Thermochemical Processing of Algal Biomass

Abstract

A thermolysis process for treating algal biomass, consisting substantially of dried algal cells, in which the algal biomass is heated from ambient to 460° C. in a flowing stream that contains one or more of carbon dioxide, acetic acid or other organic acids and that produces a condensable hydrocarbon product whose mass yield is greater than the dry, ash-free mass fraction of lipids in the starting algal biomass and whose higher enthalpy of combustion exceeds 25 MJ/kg plus a char, and a hydrocarbon-laden gaseous product. In another feature, the present invention includes heating the previously dried, algal biomass in a readily available, waste acid gas, such as flue gas that is rich in carbon dioxide, or to intimately mix the algal biomass with a solid acid, such as a protonated, large pore zeolite, and then heating the mixture in a non-oxidizing sweep gas.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS

This patent application claims the benefit of provisional patent application No. 61/176,152, filed on May 7, 2009, which is incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISC AND AN INCORPORATION BY REFERENCE OF THE MATERIAL ON THE COMPACT DISC

None.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates generally to the production of fuels, chemicals, and soil amendments from biomass by means of thermolysis. More specifically, the invention relates to the acid-catalyzed thermolysis of algae.

(2) Description of the Related Art

The depletion of economically accessible petroleum and impending climate changes that follow from the accumulation of anthropogenic carbon dioxide in the atmosphere and the oceans, have motivated the search for carbon-neutral fuels that can be produced economically and domestically. Biomass, which derives its energy content from sunlight, and whose carbon comes from already oxidized carbon, promises to be a renewable feedstock from which to produce liquid fuels that can substitute for fuels derived currently from petroleum.

Aquatic microalgae are widely distributed organisms that accumulate carbon dioxide and nutrients from their environment into a material, algal biomass, which can be harvested (separated from the water). Algal biomass grows more rapidly than do terrestrial plants, as evidenced by much higher areal productivities. It has long been thought that algae, which can grow very rapidly compared to terrestrial plants, might be a suitable source of biomass from which to produce liquid fuels.

A much discussed route to convert algal biomass into liquid fuels is to extract lipids (plant fats), and to convert them into either biodiesel through transesterification with a light alcohol, or to hydrotreat the lipids to make what is termed “green” diesel. This route (oil extraction) leaves behind a large amount of protein and carbohydrate. In principle, that material can be employed as an animal feed, but comparison of the flows of mass to the fuel market with those to the feed market suggest that the feed market would be rapidly saturated once algae were converted routinely to renewable fuel by that process, generating a disposal problem rather than an economic opportunity. Moreover, each of those processes typically convert only a small (and, to date, uneconomic) fraction of the heating value of the algae into the heating value of the produced fuels—either because the target fraction (e.g. the lipids) is present at low concentration in the algae, or because the conversion process itself is not energy efficient, or both.

A second route, steam reforming, produces synthesis gas that can be converted, for example, by the Fischer Tropsch reaction, into fuel range hydrocarbons. However, this route requires an investment in energy (both the steam reforming reaction and the Fischer-Tropsch reactions are typically carried out at high pressure), and is not very carbon efficient because some of the input carbon is diverted back to carbon dioxide or light hydrocarbons, which are frequently disposed by flaring.

A third route, hydrothermal processing, produces a high yield of liquid hydrocarbon products, but also a large quantity of hydrocarbon-laden water that can present a disposal cost, and a dilution of some of the desired products.

A fourth route, pyrolysis, is very general but has previously been carried out at high temperatures that exacerbate the corrosivity of the products and necessitates the use of expensive, refractory reactors.

Other processes have also been explored, but none has yet offered compelling financial economics or attractive carbon efficiencies, despite research campaigns that seem to recrudesce about every thirty years. What is needed in the art is that the algal biomass-derived feed stocks be amenable to further refining together with conventional fuel feed stocks to take advantage of the existing capital investment in petroleum refining, and to make the algal biomass-derived fuel fungible with conventional petroleum-derived fuels. It is further desirable that any solid residuum from the production of the algal biomass-derived, liquid fuel feedstock also have economic value, for example as a solid fuel or as a soil amendment where minerals and heteroatoms (e.g., N, P) can be returned to the biosphere, albeit possibly in a different venue from which they came.

BRIEF SUMMARY OF THE INVENTION

A thermolysis process for treating algal biomass, consisting substantially of dried algal cells, in which the algal biomass is heated from ambient to 460° C. in a flowing stream that contains one or more of carbon dioxide, acetic acid or other organic acids and that produces a condensable hydrocarbon product whose mass yield is greater than the dry, ash-free mass fraction of lipids in the starting algal biomass and whose higher enthalpy of combustion exceeds 25 MJ/kg plus a char, and a hydrocarbon-laden gaseous product.

Another feature of the method of the present invention is heating the previously dried, algal biomass in a readily available, waste acid gas, such as flue gas that is rich in carbon dioxide, or to intimately mix the algal biomass with a solid acid, such as a protonated, large pore zeolite, and then heating the mixture in a non-oxidizing sweep gas.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a temperature profile, illustrated by a solid curve, employed in TGA/GC/MS experiments detailed in Examples 1 and 2, discussed below.

FIG. 2 shows chromatograms obtained at the sequence of the indicated sample temperatures (100° C., 290° C., 460° C.) in Example 1 during the thermolysis of a sample of algal biomass heated along the ramp shown in FIG. 1 in a flowing stream consisting of 66.7 mol % CO₂ and 33.3 mol % N₂.

FIG. 3 shows an expanded view of a chromatogram obtained in Example 1 of the gas stream produced during the TGA/GC-MS experiment, sampled at 50° C.

FIG. 4 compares the expanded chromatograms obtained in Example 1 at 100° C. during the thermolysis of a sample of algal biomass heated along the temperature trajectory shown in FIG. 1 in a flowing stream consisting either of pure N₂, as illustrated by a light weight curve or of 66.7 mol % CO₂ and 33.3 mol % N₂, as illustrated by a heavy weight curve.

FIG. 5 shows chromatograms obtained in Example 1 at the indicated sequence of sample temperatures (100° C., 290° C. and 560° C.) during the thermolysis of a sample of algal biomass intimately mixed with H-ZSM-5 heated according to the temperature ramp shown in FIG. 1 in a flowing stream consisting of 66.7 mol % CO₂ and 33.3 mol % N₂. The effluent stream from the sample was analyzed with the aid of a GC/MS at the end of the soak periods or when the temperature first reached the indicated value during the ramp periods.

FIG. 6 compares chromatograms obtained in Example 2 at 50° C. heated according to the temperature trajectory shown in FIG. 1 during the thermolysis in a flowing stream consisting of 66.7 mol % CO₂ and 33.3 mol % N₂ of a sample of algal biomass, as illustrated by a heavy curve, and another sample that had been previously, intimately mixed with H-ZSM-5, as illustrated by a light curve.

FIG. 7 is a schematic diagram of a process in which the thermolysis of algal biomass is integrated with the flue gas and waste heat from an industrial process.

FIG. 8 shows the temperature trajectory followed and the evolution of thermolysis products from the experiment described in Example 3, discussed below.

DETAILED DESCRIPTION OF THE INVENTION

The process of the present invention includes thermolysis that can be carried out at temperatures less than 460° C. when assisted by the presence of carbon dioxide or a solid acid catalyst. In one advantageous embodiment, dry biomass consisting substantially of algal cells is contacted in the absence of additional catalysts with a stream of hot gas containing carbon dioxide. In another advantageous embodiment, dry biomass is intimately mixed with a solid acid catalyst, such as H-ZSM-5, for example, and then contacted with a stream of hot gas. The hot gas may be carbon dioxide, diluted carbon dioxide, or any other suitable hot gas. The different advantageous embodiments provide a process that evolves thermolysis products at temperatures below 100° C. and even as low as 50° C. in the presence of a solid acid catalyst. As will be seen from the examples below, the thermolysis products span compositions that are different from those seen in the pyrolysis of cellulosic biomass. The high heating value of the oily product is an advantageous result in view of much lower values typically found for pyrolysis products from cellulose (Table 1).

TABLE 1
Comparison of the specific heating values of
petrofuels and some biofuels:
Material                       HHV/MJ kg−1
Algae derived thermolysis-oilc 36
Crude petroleum                45-48
Jet fuel (minimum)             43
Refined biodiesel              38
Wood-derived py-oil            ~20

Because both CO₂-assisted and solid acid-catalyzed thermolysis of algal biomass occur at comparatively low temperatures, a process deploying either embodiment can be integrated with an industrial facility to employ heat that would otherwise be wasted and/or deoxygenated flue gas from a combustion process that would otherwise be vented. A schematic of a process flow is shown in FIG. 7. Algae are grown in helioreactors (738), harvested continuously via flocculation (734) and pressed to remove bulk water (736). The partially dried algae are conveyed to a drying kiln (730) that can be heated using hot flue gas from the industrial partner. The temperature and flow rate of the flue gas is lowered by mixing a stream of gas from the flue (724), throttled by valve (728) and mixing the hot gas with ambient air whose inlet flow rate is controlled by the air mixing valve (732). The gases are drawn by the action of the induction fan (718) through the drying kiln and through the particle separator (720) and then a cooled in heat exchanger 722. The now dry algae are conveyed to Kiln 710 where they are treated with hot, gas that has been deoxygenated by reaction with thermolysis char in kiln (714) and cooled in heat exchanger (712). The treated char is accumulated in storage vessel (716). The volatile products of thermolysis are condensed by passage through heat exchanger (702) and the condensibles are collected in storage vessel (704). The char is collected in vessel 706 before it is transferred to the inlet of the deoxygenation kiln (704). The hot thermolysis gas and the volatile products are transported through the kilns and heat exchangers by means of the induction fan (708), which also transports the noncondensable products of thermolysis to a flare (726) where they can be safely combusted. Because this process reuses heat from the industrial partner, there could be an allowance for the carbon dioxide that would have been produced had, instead, a carbon-based fuel been combusted to supply that heat.

Example 1

A small quantity of unwashed algal biomass, about 30 mg was placed in the pan of a thermal gravimetric balance. The gas outlet of the TGA was connected via heat-traced stainless steel tubing to a 6-port sampling valve mounted on the inlet to an HP5890 gas chromatograph equipped with a capillary column and an HP mass selective detector. Either N₂ or a mixture of 66.7 mol % CO₂ plus 33.3% N₂ was flowed through the heated chamber at about 100 ml/min. The sample was then heated according to the trajectory shown in FIG. 1. When the sample had been heated to the temperatures indicated in FIG. 2, constant volume samples of the effluent stream were injected into the GC/Ms through the approximately 1 ml loop attached to the 6-port sampling valve. The identity of the eluted compounds was determined by comparing the cracking pattern of the mass spectrogram of each peak against spectra drawn from the library of the instrument.

FIG. 1 depicts the weight losses in Example 1 by a sample of algae heated in either pure nitrogen, as illustrated by a short dashed curve or in a mixture consisting of 66.7% CO₂ and 33.7% N₂, as illustrated by a long dashed curve. As indicated in FIG. 1, the sample heated in the gas stream that contained carbon dioxide lost more weight than did the sample heated in the stream containing only dinitrogen. Buoyancy effects are suppressed in this presentation of the data because we normalized the initial weights of the samples (also measured in the reaction gases) to 100%.

The effluent stream obtained in Example 1 from the sample was analyzed with the aid of a GC/MS at the end of the soak periods or when the temperature first reached the indicated value during the ramp periods.

At the end of the first 50° C. soak period, the gas stream consisted of the compounds listed in Table 2, which eluted through the GC at times and in amounts illustrated in FIG. 3. In particular, four compounds, which appeared at this low temperature at significantly greater abundance when the sweep gas contained CO₂ than when the sweep gas was pure N₂, include indole, methylindole, trimethyl-bicyclo[3.1.1]heptanes, and propylcyclohexanol.

In Table 2, shown below, are compounds identified in the GC/MS chromatogram of the TGA effluent from an algae sample treated in 60 ml/min CO₂—F30 ml/min N₂ flow gas sampled at 50° C. In FIG. 3, the numbers labeling the peaks correspond to the compounds listed in Table 2, depicted below.

Peak #	RT/min	Compounds	Formula
301	4.681 to 4.754	Pyrrolidinedione	C4H5NO2
302	5.177 to 5.236	Butenoic acid, ethyl ester	C6H10O2
303	5.604 to 5.691	Indole	C8H7N
304	6.041 to 6.119	Methyl-1H-Indole	C9H9N
305	7.806 to 7.833	TrimethylBicyclo[3.1.1]heptane,	C10H18
306	7.961 to 7.997	Propylcyclohexanol	C9H18O

Identifications of the compounds represented by peaks in the chromatographic analysis of the TGA effluent for this sample at successive temperatures along the trajectory shown in FIG. 1 are presented in Tables 3-9.

Table 3, shown below, is a GC/MS chromatogram of the TGA effluent from an algae sample treated in 60 ml/min CO₂+30 ml/min N₂ flow gas sampled at 100° C. Entries in italics (Peaks 407-410) describe compounds that did not appear at 50° C. In FIG. 4, the numbers labeling the peaks correspond to the compounds listed in Table 3, depicted below.

Peak #	RT/min	Compounds	Formula
401	4.681 to 4.754	2,5-Pyrrolidinedione	C4H5NO2
402	5.177 to 5.236	2-Butenoic acid, ethyl ester	C6H10O2
403	5.604 to 5.691	Indole	C8H7N
403	6.041 to 6.119	Methyl-1H-Indole	C9H9N
405	7.806 to 7.833	trimethyl-bicyclo[3.1.1]heptane	C10H18
406	7.961 to 7.997	2-Propylcyclohexanol	C9H18O
407	4.789 to 4.844	1,2,4-Triazine-3,5(2H,4H)-dione	C3H3N3O2
408	6.491 to 6.532	2,4,6-trimethyl-Benzonitrile,	C10H11N
409	6.536 to 6.563	2,7-dimethyl-Indolizine,	C10H11N
410	7.955 to 8.001	3,7,11,15-Tetramethyl-2-hexadecen-1-ol	C20H40O

Table 4, shown below, is a GC/MS chromatogram of the TGA effluent from an algae sample treated in 60 ml/min CO₂+30 ml/min N₂ flow gas sampled at 200° C. Entries in italics (Peaks 11-12) describe compounds that did not appear at 100° C.

Peak #	RT/min	Compounds	Formula
1	4.681 to 4.754	2,5-Pyrrolidinedione	C4H5NO2
2	5.177 to 5.236	2-Butenoic acid, ethyl ester, (E)-	C6H10O2
3	5.604 to 5.691	Indole	C8H7N
4	6.041 to 6.119	Methyl-1H-Indole	C9H9N
5	7.806 to 7.833	trimethyl-,Bicyclo[3.1.1]heptane	C10H18
6	7.961 to 7.997	2-Propylcyclohexanol	C9H18O
7	4.789 to 4.844	1,2,4-Triazine-3,5(2H,4H)-dione	C3H3N3O2
8	6.491 to 6.532	2,4,6-trimethyl-Benzonitrile,	C10H11N
9	6.536 to 6.563	Indolizine, 2,7-dimethyl-	C10H11N
10	7.955 to 8.001	3,7,11,15-Tetramethyl-2-	C20H40O
		hexadecen-1-ol
11	5.037 to 5.142	Dodecane	C12H26
12	5.933 to 5.979	1,2-dihydro-1,1,6-trimethyl	C13H16
		Naphthalene

Table 5, shown below, is a GC/MS chromatogram of the TGA effluent from a sample of algal biomass treated in 60 ml/min CO₂+30 ml/min N₂ flow gas sampled at 290° C. Entries in italics (Peaks 13-15) describe compounds that did not appear at 200° C.

	Retention
Peak #	Time/min	Compounds	Formula
1	4.681 to 4.754	2,5-Pyrrolidinedione	C4H5NO2
2	5.177 to 5.236	2-Butenoic acid, ethyl ester, (E)-	C6H10O2
3	5.604 to 5.691	Indole	C8H7N
4	6.041 to 6.119	Methyl-1H-Indole	C9H9N
5	7.806 to 7.833	2,6,6-trimethyl-bicyclo[3.1.1]heptane,,	C10H18
6	7.961 to 7.997	2-Propylcyclohexanol	C9H18O
7	4.789 to 4.844	1,2,4-Triazine-3,5(2H,4H)-dione	C3H3N3O2
8	6.491 to 6.532	Benzonitrile, 2,4,6-trimethyl-	C10H11N
9	6.536 to 6.563	Indolizine, 2,7-dimethyl-	C10H11N
10	7.955 to 8.001	3,7,11,15-Tetramethyl-2-hexadecen-1-ol	C20H40O
11	5.037 to 5.142	Dodecane	C12H26
12	5.933 to 5.979	Naphthalene, 1,2-dihydro-1,1,6-trimethyl	C13H16
13	6.064 to 6.109	1H-Indole, 3-methyl-	C9H9N
14	6.310 to 6.341	Dodecane	C12H26
15	7.274 to 7.324	Dodecane	C12H26

Table 6, shown below, is a GC/MS chromatogram of the TGA effluent from an algae sample treated in 60 ml/min CO₂+30 ml/min N₂ flow gas sampled at 460° C. Entries in italics (Peaks 13, 16-38) describe compounds that did not appear at 290° C.

Peak #	RT/min	Compounds	Formula
3	5.604 to 5.691	Indole	C8H7N
5	7.806 to 7.833	2,6,6-trimethyl-	C10H18
		Bicyclo[3.1.1]heptane
6	7.961 to 7.997	2-Propylcyclohexanol	C9H18O
13	6.064 to 6.109	3-methyl-1H-Indole	C9H9N
16	1.383 to 1.501	Pentane	C5H12
17	2.515 to 2.606	Toluene	C7H8
18	2.656 to 2.707	Cyclooctane	C8H16
19	2.711 to 2.797	2,4-dimethyl-Heptane	C9H20
20	4.417 to 4.485	3-methyl-Phenol,	C7H8O
21	4.517 to 4.567	Cyclododecane	C12H24
22	4.567 to 4.617	Dodecane	C12H26
23	5.049 to 5.085	1-methyl-2-octyl-	C12H24
		Cyclopropane
24	5.085 to 5.122	Dodecane	C12H26
25	5.536 to 5.568	1-Tridecene	C13H26
26	5.581 to 5.604	Dodecane	C12H26
27	5.827 to 5.863	4-Decene	C10H20
28	6.004 to 6.032	2-Tetradecene	C14H28
29	6.036 to 6.063	Dodecane	C12H26
30	5.931 to 5.963	Dodecane	C12H26
31	6.291 to 6.314	Dodecane	C12H26
32	6.314 to 6.341	Dodecane	C12H26
33	6.441 to 6.468	1-Pentadecene	C15H30
34	6.473 to 6.500	Dodecane	C12H26
35	6.859 to 6.882	1-Hexadecene	C16H32
36	6.882 to 6.909	Dodecane	C12H26
37	7.273 to 7.371	Dodecane	C12H26
38	7.401 to 7.428	Z-5-Nonadecene	C19H38

Table 7, shown below, is a GC/MS chromatogram of the TGA effluent from an algae sample treated in 60 ml/min CO₂+30 ml/min N₂ flow gas sampled when cooled to 350° C. Entries in italics (Peaks 39-46) describe compounds that did not appear at 460° C.

Peak #	RT/min	Compounds	Formula
3	5.621 to 5.661	Indole	C8H7N
13	6.064 to 6.109	3-methyl-1H-Indole	C9H9N
33	6.445 to 6.463	1-Pentadecene	C15H30
34	6.472 to 6.495	Dodecane	C12H26
35	6.850 to 6.882	1-Hexadecene	C16H32
36	6.882 to 6.909	Dodecane	C12H26
37	7.273 to 7.371	Dodecane	C12H26
38	7.401 to 7.428	Z-5-Nonadecene	C19H38
39	3.852 to 3.980	Phenol	C6H6O
40	4.303 to 4.380	2-methyl-Phenol	C7H8O
41	4.407 to 4.526	4-methyl-Phenol	C7H8O
42	4.685 to 4.730	2,5-Pyrrolidinedione	C4H5NO2
43	4.835 to 4.885	2,4-dimethyl-Phenol	C8H10O
44	4.903 to 4.971	4-ethyl-Phenol	C8H10O
45	7.250 to 7.273	3-Heptadecene, (Z)-	C17H34
46	7.396 to 7.437	3,7,11-trimethyl-1-	C15H32O
		Dodecanol

Example 2

Algal biomass was comminuated with a commercial sample of H-ZSM-5 powder. A small quantity of that mixture or the algal biomass alone, about 30 mg in each case, was placed in the pan of a thermal gravimetric balance. The gas outlet of the TGA was connected via heat-traced stainless steel tubing to a 6-port sampling valve of an HP5890 gas chromatograph equipped with a capillary column and an HP mass selective detector. The samples were heated according to the temperature trajectory shown in FIG. 1 while contacted with a 90 ml/min flow of N₂. When the sample had been heated to 50° C., 100° C., 200° C., 290° C. and 460° C., constant volume samples of the effluent stream were injected into the GC/Ms through an approximately 1 ml loop attached to the 6-port sampling valve. The full chromatograms are shown in FIG. 5 at the indicated temperatures. The identity of the eluted compounds was determined by comparing the cracking pattern of the mass spectrogram of each peak against spectra drawn from the library of the instrument.

At the end of the first 50° C. soak period, the gas stream consisted of the compounds listed in Table 8. All twelve of the peaks listed in Table 8 appeared at this low temperature only when the sample contained the acid catalyst, in this example.

In Table 8, shown below, are compounds identified in the GC/MS chromatogram shown in FIG. 6 of the TGA effluent in Example 2 from an algal biomass and algal biomass+zeolite samples treated in 90 ml/min of N₂, sampled at 50° C. In FIG. 6, the numbers labeling the peaks correspond to the compounds listed in Table 8, depicted below.

	Peak #:	RT (min)	Compounds	Formula
	601	4.345 to 4.545	Phenol, 4-methyl-	C7H8O
	602	4.691 to 4.754	2,5-Pyrrolidinedione	C4H5NO2
	603	4.841 to 4.895	2,4-dimethyl-Phenol	C8H10O
	604	4.900 to 4.973	4-ethyl-Phenol	C8H10O
	605	5.623 to 5.664	Indole	C8H7N
	606	6.064 to 6.105	4-methyl-1H-Indole,	C9H9N
	607	6.856 to 6.883	Cyclohexadecane	C16H32
	608	6.883 to 6.956	Dodecane	C12H26
	609	7.081 to 7.115	Dodecane	C12H26
	610	7.256 to 7.279	3-Heptadecene, (Z)-	C17H34
	611	7.279 to 7.306	Dodecane	C12H26
	612	7.816 to 7.838	Phytol	C20H40O

Table 9, shown below, lists compounds identified in the GC/MS chromatogram of the TGA effluent from an algal biomass and algal biomass+zeolite samples treated in 90 ml/min of N₂, sampled at 100° C. Lines in italics (Peaks 13-14) describe compounds that did not appear at 50° C.

Peak	RT (min)	Compounds	Formula
1	4.345 to 4.545	Phenol, 4-methyl-	C7H8O
2	4.691 to 4.754	2,5-Pyrrolidinedione	C4H5NO2
3	4.841 to 4.895	Phenol, 2,4-dimethyl-	C8H10O
4	4.900 to 4.973	Phenol, 4-ethyl-	C8H10O
5	5.623 to 5.664	Indole	C8H7N
6	6.064 to 6.105	1H-Indole, 4-methyl-	C9H9N
7	6.856 to 6.883	Cyclohexadecane	C16H32
8	6.883 to 6.956	Dodecane	C12H26
9	7.081 to 7.115	Dodecane	C12H26
10	7.256 to 7.279	3-Heptadecene, (Z)-	C17H34
11	7.279 to 7.306	Dodecane	C12H26
12	7.816 to 7.838	Phytol	C20H40O
13	7.392 to 7.433	1-Heptene, 2-isohexyl-	C14H28
		6-methyl-
14	7.956 to 7.988	3,7,11,15-Tetramethyl-2-	C20H40O
		hexadecen-1-ol

Table 10, shown below, lists compounds identified in the GC/MS chromatogram of the TGA effluent from an algae and algae+zeolite samples treated in 90 ml/min of N₂, sampled at 200° C. Lines in italics (Peaks 15-19) describe compounds that did not appear at 100° C.

Peak	Retention
#:	Time (min)	Compounds	Formula
1	4.345 to 4.545	Phenol, 4-methyl-	C7H8O
2	4.691 to 4.754	2,5-Pyrrolidinedione	C4H5NO2
3	4.841 to 4.895	Phenol, 2,4-dimethyl-	C8H10O
4	4.900 to 4.973	Phenol, 4-ethyl-	C8H10O
5	5.623 to 5.664	Indole	C8H7N
6	6.064 to 6.105	1H-Indole, 4-methyl-	C9H9N
7	6.856 to 6.883	Cyclohexadecane	C16H32
8	6.883 to 6.956	Dodecane	C12H26
9	7.081 to 7.115	Dodecane	C12H26
10	7.256 to 7.279	3-Heptadecene, (Z)-	C17H34
11	7.279 to 7.306	Dodecane	C12H26
12	7.816 to 7.838	Phytol	C20H40O
13	7.392 to 7.433	1-Heptene, 2-isohexyl-6-methyl-	C14H28
14	7.956 to 7.988	3,7,11,15-Tetramethyl-2-	C20H40O
		hexadecen-1-ol
15	5.182 to 5.218	1,4:3,6-Dianhydro-.alpha.-d-	C6H8O4
		glucopyranose
16	5.241 to 5.273	Phenol, 2-ethyl-6-methyl-	C9H12O
17	5.296 to 5.332	Benzene, 1-ethyl-4-methoxy-	C9H12O
18	7.606 to 7.652	1-Octadecene	C18H36
19	7.652 to 7.697	Dodecane	C12H26

Table 11, shown below, lists compounds identified in the GC/MS chromatogram of the TGA effluent from an algal biomass and algal biomass+zeolite samples treated in 90 ml/min of N₂, sampled at 290° C. Lines in italics (Peaks 20-29) describe compounds that did not appear at 200° C.

Peak	RT (min)	Compounds	Formula
1	4.419 to 4.519	Phenol, 4-methyl-	C7H8O
2	4.664 to 4.746	2,5-Pyrrolidinedione	C4H5NO2
3	4.841 to 4.895	Phenol, 2,4-dimethyl-	C8H10O
4	4.900 to 4.973	Phenol, 4-ethyl-	C8H10O
5	5.623 to 5.664	Indole	C8H7N
6	6.064 to 6.105	1H-Indole, 4-methyl-	C9H9N
8	6.883 to 6.907	Dodecane	C12H26
9	7.081 to 7.115	Dodecane	C12H26
10	7.256 to 7.279	3-Heptadecene, (Z)-	C17H34
11	7.279 to 7.306	Dodecane	C12H26
12	7.816 to 7.838	Phytol	C20H40O
13	7.392 to 7.433	1-Heptene, 2-isohexyl-6-methyl-	C14H28
14	7.956 to 7.988	3,7,11,15-Tetramethyl-2-hexadecen-1-ol	C20H40O
15	5.182 to 5.218	1,4:3,6-Dianhydro-.alpha.-d-glucopyranose	C6H8O4
16	5.237 to 5.269	Phenol, 2-ethyl-6-methyl-	C9H12O
17	5.296 to 5.332	Benzene, 1-ethyl-4-methoxy-	C9H12O
18	7.606 to 7.652	1-Octadecene	C18H36
19	7.652 to 7.697	Dodecane	C12H26
20	1.585 to 2.190	Acetic acid	C2H4O2
21	2.435 to 2.499	Pyridine	C5H5N
		Pyrrole	C4H5N
22	2.513 to 2.563	Toluene	C7H8
23	2.631 to 2.708	Propanoic acid, 2-oxo-, methyl ester	C4H6O3
24	4.746 to 4.773	Benzene, (2-methyl-1-propenyl)-	C10H12
25	5.933 to 5.979	Naphthalene, 1,2-dihydro-1,1,6-trimethyl	C13H16
26	6.493 to 6.520	Ethaneperoxoic acid, 1-cyano-1-(2-methyl	C12H13NO3
27	6.529 to 6.570	1H-Indole, 2,5-dimethyl-	C10H11N
28	6.857 to 6.884	3-Hexadecene, (Z)-	C16H32
		7-Hexadecene, (Z)-	C16H32
29	7.207-7.230	3-Heptadecene, (Z)-	C17H34

Table 12, shown below, lists compounds identified in the GC/MS chromatogram of the TGA effluent from an algae and algae+zeolite samples treated in 90 ml/min of N₂, sampled at 460° C. Entries in italics (Peaks 30-44) describe compounds that did not appear at 390° C.

Peak	RT (min)	Compounds	Formula
1	4.419 to 4.519	Phenol, 4-methyl-	C7H8O
5	5.623 to 5.664	Indole	C8H7N
6	6.064 to 6.105	1H-Indole, 4-methyl-	C9H9N
10	7.253 to 7.275	3-Heptadecene, (Z)-	C17H34
11	7.279 to 7.306	Dodecane	C12H26
12	7.816 to 7.838	Phytol	C20H40O
14	7.956 to 7.988	3,7,11,15-Tetramethyl-2-	C20H40O
		hexadecen-1-ol
18	7.606 to 7.652	1-Octadecene	C18H36
19	7.652 to 7.697	Dodecane	C12H26
22	2.499 to 2.581	Toluene	C7H8
30	1.908 to 1.999	Benzene	C6H6
31	3.141 to 3.181	Ethylbenzene	C8H10
32	3.186 to 3.241	p-Xylene	C8H10
33	3.341 to 3.400	Styrene	C8H8
		Xylene	C8H10
34	3.796 to 3.832	Benzene, 1-ethyl-2-methyl-	C9H12
35	3.987 to 4.023	Benzene, 1,3,5-trimethyl-	C9H12
36	4.319 to 4.355	Benzene, 1-propynyl-	C9H8
37	4.787 to 4.887	Benzyl nitrile	C8H7N
38	4.901 to 4.937	Benzene, (1-methyl-2-	C10H10
		cyclopropen-1-yl)-
39	4.937 to 4.969	2-Methylindene	C10H10
40	5.078 to 5.110	Dodecane	C12H26
41	5.110 to 5.160	Naphthalene	C10H8
42	5.656 to 5.711	Naphthalene, 2-methyl-	C11H10
43	6.311 to 6.343	Dodecane	C12H26
44	6.470 to 6.493	Dodecane	C12H26

Table 13, shown below, lists compounds identified in the GC/MS chromatogram of the TGA effluent from an algal biomass and algal biomass+zeolite samples treated in 90 ml/min of N₂, sampled at 350° C. Entries in italics (Peaks 46-51) described compounds that did not appear at 460° C.

Peak	RT (min)	Compounds	Formula
1	4.419 to 4.519	Phenol, 4-methyl-	C7H8O
2	4.664 to 4.746	2,5-Pyrrolidinedione	C4H5NO2
3	4.841 to 4.895	Phenol, 2,4-dimethyl-	C8H10O
4	4.900 to 4.973	Phenol, 4-ethyl-	C8H10O
5	5.623 to 5.664	Indole	C8H7N
6	6.064 to 6.105	1H-Indole, 4-methyl-	C9H9N
10	7.253 to 7.275	3-Heptadecene, (Z)-	C17H34
11	7.279 to 7.306	Dodecane	C12H26
12	7.816 to 7.838	Phytol	C20H40O
13	7.392 to 7.433	1-Heptene, 2-isohexyl-6-methyl-	C14H28
14	7.956 to 7.988	3,7,11,15-Tetramethyl-2-hexadecen-1-ol	C20H40O
41	5.110 to 5.160	Naphthalene	C10H8
42	5.656 to 5.711	Naphthalene, 2-methyl-	C11H10
45	3.852 to 3.984	Phenol	C6H6O
46	5.184 to 5.239	1,4:3,6-Dianhydro-.alpha.-d-glucopyranos	C6H8O4
		Benzofuran, 2,3-dihydro-	C8H8O
47	5.339 to 5.398	Benzenepropanenitrile	C9H9N
48	6.126 to 6.158	Amobarbital	C11H18N2O3
49	6.176 to 6.212	Pentobarbital	C11H18N2O3
50	6.444 to 6.467	1-Pentadecene	C15H30
51	6.472 to 6.499	Dodecane	C12H26

Example 3

A preparatory scale reactor constructed from a vertical alumina tube (7 cm OD) placed in the center of an electrically heated tube furnace was loaded with approximately 200 g of algal biomass and then connected to a gas cylinder. The gas cylinder permitted the interior of the vertical alumina tube to be swept with carbon dioxide that had bubbled at ambient temperature through an aqueous solution of 5% acetic acid and then in to the reactor tube at a flow rate of 0.2 standard L/min. The effluent from the reactor was directed into a glass receiver whose outside walls were cooled in an ice bath. The temperature of the reactor tube was ramped to 400° C., as shown in FIG. 8, and maintained at that temperature for 100 minutes, with CO₂ flowing at 45 ml/min. Approximately 100 ml of oily/waxy material was collected, from which was estimated a mass yield of 27 wt % in the oil fraction. During the heating, the nature of the effluent from the heated tube changed as indicated in Table 14.

Table 14, shown below, shows changes in the character of the effluent from the preparatory scale reactor as the reaction temperature increases.

Marker shown
in FIG. 8 Character of the reactor effluent stream
802       Smoke starts to appear
804       Smoke stops evolving
806       Clear liquid commences to collect in the chilled receiver
          vessel.
808       White smoke appears in the receiver and flows out of the
          receiver
810       Yellow smoke starts to fill the receiver and a yellow wax
          collects on the sides of the receiver
812       An orange liquid starts to collect in the receiver as a
          dense vapor
814       A thick, dark brown tar collects in the rceiver

Analysis of the initial algal biomass showed a lipid content of 3.5%. Subsequently, the enthalpy of combustion of the oil/wax was measured in a bomb calorimeter and found to be 36 MJ/kg, with a sulfur content of 0.22%.

There are many advantages to the method of the present invention. This invention is directed at obtaining feed stocks from which to prepare liquid fuels from a renewable source, such as algal biomass that grows rapidly, with little impact on available water or food resources.

The different advantageous embodiments provide a process that converts biomass, consisting substantially of whole, dry algae cells, into an oily material that exhibits a heating value approximating that of petroleum, along with a solid carbonaceous char, a hydrocarbon-laden gas stream, and an aqueous stream that contains polar organic compounds.

In an advantageous embodiment, the algal biomass can be processed into the feedstock with a net decrease in carbon dioxide emissions, for example by using carbon dioxide and heat from an existing process that would otherwise be wasted. The process of the present invention converts a broad range of microalgae and the co-harvested micro-organisms, referred to as algal biomass, into three products: a hydrocarbon-laden gas, a carbonaceous char, a new oily material that exhibits many of the characteristics of crude petroleum, and an aqueous stream that dissolves polar compounds. The process produces significant quantities of oily product from algal biomass that does not contain high concentrations of lipids. Therefore, the process can be applied even to algal biomass that has not been selected or nurtured to generate lipids.

The thermolysis produces a range of products that commence to evolve at unexpectedly low temperatures—as low as 50° C., i.e., hundreds of degrees lower than the temperatures at which cellulosic biomass must be heated to produce pyrolysis oils. The temperature range of the thermolysis of the algal biomass is low enough that the process can be carried out using waste heat generated by other industrial processes, for example cement manufacturing. The low temperature processing confers an economic advantage and offers a possible route to so-called carbon credits for the partner industry. Moreover, the oily material derived from the algae has an unexpectedly high enthalpy of combustion—around 36 MJ/kg, which approaches the heating value of petroleum (ca. 44 MJ/kg) and is about twice as large as the heating value of pyrolysis oils derived from cellulosic biomass (ca. 20 MJ/kg).

In addition, the algal biomass-derived oily material can constitute more than 15 wt % of the original, ash-free, dry weight of the algae, even for starting material that contains less than 5 wt % lipids. Finally, the composition of the algal biomass-derived oily material suggests that it would be amenable to subsequent processing along side conventional petroleum-derived gas oil, unlike pyrolysis oils derived from cellulosic biomass. For example, the elemental analyses performed, and the heating value mentioned above, provide an inference that the oily material from the described thermolysis of algal biomass presents fewer oxygen-containing components than does cellulose-derived pyrolysis oil, along with a concentration of sulfur that is low enough to be considered for blending into low sulfur feed stocks, yet high enough to maintain the activity of conventional hydroprocessing catalysts.

These conventional hydroprocessing catalysts can be used in conventional refinery processes to hydro-upgrade the oily material, for example to remove nitrogen, metals, and oxygen heteroatoms.

Claims

1. A thermolysis process for treating algal biomass, consisting substantially of dried algal cells, in which the algal biomass is heated from ambient to 460° C. in a flowing stream that contains one or more of carbon dioxide, acetic acid or other organic acids and that produces a condensable hydrocarbon product whose mass yield is greater than the dry, ash-free mass fraction of lipids in the starting algal biomass and whose higher enthalpy of combustion exceeds 25 MJ/kg plus a char, and a hydrocarbon-laden gaseous product.

2. A thermolysis process for treating algal biomass, consisting substantially of dried algal cells, in which the algal biomass is intimately mixed with a solid acid catalyst and is heated from ambient to 460° C. in a flowing gas stream that produces a condensable hydrocarbon product whose mass yield is greater than the dry, ash-free mass fraction of lipids in the starting algal biomass and whose higher enthalpy of combustion exceeds 25 MJ/kg, plus a char, and a hydrocarbon-laden gaseous product.

3. The process of claim 1 in which the thermolysis products are collected fractionally as the temperature of the biomass increases.

4. The process of claim 2 in which the thermolysis products are collected fractionally as the temperature of the biomass increases.

5. The process of claim 1 in which the condensed product stream contains:

a. Indole;

b. Methyl indole;

c. Succinimide;

d. Propylcyclohexanol;

e. Dodecane;

f. Dodecene;

g. Tridecene;

h. Pentadecene;

i. Heptadecene;

j. Nonadecene; and

k. at least 0.1 wt % sulfur.

6. The process of claim 2 in which the condensed product stream contains:

a. Methylphenol;

b. Indole;

c. Methylindole;

d. Dimethylphenol;

e. Ethylphenol;

f. Succinimide;

g. Propylcyclohexanol;

h. Trimethylbicycloheptane;

i. Succinimide;

j. Propylcyclohexanol;

k. Trimethylbicycloheptane;

I. Dodecane;

m. Pentadecene;

n. Heptadecene;

o. Phytol;

p. Amobarbital;

q. Pentobarbital; and

r. at least 0.1 wt % sulfur.

7. The process of claim 1 in which condensed product fractions produced at temperatures less than or equal to 50° C. contain:

a. Indole;

b. Methylindole;

c. Succinimide;

d. Propylcyclohexanol; and

e. Trimethylbicycloheptane

8. The process of claim 2 in which condensed product fractions produced at temperatures less than or equal to 50° C. contain:

a. Methylphenol;

b. Indole;

c. Methylindole;

d. Dimethylphenol;

e. Ethylphenol;

f. Succinimide;

g. Propylcyclohexanol;

h. Trimethylbicycloheptane;

i. Dodecane;

j. Heptadecene; and

k. Phytol

9. The process of claim 1 in which the temperature of the algal biomass is raised using waste heat from an industrial process.

10. The process of claim 2 in which the temperature of the algal biomass is raised using waste heat from an industrial process.

11. The process of claim 1 in which the sweep gas comes from the flue gas of another industrial process and is deoxygenated by reacting it with the char produced in the process of claim 1.

12. The process of claim 2 in which the sweep gas comes from the flue gas of another industrial process and is deoxygenated by reacting it with the char produced in the process of claim 2.

13. The process integration of claim 9 in which the partner industrial process receives greenhouse gas credits in proportion to the fuel whose heat has been used to thermolyze the algal biomass.

14. The process integration of claim 10 in which the partner industrial process receives greenhouse gas credits in proportion to the fuel whose heat has been used to thermolyze the algal biomass.

15. The process integration of claim 11 in which the partner industrial process receives greenhouse gas credits in proportion to the fuel whose heat has been used to thermolyze the algal biomass.

16. The process integration of claim 12 in which the partner industrial process receives greenhouse gas credits in proportion to the fuel whose heat has been used to thermolyze the algal biomass.