METHOD OF PROCESSING ALGAE, CARBONACEOUS FEEDSTOCKS, AND THEIR MIXTURES TO BIOCRUDE AND ITS CONVERSION INTO BIOFUEL PRODUCTS

The present invention relates to an integrated method for processing algal biomass comprising a marine algal strain or a freshwater (non-marine) algal strain or a plurality of marine algal strains or a plurality of freshwater (non-marine) algal strains or any combination thereof or other carbonaceous feedstocks like biosolids or any combination of algae/algae mixtures and carbonaceous feedstocks to produce biofuel. The method includes subjecting the algae/algal mixture to hydrothermal liquefaction/co-liquefaction using sub-critical water to produce a biocrude. The biocrude is pretreated using a renewable biocatalyst to remove impurities which include Nitrogen (N), Sulfur (S), Oxygen (O) and salts and the pretreated biocrude is mixed with heteroatoms a petrocrude to form a biocrude-petrocrude blend. The biocrude-petrocrude blend is distilled and the distillate fractions are treated using the renewable biocatalyst to remove impurities and finally hydrotreated to produce fractions biofuels. The recovered biocatalyst/biochar which is rich in nutrients is used for agricultural applications to improve soil fertility.

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Description
FIELD OF THE INVENTION

The present invention generally relates to thermochemical processing of biomass to produce biofuel products and useful by-products. More particularly, the invention relates to methods of processing algal biomass, carbonaceous feedstocks and their mixtures to produce biocrude and its conversion into biofuels.

BACKGROUND OF THE INVENTION

Mankind continues to increase fossil fuel usage as the demand for energy and transportation fuels grows every year. World's primary energy consumption will increase by 37% between 2013 and 2035, with growth averaging 1.4% p.a. In India, about 85% of the crude oil requirements i.e. 189 MMT is met through imports from Middle East and other countries. India spends about Rs. 8.6 lakh crore ($144 billion) per year for the import of crude oil which is a huge drain on the country's foreign exchange reserves. Considering the environmental pollution caused by the release of CO2, NOx and SOx from fossil fuel sources, production of alternative fuels from sustainable sources is paramount to meet world's future energy demands and reduce carbon emissions.

Plant based first generation biofuels such as biodiesel from oil crops and ethanol from corn are considered not sustainable as they compete with food crops for arable land, fresh water and agricultural fertilizers. Bioethanol which is a second generation biofuel produced from lignocellulosic biomass residues has a major limitation as the availability of surplus biomass residues for conversion into fuel is limited. Algae are considered as a sustainable biomass feedstock source for the production of advanced biofuels in view of their superlative biomass production potential compared to higher plants. Biomass productivity of algae is 3-5 times higher than that of terrestrial crops. Algae can be cultivated on unproductive lands and poor quality waters such as seawater, brackish water and municipal, agricultural and industrial wastewaters. Algae biomass is currently used for a wide range of applications which include food, feed, nutraceuticals, cosmeceuticals, biofertilizers and recently biofuels.

Algae biomass is rich in lipids, carbohydrates and proteins. Oil yield of microalgae per hectare is comparatively much higher than that of traditional oil seed crops such as soybean. Worldwide, the current research focus is mainly on identifying algal strains with higher lipid content (i.e. above 40% triglycerides in the biomass) and biomass productivity for mass cultivation. By growing lipid rich strains on large-scale, oil yield can be enhanced which can be converted into biodiesel and blended with petro-diesel to replace significant quantities of fossil fuels. However, the algal strains isolated and reported to-date were found to contain only 30-40% of total lipids in the biomass. The strains which are capable of accumulating more lipids are reported to be slow growers and their biomass production potential is poor.

Biomass productivity and lipid content of algal strains are always mutually exclusive and inversely related parameters, as the synthesis of lipids has a higher metabolic cost than proteins or carbohydrates. Oil rich strains of algae need to be cultivated in open ponds where contamination from other weed algae and cyanobacteria is a major problem. In addition, the algal biomass needs to be dried to facilitate maximum recovery of lipids to produce biodiesel, which is an energy intensive process. This extraction process has to be preceded by cell disruption to facilitate effective extraction of lipids for conversion into biodiesel. Thus, in order to overcome the problems observed in biodiesel production, a novel method of producing biofuels using algae and other carbonaceous feedstocks by hydrothermal liquefaction (HTL) has been developed. Algal biomass has become a popular feedstock of HTL as they do not contain complex molecules like lignin. The wet biomass after harvesting (with 10-20% solid content) can directly be converted to biocrude.

In the conventional system, there are methods available for the conversion of the algal biomass into biofuel. United States Patent No. 20130137154 and PCT Publication No. 2013055819 describe a method and system for processing biomass feedstock to produce liquid biofuel using a hydrothermal liquefaction process (HTL). The biomass feedstock comprises algae feedstock and herbaceous/woody feedstock. The HTL process involves water at elevated temperatures and pressures in the range of 250° C.-350° C. and 40-165 bar respectively. A catalyst can be used to facilitate the processing or refining of the feedstock and/or feedstock compositions

PCT Publication No. 2014022218 to Patrick G. Hatcher entitled “Production of hydrocarbons from select coal and algal biomass mixtures” discusses a process for producing bio-oil/ hydrocarbon which involves mixing of coal with an algal biomass and subjecting the blend to a fuel conversion process such as hydrothermal liquefaction. The HTL process is used to convert biomass components to biocrude and it is carried out using subcritical water with a temperature range between 320° C. and 360° C.

U.S. Pat. No. 8,704,020 to Roberts Virginia M. et al., entitled “Catalytic hydrothermal treatment of biomass” relates to hydrothermal treatment of various types of biomass such as algae to produce hydrocarbon products such as distillate fuel. The treatment comprises contacting an algae based biomass with water at supercritical or near-supercritical temperatures in the presence of a dissolved metal catalyst. The dissolved metal catalyst is a biocompatible material used to reduce impurity levels in distillate products.

PCT Publication No. 2013063085 to Shulin Chen and Moumita Chakraborty entitled “Sequential hydrothermal liquefaction for extraction of superior quality bio-oil and other organic compounds from oleaginous biomass” discloses a sequential hydrothermal liquefaction process for extraction of bio-oil from oleaginous biomass such as algae biomass. The method involves heating a mixture of oleaginous biomass and an aqueous medium to a temperature range of 237° C. to 243° C. The char particles act as a catalyst to promote polymerization reactions between bio-oil functional groups.

PCT Publication No. 2013050860 to Shrikumar Suryanarayan et al., entitled “Process of production of renewable chemicals and biofuels from seaweeds” describes systems and methods for hydrothermal conversion of algae into biofuel comprising treatment of algae with near-critical or supercritical water at a temperature between 100° C. and 450° C. or between 325° C. and 425° C. The system further comprises a separator/polisher for removing water and other impurities such as phosphorus from produced biofuel.

PCT Publication No. 2011049572 and 2011163111 relate to a process of hydrothermal conversion of algae to biofuel using subcritical water at the elevated temperatures between 200° C.-350° C. and below 374° C. respectively

All existing art though disclose various methods for the conversion of algal biomass to biofuel by hydrothermal liquefaction, the co-liquefaction of algal biomass with biosolids and blending of biocrude and petrocrude during the process of converting algal mixtures to biofuel have not been disclosed which are important steps in the present invention of converting algae, carbonaceous feedstocks and their mixtures to biofuel. Further the method includes the use of biochar as renewable biocatalyst for the upgradation of biocrude/biocrude blend/petrocrude and the distillate fuel fractions through the removal of heteroatoms and other impurities, which is a novel approach. This method also advocates the utilization of biochar used for removal of heteroatoms in biocrude or biocrude blend or petrocrude for agricultural applications as soil amendment. In addition, this invention advocates an integrated process to produce drop-in biofuels from algae, carbonaceous feedstocks and their mixtures which involves the following steps: [i] Hydrothermal liquefaction/co-liquefaction to produce biocrude [ii] use of renewable biocatalyst (biochar) to remove heteroatoms in the biocrude (pretreatment 1) [iii] washing of biocrude with water for desalting (pretreatment 2) [iv] blending of biocrude and petrocrude for distillation [v] removal of heteroatoms/impurities in biocrude blend using renewable biocatalyst (pretreatment 3) [vi] removal of heteroatoms/impurities in the distillate fractions using renewable biocatalyst [vii] hydrotreating/upgradation of distillate fuel fractions to drop-in fuels and [viii] recycling of biocatalysts (biochar) for agricultural application.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an integrated method for processing algal biomass comprising a marine algal strain or a freshwater (non-marine) algal strain or a plurality of marine algal strains or a plurality of freshwater (non-marine) algal strains or any combination thereof or other carbonaceous feedstock/biosolids or any combination of algae/algae mixtures and carbonaceous feedstocks to produce biofuel. Biomass from any specific algal strain or mixture of algal strains is called as primary feedstock. Any carbonaceous feedstock or mixtures of carbonaceous feedstock is called as secondary feedstock. The method includes subjecting the algae, carbonaceous feedstocks and their mixtures to hydrothermal liquefaction or co-liquefaction under subcritical water temperatures and pressures to obtain a biocrude. The biocrude is pretreated using a renewable biocatalyst such as biochar to remove impurities which include Nitrogen (N), Sulfur (S), Oxygen (O) and salts. The biocrude is mixed with a petrocrude to form a biocrude-petrocrude blend. The biocrude-petrocrude blend is distilled and the distillate fractions are treated using a biocatalyst to remove heteroatoms and other impurities and finally hydrotreated to produce drop-in biofuels.

BRIEF DESCRIPTION OF THE DRAWINGS

The objective of the present invention will now be described in more detail with reference to the accompanying drawing, in which:

FIG. 1 is a schematic diagram showing the step-by-step process for the production of biofuel from algae, other carbonaceous feedstocks and their mixtures;

FIG. 2 shows HTL process and its various product fractions;

FIG. 3 shows FT-IR Spectrum of algae biocrude blends (with Narimanam petrocrude); FIG. 4 shows FT-IR Spectrum of Diesel Fraction of algae biocrude blends (with Narimanam petrocrude);

FIG. 5 shows SIMDIST showing distribution of Carbon,Sulfur and Nitrogen in the Narimanam petrocrude and algal biocrude blends;

FIG. 6 shows different cuts obtained in True Boiling Point (TBP) distillation of algal biocrude blend of marine alga.Tetraselmis sp.;

FIG. 7 shows changes in the sulfur content of middle distillate fraction (270-370° C.) derived from biocrude blend of Tetraselmis sp. (marine alga) treated with biochar;

FIG. 8 shows changes in the sulfur content of biochar used for the treatment of middle distillate fraction (270-370° C.) derived from biocrude blend of marine alga Tetraselmis sp.;

FIG. 9 shows changes in the nitrogen content of middle distillate fraction (270-370° C.) derived from biocrude blend of marine alga Tetraselmis sp. treated with biochar;

 DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the production of biofuel from algae, other carbonaceous feedstock and their mixtures.

Referring to the invention in detail, FIG. 1 illustrates the process of producing biofuel from algae and other carbonaceous feedstocks which involves mixing the algal biomass along with other carbonaceous feedstock sources (e.g. algae with biosolids, algae with lignite, algae with agave biomass, algae with yeast sludge, algae with municipal sludge and algae with renewable waste biomass etc). Biomass from any specific algal strain or mixture of algal strains is called as primary feedstock. Any carbonaceous feedstock or mixtures of carbonaceous feedstock are called as secondary feedstock. The first step of the process is that the algal mixture is subjected to hydrothermal co-liquefaction. The algal biomass along with other carbonaceous feedstocks is processed below the critical temperature of water (100° C. to 374° C.) and pressure. This water is referred to as subcritical water and/or hot compressed water. The subcritical water has several advantages over water at room temperature because of changes in properties such as solubility, density, dielectric constant and reactivity as water approaches its critical point (374° C., 22.1 MPa). This reactive water medium enhances depolymerization and repolymerization of lignins, celluloses, lipids, proteins and carbohydrates and then transforms them into biocrude/bio-oil, gas and/or char. Higher pressures are maintained during hydrothermal processing treatments to avoid energy losses due to phase change of water to steam.

The biocrude obtained from the algal biomass/carbonaceous feedstocks and their mixtures is subjected to a pretreatment process using a renewable biocatalyst such as “biochar” to remove impurities like heteroatoms (N, O and S) and salts. Further, desalting of biocrude is achieved through water washing. The pretreated biocrude is then blended with petrocrude to produce a biocrude-petrocrude blend. This blend if needed is treated with biochar to remove impurities.

The blend is further subjected to distillation and the distillate fractions thus obtained are treated with the biocatalyst to remove impurities like heteroatoms in order to upgrade the quality of distillate fractions.

Further, the process involves hydrotreatment of the distillate fractions to upgrade and produce drop-in biofuels. The renewable biocatalyst i.e. biochar recovered from the process which is rich in nutrients (absorbed from biocrude and distillate fractions) are used for agricultural applications as soil amendment.

The following examples disclose additional embodiments of one or more of the steps in the production of biofuel from algae and other carbonaceous feedstock mixtures.

Fresh water algal biomass of Arthrospira platensis is combined with the biosolids obtained from wastewater treatment plant. The biosolids mostly contain biomass derived from bacteria, fungi, actinomycetes and algae. Ultimate analysis of both the feedstocks along with the mixture (1:1 ratio) is carried out to estimate their C, H, N, S and O content. The elemental carbon (C), hydrogen (H), nitrogen (N), and sulfur (S) contents of the microalgae and biocrude are analyzed using VarioEL III elemental analyser system. The oxygen content is determined by difference (100%-C+H+N+S+ash content). The higher heating values (HHV) of biomass and biocrude are determined using the Dulong's formula given below:


Higher Heating value (MJ/kg)=0.338 C+1.428(H—O8)+0.095 S

where C,H,O and S represent the mass of carbon, hydrogen, oxygen, and sulphur on a dry weight basis.

Ash content of both the feedstock is estimated by ashing the biomass in a muffle furnace maintained at 450° C. for 4 hours.

Example 01

For the co-liquefaction trials, 40 g of each feedstock i.e. microalga, and biosolids are weighed and mixed together thoroughly. Then 80 g of the biomass mixture is dissolved in deionized water to make a slurry of 400 ml containing 20% w/v solids. This mixture is treated at 350° C. at 5 min in a 1L capacity high pressure reactor. Stirring speed of 300 rpm is maintained'for all the runs. The reaction is terminated by switching off the heaters and the chamber is cooled by pumping tap water through cooling coils. The gas phase is collected in Tedlar bags after cooling the reactor and analysed. After attaining room temperature, the product mixture in the reactor is removed and poured into a separating funnel for phase separation. The product mix forms three phases in the separating funnel. The light oil fraction floating as top layer in the separating funnel is decanted. The remaining two phases consisting of aqueous fraction and water insoluble solid residues are filtered. The solid fraction is then extracted with solvents such as dichloromethane or acetone to separate the hydrocarbons. After the extraction, the solid fraction is dried in an oven and stored for elemental analysis. HTL oil or the heavy fraction of biocrude derived from the biomass is recovered by evaporating the solvent fraction under vacuum. The remaining aqueous phase is stored for nutrient analysis. Each product fraction yield is determined as the ratio of their mass to the initial mass of the biomass feedstock used. Biocrude yield is calculated by combining the total weight of both light and heavy fraction of biocrude and the results are expressed as dry wt % of initial biomass used. Algal biomass (Arthrospira platensis) and the biosolids used in the co-liquefaction experiment are also treated through HTL process separately and the yield and quality of biocrude are compared with the biocrude obtained in the co-liquefaction process using the mixture of microalga and biosolids.

Elemental analysis of biomass feedstock, biocrude and solid residues are carried out in the CHNSO analyser (Elementar Vario ELIII) following methods outlined in ASTM D 5291 and D 3176. The analyzer is calibrated using sulfanilamide. Atomic ratios such as H/C, O/C and N/C of raw feedstock and the biocrude samples are derived from the elemental results. The energy value is calculated using the Dulong's formula given below.


Heating value (MJ/kg)=0.338 C+1.428(H−O/8)+0.095 S

Co-liquefaction trial results are furnished in Tables 1, 2 and 3. The carbon content in the biosolids is very low due to higher ash content (Table 1). However, when it is mixed in 1:1 ratio with the algal biomass containing less ash and higher C, the carbon, hydrogen and calorific value of the mixture increased by 40%, 41% and 88%, respectively. Similarly, the H/C ratio also showed an increase in the mixture.

TABLE 1 Elemental and energy analyses of biomass feedstock used for the hydrothermal co-liquefaction experiments Biomass Analysis HHV Feedstock C % H % N % S % O % (MJ/kg) Ash H/C N/C O/C Arthrospira 47.20 7.80 11.02 0.86 33.12 22.39 6.30 1.98 0.20 0.43 platensis Biosolids 28.19 5.60 4.46 0.99 27.05 12.79 33.71 2.38 0.14 0.72 Mixture 39.42 7.91 8.20 0.96 23.50 20.52 20.00 2.40 0.18 0.45 (1:1) ratio

Energy content and H/C ratio of biocrude derived from biosolids are 25 MJ/kg and 1.41, respectively (Table 2). It is interesting to note that biocrude derived from co-liquefaction trials using the algal and biosolids mixture showed significant increase in HHV value (28.45 MJ/kg), compared to the value obtained for biocrude derived from biosolids (25 MJ/kg). Similarly the biocrude obtained from the mixture recorded a H/C value of 1.52 compared to 1.41 for the crude obtained from biosolids.

TABLE 2 Elemental and energy analyses of biocrude produced in the hydrothermal co-liquefaction of [a] Arthrospira platensis [b] Biosolids and [c] 1:1 ratio of Arthrospira and biosolids mixture Biocrude Analysis Feedstock C % H % N % S % O % HHV (MJ/kg) H/C N/C O/C Arthrospira 64.67 8.52 5.71 0.77 20.33 30.47 1.58 0.08 0.24 platensis Biosolids 59.52 7.00 3.84 0.64 29.00 25.00 1.41 0.06 0.37 Mixture 62.77 7.93 5.18 0.80 23.32 28.45 1.52 0.07 0.28 (1:1) ratio

Biocrude yield from Arthrospira platensis is the highest (78% on ash free basis) whereas it is 51% and 56% for the treatments using biosolids alone and the biosolids and algal mixture. The solid residue yield is significantly reduced in the mixture (Table 3).

TABLE 3 Yields of various products in the hydrothermal co-liquefaction process of algal biomass and biosolids Quantity of Biocrude yield Total Gas biomass used As received As received Ash free basis solids yield yield Feedstock (dry g) (g) (%) (%) g % g % Arthrospira 80 58.1 73 78 5.34 6.7 16.4 20.5 platensis Biosolids 80 26.9 34 51 27.09 33.9 12.4 15.5 Mixture 80 35.6 45 56 16.62 20.8 13.2 16.5 (1:1) ratio

Example 02

Hydrothermal liquefaction experiments are carried out in a custom made 1L stirred high pressure reactor. The experiments are conducted at 250-350° C. for 30 minutes. The heat is applied by an electrical heater installed at the bottom of the reactor. For the present investigation, the reactor is held at 350±3° C. (corresponding to 180 bar pressure) for the predefined holding time of 30 min. A stirring speed of 300 rpm is maintained for all the runs. The reaction is terminated by switching off the heaters and the chamber is cooled by pumping tap water through cooling coils. The gas phase is collected in Tedlar bags after cooling the reactor and analyzed. After attaining room temperature, the product mixture in the reactor is removed and poured into a separating funnel for phase separation. Various product streams are separated by following a series of filtration and extraction procedures as showed in FIG. 2. The product mix forms three phases in the separating funnel. The light oil fraction floating as top layer in the separating funnel is decanted. The remaining two phases consisting of aqueous fraction and water insoluble solid residues are filtered. The solid fraction is then extracted with solvents such as dichloromethane or acetone to separate the hydrocarbons. After the extraction, the solid fraction is dried in an oven and stored for elemental analysis. HTL oil or the heavy fraction of biocrude derived from the biomass is recovered by evaporating the solvent fraction under vacuum. The remaining aqueous phase is stored for nutrient analysis. Each product fraction yield is determined as the ratio of their mass to the initial mass of the biomass feedstock used. Biocrude yield is calculated by combining the total weight of both light and heavy fraction of biocrude and the results are expressed as dry wt. % of initial biomass used. The biocrude yields of the algae strains used are given in Table 4.

TABLE 4 Comparison of biocrudes yields of freshwater alga Arthrospira platensis and marine alga Tetraselmis sp. Strains Biocrude yield (wt. %) Freshwater alga Arthrospira platensis 35.0 Marine alga Tetraselmis sp. 40.0

Elemental analysis: Elemental analysis of biomass feedstock, biocrude and solid residues are carried out in the Carbon Hydrogen Nitrogen Sulphur Oxygen (CHNSO) analyzer (ElementarVario ELIII) following methods outlined in ASTM D 5291 and D 3176. The analyzer is calibrated using sulfanilamide. Atomic ratios such as H/C, O/C and N/C of raw feed stocks and the biocrude samples are derived from the elemental composition.

Energy/heating value: The energy value is calculated using the Dulong's formula given below.


Heating value (MJ/kg)=0.338 C+1.428(H—O/8)+0.095 S

Biocrude Blending:

The characterization of properties such as oil yield, elemental analysis and heating value is carried out on biocrude derived from both freshwater and marine algae. Biocrude obtained from HTL process normally contains a wide variety and diverse range of chemical compounds which include aliphatic and aromatic compounds, phenols, carboxylic acids, esters and nitrogenous ring compounds. The biocrude obtained is characterized for conventional crude properties. Both biocrude fractions derived from freshwater and marine algae are blended with a light crude namely Narimanam petrocrude.

The blended crude is subjected to True boiling point (TBP) distillation to get various cuts and the properties of the various cuts are studied. The chemical composition of the biocrude and various cuts obtained from True Boiling Point (TBP) distillation are also analysed using Fourier Transform Infrared Spectroscopy (FTIR).

Example 03

The TBP (True Boiling Point) distillation gives the yields of various cuts and determines the yield of products that is obtained in a commercial unit. The TBP distillation is carried out in ROFA distillation system in the following stages: (i) Debutanisation (ii) Atmospheric Distillation (iii) Vacuum Distillation 100 Torr (iv) Vacuum Distillation 10 Torr and (v) Vacuum Distillation at 2 torr. The distillation of blends of Narimanam petrocrude (90%) with Biocrude (10%) obtained from marine and fresh water algae is carried out.

TBP Assay: A weighed sample of 4.5 L of stabilized Narimanam petroleum crude is mixed with 0.5 L of algal crude and distilled to a maximum temperature of 400° C. in a TBP unit. Distillation is done in a fractionating column having an efficiency equivalent to 15 theoretical plates. A reflux ratio of 5:1 is maintained at all operating pressures (760 Torr to 2 Torr). Observations of temperature, pressure, and other variables are recorded at specified intervals. At the end of each cut or fraction, the mass and density of each cut or fraction are obtained. Distillation yields by mass are calculated from the mass of all fractions, including liquefied gas cut and the residue.

Elemental composition and characteristics of biocrude obtained from freshwater and marine algae are given in Table 5.

TABLE 5 Elemental composition and other characteristics of biocrude obtained from freshwater alga Arthrospira platensis and marine alga Tetraselmis sp. Source of Elemental composition (wt. %) Atomic ratio (mol/mol) HHV HTL Oil C H N S O H/C O/C N/C (MJ/kg) Arthrospira 74.5 10.3 6.8 1.0 7.5 1.7 0.08 0.08 38.65 platensis Tetrasehnis sp. 71.4 9.5 5.7 1.1 12.3 1.6 0.13 0.07 35.58

The properties of Narimanam petrocrude in comparison with freshwater and marine algal biocrude blends are given in Table 6. The API gravity of the biocrude blends is in the range of 37-38 and both the blends can be categorized as light crudes. The 370° C.+yield of biocrude blend is 23 wt % compared to yield of 57% for Arab Heavy crude and 45% for Arab light crude. The Biocrude blend has higher salt content and it is greater than 800 ppm for biocrude derived from the marine alga. The higher salt content in the crude have implications in the processing of the crude in the refinery distillation unit.

TABLE 6 Comparison of Petrocrude & Biocrude from marine and fresh water algae 90% Narimanam 90% Narimanam crude + crude + 10% biocrude 10% biocrude Narimanam from from Properties crude marine alga freshwater alga Specific Gravity 0.8128 0.8389 0.8316 API Gravity 42.6 37.2 38.7 Viscosity @ 40° C., 1.85 2.16 1.66 cSt Pour Point, ° C. −3.0 +9.0 −3.0 Sulphur, ppm 676 795 1300 MCR, wt % 0.67 0.97 0.52 RVP, psi 5.97 1.92 3.82 Ni, ppm 2.0 52.2 2.1 V, ppm 0.18 <0.01 0.35 Acidity, mg KOH/g 0.02 0.9 0.22 Salt in crude, ppm 19 812 36 Nitrogen, wt % 0.03 0.18 0.20 Asphaltenes, wt % 0.12 1.95 1.82 API—American Petroleum Institute MCR—Micro Carbon Residue RVP—Reid Vapor Pressure

Petrocrudes have wide ranging characteristics. Heavier crudes such as Maya Crude/Arab Heavy crude have a high Atmospheric Residue (370° C.+) and Vacuum Residue Yields (550° C+). The comparison of various petrocrudes with Narimanam crude and the biocrude blends obtained from both freshwater and marine algae with respect to the yield of Atmospheric residue (370° C.+) is given in Table 7.

TABLE 7 Characteristics of various types of Petrocrude Atmospheric Residue (AR) Vacuum Residue (VR) Crude Yield wt % (370° C.+) Yield wt % (550° C.+) Maya Crude 61.2 16.2 Arab Heavy 57.0 31.8 Basrah Light 54.3 28.4 Bombay High 34.1 9.1 Narimanam 23.6 — Biocrude blend with 22.9 — Narimanam petrocrude (10%) - Fresh Water Algae Biocrude blend with 23.6 — Narimanam petrocrude (10%) - Marine Algae

Yields of different cuts obtained in TBP distillation of Narimanam crude and algal biocrude blends are given in Table 8.

The biocrude obtained from both fresh water and marine algae are light crudes and the blended crude has distillate yield of 76-77 wt %. The yield of light Naphtha (C5-140) of biocrude blends is 29-30% and requires hydroprocessing for removal of S and N before using as Reformer feed (Table 8).

TABLE 8 TBP Distillation of blends of biocrude derived from marine and freshwater algae and Petrocrude 90% Narimanam 90% Narimanam Narimanam petrocrude + petrocrude + 10% Petrocrude 10% biocrude from biocrude Cuts, ° C. Yield, wt % marine alga from fresh water alga C1-C4 1.6 1.5 1.7 C5-140 28.8 30.1 29.1 140-170 8.5 7.5 7.5 170-240 14.2 13.0 14.7 240-270 6.0 6.2 5.7 270-370 17.3 18.1 18.4 370+ 23.6 23.6 22.9

Properties of various distillate fractions derived from algal biocrude blend with petrocrude are given in Tables 9, 10. 11 and 12.

TABLE 9 Properties of Naphtha Fraction derived from algal biocrude blends C5-140° C. 140-170° C. Narimanam Narimanam Narimana-m petrocrude petrocrude Narimanam petrocrude 90% + 10% 90% + 10% petrocrude 90% + 10% 100% biocrude biocrude from 100% 90% + 10% biocrude from Narimanam from marine freshwater Narimanam biocrude from freshwater Properties Petrocrude alga alga petrocrude marine alga alga TBP Yield, 28.8 30.1 29.12 8.5 7.5 7.5 wt % Specific 0.7254 0.7272 0.7646 0.7804 0.7790 0.7805 Gravity API Gravity 64 63.1 53.6 50 50.1 49.8 Sulphur, ppm 14 328 200 47 599 274 Nitrogen, ppm — 97 675 — 541 2142

TABLE 10 Properties of Kerosene derived from algal biocrude blends 170-240° C. 240-270° C. Narimanam Narimanam Narimanam Narimanam petrocrude petrocrude petrocrude petrocrude 100% 90% + 10% 90% + 10% 100% 90% + 10% 90% + 10% Narimanam biocrude from biocrude from Narimanam biocrude from biocrude from Properties Petrocrude marine alga fresh water alga petrocrude marine alga fresh water alga TBP Yield, wt % 14.2 13.0 14.7 6.0 6.2 5.7 Specific Gravity 0.8115 0.8475 0.8142 0.8472 0.8475 0.8510 API Gravity 42.9 35.5 42.3 35.5 35.5 34.8 Smoke Point, mm 20 21 20 — — — Sulphur, ppm 185 611 — 369 694 — Nitrogen, ppm — 1247 — — 1939 —

The Kerosene cut meets the requirements of sulfur and smoke point (Table 10). However, high nitrogen content requires further processing although no specification exists for nitrogen content. The 240-270° C. cut of biocrude meets the Euro II diesel sulfur requirement. But to meet the Euro III and IV requirements, Diesel Hydrodesulphurisation has to be carried out which also reduces the nitrogen content in the feed.

TABLE 11 Properties of Diesel Fraction (270-370° C.) derived from algal biocrude blends Narimanam Narimanam petrocrude 90% + petrocrude 90% + 100% 10% biocrude 10% biocrude Narimanam from from Crude Petrocrude marine alga fresh water alga TBP Yield, wt % 17.3 18.1 18.4 Specific Gravity 0.8641 0.8709 0.8713 API Gravity 32.1 31.0 30.9 Viscosity@40° C., 5.13 5.16 5.41 cSt Pour Point, ° C. 0 0 −3.0 Aniline Point, ° C. 74 70 70.5 Sulphur, ppm 982 1054 950 Nitrogen, ppm 520 2008 3984 Calculated Cetane 47 45 45 Index

The 270-370° C. cut of biocrude will meet the Euro II diesel sulfur requirements (Table 11). But to meet the Euro III and IV requirements, this cut requires Diesel Hydrodesulphurisation which will also reduce the nitrogen content in the feed.

TABLE 12 Properties of Atmospheric Residue (370° C.+) derived from algal biocrude blends Narimanam Narimanam 100% petrocrude 90% + petrocrude 90% + Narimanam 10% biocrude from 10% biocrude from Crude Petrocrude marine alga fresh water alga TBP Yield, 23.6 23.6 22.9 wt % Pour Point, +45 +48 +48 ° C. Viscosity 17.65 18.62 16.07 @100° C., cSt MCR, wt % 3.97 4.86 4.70 Sulphur, wt % 0.10 0.21 0.40

The Atmospheric Residue or Reduced Crude Oil (RCO) is processed in secondary processing unit such as Fluid Catalytic Cracking (FCC) along with Heavy Vacuum Gas Oil (HVGO) as this is a light stock.

An analysis of the 10% blend of algae biocrude with Narimanam crude indicated that the following challenges need to be considered for the processing of biocrude blend:

    • presence of high Nitrogen and Oxygen/heteroatoms content in the biocrude
    • presence of High Salt content in the biocrude derived from both marine microalga and freshwater alga
    • presence of High Ni content (52 ppm) in the biocrude derived from freshwater alga. Compared to this some of the heavy crudes like Maya crude contain ppm Ni

Based on the compositional analysis of biocrude derived from Arthrospira platensis (fresh water alga) and Tetraselmis sp. (marine alga), a 10% blend of biocrude with Petrocrude is found to be ideal to minimize the impact of impurities in refining process.

Example 04

FTIR analysis of the biocrude blends (FIGS. 3 & 4) allowed for a more comprehensive comparison of “whole” oil functional group characteristics, with spectral band assignments and interpretation based on previous studies.

FTIR spectra are collected using a Bruker Fourier Transform Infrared Spectrophotometer equipped with an attenuated total reflectance (ATR). Accessory spectra are collected from 4000 to 525 cm−1. Background scans are conducted of the dry accessory at ambient temperature. Biocrude samples are applied in thin films and allowed to dry to remove any trace solvent.

Similar to Petrocrude, the high carbon and hydrogen content of HTL biocrude blend with Narimanam petrocrude produced prominent CAH stretch (2950-2850 cm−1), CH2 bending (1465 cm−1), and CH3 bending (1375 cm−1). Significant heteroatom functionality peaks at 1658 and 1605 cm−1 characteristic of NH bending is observed for fresh water algal biocrude blend. The algae biocrude blend obtained using marine alga showed a peak at 1708 cm−1 corresponding to —C═O stretch and a peak at 965 cm−1 characteristic of ═C—H stretch.

The FTIR spectrum of Diesel Fraction of blend obtained using marine alga showed a peak at 1709 cm−1 characteristic of C═O Stretch and another peak at 1035 cm−1 characteristic of C—N Stretch while the fresh water alga recorded a peak at 1708 cm−1 characteristic of C═O Stretch and another peak at 1604 cm−1 characteristic of —N—H bending distinguishing it from diesel fraction of Narimanam petrocrude.

Example 05

CNS SIMDIST: The distribution of Carbon, Sulfur and Nitrogen in Narimanam crude and algal biocrude blends of Arthrospira platensis (fresh water alga) and Tetraselmis sp. (marine alga) is studied using GC SIMDIST unit equipped with Chemiluminesence detector for Sulfur and Nitrogen which provides Sulfur and Nitrogen boiling point distribution in the temperature range between 150-700° C. The CNS Simdist HT (FIG. 5) is carried out in PAC unit with baseline compensation after diluting the biocrude blends with cyclohexane. The carbon distribution for Narimanam petrocrude and blends of biocrude (10%) obtained from both fresh water and marine algae are similar. The Nitrogen content in Narimanam crude is around 400 ppm which is much less when compared to the algal biocrude blends, where the nitrogen content is in the range of 2000-2200 ppm. The algal biocrude blend obtained using fresh water alga showed higher nitrogen content above 400° C. and it is also higher than the nitrogen content observed in the marine alga. The sulfur content in Narimanam crude is 540 ppm and it is slightly less than the sulfur content observed in both algal biocrude blends which is in the range of 650-700 ppm. The biocrude blend obtained using marine alga showed a similar distribution of sulfur as petrocrude but the concentration is slightly higher (about 650 ppm).

Example 06

For removing heteroatoms and other impurities from biocrude, rice husk biochar is used as renewable biocatalyst. Elemental analyses of biochar and biocrude are carried out in the CHNS analyser (Elementar Vario ELIII) following methods outlined in ASTM D 5291 and D 3176. The analyzer is calibrated using sulfanilamide. The oxygen content is determined by difference (100%-C+H+N+S+ash content). Initially a known quantity of biochar is weighed and washed thoroughly with distilled water to remove impurities. After washing, biochar samples are dried at room temperature. Biocrude derived from Arthrospira platensis (a fresh water alga) is used for this experiment. Elemental analysis of biocrude is carried out before the treatment as explained above. A known amount of biocrude is diluted with dichloromethane in 1:1 ratio and 100 ml of this mixture is distributed in 250 ml conical flasks. Washed biochar samples are added in the flasks containing biocrude and solvent mixture at different concentrations (10 g, 25 g, 50 g, 100 g) in triplicates. Treatment details are given in Table 13.

TABLE 13 Biochar treatment details Quantity of Biochar added to biocrude- Treatment solvent mixture (%) C 0 T1 10 T2 25 T3 50 T4 100

The mouth of the flasks are closed airtight using parafilm to prevent evaporation of solvents and agitated at 300 rpm in a temperature controlled shaker for about 1 h. The flasks are then removed from the shaker. Biochar added in the biocrude and solvent mixture is removed through filtration. Then the biochar samples are dried in room temperature. Solvent present in the biocrude mixture is evaporated using a flash evaporator and the biocrude is separated. After ensuring complete solvent removal from the biochar treated biocrude, elemental analysis is carried out as explained earlier.

Results: T1 containing 10% Biochar, recorded 819% increase in N content and 119% increase in S content in the biochar when compared to the biochar before treatment. However the N content of biochar in the treatments T2, T3 and T4 showed 604%, 399% and 279% increase, respectively. Similarly the S content of biochar in the treatments T2, T3 and T4 recorded 89%, 93% and 24% increase, respectively (Table 14).

The biocrude obtained from T1 showed 20% reduction in N content and 29% reduction in S content due to biochar treatment. The other treatments (T2, T3 and T4) showed 20-25% reduction in N content and 25-33% reduction in S content. The data clearly indicates the potential of biochar for the removal of heteroatoms from biocrude without applying high temperature conditions and using expensive catalysts.

Commercially available zeolites cost $430-516 per ton; and it is estimated that biochars are less expensive options ($86-344 per ton). Considering the expensive catalysts and high temperature conditions used in the refining process, use of biochar as low-cost renewable catalyst to remove heteroatoms in the biocrude/biocrude blend/petrocrude is a viable option for future. Though the removal efficiency of N and S is low, further optimization studies are required to standardize the type of biochar, dosage and reaction time.

There is a significant improvement in the nutrient composition of biochar in terms of N, and S. Hence, the biochar after its use is recycled for agricultural applications as soil amendment to improve the soil quality as the heteroatoms removed from crude which are adsorbed or absorbed by the biochar will ultimately contribute to soil fertility and plant growth. Biochar is an eco-friendly catalyst and it also helps in reducing the carbon foot print of the biocrude refining process.

TABLE 14 Changes in the composition of biochar and biocrude after treating the biocrude obtained from the freshwater alga Arthrospira platensis for the removal of heteroatoms Biochar Biocrude Treatment N % S % N % S % Control 0.36 0.19 7.79 1.02 T1 (10% biochar) 3.35 0.41 6.26 0.73 T2 (25% biochar) 2.56 0.36 6.27 0.73 T3 (50% biochar) 1.82 0.36 6.10 0.77 T4 (100% biochar) 1.38 0.23 5.84 0.68

Sulfur content in crude oil is typically between 0.05 and 5.0% (by weight), although values as high as 13.95% have been reported. To reduce sulfur-related air pollution, sulfur must be removed from fuel. The ability of biochar to desulfurize a middle-distillate fraction of blended biocrude is evaluated. A biocatalyst (rice husk biochar) is used for the removal of sulfur and nitrogen from the middle distillate fraction to improve its quality as a fuel.

Example 07

For this experiment rice husk biochar is used as renewable biocatalyst. Elemental analyses of biochar and biocrude are carried out in the CHNS analyser (Elementar Vario ELIII) following methods outlined in ASTM D 5291 and D 3176. The analyzer is calibrated using sulfanilamide. The oxygen content is determined by difference (100%-C+H+N+S+ash content). Initially a known quantity of biochar is weighed and it is washed thoroughly with distilled water to remove impurities. After the washing, biochar samples are dried at room temperature. Middle distillate fraction derived from the 10% algal biocrude blend of Tetraselmis sp. (a marine alga) is used for this experiment. Elemental analysis of distillate fraction is carried out before the treatment as explained above. A known amount (50 ml) of distillate fraction is taken in 250 ml conical flasks. Washed biochar samples are added in the flasks containing distillate fractions at different concentrations (5 g and 10 g) in triplicates. The mouth of the flasks are closed airtight using parafilm to prevent evaporation of distillate and agitated at 300 rpm in a temperature controlled shaker for about 1 hour. The flasks are then removed from the shaker. Biochar added in the distillate fraction is removed through filtration and dried at room temperature. Treated distillate fraction is then used for elemental analysis.

Results: Middle distillate fraction treated with 5 g and 10 g of biochar showed 49% and 59% reduction in sulfur content when compared to the untreated distillate fraction (FIG. 7). This is further confirmed by checking the sulfur content of biochar used for the treatment of distillate fraction. Compared to the untreated biochar, the biochar used in 5 g and 10 g treatments for the removal of heteroatoms in the distillate fraction recorded 17% and 99% increase in sulfur content (FIG. 8). These results confirm the potential of biochar for the removal of heteroatoms such as sulfur from the distillate fractions.

Similarly the distillate fractions treated with 5 g and 10 g of biochar showed 12-15% reduction in nitrogen content when compared to the untreated distillate fraction (FIG. 9). This could be due to the type of biochar used in this experiment which is efficient in removing the sulfur from distillate fraction.

This investigation also confirms that the heteroatom removal efficiency vary greatly among different types of biochar. However, it is clear that biochar is utilized as a potential biocatalyst for the removal of impurities/heteroatoms such as nitrogen and sulfur from the biocrude and the distillate fractions.

Crude oil contains varying amounts of inorganic salts. The presence of such salts presents difficulties during crude oil processing such as corrosion of the oil processing equipment. In order to mitigate the effects of corrosion resulting from the presence of salts, it is advantageous to reduce the salt concentration to 3-5 ppm in crude oil. Salts such as magnesium chloride, sodium chloride and calcium chloride are present and generally range between 0.9 and 90 kgs per thousand barrels (140 tons) of crude. These salts are unstable at elevated temperatures. The salts present in the crude dissociate and the chloride ion hydrolyzes to form hydrochloric acid. HCl as well as organic acids which are present to varying degrees in the petroleum crude contribute to corrosion in the main fractionator unit and other regions of the refinery system where temperatures are elevated, and where water condenses.

In addition to sodium, magnesium and calcium salts, other metal salts such as potassium, nickel, vanadium, copper, iron and zinc may be found in various concentrations. These metals contribute to heat exchanger fouling, furnace coking, catalyst poisoning and end product degradation.

Example 08

A known amount of biocrude (2 ml) obtained from the freshwater alga Arthrospira platensis is added to 10 ml of deionized water in triplicate and mixed thoroughly for 20 minutes in a shaker. After vigorous mixing, the oil and water are separated. The deionized water is analyzed for changes in its salinity, TDS and electrical conductivity. After washing, there is 58-59 times increase in the TDS and conductivity of the water used for washing the biocrude.

The results obtained in the experiment clearly indicated, removal of salts from the biocrude by water washing (Table 15). These results confirm the possibility of using water for desalting applications in biocrude which is a pretreatment technique before blending with petrocrude.

TABLE 15 Desalting of biocrude obtained from the freshwater alga Arthrospira platensis using deionized water Conductivity Sample TDS (mg/L) Salinity (ppt) (μS/cm) Deionized water 4.91 13.16 7.72 Water quality after biocrude 288.6 287.5 455.7 washing

While this invention has been particularly shown and described with references to preferred embodiments thereof it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

1. A method for processing algal biomass comprising a marine algal strain or a freshwater (non-marine) algal strain or a plurality of marine algal strains or a plurality of freshwater (non-marine) algal strains or any combination thereof or other carbonaceous feedstock or any combination of algae/algae mixtures forming primary feedstock and carbonaceous feedstocks forming secondary feedstocks to produce biofuels and the method comprising:

(i) mixing said algal biomass along with another algal biomass or mixture of algae or said carbonaceous feedstock or mixtures of carbonaceous feedstock to produce a feedstock mixture;
(ii) subjecting said feedstock mixture containing algae/carbonaceous material to hydrothermal liquefaction or co-liquefaction to produce a biocrude;
(iii) pre-treating said biocrude and petrocrude with said renewable biocatalyst (biochar) to remove impurities and heteroatoms;
(iv) pretreating said biocrude and petrocrude by water washing for desalting;
(v) blending said biocrude with petrocrude;
(vi) pre-treating said biocrude-petrocrude blend with said renewable biocatalyst to remove impurities and heteroatoms;
(vii) distilling said biocrude-petrocrude blend to produce distillate fractions
(viii) treating said distillate fuel fractions derived from algal biocrude or blend of algal biocrude and petrocrude with said renewable biocatalyst to remove further impurities and heteroatoms;
(ix) Hydrotreating said distillate fractions to produce drop in fuels;
(x) recycling the recovered renewable catalyst
(xi) Utilising the recovered renewable catalyst as soil amendment for agricultural applications.
(xii) producing drop-in biofuels from algae, carbonaceous feedstocks and their mixtures through an INTEGRATED PROCESS/METHOD involving the following steps: [i] producing biocrude through Hydrothermal liquefaction/co-liquefaction;[ii] using of renewable biocatalyst (biochar) to remove heteroatoms in said biocrude/biocrude blend [iii] washing said biocrude/biocrude blend with water for desalting [iv] blending said biocrude and petrocrude for distillation [v] removing heteroatoms/impurities from said biocrude blend using said renewable biocatalyst [vi] removing said heteroatoms/impurities in distillate fractions obtained from said biocrude/biocrude blend using said renewable biocatalyst [vii] hydrotreating/upgradation of distillate fuel fractions to drop-in fuels and [viii] recycling of biocatalysts (biochar) for agricultural application.

2. The method of claim 1, wherein said hydrothermal liquefaction/co-liquefaction is carried out at a temperature of 250-350° C. for 5-30 min at 40-200 bar pressure

3. The method of claim 1, wherein said hydrothermal liquefaction/co-liquefaction is carried out using the feedstock mixture with 10-20% solids w/v.

4. The method of claim 01, wherein said algal biocrude and petrocrude blending ratio is selected from 1:9, 0.5:9.5, 1.5:8.5, 2:8, 2.5:7.5, 3:7, 3.5:6.5, 4:6, 4.5:5.5, 5:5, 5.5:4.5, 6:4, 6.5:3.5, 7:3, 610 7.5:2.5, 8:2, 8.5:1.5, 9:1 and 9.5:0.5.

5. The method according to claim 01, wherein said algal strains belong to the taxonomic classes of Chlorophyceae (Green algae), Cryptophyceae, Phaeophyceae (Brown algae), Rhodophyceae (Red algae), Xanthophyceae (Yellow-green algae), Dinophyceae, Bacillariophyceae (Diatoms), Chloromonadineae, Eugleniae, Chrysophyceae, and Cyanophyceae/Myxophyceae (Blue green algae or cyanobacteria)

6. The method according to claim 01, wherein said carbonaceous feedstocks is selected from a group of biosolids, yeast sludge, municipal sewage sludge, municipal solid waste (MSW), manures, lignite, coal, agricultural wastes, water hyacinth, duck weed and industrial wastes.

7. A method according to claim 01, wherein said feedstock mixture include: (i) specific strains of freshwater or marine algal biomass; (ii) specific carbonaceous feedstock alone;(iii) specific carbonaceous feedstock in combination with other carbonaceous feedstocks; (iv) specific strain of algae with the biomass derived from other algal strain; (v) specific strain of algae with the biomass derived from mixed culture of algae; (vi) specific strain of algae with a specific carbonaceous feedstock; (vii) specific strain of algae with a mixture of carbonaceous feedstocks; (viii) mixture of algae with a specific carbonaceous feedstock; and (xi) mixture of algae with mixture of carbonaceous feedstocks

8. The method according to claim 01, wherein said renewable biocatalyst is biochar.

9. The method according to claim 08, wherein said biochar is obtained from rice bran, peanut hull, manures, animal wastes, pressmud/filter cake, pine, saw dust, bagasse, coconut shell, coir pith, wheat straw, paddy straw, maize cobs and sugarcane trash.

10. The method according to claim 01, wherein said impurities include heteroatoms, such as N, O and S and salts.

11. The method according to claim 01, wherein said recovered renewable catalyst is used for agricultural applications.

12. The method according to claim 01, wherein said primary feedstock of algae or algal mixtures are mixed with said secondary feedstocks at a ratio selected from 90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80 and 10:90 for said hydrothermal co-liquefaction.

Patent History
Publication number: 20170198223
Type: Application
Filed: Jun 24, 2015
Publication Date: Jul 13, 2017
Inventors: Senthil Chinnasamy (Chennai), Sailendra Bhaskar (Chennai), Jeganathan Nallasivam (Chennai), Sachitra Kumar Ratha (Chennai), David M. Lewis (Maylands), Arunachalam Meenakshisundaram (Chennai), Melcureraj Lavanya (Chennai), Vaidhyanathan Selvavathi (Chennai)
Application Number: 15/315,723
Classifications
International Classification: C10G 1/06 (20060101); C10G 45/04 (20060101); C10G 31/08 (20060101); C10G 7/00 (20060101); C10G 1/00 (20060101); C10G 3/00 (20060101);