PREPARATION OF FURFURAL USING MIXED SOLVENTS

Abstract

Processes for the preparation of furfural from a xylose containing feedstock and more particularly to an elevated temperature conversion of a xylose containing feedstock to furfural in acidic conditions are described. The described process uses a mixture of two solvents in which the humins are formed and solubilized. The described process is operated in continuous mode with no significant amounts of solid by-products formation.

Claims

1. A process for converting xylose to furfural comprising: (a) providing a first stream comprising xylose obtained from an acid pre-treated lignocellulosic biomass; (b) adjusting pH of said first stream with a metal oxide or hydroxide forming a second stream; (c) mixing said second stream with isophorone or a mixture of at least one low boiling solvent and at least one high boiling solvent forming a third stream; (d) treating said third stream in a reactor at a temperature and pressure for a specific time period so as to cause a desired reaction forming a fourth stream; (e) separating said fourth stream into an organic stream and an aqueous stream; (f) adjusting pH of said organic stream by a base; (g) separating furfural as the product from a fraction comprising or consisting of humins and the at least one high boiling solvent or isophoron; and (h) recycling or recovering the at least one high boiling solvent or isophorone.

2. The process of claim 1, wherein said first stream comprises xylose between 10% to 30% by weight.

3. The process of claim 1, wherein the pH of said organic stream is adjusted to 7.

4. The process of claim 1, wherein the metal oxide or hydroxide used to adjust the pH of said first stream is selected from the group consisting of sodium hydroxide and magnesium oxide.

5. The process of claim 1, wherein the base used to adjust the pH of said organic stream is selected from the group consisting of sodium hydroxide, monoethanolamine and sodium bicarbonate.

6. The process of claim 1, wherein further comprising recycling said solvents separated from said organic stream.

7. The process of claim 1, wherein said high boiling solvent solubilises at least a portion of the humins formed in said process.

8. The process of claim 1, wherein conversion efficiency of xylose is more than 90% by weight.

9. The process of claim 1, wherein the yield of furfural is at least 60% by weight of xylose.

10. The process of claim 1, wherein said reactor is selected from the group consisting of a batch reactor, a continuous stirred-tank reactor and a continuous plug-flow reactor.

11. (canceled)

12. A process for the preparation of furfural from lignocellulosic biomass, the process comprising: (a) acid pre-treating the lignocellulosic biomass forming a first stream comprising xylose; (b) adjusting pH of said first stream with a metal oxide or hydroxide forming a second stream; (c) mixing said second stream with isophorone forming a third stream; (d) treating said third stream in a reactor at a temperature and pressure for a specific time period so as to cause a reaction forming a fourth stream; (e) separating said fourth stream into an organic stream and an aqueous stream; (f) adjusting pH of said organic stream by a base; (g) separating furfural as the product from a fraction comprising or consisting of humins and the isophoron; and (h) recycling or recovering the at least one high boiling solvent or isophorone.

13. (canceled)

14. (canceled)

15. The process of claim 1, wherein said reactor is selected from the group consisting of a continuous stirred-tank reactor and a continuous plug-flow reactor.

16. The process of claim 1, further comprising at least of separating, recycling, or recovering the at least one low boiling solvent separated from said organic stream.

17. The process of claim 1, wherein said first stream is obtained from the acid pre-treated lignocellulosic material after removal of insoluble fraction.

18. The process of claim 1, wherein said low boiling solvent is MIBK or toluene.

19. The process of claim 1, wherein said high boiling solvent is isophorone.

20. The process of claim 1, wherein said temperature ranges from about 160° C. to about 220° C.

21. The process of claim 1, wherein said specific time period ranges from 10 minutes to 120 minutes.

22. The process of claim 1, wherein said pH of said first stream is adjusted to between 1 and 2.

23. The process of claim 12, further comprising removing an insoluble fraction from the acid pre-treated lignocellulosic to form the first stream.

Description

DESCRIPTION OF THE DRAWING

[0106] FIG. 1 depicts a process flow diagram of a preferred embodiment of the production of furfural from a LCM feedstock comprising xylose. Different elements of the process are identified and directional movement of different streams and components formed during the process are shown to describe the features of one preferred embodiment of the present invention. The ATFD-step (agitated thin film dryer) can optionally be performed.

[0107] The invention will now be explained by way of the following non-limiting examples.

EXAMPLES

[0108] Examples provided below give wider utility of the invention without any limitations as to the variations that may be appreciated by the person skilled in the art. A non-limiting summary of various experimental results is given in the examples and tables, which demonstrate the advantageous and novel aspects of the process of using a xylose-containing stream obtained from any LCM to prepare furfural in very efficient ways as disclosed herein.

Example 1

[0109] A batch of about 118 kg of corncobs having total dry solids of about 92% by weight, cellulose of about 33% by weight, hemicelluloses of about 27% by weight and lignin of about 13% by weight was used as a feedstock. It was subjected to mechanical milling for size reduction to less than 40 mm particles affording about 108 kg of the particulate material. This particulate material was soaked in water for about 30 min. Then about 360 kg slurry containing about 30% by weight total insoluble solids was prepared and continuously introduced into a hydrolyser through a plug screw reactor. Here the slurry was mixed with about 240 litres of the admixture of oxalic and sulphuric acids. This admixture of mixed acids contained about 1.08 kg of oxalic acid and about 2.16 kg of sulphuric acid on dry biomass weight basis [total 3% acid on dry biomass weight basis]. The resultant reaction mixture was then subjected to hydrolysis in said hydrolyser at a temperature of about 160° C. and pressure of about 6 bar[absolute] for a period of about 24 minutes at pH of about 1.3. At the end of this pretreatment the final slurry of about 603 kg contained about 16% of total solids. After filtration the liquid stream (said C5 stream) contained about 0.52% of glucose, about 4.8% of xylose, about 0.05% of furfural, about 0.04% of HMF and about 3800 PPM of phenolic components along with residual cellulose and lignin as detected by the HPLC methods. Herein, the efficiency of xylan to xylose [C5] conversion was about 86% and that of glucan to glucose conversion was about 8%. Then this final liquid stream [said C5 stream] was further subjected to evaporation to concentrate the amount of xylose in said stream up to about 20% by weight and formed the concentrated feedstock stream [first stream] for the preparation of furfural according to the examples below.

Example 2

See Table Serial No 1

[0110] 3.5 kg of a concentrated feedstock stream [first stream] comprising 10% xylose by weight was obtained from an acid pre-treated sugarcane bagasse. This stream also comprised 1-2% acid by weight used for said pre-treatment reaction. Then said first stream was subjected to pH adjustment to a pH value of 1.6 using a 50% NaOH solution forming a second stream. Then a mixture of 3500 g of methyl isobutyl ketone (MIBK) was added to second stream forming a third stream. This third stream was subjected to temperature of 180° C. in a closed stirred tank reactor working at 650 RPM for 1 hour. After completion of the heat treatment, the reaction mass was cooled to room temperature, and solids [humins] remaining in the mass removed by filtration. The humins were partially soluble [HS2] in the reaction mass and nominally sticky [S1] to the equipment. Then organic phase was separated from aqueous phase and subjected to pH adjustment to 7 by NaHCO.sub.3. Further said organic phase was subjected to distillation to recover MIBK that was recycled. This method achieved 99% conversion of xylose present in the feedstock with 79% yield of furfural.

Example 3

See Table Serial No 12

[0111] 3.5 kg of a concentrated feedstock stream [first stream] comprising 20% xylose by weight was obtained from an acid pre-treated corncob. This stream also comprised 1-2% acid by weight used for said pre-treatment reaction. Then said first stream was subjected to pH adjustment to a pH value of 1.5 using a 50% NaOH solution or magnesium oxide [MgO] forming a second stream. Then a mixture of 2800 g of methyl isobutyl ketone (MIBK) and 700 g of isophorone (80:20) was added to said second stream forming a third stream. This third stream was subjected to temperature of 180° C. in a stirred-tank reactor with at retention time of 1 hour. On completion of the heat treatment, the reaction mass was cooled to room temperature and collected. The humins were partially soluble [HS2] in the reaction mass and nominally sticky [S1] to the equipment. Then the organic phase was separated from aqueous phase and subjected to pH adjustment to about 6 to 7 by NaHCO.sub.3. Further said organic phase was subjected to first distillation to recover MIBK that was recycled. The remaining organic phase contained furfural and isophorone with dissolved humins; it was subjected to a second distillation to recover furfural in pure form. This method achieved 100% conversion of xylose present in the feedstock with 78% yield of furfural. The residual organic phase mostly of isophorone and dissolved humins was recycled as such in the process for up to five times without any significant loss of yield of furfural. At the end of the fifth cycle, the residual isophorone with humins up to 60% was subjected to distillation to recover pure isophorone.

Example 4

See Table Serial No 17

[0112] 3.5 kg of a concentrated feedstock stream [first stream] comprising 10% xylose by weight was obtained from an acid pre-treated sugarcane bagasse. This stream also comprised 1-2% acid by weight used for said pre-treatment reaction. Then said first stream was subjected to pH adjustment to a pH value of 1.5 using a 50% NaOH solution or magnesium oxide [MgO] forming a second stream. Then a mixture of 2800 g of toluene and 700 g of isophorone (80:20) was added to said second stream forming a third stream. This third stream was subjected to temperature of 180° C. in a reactor for a retention time of 1 hour. After completion of the heat treatment; the reaction mass was cooled to room temperature and collected. The humins were sparingly soluble [HS1] in the reaction mass and significantly sticky [S3] to the equipment. Then the organic phase was separated from aqueous phase and subjected to pH adjustment to about 6 to 7 by NaHCO.sub.3. Further said organic phase was subjected to first distillation to recover toluene that was recycled. The remaining organic phase contained furfural and isophorone with dissolved humins; it was subjected to a second distillation to recover furfural in pure form. This method achieved 98% conversion of xylose present in the feedstock with 84% yield of furfural. The residual organic phase mostly of isophorone and dissolved humins was recycled as such in the process for up to five times without any significant loss of yield of furfural. At the end of the fifth cycle, the residual isophorone with humins up to 50% was subjected to distillation to recover pure isophorone.

Example 5

See Table Serial No 16

[0113] 3.5 kg of a concentrated feedstock stream [first stream] comprising 20% xylose by weight was obtained from an acid pre-treated sugarcane bagasse. This stream also comprised 1-2% acid by weight used for said pre-treatment reaction. Then said first stream was subjected to pH adjustment to a pH value of 1.5 using a 50% NaOH solution forming a second stream. Then 3500 g of toluene was added to said second stream forming a third stream. This third stream was subjected to temperature of 180° C. in a closed stirred tank reactor working at 650 RPM for 1 hour. On completion of the heat treatment, the reaction mass was cooled to room temperature and collected. The humins were insoluble [HS0] in the reaction mass and significantly sticky [S3] to the equipment. Then the organic phase was separated from aqueous phase and subjected to pH adjustment to about 7 by NaHCO.sub.3. Further said organic phase was subjected to first distillation to recover toluene that was recycled. The remaining organic phase contained furfural, which was distilled out next leaving undissolved humins behind. This method achieved 99% conversion of xylose present in the feedstock with 81% yield of furfural.

Example 6

See Table Serial No 7

[0114] 3.5 kg of a concentrated feedstock stream [first stream] comprising 20% xylose by weight was obtained from an acid pre-treated sugarcane bagasse. This stream also comprised 1-2% acid by weight used for said pre-treatment reaction. Then said first stream was subjected to pH adjustment to a pH value of 1.5 using a 50% NaOH solution forming a second stream. Then 3500 g of isophorone was added said to second stream forming a third stream. This third stream was subjected to temperature of 180° C. in a closed stirred tank reactor working at 650 RPM for 1 hour. On completion of the heat treatment, the reaction mass was cooled to room temperature and collected. The humins were completely soluble [HS3] in the reaction mass and non-sticky [S0] to the equipment. Then the organic phase was separated from aqueous phase and subjected to pH adjustment to about 7 by NaHCO.sub.3. Further said organic phase was subjected to first distillation to recover furfural as low boiling product. The remaining organic phase contained isophorone with dissolved humins; equipment contained no humins at all. This method achieved 100% conversion of xylose present in the feedstock with 69% yield of furfural.

Example 7

See Table Serial No 10

[0115] 3.5 kg of a concentrated stream [first stream] comprising 10% xylose by weight was obtained from an acid pre-treated biomass like corncob, corn stover or sugarcane bagasse. This stream also comprised 1.5% to 2% sulphuric acid by weight and 0.5% to 1.0% oxalic acid by weight used in said pre-treatment reaction. Then said first stream was subjected to pH adjustment to a pH value of 1.6 using a 50% NaOH solution forming a second stream. Then a mixture of 2800 g methyl isobutyl ketone (MIBK) and 700 g isophorone (80:20) was added to said second stream forming a third stream. This third stream was then subjected to temperature of 180° C. in a stirred tank reactor working at 650 RPM for 1 hour. After the completion of heat treatment the reaction mass was cooled to room temperature, filtered to remove precipitated humins and then subjected to phase separation. The humins were partially soluble [HS2] in the reaction mass and non-sticky [S0] to the equipment. The organic phase was washed with alkali to neutralise acids and was subjected to distillation to recover MIBK that was recycled in the process. The remaining organic phase containing furfural and isophorone was subjected to a second distillation to recover furfural in pure form. The undistilled bottom fraction remaining after the separation of MIBK and furfural from organic mass contained mainly isophorone (ISP) with soluble humins along with small quantity of hydroxymethyl furfural (HMF). This ISP-humins mixture was recycled to the process without affecting the process performance in terms of conversion of xylose and the yield of furfural. To this end, some quantity of this ISP-humins mixture is taken out (purged) from said bottom faction and the remaining mass used in the process along with fresh make-up ISP and MIBK. This operation is continued until the soluble humins in ISP was concentrated to a level of 60% by weight. At this time, the whole ISP-humins mixture was removed and distilled to recover pure ISP solvent. This method achieved 98% conversion of xylose present in the feedstock with 80% yield of furfural.

Example 8

[0116] TABLE 1 lists different experiments of preparation of furfural from xylose under different reaction conditions and parameters including the example described herein above. All common parameters were kept at standard conditions of temperature at 180° C., reaction time at 1 hour, pH at 1.6, and RPM at 650, except the variable parameters under study as depicted in the table. The efficiencies of conversion of xylose and yield of furfural afforded by using the methods of the invention disclosed herein are listed to show the general utility of the invention and its features. It was observed that the significant amounts of humins were formed when MIBK or toluene was used as a solvent. It was also found that the humins formed in reaction were sticking to the internal part of the rectors; and this further led to the problem of processing such reaction mass for recovery of furfural and said solvent. Further, the process could not be run continuously as the reactor chambers were choked with insoluble and sticky humins. On the other hand when isophorone alone or in combination with other solvents was used, the most of the humins were dissolved in the isophorone without affecting the efficiencies of process. Further said isophorone with humins and other components could be recycled at least five times in the process significantly increasing the economics of the furfural production. The solubility of humins in reaction mass on completion of reaction at room temperature was qualitatively defined as HS0=insoluble, HS1=sparingly soluble, HS2=partially soluble and HS3=completely soluble. Similarly, the stickiness of humins to internal parts of the reactor at room temperature was qualitatively defined as S0=non-sticking, S1=nominally sticking, S3=partially sticking and S3=significantly sticking.

Example 9

[0117] A concentrated stream comprising 20% xylose by weight was obtained from an acid pre-treated biomass like corncob, corn stover or sugarcane bagasse as above. This stream was subjected to pH adjustment to a pH value of 1.6 using a 50% NaOH solution. Then 2000 g of mixture of methyl isobutyl ketone and isophorone, made in the proportion of 80:20, was charged to a 10-L closed stirred tank reactor with 2000 g of 20% xylose stream; and subjected to temperature of 180° C. and RPM of 650 for 1 hour at time of start up step. After 1 hour, the xylose stream and the mixed solvents steam each was pumped to the reactor simultaneously maintaining the temperature at about 180° C. The rate of addition for each of xylose and mixed solvents was 60 mL/min. The reaction mass was continuously discharged using a backpressure regulator at a rate of 120 mL/min. This continuous process was run for 3 hours forming 21 kg of reacted mass. This hot mass was passed through a heat exchanger to cool it to room temperature. Then the mass was filtered to remove precipitated humins and subjected to phase separation. This method achieved 78% conversion of xylose with 75% selectivity of furfural production.

Example 10

[0118] A concentrated stream comprising about 20% xylose by weight was obtained from an acid pre-treated biomass like corncob, corn stover or sugarcane bagasse as above. This stream was subjected to pH adjustment to a pH value of 1.6 using a 50% NaOH solution. This 20% xylose stream and a mixture of methyl isobutyl ketone and isophorone [made in the proportion of 80:20] was charged separately to feed tanks. Initially, the mixture of solvents at a flow rate of 10 ml/min was passed through a pre-heater set at about 160° C. and then introduced to a 4-L packed column [plug flow] reactor. Then the above pH adjusted 20% xylose stream was introduced at a flow rate of 10 ml/min maintaining the temperature of reactor about 180° C. The whole reaction system was maintained at 18 bars under nitrogen pressure. The reaction mass was discharged to a receiver [pressure vessel] held at room temperature through a heat exchanger. The pressure in the system including receiver was maintained at 18 bar using a backpressure regulator. This continuous process was run for 6 hours forming 7.2 kg of reacted mass. Then the mass was filtered to remove precipitating humins and subjected to phase separation. This method achieved 85% conversion of xylose with 75% selectivity of furfural production.

[0119] While the invention has been particularly shown and described with reference to embodiments listed in examples, it will be appreciated that several of the above disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen and unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. Although the invention has been described with reference to specific preferred embodiments, it is not intended to be limited thereto, rather those having ordinary skill in the art will recognise that variations and modifications may be made therein which are within the spirit of the invention and within the scope of the claims.

[0120] These and further experimental data are summarized in TABLE 1. Further experiments can be processed according to the above disclosure and teaching.

TABLE-US-00001 TABLE 1 PREPARATION OF FURFURAL IN DIFFERENT CONDITIONS FROM THE C5 STREAM. XYLOSE AQUEOUS: SOLVENT in C5 ORGANIC WET SELEC- CONVER- HUMINS STICK- SOLVENT MIXTURE STREAM PHASE HUMINS TIVITY SION YIELD SOLUBILITY INESS No. MIXTURE RATIO [%] RATIO [g] [%] [%] [%] * ** 1 MIBK ONLY X 10 1:1   65 80 99 79 HS2 S1 2 MIBK ONLY X 10 1:3.2  5 78 100 78 HS2 S1 3 MIBK ONLY X 20 1:1   250 70 100 70 HS2 S1 4 MIBK ONLY X 20 1:3.2  85 81 98 79 HS2 S1 5 ISP ONLY X 10 1:1   0 83 97 81 HS3 S0 6 ISP ONLY X 10 1:3.2  0 76 99 75 HS3 S0 7 ISP ONLY X 20 1:1   40 69 100 69 HS3 S0 8 ISP ONLY X 20 1:0.75 45 73 100 73 HS3 S0 9 ISP ONLY X 20 1:3.2  35 75 99 74 HS3 S0 10 MIBK:ISP 80:20 10 1:1   50 82 98 80 HS2 S0 11 MIBK:ISP 80:20 15 1:1   159 77 99 76 HS2 S1 12 MIBK:ISP 80:20 20 1:1   195 78 100 78 HS2 S1 13 MIBK:ISP 80:20 20 1:3.2  70 73 100 73 HS2 S1 14 MIBK:ISP 80:20 20 1:0.75 300 69 100 69 HS2 S1 15 MIBK:ISP 80:20 20 1:0.5  400 59 100 59 HS2 S1 16 TOLUENE X 20 1:1   221 82 99 81 HS0 S3 ONLY 17 TOLUENE:ISP 80:20 10 1:1   145 86 98 84 HS1 S3 18 TOLUENE:ISP 80:20 20 1:3.2  84 74 99 73 HS1 S3 19 TOLUENE:ISP 80:20 20 1:1   410 69 100 69 HS1 S3 20 TOLUENE:ISP 60:40 20 1:3.2  128 76 99 75 HS1 S3 21 TOLUENE:ISP 50:50 20 1:3.2  175 68 100 68 HS2 S2 22 TOLUENE:ISP 40:60 20 1:3.2  56 70 99 69 HS2 S2 23 CYCLO- X 20 1:1   50 8 100 8 HS3 S0 HEXANONE ONLY 24 MIBK:ISP 80:20 25 1:1   345 56 99 55 HS0 S3 ISP = Isophorone, MIBK = Methyl Isobutyl Ketone * Humins solubility in organic phase at room temperature: HS0: insoluble, HS1: sparingly soluble, HS2: partially soluble, HS3: completely soluble ** Stickiness to reactor internal parts at room temperature: S0: non-sticking, S1: nominally sticking, S2: partially sticking, S3: significantly sticking