Patent Grant
9309474
The present invention relates to a method of incorporating alcohol or a mixture of alcohols obtained from aqueous solutions generated by biomass fermentation processes into a fuel.
The biomass groups together all of the organic, vegetable or animal matters, notably:
The alcohols produced by biomass fermentation processes preferably are ethanol, produced through ethanolic fermentation, and butanol, as well as the ABE (acetone-butanol-ethanol) mixture produced through acetonobutylic fermentation.
The current European legislation authorizes addition of oxygen-containing compounds to fuels. In the case of gasolines, for example, the maximum oxygen content is 2.7 mass %, the ethanol content being furthermore limited to 5 vol. %, the butanol content to 10 vol. %, the methanol content to 3 vol. %, and the proportion of ether with 5 carbon atoms and more per molecule is limited to 15 vol. %.
Alcohol has to meet some characteristics to be incorporated into fuels. In the case of gasolines, in order to prevent demixing phenomena during storage, the ethanol that is incorporated has to be quasi anhydrous: the European standard regarding the water content of ethanol for incorporation into gasolines is 99.7 wt. % of ethanol minimum, i.e. 99.8 vol. % minimum. The European standards indicate that diesel fuels must contain 200 ppm water maximum.
In the current state of the technique, the preparation of anhydrous ethanol from aqueous solutions first involves producing an ethanol/water mixture containing 95 vol. % of ethanol, the ethanol/water mixture making up an azeotrope containing 95.6 wt. % of ethanol at 0.1 MPa. This operation involving a distillation process is a highly energy-consuming operation. For example, starting from an aqueous solution containing about 10 vol. % of ethanol, approximately 180 kg steam per hectoliter of ethanol are necessary to obtain this mixture.
After this first distillation stage, several options can be considered for drying the aqueous ethanol solution from about 95 vol. % to at least 99.8 vol. %:
The option using azeotropic distillation in the presence of benzene or cyclohexane involves a high energy expenditure since it requires about 110 kg steam and about 1.3 kWh per hectoliter of alcohol. Furthermore, the toxicity of benzene and cyclohexane is a major drawback of this process.
The option using membrane pervaporation is clearly more interesting as regards energy expenditure since it consumes only about 30 kg steam and about 4.5 kWh per hectoliter of alcohol produced.
Molecular sieve adsorption is a moderately energy-consuming operation that requires about 30 to 60 kg steam and about 2 to 3 kWh per hectoliter of alcohol in the case of a PSA (Pressure Swing Adsorption) process with adsorption in the vapour phase.
Alcohols being generally partly soluble in most liquids, it is obvious that any contacting operation between an aqueous phase containing an alcohol and another liquid phase containing none induces extraction of a non-zero fraction of the alcohol from the aqueous phase to the other liquid phase. U.S. Pat. No. 4,455,198 and U.S. Pat. No. 4,346,241 describe methods of preparing anhydrous ethanol wherein a liquid-liquid extraction is carried out with cyclic ketones or alcohols on the one hand, or amines on the other hand.
The possibility of extracting ethanol with gasoline has already been considered in the past, as mentioned in U.S. Pat. No. 4,297,172. In the temperature range studied and with the gasoline type used, extraction is relatively difficult so that it is considered only from a highly alcohol-enriched aqueous phase. The method described in this patent application allows to do without the extremely energy-consuming stage of azeotropic distillation that is commonly carried out. In the first stage of this process, the ethanol-containing aqueous phase is however subjected to distillation in order to concentrate the ethanol and to obtain a distillation comprising at least 75 wt. % of ethanol. This essential first concentration stage makes the process still too energy-consuming a method. Furthermore, the final yields are relatively low since this method allows to extract only 5 to 17 wt. % of ethanol.
Surprisingly enough, the applicant has observed that azeotropic distillation can be avoided while obtaining good-quality products.
In order to achieve a yet more favourable alcohol extraction as regards energy consumption, requiring no preliminary concentration stage and allowing extraction of the major part of the alcohol from the aqueous solution, the present invention provides a new process scheme allowing to achieve extraction directly with a fuel having a high aromatic compound content. Unlike distillation, extraction requires no steam expenditure. The energy expenditure is then only of electrical nature. It is linked with contacting and mixing of the fluids in the extractor, and with the pressure drops undergone by the fluids in this device.
The method according to the invention allows alcohol to be directly incorporated into the fuel without any preliminary distillation stage, which allows to greatly reduce energy expenditures.
The present invention describes a method of incorporating alcohol or a mixture of alcohols into fuels having a high aromatic compound content selected from a reformate gasoline cut, a pyrolysis gasoline cut or an LCO type diesel fuel, comprising:
The fuel into which the alcohol or the mixture is incorporated has an aromatic compound content of at least 70 wt. %. Preferably, the fuel has an aromatic compound content above 80 wt. %.
The gasoline selected is preferably a reformate gasoline cut (thus obtained from the refining process referred to as reforming) or a pyrolysis gasoline cut (steam cracking by-product) characterized by a high aromatic compound content. This type of gasoline allows to carry out a much more favourable extraction than with a gasoline obtained by mixing cuts from various refining processes. In fact, extraction of the alcohol is much less efficient if the aromatic content of the gasoline is low.
The diesel fuel selected is preferably an LCO type diesel fuel from catalytic cracking units, also characterized by a high aromatic content.
The alcohol or the alcohol mixture comes from any biomass fermentation process and it is more particularly selected from among ethanol, butanol or the acetone-butanol-ethanol (ABE) mixture.
An oxygen-containing compound or a mixture of oxygen-containing compounds can be optionally added to the fuel, which allows to further improve the alcohol extraction efficiency. These oxygen-containing additives are preferably:
The extraction stage is carried out by direct contact between the aqueous phase containing the alcohol or the alcohol mixture and the hydrocarbon phase consisting of one or more fuel bases.
The aqueous phase can contain 1 to 99 vol. % of alcohol or alcohol mixture. Preferably, the aqueous phase contains 1 to 30 vol. % of alcohol or alcohol mixture. More preferably, it contains between 5 and 15 vol. % of alcohol or alcohol mixture.
Said aqueous phase containing the alcohol or the alcohol mixture is introduced at the top of the extraction column and said hydrocarbon phase containing the fuel base is introduced at the bottom of the extraction column.
The aqueous phase and the hydrocarbon phase can be introduced into the extraction column at identical or different temperatures. Advantageously, the hydrocarbon phase can be used for heating the aqueous phase.
Extraction is all the more favoured as the temperature is high. The extraction stage is carried out at a temperature ranging between the ambient temperature and 320° C., preferably between 50° C. and 250° C., more preferably between 70° C. and 200° C.
The pressure in the extractor preferably ranges between the atmospheric pressure and 10 MPa, preferably between the atmospheric pressure and 1 MPa.
Advantageously, the extraction stage is carried out by circulating the two phases countercurrent in devices promoting dispersion, contacting and material exchange between the aqueous phase and the hydrocarbon phase.
In cases where an oxygen-containing compound is added to the fuel, the latter can be introduced with the hydrocarbon phase at the bottom of the column, or separately, at an intermediate height. Thus, the lower part of the extraction column located below the intermediate injection point behaves like a counter-extraction section for the oxygen-containing product that has entered the aqueous phase. This device advantageously allows to limit the possible oxygen-containing product losses.
At the end of the extraction stage, an extract consisting of the fuel base containing an alcohol or an alcohol mixture and part of the water from the aqueous solution is obtained, as well as a raffinate.
The raffinate is sent to a water treating plant and/or it is recycled, for example upstream to the biomass fermentation process, and the extract containing the alcohol-enriched hydrocarbon phase is sent to the drying stage. In fact, the presence of this water may lead to demixing of the alcohol through cooling of the alcohol solution during storage. In order to prevent this demixing phenomenon, the hydrocarbon phase containing the alcohol and the water consequently has to be dehydrated and/or cooled (drying).
In the sense of the present invention, drying is understood as any method allowing extraction of a fraction of the water content of a mixture. Drying can be carried out for example using the techniques mentioned below or through cooling leading to water demixing.
The drying stage can be advantageously carried out by adsorption on a molecular sieve, by pervaporation through membranes or by distillation, the first two options being preferably used, notably for reasons of lower energy consumption.
The molecular sieves used for drying alcohols are generally zeolite type adsorbents, i.e. oxides having a three-dimensional structure resulting from the grouping of tetrahedral units leading to a network of channels of molecular dimension and of pore diameter ranging between 3 and 10 Å. A zeolite is typically a silico-aluminate and it is commonly extended to other compositions leading to a uniform three-dimensional structure, notably a metallo-silicate such as, for example, an alumino-silicate, a boro-silicate, a ferro-silicate, a titano-silicate, a gallo-phosphate or a silico-alumino-phosphate. The zeolites used for dehydrating ethanol preferably have a pore size of the order of 3 Å in diameter and they have the shape of balls or rods. This opening is too small to allow passage of the ethanol whose diameter is of the order of 4.4 Å. On the other hand, the water molecules have a diameter of the order of 2.8 Å and they can therefore enter the pores of the zeolites and be adsorbed therein.
By way of example, the following zeolites can be used: the SILIPORITE® products of the CECA Company or the SYLOBEAD® products of the GRACE Davison Company.
The adsorbent molecular sieve can also be a silica.
The molecular sieves are arranged in columns working intermittently in two stages:
There are two regeneration processes: temperature difference regeneration or TSA (Temperature Swing Adsorption) and pressure difference regeneration or PSA (Pressure Swing Adsorption). In the case of alcohol drying, adsorption in the vapour phase is generally preferred and pressure difference regeneration is the desorption mode that is generally selected. In fact, the TSA process requires a neutral purge gas, long regeneration sequences and it also involves problems of degradation of the solid generated by thermal cycles (expansion-contraction). A description of this type of alcohol dehydration through adsorption in the vapour phase on molecular sieve of PSA type is given, for example, in patent FR-2,719,039-B1.
This drying process through adsorption in the vapour phase on molecular sieve requires prior vaporization of the alcohol or of the alcohol mixture. During the regeneration or desorption stage, the capacity that has collected the water is placed under vacuum.
In the case of the present invention, a mode of drying the hydrocarbon phase enriched in alcohol or alcohol mixture by adsorption can be advantageously carried out by circulating, in an adsorbent-filled column, a dry alcohol-free fuel base coming directly from its production plant, possibly heated or cooled.
The stage of drying the hydrocarbon phase containing the alcohol or the alcohol mixture and water can also be carried out by membrane pervaporation. This technology is based on the selective transfer of water through a selective layer associated with a vaporization of the water at the level of the downstream face of the membrane. This vaporization is induced by placing the compartment downstream from the membrane under vacuum, combined with condensation of the steam thus produced at the level of a cold point. The water flux density is directly proportional to the steam pressure difference between the two faces of the membrane. The steam pressure upstream from the membrane (feedstock side) depends on the composition of the feedstock and on the temperature of said feedstock. Similarly, the partial water pressure downstream from the membrane generally depends on the cold level applied at the level of the condenser, except for the pressure drops in the steam circuit. This technology is particularly advantageous because the energy required for separation is reduced only to the water vaporization enthalpy downstream from the membrane.
Several membrane materials can be used. Two commercial options are currently available on the market and they can be advantageously used in the present invention:
Other types of membrane materials based on hydrophilic vitrous polymers have also been tested at pilot scale for solvent dehydration and they can be advantageously used for the present invention: polyimides (Huang et al., J. Appl. Polymer Sci., 85 (2002) 139-152), or polymer mixtures containing polyimides (Cranford et al., J. of Membrane Sci., 155 (1999) 231-240), cellulose acetate, polysulfones or polyethersulfones.
Membrane materials based on microporous silica, as described in J. of Membrane Science 254 (2005) 267-274, can also be used.
Pervaporation on membranes is a very interesting option as regards “energy expenditure”. However, this method can lead to high operating costs in the case of polymer membranes because of their sensitivity to impurities that may be contained in industrial feedstocks. It furthermore requires using a powerful refrigerating set for minimizing the steam pressure downstream from the membrane.
Once the extraction and drying stages completed, the fuel base is enriched in alcohol or alcohol mixture and it can be mixed with other cuts so as to form a marketable fuel. It is however necessary for the residual water content of the final gasoline to be low enough not to generate demixing during storage.
According to an embodiment of the present invention, the extract is subjected to cooling allowing demixing of an aqueous phase containing alcohol, that can be recycled to the extraction column.
The constraint linked with the residual water content in the final gasoline has to be taken into account during the drying stage and/or upon incorporation of stabilizing additives.
In fact, the drying stage can be optionally complemented by adding oxygen-containing compounds to the fuel base enriched in alcohol or alcohol mixture. These oxygen-containing compounds are identical to those that can be added to the fuel base to improve the liquid-liquid extraction efficiency. They preferably are:
The aqueous phase containing the alcohol or the alcohol mixture is fed through line 1 into an exchanger E1 in order to be brought to the extraction temperature. It is thereafter sent to extractor B1 through line 2.
The hydrocarbon phase, i.e. the fuel base, is fed countercurrent to the aqueous phase into this device through line 4. It has first entered exchanger E2 through line 3 to be brought to the extraction temperature.
The temperatures of the two phases can be different. The fuel base can advantageously allow to heat the aqueous solution.
The extractor contains devices intended to promote dispersion and contacting of the aqueous and hydrocarbon phases, as well as material exchange between these two phases. Many countercurrent extraction technologies can thus be potentially applied to achieve extraction: battery of mixers-decanters, centrifuges, gravitational flow column (or sequence of columns). In the latter case, the column can be empty (spray column) or preferably equipped with internals of perforated plate, disc and crown, downcomer tray type. The column can be stirred by liquid or internals pulsation, or preferably by rotary mechanical agitation. The columns can also be filled with various packings of random or stacked type.
Two new phases are obtained at the extractor outlet: an extract and a raffinate. The extract contains the major part of the hydrocarbons, a significant part of the alcohol extracted from the aqueous phase and part of the water from this aqueous phase. It leaves the extractor through line 5 and it is sent to the drying stage.
The raffinate that predominantly consists of water also contains traces of hydrocarbons and the rest of the alcohol that has not been extracted. It is sent through line 6 to a water treating plant or it is recycled for example to the biomass fermentation process.
The drying stage produces water that is sent through line 8 to a water treating plant or recycled, for example to the alcoholic fermentation process, and the dried hydrocarbon phase containing the extracted alcohol flowing from line 7. This hydrocarbon phase is sent to the gasoline pool of the refinery.
If an oxygen-containing compound is added to the fuel base to promote extraction, and if the compound is mixed therewith prior to entering the extraction device, part of this compound may be extracted by the aqueous phase as a result of its partial or total solubility in water. In order to overcome a possible problem, one solution consists in introducing the added oxygen-containing compound at an intermediate height in the extraction column. A counter-extraction is thus achieved between the aqueous phase enriched in oxygen-containing compound and the fuel base. This embodiment is described in
Device B1 described here is an extraction column supplied at the top with the aqueous solution containing the alcohol or the alcohol mixture 2, at the bottom with the fuel base 4, and an intermediate feed point 9 is used for the oxygen-containing compound or the mixture of oxygen-containing compounds. The aqueous raffinate leaves the column at the bottom 6 and the extract enriched in alcohol and in oxygen-containing compound(s) flows from the column at the top 5. The intermediate feed point is preferably located far enough from the column bottom for at least one theoretical extraction stage to separate it from the raffinate outlet.
Another particular embodiment is diagrammatically shown in
The embodiment of the method according to the invention described in
The ethanol of a 10 vol. % aqueous solution is to be incorporated into a gasoline.
Extraction is carried out using a reformate containing about 80 wt. % aromatic compounds at a temperature of 210° C. that will later be sent to the gasoline pool.
The aqueous phase flow rate is 21,400 kg/h. The reformate flow rate is 80,000 kg/h.
Prior to being fed into the extractor, the aqueous solution and the reformate are brought to a temperature of 150° C.
Drying device B2 is a hydrophilic membrane operating on a pervaporation basis.
The extraction balance is given in Table 1.
The extractor used is a countercurrent multistage RDC type column (i.e. equipped with a contacting system consisting of a vertical axle driving circular plates into rotation). It is 1.9 m in diameter, with a total height of 9 m, and it is made up of 25 compartments. The aqueous solution circulates from top to bottom in form of dispersed drops. The organic solution or reformate is the continuous phase and it circulates from bottom to top. The number of theoretical extraction stages is 9.
Nearly 95% of the ethanol contained in the aqueous solution is extracted.
The membrane arranged downstream from the extraction allows to remove the water contained in the extract so as to reach a water content in the extract of 0.2 vol. %.
The temperature of the extract at the membrane outlet is 113° C. Considering the performances of the Mitsui membranes described above, 3770 m2 would be necessary to perform such a pervaporation operation at the desired dehydration level.
Cooling of the extract from 150° C. to 113° C. allows to provide vaporization of the water contained in the extract on either side of the membrane.
The dehydration carried out according to the above conditions allows to avoid demixing of the mixture at storage temperatures above 0° C.
Globally, the specifications imposed as regards the maximum ethanol contents in the gasoline are met.
The liquid-liquid extraction is carried out under the same temperature and pressure conditions as in Example 1, with the same reformate as in Example 1 furthermore comprising an oxygen-containing additive (10 wt. % MTBE) introduced at the column bottom.
The extraction balance is given in Table 2.
The addition of MTBE (10 wt. % MTBE in the reformate) during liquid-liquid extraction allows to extract more ethanol (99% of the ethanol instead of 95% in Example 1) with less reformate (ratio of aqueous solution to be treated/reformate=0.54 instead of 0.27 in Example 1) and limits the extraction of water (3% instead of 15% in Example 1), thus considerably reducing the cost of the reformate drying post-treatment.
The liquid-liquid extraction is carried out under the same temperature and pressure conditions as in Example 1, with the same reformate as in Example 1 furthermore comprising an oxygen-containing additive (10 wt. % MTBE) introduced at an intermediate height, at the level of the 5th compartment from the bottom of a column containing 25 compartments.
The extraction balance is given in Table 3.
Introducing the MTBE at an intermediate height in the extraction column allows to significantly decrease the amount of MTBE lost in the raffinate.
This example allows to compare the extraction performances obtained using, on the one hand, a final gasoline or, on the other hand, a cut of the final gasoline rich in aromatics. The liquid-liquid extraction is therefore carried out with the same equipment and under the same temperature and pressure conditions as in Example 1, with a mixture made up of 50 mass % of reformate used before and 50% iso-octane. The mixture used is thus closer to a final gasoline, notably in terms of aromatic compound content (about 40 wt. %). The extraction balance is given in Table 4.
The ethanol extraction carried out using a final gasoline is not as good as that obtained in Example 1. This illustrates the interest of using an aromatic-rich gasoline cut for the extraction.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07 04673 | Jun 2007 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2008/000911 | 6/26/2008 | WO | 00 | 6/21/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/016290 | 2/5/2009 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2591672 | Catterall | Apr 1952 | A |
| 4251231 | Baird | Feb 1981 | A |
| 4297172 | Kyle | Oct 1981 | A |
| 4441891 | Roth | Apr 1984 | A |
| 4445908 | Compere et al. | May 1984 | A |
| 4482768 | Somekh | Nov 1984 | A |
| 5113024 | Harandi et al. | May 1992 | A |
| Number | Date | Country |
|---|---|---|
| 2 293 375 | Mar 1996 | GB |
| Entry |
|---|
| Abstract for JP06-158064 A, Jun. 7, 1994, Mitsubishi Heavy Ind. Ltd. |
| International Search Report of PCT/FR2008/000911 (Feb. 9, 2009). |
| Number | Date | Country | |
|---|---|---|---|
| 20100263264 A1 | Oct 2010 | US |
