MODIFIED SULFURIC ACID AND USES THEREOF

Abstract

An aqueous composition comprising: sulfuric acid; a heterocyclic compound; an alkanesulfonic acid; and a peroxide. Said composition being capable of delignifying biomass under milder conditions than conditions under which kraft pulping takes place.

Claims

1. An aqueous acidic composition comprising: sulfuric acid; a heterocyclic compound; an alkanesulfonic acid; and a peroxide.

2. The composition according to claim 1, wherein sulfuric acid, said heterocyclic compound and said alkanesulfonic acid are present in a molar ratio ranging from 28:1:1 to 2:1:1.

3. The composition according to claim 1, where said heterocyclic compound has a molecular weight below 300 g/mol.

4. The composition according to claim 1, where said heterocyclic compound is a secondary amine.

5. The composition according to claim 1, where said heterocyclic compound is selected from the group consisting of: n-methylimidazole; triazole; and imidazole; and combinations thereof.

6. The composition according to claim 1, where said heterocyclic compound is imidazole.

7. The composition according to claim 1, wherein said alkanesulfonic acid is selected from the group consisting of: alkylsulfonic acids where the alkyl groups range from C1-C6 and are linear or branched; and combinations thereof.

8. The composition according to claim 1, wherein said alkylsulfonic acid is selected from the group consisting of: methanesulfonic acid; ethanesulfonic acid; propanesulfonic acid; 2-propanesulfonic acid; isobutylsulfonic acid; t-butylsulfonic acid; butanesulfonic acid; iso-pentylsulfonic acid; t-pentylsulfonic acid; pentanesulfonic acid; t-butylhexanesulfonic acid; and combinations thereof.

9. The composition according to claim 1, wherein said alkylsulfonic acid is methanesulfonic acid.

10. An aqueous composition for use in the processing and depolymerisation of cellulose from a plant source, wherein said composition comprises: sulfuric acid present in an amount ranging from 20 to 80 wt % of the total weight of the composition; a heterocyclic compound; an alkanesulfonic acid; and a peroxide; wherein the sulfuric acid and the heterocyclic compound are present in a mole ratio ranging from 2:1 to 28:1.

11. The composition according to claim 10, where the peroxide is hydrogen peroxide.

12. A one-pot process to separate lignin from a lignocellulosic feedstock, said process comprising the steps of: providing a vessel; providing said lignocellulosic feedstock; providing a composition comprising; an acid; a modifying agent comprising a heterocyclic compound; and an alkylsulfonic acid; and a peroxide; exposing said lignocellulosic feedstock to said composition in said vessel for a period of time sufficient to remove at least 80% of the lignin present said lignocellulosic feedstock; optionally, separating and removing a liquid phase comprising dissolved lignin fragments from a solid phase comprising cellulose fibres.

13. The process according to claim 12, wherein said acid is sulfuric acid.

14. The process according to claim 12, wherein said peroxide is hydrogen peroxide.

15. The process according to claim 12, wherein the period of time is sufficient to remove at least 90% of the lignin present on said plant material.

16. The process according to claim 12, wherein the period of time is sufficient to remove at least 95% of the lignin present on said plant material.

17. The process according to claim 12, wherein the temperature of the composition prior to the step of exposing it to the lignocellulosic feedstock is below 50° C.

18. The process according to claim 12, wherein said method is carried out at ambient temperature.

19. The process according to claim 12, wherein said method is carried out at ambient pressure.

20. The process according to claim 12, where said heterocyclic compound is selected from the group consisting of: n-methylimidazole; triazole; and imidazole; and combinations thereof.

21. The process according to claim 12, wherein said alkanesulfonic acid is selected from the group consisting of: alkylsulfonic acids where the alkyl groups range from C.sub.1-C.sub.6 and are linear or branched; and combinations thereof.

Description

DESCRIPTION OF THE INVENTION

[0065] The experiments carried out using an aqueous acidic composition according to a preferred embodiment of the present invention has shown that wood chips can undergo delignification under controlled reaction conditions and eliminate or at least minimize the degradation of the cellulose. Degradation is understood to mean a darkening of cellulose, which is symbolic of an uncontrolled acid attack on the cellulose and staining thereof.

[0066] The heterocyclic compound together in the presence of an alkanesulfonic acid when in admixture with sulfuric acid and the peroxide component, seems to generate a coordination of the compounds which acts as a modified sulfuric acid. In that respect, it is believed that the presence of the heterocyclic compound forms an adduct with the sulfuric acid to generate a modified sulfuric acid. The strength of the modified acid is dictated by the moles of sulfuric acid to the moles of the heterocyclic compound. Hence, a composition comprising a molar ratio of 6:1 of sulfuric acid: the heterocyclic compound would be much less reactive than a composition of the same components in a 28:1 molar ratio.

[0067] When performing delignification of wood using a composition according to a preferred embodiment of the present invention, the process can be carried out at substantially lower temperatures than temperatures used in the conventional kraft pulping process. The advantages are substantial, here are a few: the kraft pulping process requires temperatures in the vicinity of 176-180° C. in order to perform the delignification process, a preferred embodiment of the process according to the present invention can delignify wood at far lower temperatures, even as low as 20° C. According to a preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 0° C. According to a preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 10° C. According to a preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 30° C. According to another preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 40° C. According to yet another preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 50° C. According to yet another preferred embodiment of the present invention, the delignification of wood can be performed at temperatures as low as 60° C. Other advantages include: a lower input of energy; reduction of emissions and reduced capital expenditures; reduced maintenance; lower shut down/turn around costs; also there are health, safety and environment (“HSE”) advantages compared to conventional kraft pulping compositions.

[0068] In each one of the above preferred embodiments, the temperature at which the processes are carried out are substantially lower than the current energy-intensive kraft process.

[0069] Moreover, the kraft process uses high pressures to perform the delignification of wood which is initially capital intensive, dangerous, expensive to maintain and has high associated turn-around costs. According to a preferred embodiment of the present invention, the delignification of wood can be performed at atmospheric pressure. This, in turn, circumvents the need for highly specialized and expensive industrial equipment such as pressure vessels/digestors. It also allows the implementation of delignification units in many of parts of the world where the implementation of a kraft plant would previously be impracticable due to a variety of reasons.

[0070] Some of the advantages of a process according to a preferred embodiment of the present invention, over a conventional kraft process are substantial as the heat/energy requirement for the latter is not only a great source of pollution but is in large part the reason the resulting pulp product is so expensive and has high initial capital requirements. The energy savings in the implementation of a process according to a preferred embodiment of the present invention would be reflected in a lower priced pulp and environmental benefits which would have both an immediate impact and a long-lasting multi-generational benefit for all.

[0071] Further cost savings in the full or partial implementation of a process according to a preferred embodiment of the present invention, can be found in the absence or minimization of restrictive regulations for the operation of a high temperature and high-pressure pulp digestors.

Experiment #1—Preparation of a Composition according to a Preferred Embodiment

[0072] For the H.sub.2SO.sub.4:H.sub.2O.sub.2:imidazole:methanesulfonic acid (MSA) blend with a 5:5:1:1 molar ratio, 49.5 g, of concentrated sulfuric acid (93%) was mixed with 6.4 g of imidazole and 9 g of MSA (70%). Then, 55.1 g of a hydrogen peroxide solution in water (29%) was slowly added to the acid. As the mixing releases a large amount of heat the beaker was placed in an ice bath. Addition of the hydrogen peroxide solution at this scale takes about 20 minutes. The pH of the resulting composition was less than 1.

Delignification Experiments

[0073] After mixing, the resulting composition is split into 4 equal parts. One part was exposed to 1.5g of wood shavings, another part was exposed to commercially available lignin and another part was exposed to commercially available cellulose respectively and stirred at ambient conditions for 3 hours. The fourth part of the blend is kept as a blend reference sample.

[0074] Control tests were run for the respective mixtures with just kraft lignin or just cellulose added instead of biomass. Commercially available lignin (Sigma-Aldrich; Lignin, kraft; Prod #471003) was used as a control in the testing. Commercially available cellulose (Sigma-Aldrich; Cellulose, fibers (medium); Prod #C6288) was also used as a control in the testing.

[0075] The solid phase of each blend was filtered off after 3 h of reaction time, rinsed with water and dried in an oven at 45° C. to constant weight. An effective blend should dissolve all lignin and leave the cellulose as intact as possible. The results of the experiments conducted with several compositions are reported in Table 1 below.

TABLE-US-00001 TABLE 1 Recovery of solids (% of initial mass) after 3 h reaction time Molar Wood Lignin Cellulose Ratio Chemical Yield (%) Yield (%) Yield (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:Triazole:MSA 49.59% 22.17% 92.26% 5:5:1:1 H.sub.2SO.sub.4:HO.sub.2:Imidazole:MSA 48.52% 11.28% 93.79% 10:10:1 H.sub.2SO.sub.4:HO.sub.2:imidazole:MSA  45.2%    0%  96.4% 20:20:1:1 H.sub.2SO.sub.4:HO.sub.2:Imidazole:MSA 38.71%  1.13% 84.30% 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:n- 48.70%  0.00% 94.73% methylimidazole:MSA

[0076] A blend with a ratio of 10:10:1:1 of sulfuric acid (93% conc. used) to hydrogen peroxide (as 29% solution) to triazole to MSA resulted in a mass recovery of over 49% from wood and over 92% from the cellulose control. However, the lignin control indicates that the delignification was only effective up to roughly 22.5% which is not optimal for many applications.

[0077] A blend with a ratio of 10:10:1:1 of sulfuric acid (93% conc. used) to hydrogen peroxide (as 29% solution) to n-methylimidazole to MSA resulted in a mass recovery of over 46% from wood and over 98% from the cellulose control. However, the lignin control indicates that the delignification was complete, which is an indication of a very effective composition at room temperature.

[0078] The above experiment is a clear indication that a preferred composition according to the present invention not only provides an adequate dissolving acid to delignify plant material but is also valuable in controlling the delignification to prevent the ultimate degradation of cellulosic material into carbon black residue resulting in higher yields potentially for the operators thus increasing profitability while reducing emissions and the risk to the employees, contractors and public.

[0079] Additional testing was carried out to confirm the above initial results and to explore the feasibility of using other ratios or other compounds with similar chemical features or characteristics as modifying agent. The results of the experiments are set out below in Tables 2 to 4. Experiments conducted involving a reaction between indole with MSA resulted in an unstable composition, as well experiments between indole with ESA were also unstable.

TABLE-US-00002 TABLE 2 Recovery of solids (% of initial mass) after 3 h reaction time using imidazole:MSA acid as modifying agent Molar Wood Lignin Cellulose Ratio Chemicals Yield (%) Yield (%) Yield (%) 5:5:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:imidazole:MSA 48.5% 11.3% 93.8% 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:imidazole:MSA 45.2%   0% 96.4% 20:20:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:imidazole:MSA 38.7%  1.1% 84.3%

TABLE-US-00003 TABLE 3 Recovery of solids (% of initial mass) after 3 h reaction time using imidazole:ESA acid as modifying agent Molar Wood Lignin Cellulose Ratio Chemicals Yield (%) Yield (%) Yield (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:imidazole:ESA 44.5% 0% 94.4%

TABLE-US-00004 TABLE 4 Recovery of solids (% of initial mass) after 3 h reaction time using N-methylimidazole:MSA acid as modifying agent Molar Wood Lignin Cellulose Ratio Chemicals Yield (%) Yield (%) Yield (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:N- 48.7% 0% 94.7% methylimidazole:MSA

TABLE-US-00005 TABLE 5 Recovery of solids (% of initial mass) after 3 h reaction time using N-methylimidazole:ESA acid as modifying agent Molar Wood Lignin Cellulose Ratio Chemicals Yield (%) Yield (%) Yield (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:N- 48.1% 17.0% 95.6% methylimidazole:ESA

TABLE-US-00006 TABLE 6 Recovery of solids (% of initial mass) after 3 h reaction time using triazole:MSA acid as modifying agent Wood Lignin Cellulose Molar Yield Yield Yield Ratio Chemicals (%) (%) (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:triazole: 49.6% 22.2% 92.3% MSA

TABLE-US-00007 TABLE 7 Recovery of solids (% of initial mass) after 3 h reaction time using triazole:ESA acid as modifying agent Wood Lignin Cellulose Molar Yield Yield Yield Ratio Chemicals (%) (%) (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:triazole:ESA 38.2% 3.5% 96.4%

TABLE-US-00008 TABLE 8 Recovery of solids (% of initial mass) after 3 h reaction time using benzotriazole:MSA acid as modifying agent Wood Lignin Cellulose Molar Yield Yield Yield Ratio Chemicals (%) (%) (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:benzotriazole: 56.4% 0% 100% MSA

TABLE-US-00009 TABLE 9 Recovery of solids (% of initial mass) after 3 h reaction time using benzotriazole:ESA acid as modifying agent Wood Lignin Cellulose Molar Yield Yield Yield Ratio Chemicals (%) (%) (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:benzotriazole: 52.8% 0% 96.3% ESA

TABLE-US-00010 TABLE 10 Recovery of solids (% of initial mass) after 3 h reaction time using quinoline:MSA acid as modifying agent Wood Lignin Cellulose Molar Yield Yield Yield Ratio Chemicals (%) (%) (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:quinoline:MSA 61.1% 12.4% 95.9%

TABLE-US-00011 TABLE 11 Recovery of solids (% of initial mass) after 3 h reaction time using quinoline:ESA acid as modifying agent Wood Lignin Cellulose Molar Yield Yield Yield Ratio Chemicals (%) (%) (%) 10:10:1:1 H.sub.2SO.sub.4:H.sub.2O.sub.2:quinoline:ESA 72.1% 15.7% 96.1%

[0080] A method to yield glucose from wood pulp would represent a significant advancement to the current process where the conversion of such is chemical and energy intensive, costly, emissions intensive and dangerous all while not resulting in highly efficient results, especially in large-scale operations. It is desirable to employ a composition which may delignify wood but also allows the operator some control in order to preserve the cellulose rather than degrading it to carbon black resulting in higher efficiencies and yields along with increased safety and reduced overall costs.

[0081] According to a preferred embodiment of the method of the present invention, the separation of lignin can be effected and the resulting cellulose fibers can be further processed to yield glucose monomers. Glucose chemistry has a multitude of uses including as a starting block in the preparation of widely used chemicals including but not limited to diacetonide, dithioacetal, glucoside, glucal and hydroxyglucal to name but a few.

[0082] According to another preferred embodiment of the present invention, the composition can be used to decompose organic material by oxidation such as those used in water treatment, water purification and/or water desalination. An example of this is the removal (i.e. destruction) of algae on filtration membranes. As such membranes can be quite expensive, it is imperative that they be used for as long as possible. However, given the difficulty to remove organic matter which accumulates on it over time, new approaches are necessary to do so efficiently and with as little damage to the membrane as possible. Mineral acids are too strong and, while they will remove the organic matter, will damage the filtration membranes. A preferred composition of the present invention remedies this issue as it is less aggressive than the mineral acids and, as such, will remove the organic contaminants in a much milder approach, therefore sparing the membrane.

[0083] While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be appreciated by those skilled in the relevant arts, once they have been made familiar with this disclosure that various changes in form and detail can be made without departing from the true scope of the invention in the appended claims.