthrough curve of the commercial adsorbent Z-Sorb-III has been included for comparison.

In Figure 1, the rupture curves show a great difference between the different samples investigated: at one extreme, the BMO2 sample proves to be better than the others, at the other, the BMO4 sample is inferior to the others. Between both, the samples BMO1 and BMO3 have a quite similar behavior between them.

When comparing them with the curve of the commercial adsorbent Z-Sorb-III, two of the samples break before the commercial adsorbent and the other two break later, showing greater efficiency when it comes to removing sulfur. In addition, the two samples that showed the highest adsorption capacity also show an almost vertical rupture slope, suggesting a rapid H2S capture reaction when adsorption centers are no longer available.

The adsorption capacity of the samples is expressed in grams of adsorbed sulfur divided by the mass (g) of the adsorbent and multiplied by 100, according to formula [5]:

St = (Sadsob(g)/Msorbent(g))*100

Table 3 lists the calculated S capture capacities until H2S reaches 1% of the inlet gas composition.

Table 3: S removal capacity and efficiency (g/g %)

to Commercial

b Recovered from batteries

According to the results obtained, the order in terms of sulfur removal capacity is: BMO2 > BMO1 > BMO3 > BMO4, in complete consistency with the efficiency calculated and represented in table 3 above.

According to the composition of the samples (seen in table 1) it should be noted that those samples with lower Zn content and higher Mn content (BMO1 and BMO2) showed a better performance in terms of sulfur removal than and a higher efficiency than samples with higher Zn content and lower Mn content (BMO3 and BMO4).

Sulfidation process: influence of the composition of the samples

The characterization of the used adsorbents BMO1, BMO2, BMO3 and BMO4 (used samples) was carried out and the results were compared with the fresh samples BMO1, BMO2, BMO3 and BMO4 in order to investigate the mechanisms of sulfidation and the role of Mn in the process. The term "spent or used" adsorbent/sample refers to samples BMO1, BMO2, BMO3 and BMO4 after exposing them to sulfur under the experimental conditions of 10 bar pressure, 400 °C and a gas stream of 0.9% H2S / N2.

Morphological characterization of fresh and used samples was carried out by transmission electron microscopy (TEM), using a JEOL JEM 2100 instrument. Samples were dispersed in butanol and suspensions were spotted on carbon-coated copper grids. X-ray dispersive spectroscopy (XEDS) measurements were performed on an OXFORD INCA instrument.

The physical-chemical characterization of the fresh and used samples investigated showed significant differences in composition, structure and formation of sulfur species. Three different analyzes were carried out: XRD analysis provided information on the structure, crystallinity and the main crystalline phases after sulfidation; the XPS analysis allowed the identification of different oxidized phases of sulfidated species and finally the TEM analysis confirmed the presence of phases, oxides and sulfides. Based on these characterization results, some plausible mechanisms for H2S removal are described in this section.

XRD analysis

Initially, the XRD analysis showed that, after sulfidation, a loss of crystallinity was observed in the samples studied, which may be indicative of the formation of amorphous sulfur species. As the adsorbents used are recovered materials, there are no reference standards of these materials for direct comparison, and it is only possible to use the differences between them and use the comparison with the standards of pure ZnO and MnO oxides.

In the case of the XRD diffraction patterns of the fresh samples, the most intense diffraction maxima for all the samples of the binary oxides obtained can be indexed to a tetragonal symmetry, with space group I41/amd (JCPDS 24-1133) which is consistent with a spinel-like structure, with the general formula ZnxMn3-xO4, with the corresponding Miller indices (hkl) shown in FIG 2.

The additional peaks, marked in the XRD patterns with crosses (x), corresponded to some impurities related to the production process.

In the case of the BMO4 sample, diffraction maxima indexed to the ZnO phase were recorded, marked in the XRD pattern with circles (o).

Regarding the diffraction patterns of the samples used, a spinel-type structure was found, with a general formula ZnxMn3-xO4, as well as the formation of new additional phases as a consequence of the sulfurization process, for which clear differences were found between the samples (see FIG.2):

• In the case of the BMO2 sample, diffraction maxima were observed that can be indexed to an a-MnO2 phase with a cubic structure (JCPDS 06-0518).

• On the contrary, in the BMO1 sample, the a-MnO2 and B-MnO2 phases were found (JCPDS 40-1289).

• The samples BMO3 and BMO4 present diffraction maxima attributable to the phase ^and -MnO2.

• Unexpected elemental S formation was identified in samples BMO1 and BMO2; the formation of elemental S occurs in the samples with higher Mn content.

• The diffraction pattern of the used or spent Z-sorb-III commercial sample exhibits the presence of the wurtzite-type hexagonal ZnS phase (JCPDS 36-1450).

Table 3 shows the results obtained from the Rietveld refinements of the XRD data of the fresh and used samples.

Table 3. Results obtained from the Rietveld refinements of the fresh and used samples.

to Commercial; Composition of fresh sample obtained by X-ray fluorescence b Recovered from batteries

One explanation for the observation of additional phases is that manganese sulfide can crystallize in three different structures ^a -, B- and r-MnS and at low temperatures (between 100-400 °C) the B- and r-MnS phases are formed. , and transform to ^a -MnS.

As expected, the main sulfide species formed were Zn and Mn sulfides, in the ZnS and MnS forms. However, the analyzes show the unexpected presence of elemental sulfur (S) in the samples used and it should be noted that this sulfur formation was identified quantitatively (> 8%) in those samples with the highest sulfur removal capacity that were those with the highest manganese content. This elemental sulfur formation was initially unexpected because all experiments were performed in a reducing medium, using a H2S/N2 gas mixture, in the absence of oxygen.

XPS analysis

Table 4 summarizes the results of the XPS characterization of the fresh (a) and used (b) samples BMO1, BMO2, BMO3 and BMO4.

Table 4: a) XPS results of fresh samples

Sample Fresh Samples

Mn/Zn Mn2+ Mn3+ Mn4+

BMO1 8.3 14.5 3 7.8

BMO2 12.2 15.4 4.4 8.5

BMO3 1.3 6.3 7.3 5.5

BM04 0.6 3.4 2.1 7.1

Table 4: b) XPS results of the samples used

Sample Samples used

ZnS NiS MnS/MnS2 MnSO4 NISO4 S

BMO1 16.5 - 50.6 26.7 - 13.3

BMO2 24.6 - 33.6 38.4 - 13.7

BMO3 7.2 - 78.1 14.7 - 16.4

BM04 7.8 - 82.2 8.8 - 14.4

Z-Sorb III 74.7 10.1 - - 15.6 11.8

In the case of the fresh samples BMO1, BMO2, BMO3, and BMO4, the bands obtained can be attributed to the binding energies of MnO, Mn2O3, and MnO2, showing that Mn(II), Mn(III), and Mn(IV) are present in the samples.

The analyzes of the used samples BMO1, BMO2, BMO3 and BMO4 show the presence of different sulfur species, which include sulfides (ZnS, MnS, MnS2, NiS) as well as sulfates (MnSO4, NiSO4). It should be noted that the samples that comprise a higher amount of MnS have a lower sulfur retention capacity (see the results for samples BMO3 and BMO4).

When the XPS bands of the fresh and used samples are compared, a small shift in the binding energies is observed (Table 5), which suggests that transformations may have occurred during the sulfidation process in this work (as reference: MnO2 (641.9 eV-642.6 eV) and MnO (640 eV-641.7 eV)).

Table 5: Binding energies for Mn-O oxides identified by XPS before and after sulfidation tests.

During the oxidative removal of H2S, several massive manganese oxides were shown to be active or catalytic adsorbents and the O/S exchange reaction generates water and sulfur-containing manganese oxides. According to this approximation, the formation of MnS2 from MnO2 could be explained by the exchange between oxygen and sulfur in the samples during the sulfidation tests according to the following sequence:

MnO2H2S = MnOSH2O

MnOSH2S = MnS2H2O

The formation of sulfates is evident in all the samples used BMO1, BMO2, BMO3 and BMO4 and, although it is unexpected due to the reducing atmosphere in the reaction medium, it is somehow consistent with the formation of elemental sulfur observed by XRD. The coexistence of different oxidation states of Mn in materials fresh recovered, already confirmed by XPS (see Table 4), could facilitate the availability of O2 during the sulfidation process, which could combine with H2S to form SO2 (reaction 5):

H2S 3O2 = SO2 H2O (5)

The temperature (T = 400 °C) and pressure (P = 10bar) used here could facilitate the formation of S-O bonds that also lead to the formation of SO2.

The presence of sulfates in the used samples BMO1, BMO2, BMO3 and BMO4 can only be explained if there is some oxygen and SO2 available during the sulfurization process, their presence in these samples suggests the formation of SO2 as an intermediate species and the reaction with oxidized species of Mn following some of the following reactions:

2Mn2O3 4SO2 O2 = 4MnSO4

Mn3O4 3 SO2 O2 = 3MnSO4

MnS2O2 = MnSO4

MnO2 SO2 = MnSO4

The sulfites/sulfates/S ratio formed in the sulfidation process of each of the samples studied seems to depend a lot on their structure (spinel) and their composition, since they determine the availability of O2 and the formation of SO2 under operating conditions. used (400 °C and 10 bar). In line with the results obtained in the XRD analysis, those samples with a higher concentration of MnS (BMO3 and BMO4) show a lower formation of sulfates, which is consistent with the existence of a balance between MnS and MnSO4. Note that MnSO4 requires at least 600 °C, no decomposition is expected at the process temperatures used (400 °C).

TEM analysis

TEM micrographs of the fresh samples (FIG. 3) confirm that the main phase was spinel ZnxMn3-xO4, as previously identified by XRD analysis.

Fresh samples BMO1 and BMO2 with higher Mn content show particles with a regular shape (FIG. 3(a), 4(a) and 3(b), 4(b)) while fresh samples BMO3 and BMO4 with lower Mn content show a nearly spherical shape (FIG. 3(c), 4(c) and 3(d), 4(d)). particularly in the image that corresponds to the BMO4 sample (FIG. 3(d), 4(d)), tube-shaped structures can be found that are associated with the presence of ZnO.

In the samples used, an increase in agglomerated particles can be observed in addition to particles without a determined shape (FIG. 5).

The loss of polyhedral shapes in the particles seems to indicate the transformation of ZnxMn3-xO4 from the spinel phases to other less crystalline and/or totally amorphous phases. These results agree with those of the XRD analysis described above, where the measurements obtained with the XRD analysis indicated that the sulfidation process of the samples gave rise to a lower degree of crystallinity for all the samples analyzed and this is confirmed by the micrographs of the samples. TEM analysis.

The obtained energy dispersive spectra of the fresh and used samples (FIG. 4, 6) obtained from the TEM-EDS analysis also confirm the changes that occurred during the sulfidation process. It can be seen that for the fresh samples the phases contained two characteristic peaks corresponding to Zn and Mn. Instead, in the samples used, a characteristic peak corresponding to the Ka of S is also seen. And these results confirm the adsorption of H2S in the samples.

Finally, additional peaks attributable to the carbon-coated copper grids were also found.

The performance and characterization results obtained have shown that the spinel-based structure and composition of the mixed oxides recovered from recycled batteries, especially manganese species, play a crucial role in the desulfurization mechanism.

Claims (3)

1. Use of recovered spinel-based adsorbents with the formula Zno,85Mn2,i5O4 or Zno,25Mn2,75O4 that work at a temperature between 300 °C and 500 °C for the removal of sulfur in gasification processes. 2. The use according to claim 1 for the removal of sulfur in carbon, biomass and waste gasification processes. 3. The use according to any of claims 1 or 2, wherein the adsorbent has been obtained from alkaline batteries or recycled Zn/C batteries.