WO2010098585A2

WO2010098585A2 - Method for producing biofuels via hydrolysis of seaweed extract using heterogeneous catalyst

Info

Publication number: WO2010098585A2
Application number: PCT/KR2010/001158
Authority: WO
Inventors: Young Seek Yoon; Gi Ho Goh; Jong Hee Song; Seung Hoon Oh; In Ho Cho; Sin Young Kang; Cher Hee Park; Seong Ho Lee
Original assignee: Sk Energy Co., Ltd.
Priority date: 2009-02-24
Filing date: 2010-02-24
Publication date: 2010-09-02
Also published as: KR20100096408A; WO2010098585A3

Abstract

Disclosed is a method for producing a biofuel. It comprises hydrolyzing an extract from a seaweed selected from a group consisting of red algae, brown algae, green algae or a combination therof in a presence of a heterogeneous catalyst; and converting the hydrolysate through enzymatic fermentation or chemical reaction into the biofuel. The heterogeneous catalyst can be recycled without a load of wastewater treatment and make the process simpler, thus enjoying a comparative advantage in terms of production cost and by-product treatment expense. In addition, the heterogeneous catalyst can be applied to a fixed bed reactor, allowing the process to be performed in a continuous manner. As a result, a smaller reactor can be employed at higher efficiency and productivity.

Description

METHOD FOR PRODUCING BIOFUELS VIA HYDROLYSIS OF SEAWEED EXTRACT USING HETEROGENEOUS CATALYST

The present invention relates to a method for the production of biofuels from seaweed extracts. More particularly, the present invention relates to a method for producing biofuels by hydrolyzing an extract from a seaweed selected from a group consisting of red algae, brown algae, green algae or a combination therof in a presence of a heterogeneous catalyst; and converting the hydrolysate through enzymatic fermentation or chemical reaction into the biofuels.

On the whole, enzymatic hydrolysis using microorganisms and acid hydrolysis using homogeneous acid catalysts are among the techniques for hydrolysis technology. Of course, these techniques are used for commercial applications.

A number of processes for producing biofuels from biomass have been developed over the years. Of these that are essential, the hydrolysis techniques by which after being obtained as extracts from biomass by pretreatment, polysaccharides such as cellulose can be degraded into fermentable monosaccharides such as glucose. The vast majority of processing schemes utilizes either cellulolytic enzymes or acids of various concentrations.

The study of Professor Y.Y. Lee's lab at Auburn University in the U.S. elucidates the mechanism of the acid hydrolysis of cellulose in three steps as illustrated in FIG. 2 (Q. Xiang, Y.Y. Lee et.al., Appl. Biochem. and Biotech., 107, 2003, 505). The glycosidic oxygen responsible for the beta-1,4-glycosidic bond through which two sugar units are linked to each other rapidly interacts with the proton (H⁺) of the acid catalyst to form a so-called conjugated acid. Then, the C-O bond undergoes a slow cleavage to form a monosaccharide in half-chair conformation with the concomitant formation of a cyclic carbonium ion therein. Finally, the carbon cation starts a rapid addition of a water molecule, resulting in a stable final product and in the proton release. An additional study into effects of acid concentrations and temperatures indicated that hydrogen bonds are mainly responsible for the maintenance of cellulose structure, adding that the effective interruption of hydrogen bonds, if found, will bring about an innovation in the hydrolysis of biomass. Although there is almost no data thereabouts, the hydrolysis mechanism of seaweed extracts composed mainly of galactan is thought to proceed like that of cellulose.

In 2007, the KITECH performed a study on the production of bioenergy using seaweeds as a Korean national strategic project. As a result, galactose was produced at a yield of about 37 % by hydrolyzing agar-agar (i.e. Gelidium amansii) in the presence of a homogenous acid catalyst, such as H₂SO4, HNO₃, HCl, etc, in a batch reactor.

JP 2006-129735 discloses a method for hydrolyzing cellulose using a catalyst such as active carbon and for producing cellulose. Nowhere is the production of biofuels from seaweed found in this patent.

Enzymatic hydrolysis allows too slow reaction rates for economical production of biofuels from biomass. Requiring product neutralization and wastewater treatment, the acid hydrolysis using a homogeneous acid catalyst, such as sulfuric acid, renders the entire process complicated. In addition, the acid hydrolysis consumes excessive quantities of homogeneous acid catalysts and energy to enjoy a comparative advantage in terms of price competitiveness.

Also, the batch-type production by both the enzymatic hydrolysis and the acid hydrolysis imposes a limitation in scale-up.

Agar-agar (e.g., Gelidium amansii) is usually comprised of 60% agar, 20% fibers, 10% proteins and 10% ash as illustrated in the graph of FIG. 3, even though its composition may vary depending on the habitats or environments thereof.

The agar found in agar-agar is composed of a mixture of agarose and agaropectin. Agarose, as shown in FIG. 4, is a linear polymer consisting of repeating 1-3-alpha linked agarobiose units, each being based on D-galatose (-1-4-α)-3,6-anhydro-L-galactose.

It has been known that acid readily cleaves the alpha linkage to degrade agarose in the disaccharide agarobiose which is then separated into D-galactose and 3,6-anhydro-L-galactose by the enzymatic hydrolysis of the 1-4-beta linkage. At this time, the L-galactose is known as an inhibitor of the fermentation of D-galactose. Thus, it is particularly difficult to produce bioalcohols from hydrolysates of agar among seaweed.

Therefore, there is a need for a technique by which when agarobiose is hydrolyzed, whereby either other compounds than L-galactose can be formed or the L-galactose thus formed can be converted into a fermentable material, thus greatly improving the productivity of bioalcohols from agar.

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method for producing biofuels without the use of a homogeneous acid catalyst such as sulfuric acid in a batch rector or enzymatic fermentation using microorganism and a method comprising: hydrolyzing an extract from a seaweed selected from a group consisting of red algae, brown algae, green algae or a combination therof in a presence of a heterogeneous catalyst in a continuous manner in a flow reactor or a fixed-bed reactor as well as a batch reactor; and converting the hydrolysate through enzymatic fermentation or chemical reaction into the biofuels.

It is another object of the present invention to provide a method for economically producing biofuels from hydrolysates of seaweed extracts through enzymatic fermentation or chemical reaction.

It is a further object of the present invention to provide a method for Producing bioalcohol at high yield by fermentating monosaccharides obtained the hydrolysis of agar.

In accordance with an aspect, a method is provided for producing a biofuel, which comprises hydrolyzing an extract from a seaweed selected from a group consisting of red algae, brown algae, green algae or a combination therof in a presence of a heterogeneous catalyst; and converting the hydrolysate through enzymatic fermentation or chemical reaction into the biofuel.

In an embodiment of the method, the red algae comprises laver, agar-agar, sea string, and Grateloupiaceae, the brown algae comprises sea mustard, laminaria, seaweed fusiforme, gulfweed, Ecklonia stolonifera, rhubarb, and Potamogeton oxyphyllus, and the green algae comprises green laver, sea lattuce, Monostroma nitidum, and sea staghorn.

In another embodiment, the extract comprises a red alga extract selected from among agar, cellulose, carrageenan, xylan, and mannan, a green alga extract selected from among cellulose, xylan, mannan, starch, fructan, and paramylon, or a brown alga extract selected from among cellulose, alginate, fucoidan and laminaran.

In another embodiment, the hydrolysate is a monosaccharide, a furan compound or an organic acid.

In another embodiment, the hydrolysate comprises a compound selected from among galactose, glucose, xylose, mannose and a combination thereof when the extract from red algae is hydrolyzed, from among glucose, xylose, mannose, fructose and a combination thereof when the extract from green algae is hydrolyzed, or from among glucose, glucuronic acid, fucose, galactose, xylose, mannitol and a combination thereof when the extract from brown algae is hydrolyzed.

In another embodiment, the biofuel comprises an oxygen-containing compound or a biohydrocarbon.

In another embodiment, the oxygen-containing compound is selected from among ethanol, propanol, butanol, pentanol, hexanol and a combination thereof.

In another embodiment, wherein the biohydrocarbon is selected from among biogasoline, biodiesel, a jet fuel, an additive and a combination thereof.

In another embodiment, the heterogeneous catalyst is of acidity and is selected from a group consisting of an ion exchange resin, zeolite, a heteropoly acid, a metal, a metal oxide and a combination thereof.

In another embodiment, the metal or the metal oxide is selected from a group consisting of copper, zinc, chrome, nickel, cobalt, molybdenum, tungsten, platinum, palladium, ruthenium, rubidium, an oxide thereof, and a combination thereof.

In another embodiment, the extract from the seaweed is hydrolyzed in a continuous manner in a batch reactor, a flow reactor or a fixed bed reactor into which the heterogeneous catalyst selected from a group consisting of an ion exchange resin, zeolite, heteropoly acid, metal, metal oxide and a mixture thereof is loaded.

In another embodiment, the hydrolyzing step is carried out at a reaction temperature of 110 ~ 200℃ under a pressure of 1 ~ 20 atm in a saturated vapor pressure condition with a weight ratio of seaweed extract to water ranging from 0.1 to 20% and catalyst to seaweed extract ranging from 0.05 to 20 %.

In another embodiment, the hydrolyzing step is carried out at a reaction temperature of 140 ~ 180℃ under a pressure of 1 ~ 10 atm in a saturated vapor pressure condition with a weight ratio of seaweed extract to water ranging from 0.5 to 10% and catalyst to seaweed extract ranging from 0.1 to 15 %.

As described above, the heterogeneous catalyst of the present invention can be recycled without a load of wastewater treatment and make the process simpler, thus enjoying a comparative advantage in terms of production cost and by-product treatment expense. In addition, the heterogeneous catalyst can be applied to a fixed bed reactor, allowing the process to be performed in a continuous manner. As a result, a smaller reactor can be employed at higher efficiency and productivity.

FIG. 1 is a schematic diagram showing a process of hydrolyzing a seaweed extract into a fermentable sugar or furan compound and of producing an oxygen-containing compound and a bio-hydrocarbon.

FIG. 2 shows the mechanism of the acid hydrolysis of cellulose.

FIG. 3 shows the composition of agar-agar.

FIG. 4 shows the structure of agar.

FIG. 5 is of graphs showing effects of gas and reaction pressure on the hydrolysis of agar in the presence of a heterogeneous catalyst.

FIG. 6 is of graphs showing effects of reaction temperature on the hydrolysis of agar in the presence of a heterogeneous catalyst.

FIG. 7 is of graphs showing effects of material at low concentrations on the hydrolysis of agar in the present of a heterogeneous catalyst.

FIG. 8 is of graphs showing effects of material at high concentrations on the hydrolysis of agar in the presence of a heterogeneous catalyst.

FIG. 9 is of graphs showing effects of catalyst concentrations on the hydrolysis of agar in the presence of a heterogeneous catalyst.

FIG. 10 is a graph showing data of the hydrolysis of agarose and agar in the presence of a heterogeneous catalyst.

FIG. 11 is a graph showing data of the alcohol fermentation of the hydrolysate obtained from agar using a heterogeneous catalyst.

The present invention pertains to a method for producing biofuels from biomass, comprising hydrolyzing an extract from seaweed in a continuous manner in the presence of a heterogeneous catalyst in a catalyst bed, the seaweed being selected from a group consisting of red algae, brown algae, green algae and a combination thereof; and converting the hydrolysate into the biofuels through enzymatic fermentation or chemical reaction.

As the biomass useful in the present invention, seaweed is selected from among red algae, brown algae, green algae and a combination thereof. Examples of the red algae include laver, agar-agar, sea string, and Grateloupiaceae. Among the brown algae are sea mustard, laminaria, seaweed fusiforme, gulfweed, Ecklonia stolonifera, rhubarb, and Potamogeton oxyphyllus. As for the green algae, they may be exemplified by green laver, sea lattuce, Monostroma nitidum, and sea staghorn.

Seaweeds are of polymeric biomass containing a variety of sugars, with a carbohydrate content ranging from 25 to 60%, although it varies according to the seaweed species. Extracts from seaweeds, obtained using various methods, may somewhat differ in composition from one to another depending on species. Extracts from red algae comprises agar, cellulose, carrageenan, xylan, and mannan. Agar is a mixture of 70:30 agarose : agaropectin. The hydrolysis of agar produces the monosaccharide galactose. Likewise, hydrolysis degrades cellulose into glucose, carrageenan into galactose, xylan into xylose and mannan into mannose. Extracts of green algae comprise cellulose, xylan, mannan, starch, fructan, and paramylon, which can be hydrolyzed into their respective monosaccharides, i.e., glucose, xylose, mannose, glucose, fructose, and glucose. Unlike red algae, green algae does not produce galactose when they are hydrolyzed. Extracts from brown algae include cellulose, alginate, fucoidan, and laminaran which are respectively hydrolyzed into glucose, glucuronic acid, fucose, galactose, xylose, and mannitol.

When being extracted from most seaweeds, carbohydrates or polysaccharides, such as cellulose, consist of monosaccharides which are linked to each other via a glycosidic oxygen atom. Hence, they can be readily hydrolyzed into their monosaccharides by the heterogeneous acid catalyst of the present invention even if there is a difference in condition therebetween.

Particularly, as long as a proper condition is selected within the allowable working temperature (190℃) of the catalyst useful in the present invention, a continuous reactor with the heterogeneous catalyst loaded onto the fixed bed thereof can hydrolyze seaweed extracts into monosaccharides and/or components in a continuous manner at high yield and productivity.

The resulting hydrolysates contain monosaccharides, furan and organic acids. Examples of the monosaccharides include glucose, galactose, xylose, mannose, fructose, and fucose. Glucuronic acid and mannuronic acid are produced.

Among the biofuels produced by the method of the present invention are bioalcohols, bioketones and biocarbohydrates. In detail, ethanol, propanol, butanol, pentanol, hexanol, acetone, etc. can be produced and used as biogasoline, biodiesel, bio-jet fuel and additives.

When acid hydrolysis using a homogeneous acid catalyst such as sulfuric acid is applied to seaweeds, the products must be neutralized so as to prevent the facility from corroding. In this regard, there is the problem of treating the wastewater thus generated, complicating the entire process. In addition, the homogeneous acid catalyst requires the use of a batch reactor, which is disadvantageous in scale-up.

In contrast, the heterogeneous catalyst useful in the present invention has acidity and is selected from among ion exchange resin, zeolite, heteropoly acid, metal, metal oxide, and a combination thereof. Thus, the heterogeneous catalyst of the present invention can be recycled without a load of wastewater treatment and make the process simpler, thus enjoying a comparative advantage in terms of production cost and by-product treatment expense. In addition, the heterogeneous catalyst can be applied to a fixed bed reactor, allowing the process to be performed in a continuous manner.

For use as a heterogeneous catalyst, the metal or metal oxide is selected from a group consisting of copper, zinc, chrome, nickel, cobalt, molybdenum, tungsten, platinum, palladium, ruthenium, rubidium, oxides thereof, and a combination thereof.

For the hydrolysis step, the heterogeneous catalyst selected from among ion exchange resin, zeolite, heteropoly acid, metal, metal oxide and a combination thereof may be loaded onto a batch reactor, a plug flow reactor or a fixed bed reactor in which seaweed extracts are hydrolyzed in a continuous manner.

The monosaccharides thus obtained are subjected to post-processes which may differ from one to another depending on the types of final products. For example, the fermentable monosaccharides obtained after the hydrolysis of seaweed extracts may be fermented with microorganisms or may be subjected to chemical reactions so as to produce bioalcohols such as ethanol or butanol or biohydrocarbons. In addition, furan compounds may be produced in a modified hydrolysis condition, followed by aldol condensation and hydrogenation to afford hydrocarbons such as biogasoline. Alternatively, the furan compounds may be further decomposed into levulinic acid which is then converted by hydrogenation into pentanol, useful as a biofuel or an additive.

The hydrolysis step using a heterogeneous catalyst in accordance with the present invention may be conducted under the following reaction conditions: a weight ratio of seaweed extract to the solvent water of from0.1 to 20%, a weight ratio of catalyst to seaweed extract of from0.05 to 5%, a reaction temperature of from 110 to 190℃, and a reaction pressure of from 3 to 20 atm. Preferably, the hydrolysis is performed at a reaction temperature of 140 ~ 170℃ under a pressure of 4 ~ 10 atm in a saturated vapor pressure condition with a weight ratio of seaweed extract to water ranging from 0.5 to 10% and catalyst to seaweed extract ranging from 0.1 to 2%.

When the weight ratio of seaweed extract to water is below 0.1%, the hydrolysis may proceed well, but monosaccharides are obtained at very low concentrations, so that a significant amount of water has to be evaporated to give a concentration of the desired products. On the other hand, a weight ratio of seaweed extract to water exceeding 20% reduces the hydrolysis yield.

When the weight ratio of catalyst to seaweed extract is less than 0.05%, the hydrolysis yield is lowered. On the other hand, when the catalyst is used at a weight ratio to seaweed extract of more than 5%, the hydrolysis productivity per weight of catalyst is reduced.

A reaction temperature of less than 110℃ lowers the hydrolysis yield whereas the obtained monosaccharides are decomposed at a reaction temperature higher than 190℃. In addition, ion exchange resin may also be decomposed at such a high temperature although its decomposition temperature differs depending on the types thereof. As for the reaction pressure, its most preferable condition is a saturated vapor pressure corresponding to a predetermined reaction temperature. When the reaction pressure is less than a saturated vapor pressure at a predetermined reaction temperature, the reaction temperature is difficult to increase to the predetermined reaction temperature because the solvent vaporizes faster. On the other hand, at a reaction pressure higher than a saturated vapor pressure at a predetermined reaction temperature, particularly, higher than 10 atm, the hydrolysis yield is lowered.

When 3,6-anhydro-L-galactose was subjected to the hydrolysis, as will be explained in the following examples, it was, for the most part, decomposed into other than L-galactose, with only a trace amount of L-galactose left. As is apparent in Example 4, when the hydrolysates of agar were fermented, all galactose was found to be converted into ethanol. Hence, all of the monosaccharides present in the hydrolysates of agar were D-galactose, which can be fermented to alcohols. Meanwhile, it is inferred that when the glycosidic bond is cleaved, 3.6-anhydro-L-galactose, known as a fermentation inhibitor, is broken into compounds other than monosaccharides, so that no sugars are detected after the fermentation.

Under the conditions set in the following examples, the hydrolysis of agar was found to leave D-galactose only, which is fermentable, while 3,6-anhydro-L-galactose was decomposed into compounds other than L-galactose, known as an inhibitor of alcohol fermentation.

COMPARATIVE EXAMPLE 1 : Hydrolysis of Agar with Sulfuric Acid

To 200 mL of water were added 4 g (dry weight) of powdered agar and 1 g of sulfuric acid, and the mixture was placed in a 300 mL autoclave equipped with a stirrer. After the autoclave was purged with nitrogen, the mixture was heated to a reaction temperature of 130℃ with stirring at 780 rpm while the internal pressure of the autoclave was adjusted into 10 bar to hydrolyze the agar into monosaccharides. After the reaction temperature was obtained, samples were taken four times at regular intervals of 30 min, and analyzed using HPLC coupled with an ELSD (Evaporative Light Scattering Detector) and a REZEK column.

The powdered agar, prepared from agar-agar grown in Jeju Island, South Korea, was found to consist of 21% moisture, 51.35% agarose, 25.28% agaropectin, and 2.37% ash and proteins.

The production yields of monosaccharides were calculated as percentages of the concentrations of produced galactose to the concentrations of agarose plus agaropectin in the agar, as given in the following formula.

Yield of Monosaccharide (%) = Conc. Of Produced Galactose /(Conc. Of Agarose + Agaropectin) x 100

The production yields according to reaction temperatures and times are summarized in Table 1 below. The produced monosaccharides were, for the most part, galactose, with unidentified materials detected in such trace an amount as to be negligible. At a reaction temperature of 130℃, the production yield of monosaccharides converged into about 55% with the lapse of 1.5 hrs. At a reaction temperature of 150℃, the production yield peaked to about 52% with the lapse of 1 hr, after which it started to decline as the monosaccharides were decomposed.

Table 1

COMPARATIVE EXAMPLE 2 : Heat Hydolysis of Agar in the Absence of Catalyst

The same procedure as in Comparative Example 1 was repeated with the exception that a solution of 4 g (dry weight) of powdered agar in 200 mL of water was heated to 150℃ in a 300 mL autoclave to conduct heat hydrolysis in the absence of an acid catalyst (sulfuric acid). The results are summarized in Table 2 below.

Although hydrolysis started one hour later, disaccharides were the main products with the production of monosaccharides in a trace amount until a reaction time of 2.5 hrs. Only with the lapse of a reaction time of 3 hrs was the main product changed into monosaccharides. At this time, the production yield increased, but to a level far lower than the level in the presence of the catalyst.

Table 2

EXAMPLE 1: Hydrolysis of Agar with Heterogeneous Catalyst in Batch Reactor - Comparison of Activity According to Catalysts

For use as heterogeneous catalysts, five kinds of Amberlyst lineage ion exchange resins were compared for hydrolysis activity. The same procedure as in Comparative Example 1 was repeated with the exception that 1 g of the ion exchange resin was placed, together with 4 g (dry weight) of powdered agar and 200 mL of water, in a 300 mL autoclave and heated to 130℃ or 150℃ in consideration of the maximal operating temperatures of the catalysts to conduct hydrolysis. The results are summarized in Table 3, below.

Maximal operating temperatures are 150℃ for

Amberlyst

36, 190℃ for

Amberlyst

70 and 130℃ for Amberlyst 39, 121 and 131. Thus, hydrolysis was conducted with Amberlyst 36 and Amberlyst 70 at 150℃ and with the other catalysts at 130℃. After hydrolysis of 2 hrs for each catalyst, monosaccharides were produced at a yield of about 55% with regard to both Amberlyst 36 and Amberlyst 70, indicating that the activity of the catalysts has no relation to acid concentration, but is influenced by reaction temperature. In due consideration of the thermal stability and durability of ion exchange resin catalysts, Amberlyst 70 was used for the hydrolysis. Given below are the data which were obtained with Amberlyst 70 catalyst.

Table 3

EXAMPLE 2: Hydrolysis of Agar with Heterogeneous Catalyst in Batch Reactor - Effect of Atmosphere Gas and Reaction Pressure

The same procedure as in Example 1 was repeated with the exception that air was used, instead of nitrogen gas, as an atmosphere gas or that the internal pressure of the autoclave was adjusted to a saturated vapor pressure (about 5.8 bar), 15 bar or 20 bar, instead of 10 bar. The effects of atmosphere gas and reaction pressure are shown in FIG. 5.

As seen in FIG. 5a, a nitrogen atmosphere increased the yield of hydrolysis into monosaccharides by about 10%, compared to an air atmosphere, which is, in our opinion, attributed to the fact that the monosaccharides thus formed are further decomposed by oxygen in the air.

In order to determine proper reaction conditions for hydrolysis in a continuous reactor, the reaction was conducted at varying pressures in a nitrogen atmosphere. As seen in the right panel of FIG. 5, the production yield of monosaccharides peaked when the hydrolysis was conducted at 150℃ under a pressure of about 5 ~ 6 bars, that is, around the saturated vapor pressure. Also, the yield of monosaccharides was found to decrease with increasing of reaction pressure. In a vapor-liquid condition, more active hydrolysis into monosaccharides proceeded with less vapor fraction. However, because the saturated vapor pressure changed with reaction conditions, reactions were performed at a nitrogen pressure of 10 bars so as to obtain consistent data and to examine the applicability of sequencing reactions.

EXAMPLE 3: Hydrolysis of Agar Using Heterogeneous Catalyst in Batch Reactor - Effect of Reaction Temperature

The same procedure as in Comparative Example 1 was repeated with the exception that 1 g of the heterogeneous catalyst Amberlyst 70, an ion exchange resin catalyst made by Rohm & Haas, was placed, along with 4 g (dry weight) of powdered agar and 200 mL of water, in a 300 mL autoclave and subjected to hydrolysis at varying temperatures of from 140 to 180℃. The results are given in TABLE 4 and FIG. 6.

After hydrolysis for 2 hrs at 150℃, the best results were obtained with the yield of monosaccharides converging on about 55%. At 140℃, the reactivity was too low for the yield to reach at 40% even after reaction of 2 hrs. At a reaction temperature of 160℃, the yield increased up to 50 ~ 55% with time, and then decreased as the monosaccharides were decomposed. These results were similar to those obtained using sulfuric acid in Comparative Example 1 although there was a little difference therebetween.

Thus, the heterogeneous catalyst according to the present invention guarantees the same reactivity as with a homogeneous catalyst such as sulfuric acid, and allows the development of a process which has an advantage over that of the homogeneous catalyst in terms of the reuse of catalyst, the simplification of process, the easiness of scale-up, and the feasibility of continuous process.

Table 4

EXAMPLE 4 : Hydrolysis of Agar Using Heterogeneous Catalyst in Batch Reactor - Effect of Material Amount at Low Concentrations

The same procedure as in Example 1 was repeated with the exception that powdered agar was used in amounts of 2, 4, 8 and 12 g (dry weight) at a reaction temperature of 150℃. The results are shown in FIG. 7.

Upon hydrolysis at 150℃ for 2 hrs, the concentration of monosaccharides in the product increased up to 11 g/L with increasing of the material concentration, but the yield peaked up to about 55% at a material concentration of 2 % corresponding to 4 g of agar, and did not increase with reaction time.

EXAMPLE 5 : Hydrolysis of Agar Using Heterogeneous Catalyst in Batch Reactor - Effect of Material Amount at High Concentrations

Since higher concentrations of fermentable monosaccharides in the product mixture lead to higher yields of alcohol fermentation, an examination was made of the maximum concentration of monosaccharides which could be achieved. The same procedure as in Example 1 was repeated with the exception that powdered agar was used in an amount of 4, 20 or 40 g (dry weight), along with 4 g of the ion exchange resin catalyst, at 150℃. The results are shown in FIG. 8.

When hydrolysis was conducted at 150℃ for 2 hrs with the material concentration increasing to 20%, the concentration of monosaccharides increased up to 55 g/L, but the yield was limited to about 55% irrespectively of material concentrations.

Correlations between the concentrations and yields of monosaccharides and the weight ratio of material to catalyst were examined in order to analyze the contact efficiency of reactant to catalyst. The results are shown in FIG. 8C. Higher weight ratios of material to catalyst resulted in higher concentrations of monosaccharides which exceeded 50 g/L, but the hydrolysis yield remained at around 50%.

EXAMPLE 6 : Hydrolysis of Agar Using Heterogeneous Catalyst in Batch Reactor-Effect of Catalyst Concentration

Contract efficiency between reactant and catalyst is a factor that has a great influence on catalytic activity. This can be analyzed in terms of contact time (catalyst weight/fuel flow rate) or space velocity (time^-1) in a fixed-bed reactor or in terms of material concentration and catalyst concentration in a batch reactor. The same procedure as in Example 1 was conducted with the exception that 4 g of powdered agar was reacted, along with 0.5, 1, 2 or 4 g of the ion exchange resin catalyst, at 150℃. The results are shown in FIG. 9.

Upon hydrolysis at 150℃ for 2 hrs, the hydrolysis yield reached the highest limit of about 55% largely irrespective of catalyst concentrations, as long as the catalyst was used in an amount of 1 g or more, that is, the concentration of the catalyst was over about 0.5 wt%.

EXAMPLE 7 : Continuous Hydrolysis of Agar Using Heterogeneous Catalyst in Fixed-Bed Reactor

To 1.5 L of water in a tank was added 35 g (70 mL) of powdered agar comprising 68.8% of agarose and agaropectin, followed by slowly heating to 80 ~ 90 C with stirring to completely dissolve the agar. This material was fed at a rate of 0.27 cc/min (space velocity: 0.9^-1) to a column reactor 10 mm in internal diameter with 12 g (18 ml) of the heterogeneous catalyst Amberlyst 70 loaded thereinto. The front feeding line of the catalyst reactor was heated at about 70℃ to feed the material smoothly. Hydrolysis was performed at a reaction temperature of 150℃ under a pressure of 8~10 atm with N₂ gas flowing into the reactor. The reaction products were analyzed using Bio-LC coupled to PAD (Pulsed Amperometic Detector) and an ion exchange resin-loaded CarboPac MA1(4*250 mm) column. Most of the monosaccharides thus produced were identified as galactose, with unidentified materials detected in such trace an amount as to be negligible, as in the batch reactor. Compared to the reaction in the batch reactor, the reaction in fixed-bed reactor was slightly lower in maximum yield of monosaccharides, measured to be about 49%, but far superior in terms of continuous productivity per weight of catalyst.

EXAMPLE 8 : Hydrolysis of 3,6-Anhydro-D-Galactose Using Heterogeneous Catalyst

The same procedure as in Comparative Example 1 was repeated with the exception that the ion exchange resin Amberlyst 70 was placed, along with 0.1 g of galactose and 100 mL of water, in a 300 mL autoclave, followed by hydrolysis at 150℃. After reaction for 30 min, galactitol and low-molecular weight materials smaller than monosaccharides were detected as main products. After hydrolysis for 2 hrs, however, even the low-molecular weight materials were degraded, with a trace amount of 3,6-anhydro-D-galactose remaining unreacted.

EXAMPLE 9 : Hydrolysis of Agarose Using Heterogeneous Catalyst

The same procedure as in Comparative Example 1 was repeated with the exception that 4 g (dry weight) of agarose with a moisture content of 10 wt% was added, together with 1 g of Amberlyst 70, to 200 mL of water and hydrolyzed at 150℃. The results are shown in FIG. 10. The hydrolysis of agarose consisting of 50% D-galactose and 50% 3,6-anhydro-L-galactose produced galactose at a yield of 50%. On the other hand, when agar consisting of 70% agarose and 30% agaropectin, that is, 35% D-galactose, 35% 3,6-anhydro-L-galactose and 30% agaropectin, was hydrolyzed, galactose was produced at about 57%. These results, as inferred from the data of Example 8, indicate that 3,6-anhydro-L-galactose, constituting the half of agarose, is degraded into smaller compounds during the hydrolysis and remains only in a trace amount.

EXAMPLE 10 : Alcohol Fermentation of Monosaccharides Hyrolyzed Using Heterogeneous Catalyst

The monosaccharides hydrolyzed, as in Example 1, in the presence of the heterogeneous catalyst Amberlyst 70 was used in an amount corresponding toa 31 g/L of galactose in ethanol fermentation. After fermentation for 4 days, no galactose was detected, showing a conversion rate of almost 100 %. Compared to theoretical yield, an ethanol conversion rate of about 88% was obtained. The results are shown in FIG. 11. Taken together, the data of this alcohol fermentation and of Examples 8 and 9 indicate that upon the hydrolysis with an acid catalyst under the condition of the present invention, most of the hydrolysate is D-galactose which is readily fermented into alcohol while 3,6-anhydro-L-galactose, known to be difficult to ferment, is degraded into smaller compounds or remains only in a trace amount.

When used to hydrolyze the polysaccharides extracted from seaweed in a batch reactor, a plug flow reactor or a fixed bed reactor, as described hitherto, heterogeneous catalysts can be recycled for a long period of time in accordance with the present invention. In addition, the method of the present invention produces monosaccharides in a continuous manner at high productivity. Further, the monosaccharides can be fermented into oxygen-containing compounds such as ethanol, butanol, or hydrocarbons such as biogasoline or biodiesels, according to post-processes.

Claims

A method for producing a biofuel, comprising:

hydrolyzing an extract from a seaweed selected from a group consisting of red algae, brown algae, green algae or a combination therof in a presence of a heterogeneous catalyst; and

converting the hydrolysate through enzymatic fermentation or chemical reaction into the biofuel.
The method according to claim 1, wherein the red algae comprises laver, agar-agar, sea string, and Grateloupiaceae, the brown algae comprises sea mustard, laminaria, seaweed fusiforme, gulfweed, Ecklonia stolonifera, rhubarb, and Potamogeton oxyphyllus, and the green algae comprises green laver, sea lattuce, Monostroma nitidum, and sea staghorn.
The method according to claim 1, wherein the extract comprises a red alga extract selected from among agar, cellulose, carrageenan, xylan, and mannan, a green alga extract selected from among cellulose, xylan, mannan, starch, fructan, and paramylon, or a brown alga extract selected from among cellulose, alginate, fucoidan and laminaran.
The method according to claim 1, wherein the hydrolysate is a monosaccharide, a furan compound or an organic acid.
The method according to claim 1 or 4, wherein the hydrolysate comprises a compound selected from among galactose, glucose, xylose, mannose and a combination thereof when the extract from red algae is hydrolyzed, from among glucose, xylose, mannose, fructose and a combination thereof when the extract from green algae is hydrolyzed, or from among glucose, glucronic acid, fucose, galactose, xylose, mannitol and a combination thereof when the extract from brown algae is hydrolyzed.
The method according to claim 1, wherein the biofuel comprises an oxygen-containing compound or a biohydrocarbon.
The method according to claim 6, wherein the oxygen-containing compound is selected from among ethanol, propanol, butanol, pentanol, hexanol and a combination thereof.
The method according to claim 6, wherein the biohydrocarbon is selected from among biogasoline, biodiesel, a jet fuel, an additive and a combination thereof.
The method according to claim 1, wherein the heterogeneous catalyst is of acidity and is selected from a group consisting of an ion exchange resin, zeolite, a heteropoly acid, a metal, a metal oxide and a combination thereof.
The method according to claim 9, wherein the metal or the metal oxide is selected from a group consisting of copper, zinc, chrome, nickel, cobalt, molybdenum, tungsten, platinum, palladium, ruthenium, rubidium, an oxide thereof, and a combination thereof.
The method according to claim 1, wherein the extract from the seaweed is hydrolyzed in a continuous manner in a batch reactor, a flow reactor or a fixed bed reactor into which the heterogeneous catalyst selected from a group consisting of an ion exchange resin, zeolite, heteropoly acid, metal, metal oxide and a mixture thereof is loaded.
The method according to claim 1, wherein the hydrolyzing step is carried out at a reaction temperature of 110 ~ 200℃ under a pressure of 1 ~ 20 atm in a saturated vapor pressure condition with a weight ratio of seaweed extract to water ranging from 0.1 to 20% and catalyst to seaweed extract ranging from 0.05 to 20 %.
The method according to claim 12, wherein the hydrolyzing step is carried out at a reaction temperature of 140 ~ 180℃ under a pressure of 1 ~ 10 atm in a saturated vapor pressure condition with a weight ratio of seaweed extract to water ranging from 0.5 to 10% and catalyst to seaweed extract ranging from 0.1 to 15 %.