Patent Application
20120151832
The present invention relates to a process for catalytic cracking of a lipid-containing feedstock.
Various processes for catalytic cracking of heavy hydrocarbons are known in the art. In these processes, heavy hydrocarbons, such as heavy oils and vacuum residues, are brought in contact with a cracking catalyst and are converted into lighter products having lower boiling points. Exemplary descriptions of such processes have been provided for instance in U.S. Pat. No. 4,917,790 and in U.S. Pat. No. 6,905,591.
However, with the diminishing supply of crude oil, use of renewable energy sources is becoming increasingly important for the production of chemicals and fuels. Plant and animal biomass, are being used to produce liquid and gaseous fuels through the catalytic cracking process. One of the advantages of using biomass is that the CO2 balance is more favourable as compared with the conventional hydrocarbon feedstock.
US2009/0047721 describes a process for producing hydrocarbons for use in diesel and jet fuels by subjecting lipids derived from algae to a catalytic cracking process. However, the products obtained through this cracking process predominantly include a mixture of C2 to C5 olefins and need additional chemical treatment to produce usable fuel products.
EP1970425 describes a process for producing gaseous and liquid fuels by cracking lipids derived from high viscosity carbon-based energy carrier materials and WO-A-2009/000838, describes a process for producing bio oils by cracking of lipids derived from aquatic biomass. However, these references disclose using a cracking temperature of below 450° C., and only yield products in low yields and with limited selectivity.
Kitazato et al. describe in their article titled “Catalytic cracking of hydrocarbons from microalgae”, International Chemical Engineering, Volume 31, no 3, July 1991, a process for the production of gasoline by catalytic cracking of hydrocarbons obtained from the microalgae Botryococcus braunii Berkeley (a green algae). For the catalytic cracking process a commercial FCC zeolite was used. Exemplified reaction conditions included temperatures in the range from 450 to 500° C. Also Kitazato et al. teach, however, that low temperatures of cracking (below 450° C.) are necessary to ensure a high yield of gasoline. In addition, the use of a catalyst comprising 100 wt % zeolite is too expensive for commercial operation.
It would be an advancement in the art if a process would be provided for catalytic cracking of biomass with improved efficacy.
Accordingly, the present invention provides a process for catalytic cracking of a lipid-containing feedstock, the process comprising contacting the lipid-containing feedstock with at least one cracking catalyst at a temperature of at least 450° C., to obtain a product stream; and separating at least one hydrocarbon fraction from the product stream; wherein the lipid-containing feedstock comprises lipids derived from a diatomic microalgae species.
According to a further embodiment, the present invention provides a gasoline product prepared from a hydrocarbon fraction of the at least one hydrocarbon fraction.
According to yet another embodiment, the present invention provides a liquefied gaseous fuel composition comprising a liquefied gaseous fuel product prepared from a hydrocarbon fraction of the at least one hydrocarbon fraction, less than 1000 ppmw sulfur, and one or more additives.
It was found that, when using lipids derived from a diatomic microalgae species as a feedstock, contrary to the teachings in the prior art, a higher cracking temperature gives a higher conversion and hence more valuable lighter products (that is, more products having a boiling point below 221° C. such as, for example, LPG and gasoline).
The process according to the invention is further advantageous because diatomic microalgae have high growth rates, utilise a large fraction of solar energy and can grow in conditions that are not favourable for terrestrial biomass. Additionally, diatomic microalgae consume CO2 at a high rate, and may reduce the carbon footprint of the overall process. Further diatomic microalgae contain high concentrations of lipids.
It has now been found that cracking of a lipid-containing feedstock, that comprises lipids derived from a diatomic microalgae species, over a cracking catalyst at a temperature of at least 450° C. results in a desirable product stream.
Diatomic microalgae as referred to in the present invention are a large and diverse group of microorganisms living in an aquatic environment that have a cell wall comprising silica. They can be unicellular or multicellular, but are preferably unicellular. The diatomic microalgae preferably have a diameter smaller than 1 mm, more preferably a diameter smaller than 0.6 mm and still more preferably a diameter smaller than 0.4 mm. The diameter is measured at its largest point. Most preferably the diatomic microalgae comprise a diameter in the range from 0.5 to 200 micrometer, even more preferably in the range from 1 to 100 micrometer. The diatomic microalgae can be cultivated under difficult agro-climatic conditions, including cultivation in freshwater, saline water, moist earth, dry sand and other open-culture conditions known in the art. The diatomic microalgae can also be cultivated and genetically engineered in controlled closed-culture systems, for example, in closed bioreactors. Preferably, the diatomic microalgae used in the present invention are marine diatomic microalgae cultivated in fresh water, saline water or other moist conditions, more preferably marine diatomic microalgae cultivated in saline water. Yet more preferably, the marine diatomic microalgae are cultivated in open-culture conditions, for example, in open ponds.
Lipids as referred to in the present invention are a group of naturally occurring compounds that are usually hydrophobic in nature and contain long-chain aliphatic hydrocarbons and their derivatives such as fatty acids, alcohols, amines, amino alcohols and aldehydes. The lipid-containing feedstock as disclosed in the invention includes lipids derived from marine diatomic microalgae. These lipids include monoglycerides, diglycerides and triglycerides, which are esters of glycerol and fatty acids, and phospholipids, which are esters of glycerol and phosphate group-substituted fatty acids.
The fatty acid moiety in the lipids used in the invention ranges from 4 carbon atoms to 30 carbon atoms, and includes saturated fatty acids containing one, two or three double bonds. Preferably, the fatty acid moiety includes 8 carbon atoms to 26 carbon atoms, more preferably the fatty acid moiety includes 10 carbon atoms to 25 carbon atoms, again more preferably the fatty acid moiety includes 12 carbon atoms to 23 carbon atoms, and yet more preferably 14 carbon atoms to 20 carbon atoms. The lipids may contain variable amounts of free fatty acids and/or esters, both of which may also be converted into hydrocarbons during the process of this invention. In one embodiment the lipids may be composed of natural glycerides only. Alternatively, the lipids may also include carotenoids, hydrocarbons, phosphatides, simple fatty acids and their esters, terpenes, sterols, fatty alcohols, tocopherols, polyisoprene, carbohydrates and proteins. It is to be understood that for the purpose of this invention, a mixture of lipids extracted from different diatomic microalgae sources can also be used in the lipid-containing feedstock.
The diatomic microalgae may be processed to extract lipids using processes known in the art. The said processes may include the steps of harvesting the diatomic microalgae, dewatering the diatomic microalgae, disrupting the diatomic microalgae's cell walls to liberate lipids, and then extracting the lipids using solvents, supercritical fluids or other extraction processes. In a preferred embodiment, the diatomic microalgae are cultivated, harvested, dried, milled and then lipids are extracted using a water immiscible solvent at 25° C. Suitable solvents for the extraction are organic solvents such as aromatic or aliphatic hydrocarbons, higher alcohols, ethers and esters. Examples for such solvents are toluene, hexane, heptane, dimethyl ether, acetic acid ester and mixtures thereof. Other solvents include supercritical liquids, such as supercritical carbon dioxide.
The extracted lipids may conveniently be isolated by evaporating the solvent, or by other methods, such as membrane separation.
Preferably, the lipid-containing feedstock includes lipids in the range of 1 wt % to 50 wt %, more preferably in the range of 2 wt % to 40 wt %, more preferably in the range of 3 wt % to 30 wt %, and yet more preferably in the range of 5 wt % to 20 wt %, based on the total weight of lipid-containing feedstock.
The lipid-containing feedstock further preferably comprises a hydrocarbon feedstock. That is, the lipids (also referred to as lipid feedstock) may preferably be co-fed together with a hydrocarbon feedstock. The co-feeding may be attained by blending the two feedstock streams prior to entry into the cracking unit, or alternatively, by adding them at different stages.
The hydrocarbon feedstock preferably comprises hydrocarbons with a boiling point of at least 220° C., as measured by Gas Chromatograph Distillation (GCD) according to ASTM D-6352-98. Preferably, the boiling points range from 220° C. to 650° C., more preferably from 300° C. to 600° C. Furthermore, the hydrocarbon feedstock preferably has an initial boiling point above 180° C., as measured by Gas Chromatograph Distillation (GCD) according to the methods described in ASTM D-6352-98.
In one embodiment the hydrocarbon feedstock includes hydrocarbons having a mineral origin. Preferably such hydrocarbon feedstock comprises a mineral oil or a derivative of a mineral oil. The hydrocarbon feedstock may be a conventional fluid catalytic cracking feedstock. Examples of the hydrocarbon feedstock include high boiling, non-residual oils such as straight run (atmospheric) gas oils, vacuum gas oils, flashed distillate, coker gas oils, or atmospheric residue ('long residue') and vacuum residue (‘short residue’).
In another embodiment the hydrocarbon feedstock may include a paraffinic feedstock, for example, an optionally hydroisomerised fraction of the synthesis product of a Fischer-Tropsch reaction, or the fraction boiling above the middle distillate boiling range of the effluent of fuel hydrocracker, also referred to as hydrowax. An advantage of using said paraffinic feedstock in admixture with the lipids is that the aromatic content of gasoline fraction, can be reduced by co-processing the paraffinic feedstock. It has been found that on cracking a paraffinic feedstock a gasoline having a very low aromatic content can be obtained.
Further, lipids derived from other biomass sources such as plant and vegetable oils may also be added to the lipid-containing feedstock as an additional cracking feedstock.
Preferably, the total feed going into the catalytic cracking unit may comprise the hydrocarbon feedstock in the range of 50 wt % to 99 wt %, preferably in the range from 60 wt % to 98 wt %, more preferably 70 wt % to 98 wt %, more preferably 70 wt % to 97 wt %, most preferably in the range of 80 wt % to 95 wt % based on the total weight of lipid-containing feedstock, the remainder being the lipid feedstock.
The process of catalytic cracking of the lipid-containing feedstock according to the invention preferably comprises a catalytic cracking step, which may be followed with a regeneration step.
More preferably the catalytic cracking process includes a catalytic cracking step, in which the cracking reaction takes place in the presence of a catalyst; a regeneration step, in which the catalyst is regenerated, for example by burning off the coke deposited on the catalyst as a result of the reaction, to restore the catalytic activity; and a recycle step, wherein the regenerated catalyst is recycled to the catalytic cracking step. The heat generated in the exothermic regeneration step is preferably employed to provide energy for the endothermic cracking step.
The catalytic cracking step comprises contacting the lipid-containing feedstock with a cracking catalyst, preferably in the reaction zone of a fluidized catalytic cracking (FCC) apparatus. The reaction temperature preferably ranges from equal to or more than 450° C. to equal to or less than 650° C., more preferably from equal to or more than 480° C. to equal to or less than 600° C., and most preferably from equal to or more than 480° C. to equal to or less than 560° C. The pressure in the reaction zone preferably ranges from equal to or more than 0.5 bar to equal to or less than 10 bar (0.05 MPa-1 MPa), more preferably from equal to or more than 1.0 bar to equal to or less than 6 bar (0.15 MPa to 0.6 MPa). The residence time of the cracking catalyst in the reaction zone preferably ranges from equal to or more than 0.1 seconds to equal to or less than 15 seconds, more preferably from equal to or more than 0.5 seconds to equal to or less than 10 seconds. The product stream obtained from the cracking step may be separated into one or more hydrocarbon fractions using, for example, a fractionator.
Preferably, a catalyst to lipid-containing feedstock mass ratio ranging from equal to or more than 3 to equal to or less than 8 is used. Preferably, the catalyst to feedstock mass ratio used is at least 3.5. The use of a higher catalyst to feedstock mass ratio results in an increase in conversion.
The process according to the invention further preferably comprises a catalyst regeneration step. A regeneration step preferably may comprise burning off the coke to restore the catalyst activity by combusting the cracking catalyst in the presence of an oxygen-containing gas in a regenerator. The regeneration temperature preferably ranges from equal to or more than 575° C. to equal to or less than 950° C., more preferably from equal to or more than 600° C. to equal to or less than 850° C. The pressure in the regenerator preferably ranges from equal to or more than 0.5 bar to equal to or less than 10 bar (0.05 Mpa to 1 MPa), more preferably from equal to or more than 1.0 bar to equal to or less than 6 bar (0.1 MPa to 0.6 MPa.
Cracking catalysts suitable for use in the process according to the invention are well known in the art. Preferably, the cracking catalyst comprises a zeolitic component, and more preferably, an amorphous binder. Examples of such binder materials include silica, alumina, titania, zirconia and magnesium oxide, or combinations of two or more of them.
The zeolite is preferably a large pore zeolite. The large pore zeolite includes a zeolite comprising a porous, crystalline aluminosilicate structure having a porous internal cell structure on which the major axis of the pores is in the range of 0.62 nanometer to 0.8 nanometer. The axes of zeolites are depicted in the ‘Atlas of Zeolite Structure Types’, of W. M. Meier, D. H. Olson, and Ch. Baerlocher, Fourth Revised Edition 1996, Elsevier, ISBN 0-444-10015-6. Examples of such large pore zeolites include FAU or faujasite, preferably synthetic faujasite, for example, zeolite Y or X, ultra-stable zeolite Y (USY), Rare Earth zeolite Y (=REY) and Rare Earth USY (REUSY). According to the present invention USY is preferably used as the large pore zeolite.
The cracking catalyst can also comprise a medium pore zeolite. The medium pore zeolite that can be used according to the present invention is a zeolite comprising a porous, crystalline aluminosilicate structure having a porous internal cell structure on which the major axis of the pores is in the range of 0.45 nanometer to 0.62 nanometer. Examples of such medium pore zeolites are of the MFI structural type, for example, ZSM-5; the MTW type, for example, ZSM-12; the TON structural type, for example, theta one; and the FER structural type, for example, ferrierite. According to the present invention, ZSM-5 is preferably used as the medium pore zeolite.
According to another embodiment, a blend of large pore and medium pore zeolites may be used. The ratio of the large pore zeolite to the medium pore size zeolite in the cracking catalyst is preferably in the range of 99:1 to 70:30, more preferably in the range of 98:2 to 85:15.
The total amount of the large pore size zeolite and/or medium pore zeolite that is present in the cracking catalyst is preferably in the range of 5 wt % to 40 wt %, more preferably in the range of 10 wt % to 30 wt %, and even more preferably in the range of 10 wt % to 25 wt % relative to the total mass of the cracking catalyst, the remainder being amorphous binder.
According to the invention, the reaction zone is usually an elongated tube-like reactor, preferably a vertical reactor in which the lipid-containing feedstock and the cracking catalyst flow in an upward direction. The lipid-containing feedstock and the cracking catalyst may also flow in a downward direction. Combinations of downward and upward flow are also within the scope of the present invention. The lipid-containing feedstock and the cracking catalyst may be contacted in counterflow or crossflow configurations.
According to an embodiment of the invention, the CO2 produced in the cracking step and the catalyst regeneration step may be reused for cultivation and propagation of the diatomic microalgae being used in the process. This process integration preferably mitigates the emissions from the overall process and facilitates cultivation of diatomic microalgae.
The product stream can comprise products that may include gaseous hydrocarbons with four or less carbon atoms, gasoline, diesel, cycle oils and other hydrocarbons.
The product stream, comprising cracked hydrocarbons, obtained from the FCC apparatus is preferably sent to a fractionation zone, where it is separated into one or more hydrocarbon fractions. Preferably, these hydrocarbon fractions include dry gas, propylene, Liquefied Petroleum Gas (LPG), gasoline, light cycle oils and coke. According to an embodiment, the product stream composition includes a gasoline fraction ranging from 30 wt % to 60 wt %, preferably from 40 wt % to 50 wt %, based on the total product stream composition, as measured by Gas Chromatograph Distillation (GCD) according to the methods described in ASTM D-2887. Further, the total product stream composition includes a LPG fraction ranging from 5 wt % to 20 wt %, preferably from 10 wt % to 15 wt % of the total product stream composition (ASTM D-2887).
These hydrocarbon fractions may undergo further processing before they are provided for commercial use. Examples of the said processing may include desulfurization, cracking of heavier fractions and addition of additives.
The commercial products obtained from these hydrocarbon fractions are also within the scope of the invention. For example, the gasoline fraction may be desulfurized to reduce the sulfur content to less than 1000 ppmw, preferably to less than 500 ppmw, more preferably to less than 200 ppmw to prepare a gasoline product. One or more additives may be added to the desulfurized gasoline product to prepare a gasoline composition for commercial use. The additives may include performance enhancers such as anti-oxidants, corrosion inhibitors, ashless detergents, dehazers, dyes, lubricity improvers, synthetic or mineral oil carrier fluids. Examples of such suitable additives may also be identified in U.S. Pat. No. 5,855,629, which is incorporated herein by reference. For the purpose of the invention, it should be understood that the one or more additives can be added separately to the gasoline product or can be blended with one or more diluents, forming an additive concentrate, and together added to the gasoline product. The gasoline composition according to the invention preferably comprises a major amount (more than 50 wt %) of the gasoline product and a minor amount of the one or more additives described above, preferably ranging from 0.005 wt % to 10 wt %, more preferably from 0.01 wt % to 5 wt %, and most preferably from 0.02 wt % to 1 wt %, based on the gasoline composition.
It may be understood that processing of the aforementioned hydrocarbon fractions is well known in the art and is in no way limiting to the scope of the invention. While some of the methods have been described herein, several other processes may be used to convert the hydrocarbon fractions into commercially usable products. These processes may include isomerisation, cracking into more valuable lighter products, blending with other fuels for commercial use, and other similar uses that have been disclosed in the art.
The invention is further illustrated by the following experiments.
A batch of marine microalgae of species Chlorella was partially dried and milled. Lipids were then extracted from the marine microalgae using toluene as a solvent in a solvent extraction process. The extracted lipids were analysed online using gas chromatography (GC) and inductively coupled plasma mass spectrometry (ICP-MS) and were found to have the following distribution:
A blend of 20 wt % of these extracted lipids and 80 wt % of a mineral oil derived vacuum gas oil was mixed. The Blend had the following metal content (see table 2 in mg/kg as determined by ICP-AES).
The lipids obtained from experiment 1 were blended with mineral Vacuum Gas Oil (VGO) to form a first batch of the lipid-containing feedstock comprising 20% extracted lipids from microalgae and 80% VGO (by weight). The first batch was subjected to catalytic cracking in a small-scale fluidised catalytic cracking reactor. A commercial equilibrium catalyst comprising ultra stable zeolite Y (USY) in an amorphous alumina matrix was used as the cracking catalyst. The reaction temperature was kept at 500° C., and the pressure was maintained at 1.1 bar (0.11 MPa). For the feedstock containing 20 wt % extracted lipids from microalgae and 80 wt % VGO a catalyst to oil ratio of about 8 was used. The product stream obtained was separated in a small-scale fractionator and analysed online using gas chromatography (GC) and inductively coupled plasma mass spectrometry (ICP-MS). The results of the experiment with regard to product distribution at 67 wt % conversion are provided in Table 3.
Dry gas includes ethylene and LPG includes propane and butane gas. Gasoline is defined as the fraction starting with C5 isomers, and boiling up to 221° C. (EP); Light Cycle Oil (LCO) as the fraction boiling from 221-370° C. (IBP-EP); Heavy Cycle Oil (HCO) as the fraction boiling from 370-425° C. (IBP-EP); and Slurry Oil as the fraction boiling above >425° C., determined according to ASTM 2887, using the total boiling point method.
To establish the efficacy of the cracking process of the invention, the product stream was compared with the products obtained from the cracking of other conventionally used feedstock. VGO was used as the second batch and a blend of 20% rapeseed oil and 80% VGO was used as the third batch. The experiments were conducted in the same fluidised catalytic cracking reactor and under the same conditions as were used in experiment 2, except that a different catalyst to oil ratio may be used to achieve the constant conversion rate of 67 wt %. A comparison of the product stream obtained from experiments 2 and 3 is provided in Table 4.
The product yield of each batch of cracking feedstock was calculated at 67 wt % conversion of the cracking feedstock. It is evident from the results above that the product stream obtained from the first batch of cracking feedstock comprising lipids derived from marine microalgae is substantially similar to the product stream obtained from the two conventional cracking feedstock. This is highly surprising in view of the high content in heteroatoms such as phosphorus and metals. Moreover, the amount of light cycle oil obtained was above that generated from rapeseed oil.
The additional coke formed in the process according to the invention can be advantageous when co-processing a further paraffinic feedstock such as for example an optionally hydroisomerised fraction of the synthesis product of a Fisher-Tropsch reaction.
