DEWATERING OF THERMOCHEMICAL OIL

Abstract

A process for dewatering a thermochemical oil. The process comprises providing a thermochemical oil comprising water; adding a solvent selected from mesityl oxide, 2-methyltetrahydrofuran, dioxane and furfural to the thermochemical, oil, to form a mixture comprising the thermochemical oil and the solvent; heating the mixture to remove an azeotrope comprising water and the solvent from the mixture, thereby forming a dewatered thermochemical oil. A dewatered thermochemical oil. A fuel precursor.

Claims

1. A process for producing a dewatered thermochemical oil comprising: a) providing a thermochemical oil comprising water; b) adding a solvent selected from mesityl oxide, 2-methyltetrahydrofuran, dioxane and furfural to the thermochemical oil, to form a mixture comprising the thermochemical oil and the solvent; c) heating the mixture to remove an azeotrope comprising water and the solvent from the mixture, thereby forming a dewatered thermochemical oil.

2. The process according to claim 1, wherein the solvent is mesityl oxide.

3. The process according to claim 1, wherein the thermochemical oil is a pyrolysis bio oil.

4. The process according to claim 1, wherein the heating is performed at a temperature of less than 80° C., such as in the range of from 40° C. to 80° C.

5. The process according to claim 4, wherein the heating is performed under a pressure in the range from 10 to 100 mbar.

6. The process according to claim 1, further comprising recovering the solvent from the azeotrope removed from the mixture.

7. The process according to claim 6, wherein the step of recovering the solvent comprises phase separation means, such as liquid-liquid phase separation.

8. The process according to claim 7, wherein at least 90 mass-% of said solvent is recovered, such as at least 95 mass-%, preferably at least 99 mass-%.

9. The process according to claim 1, wherein the thermochemical oil comprises a compound having a hydroxyl group.

10. The process according to claim 9, wherein the compound having a hydroxyl group is an alcohol or a phenol.

11. The process according to claim 9 or 10, which after the step of heating the mixture further comprises the following steps: adding a compound having an acyl group to the dewatered thermochemical oil comprising a compound having a hydroxyl group; and reacting the compound having a hydroxyl group with the compound having an acyl group, thereby forming an ester between said compounds.

12. The process according to claim 11, wherein the compound having an acyl group is a carboxylic acid, an ester, carboxylic acid halide or a carboxylic acid anhydride, such as acetic anhydride.

13. The process according to claim 12, wherein the carboxylic acid is provided as renewable feedstock, preferably as raw tall diesel, tall oil fatty acids, palm oil fatty acids, palm fatty acid distillate, algae oil fatty acids or volatile fatty acids having 3 to 6 carbons, or a blend thereof; and/or the ester is provided as renewable feedstock, preferably as vegetable oil, such as rapeseed oil or technical corn oil, animal fat, marine oil, algae oil, used cooking oil or fatty acid methyl esters.

14. A dewatered thermochemical oil obtainable by the process according to claim 1.

15. A fuel precursor obtainable by the process according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The above objects, as well as other apparent objects of the invention will now be described with reference to the following detailed description and drawings, wherein

[0063] FIG. 1 shows a flow-sheet explaining the steps of the process in accordance with some embodiments of the invention.

AZEOTROPIC DISTILLATION

[0064] Azeotropic distillation is based on the formation and removal of an azeotrope comprising at least two components. In the present invention, the azeotrope in question comprises water from the thermochemical oil and a solvent selected from mesityl oxide, 2-methyltetrahydrofuran, 2-butanone, dioxane and furfural. An azeotrope refers to a constant, or near constant, boiling point mixture. An azeotrope formed by water contained in the thermochemical oil and one of the above solvents has been found to boil at mild conditions, such as at temperatures of below 80° C. under a reduced pressure of less than 100 mbar, such as less than 50 mbar. Compared to conventional distillation of water, which takes place at elevated temperatures, the azeotropic distillation of the invention involves much milder conditions. Such mild conditions ensure that the desired organic components of the pyrolysis oils remain intact and avoid extensive oligomerization and polymerization reactions in the pyrolysis oils thereby decreasing the risks of clogging transfer lines by undesired separation of poorly soluble components, as well as by potentially lowering the coking tendency of the feed during subsequent hydrotreatment upgrading. At the same time, the mild conditions are sufficient for removing undesired low molecular weight organic compounds from the thermochemical oil.

[0065] Herein, the solvent may be mesityl oxide, such as unsubstituted mesityl oxide, but the term also refers to substituted mesityl oxide, such as mono-substituted mesityl oxide or di-substituted mesityl oxide.

[0066] Techniques for azeotropic distillation, or co-evaporation, of a mixture comprising a thermochemical oil comprising water and one of the above-described solvents are exemplified by, but not limited to, the following.

[0067] FIG. 1 shows a conceptual flow chart illustrating an embodiment of the inventive process 100 for producing a dewatered pyrolysis oil.

[0068] The process steps are briefly described as follows.

[0069] A pyrolysis oil and raw tall diesel is charged 101 to a reactor. Mesityl oxide (technical grade, 85%) w/w is charged 103 to the reactor to form a mixture. The mixture may be formed by means known to a person skilled in the art. The mixture is then heated 105 to approximately 60° C. at a reduced pressure (typically below 50 mbar) during stirring of the mixture. An azeotrope comprising mesityl oxide and water, and preferably also volatile low-molecular weight organic components is boiled off, to form a dewatered pyrolysis oil. A dewatered pyrolysis oil containing some residual mesityl oxide is obtained 107. The residual solvent will eventually give isohexane after hydrotreatment. The azeotrope boiled off may be recovered 109 and a mesityl oxide phase is separated 111 from an aqueous phase, preferably by means of liquid-liquid phase separation. The mesityl oxide phase may then be distilled 113 for removal of undesirable organics. Optionally, the distilled mesityl oxide can be recirculated in the charging 103.

[0070] If the water content of the dewatered pyrolysis oil is deemed too high, the dewatered pyrolysis oil may be recirculated 115 in the charging 101, to be dewatered once more. The dewatered pyrolysis oil may be recirculated until a desired water content has been achieved.

EXAMPLES

Analyses

[0071] Hydroxyl numbers related to aliphatic alcohols (ROH), phenols (ArOH) and carboxylic acids (COOH) were determined by .sup.31P-NMR.

Raw Materials

[0072] Wood oil characterization: Pyrolysis oil produced by fast pyrolysis of wood material and subsequent condensation of the vapors was obtained from BTG Biomass Technology Group BV, Netherlands.

[0073] Raw tall diesel characterization: Tall oil is a by-product from the pulp and paper industry and mainly consists of resin acids and free fatty acids. Raw tall diesel (RTD) is produced from tall oil through a (vacuum distillation process, during which the content of free fatty acids is increased relative to the resin acids and other components. Raw tall diesel was obtained from Sunpine AB, Sweden.

[0074] Solvents and other chemical used herein are readily available off-the-shelf chemicals.

Example 1. Dewatering of Pyrolysis Oil and RTD with Mesityl Oxide

[0075] A 50 L stainless steel reactor was evacuated and purged with nitrogen (three cycles). Pyrolysis oil (10.06 kg, water content 22% w/w) and raw tall diesel (RTD) (13.14 kg) were charged to the reactor, followed by mesityl oxide (7.99 kg). The mixture was heated to 57° C., initially at ambient pressure, then vacuum was applied, resulting in distillation of the mesityl oxide/water azeotrope. The water was separated in a siphon and was directed to one of the receiving vessels, while the mesityl oxide was recirculated to the reactor. The distillation was continued for at least 3 h. A second portion of mesityl oxide (8.17 kg) was charged to the reactor, and the distillation was continued at reduced pressure (T.sub.i 77° C., T.sub.d 48-56° C.) over ca 30 min until dewatering was complete. The collected water (2.52 kg) contained some polar low molecular weight organic components. T.sub.m was set to 90° C., and the pressure was decreased gradually. The distillation was continued over ca 5 h, end conditions T.sub.i 87° C. The system was purged with nitrogen to equalize the pressure, and T.sub.m was set to 75° C. The distillate (16.31 kg, recovered mesityl oxide) was collected. The contents of the reactor were treated as described below in Example 4.

Example 2. Dewatering of Pyrolysis Oil with Various Solvents

[0076] A pyrolysis oil containing 17% water (5 g) was placed in a 100 mL round bottomed flask and the solvent (25 mL) was added. The flask was placed on a rotary evaporator and heated at 60° C. for 15 minutes before reduced pressure was applied. After 1 h at this temperature and pressure, the flask was removed, and the water content in the residue was measured using a Karl Fischer titrator with titrating reagent Hydranal Composite K. The results for various solvents are shown in Table 1.

TABLE-US-00001 TABLE 1 Comparison of the dewatering efficiency of selected solvents. Residual Solvent water (% w/w) Furfural  0.04 2-Methyl tetrahydrofuran  0.52 Acetic acid  0.56 Mesityl oxide  0.46 Toluene 2.1 Methyl iso-butyl ketone  0.58

Example 3. Dewatering of Pyrolysis Oil and RTD with Various Solvents

[0077] A pyrolysis oil containing 21% water (2 g) and RTD (5 g) were placed in a 100 mL round bottomed flask and the solvent (25 mL) was added. The flask was placed on a rotary evaporator and heated at 60° C. for 15 minutes before reduced pressure was applied. After 1 h at this temperature and pressure, the flask was removed, and the water content was measured using Karl Fischer titrator with titrating reagent Hydranal Composite K. The results for various solvents are shown in Table 2.

TABLE-US-00002 TABLE 2 Comparison of the dewatering efficiency of selected solvents when applied to pyrolysis oil/RTD mixtures. Residual Solvent water (% w/w) Heptane 0.66 Toluene 0.65 2-Methyl tetrahydrofuran 0.14 Mesityl oxide 0.10 Methyl iso-butyl ketone 0.28 n-Butanol 0.14 Pyridine 0.13 Furfural 0.14

Example 4. Derivatization

[0078] Acetic anhydride (8.09 kg) was charged to the reactor (T.sub.i 73° C.) of Example 1. After 1 h, T.sub.m was set to 90° C., and the mixture was stirred for 30 min (T.sub.i 80° C.). After ca 2 h (T.sub.i 89° C.), T.sub.m was set to 120° C. The reaction was continued for ca 2 h, whereupon vacuum was applied (T.sub.m 119° C., T.sub.i 116° C.). The distillation was carried out over a period of ca 3 h at reduced pressure, while gradually adjusting T.sub.m to 165° C. The system was purged with nitrogen, T.sub.m was set to 25° C. The distillate (7.96 kg) was collected, containing acetic acid (5.60 kg), acetic anhydride (1.51 kg) and mesityl oxide (0.48 kg). The intermediate derivatized pyrolysis oil product (19.58 kg) as a brown homogeneous liquid was transferred to containers. A sample was evaluated for miscibility with LLGO at 20% concentration failed to give a homogeneous mixture. The intermediate product subjected to post-treatment at 170° C. under vacuum in an 8 L autoclave equipped with a condenser followed by a cold-trap in the vacuum line as four separate portions (total treated 18.88 kg). Heating was maintained overnight. After cooling to ambient temperature, each product mixture was transferred to a container, and the distillate fractions in the receiving vessel on the condenser and in the cold trap were collected. The details for each sub-batch are provided in Table 4. Each of the sub-batches was tested for miscibility with LLGO at 20% v/v concentration, which proved to be satisfactory in all cases (brown homogeneous liquid). The total product yield was 17.99 kg as a brown homogeneous liquid.

TABLE-US-00003 TABLE 3 Post-treatment of intermediate product from derivatization, with yields and hydroxyl number measurements for each split batch after post- treatment (final derivatized pyrolysis oil product). Intermediate Final Carboxylic Experiment/ product product Yield Distillate Aliphatic-OH Phenols acids Batch # charged (kg) (kg) (% w/w) (kg) (mmol/g) (mmol/g) (mmol/g) Intermediate 0.29 0.09 0.62 product Split batch 1  4.73  4.41 93 0.214 0.10 0.04 0.98 Split batch 2  4.69  4.57 97 0.232 0.08 0.01 0.98 Split batch 3  4.67  4.41 94 0.167 0.10 0.03 1.12 Split batch 4  4.79  4.60 96 0.196 0.08 0.02 1.00 Total 18.88 17.99 95 0.809 Abbreviations T.sub.i = Inner temperature measured in the reaction mixture T.sub.m = Temperature of medium in heating mantle T.sub.d = Temperature of the distillate (vapor phase) LLGO = Light light gas oil

REFERENCES

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