Patent Application
20100282588
None.
None.
(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.
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.
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).
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
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
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
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
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
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
407
4.789 to 4.844
1,2,4-Triazine-3,5(2H,4H)-dione
C
3
H
3
N
3
O
2
408
6.491 to 6.532
2,4,6-trimethyl-Benzonitrile,
C
10
H
11
N
409
6.536 to 6.563
2,7-dimethyl-Indolizine,
C
10
H
11
N
410
7.955 to 8.001
3,7,11,15-Tetramethyl-2-hexadecen-1-ol
C
20
H
40
O
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.
11
5.037 to 5.142
Dodecane
C
12
H
26
12
5.933 to 5.979
1,2-dihydro-1,1,6-trimethyl
C
13
H
16
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.
13
6.064 to 6.109
1H-Indole, 3-methyl-
C
9
H
9
N
14
6.310 to 6.341
Dodecane
C
12
H
26
15
7.274 to 7.324
Dodecane
C
12
H
26
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.
16
1.383 to 1.501
Pentane
C
5
H
12
17
2.515 to 2.606
Toluene
C
7
H
8
18
2.656 to 2.707
Cyclooctane
C
8
H
16
19
2.711 to 2.797
2,4-dimethyl-Heptane
C
9
H
20
20
4.417 to 4.485
3-methyl-Phenol,
C
7
H
8
O
21
4.517 to 4.567
Cyclododecane
C
12
H
24
22
4.567 to 4.617
Dodecane
C
12
H
26
23
5.049 to 5.085
1-methyl-2-octyl-
C
12
H
24
Cyclopropane
24
5.085 to 5.122
Dodecane
C
12
H
26
25
5.536 to 5.568
1-Tridecene
C
13
H
26
26
5.581 to 5.604
Dodecane
C
12
H
26
27
5.827 to 5.863
4-Decene
C
10
H
20
28
6.004 to 6.032
2-Tetradecene
C
14
H
28
29
6.036 to 6.063
Dodecane
C
12
H
26
30
5.931 to 5.963
Dodecane
C
12
H
26
31
6.291 to 6.314
Dodecane
C
12
H
26
32
6.314 to 6.341
Dodecane
C
12
H
26
33
6.441 to 6.468
1-Pentadecene
C
15
H
30
34
6.473 to 6.500
Dodecane
C
12
H
26
35
6.859 to 6.882
1-Hexadecene
C
16
H
32
36
6.882 to 6.909
Dodecane
C
12
H
26
37
7.273 to 7.371
Dodecane
C
12
H
26
38
7.401 to 7.428
Z-5-Nonadecene
C
19
H
38
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.
39
3.852 to 3.980
Phenol
C
6
H
6
O
40
4.303 to 4.380
2-methyl-Phenol
C
7
H
8
O
41
4.407 to 4.526
4-methyl-Phenol
C
7
H
8
O
42
4.685 to 4.730
2,5-Pyrrolidinedione
C
4
H
5
NO
2
43
4.835 to 4.885
2,4-dimethyl-Phenol
C
8
H
10
O
44
4.903 to 4.971
4-ethyl-Phenol
C
8
H
10
O
45
7.250 to 7.273
3-Heptadecene, (Z)-
C
17
H
34
46
7.396 to 7.437
3,7,11-trimethyl-1-
C
15
H
32
O
Dodecanol
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
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
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.
13
7.392 to 7.433
1-Heptene, 2-isohexyl-
C
14
H
28
6-methyl-
14
7.956 to 7.988
3,7,11,15-Tetramethyl-2-
C
20
H
40
O
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.
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
C
12
H
26
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.
20
1.585 to 2.190
Acetic acid
C
2
H
4
O
2
21
2.435 to 2.499
Pyridine
C
5
H
5
N
Pyrrole
C
4
H
5
N
22
2.513 to 2.563
Toluene
C
7
H
8
23
2.631 to 2.708
Propanoic acid, 2-oxo-, methyl ester
C
4
H
6
O
3
24
4.746 to 4.773
Benzene, (2-methyl-1-propenyl)-
C
10
H
12
25
5.933 to 5.979
Naphthalene, 1,2-dihydro-1,1,6-trimethyl
C
13
H
16
26
6.493 to 6.520
Ethaneperoxoic acid, 1-cyano-1-(2-methyl
C
12
H
13
NO
3
27
6.529 to 6.570
1H-Indole, 2,5-dimethyl-
C
10
H
11
N
28
6.857 to 6.884
3-Hexadecene, (Z)-
C
16
H
32
7-Hexadecene, (Z)-
C
16
H
32
29
7.207-7.230
3-Heptadecene, (Z)-
C
17
H
34
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.
30
1.908 to 1.999
Benzene
C
6
H
6
31
3.141 to 3.181
Ethylbenzene
C
8
H
10
32
3.186 to 3.241
p-Xylene
C
8
H
10
33
3.341 to 3.400
Styrene
C
8
H
8
Xylene
C
8
H
10
34
3.796 to 3.832
Benzene, 1-ethyl-2-methyl-
C
9
H
12
35
3.987 to 4.023
Benzene, 1,3,5-trimethyl-
C
9
H
12
36
4.319 to 4.355
Benzene, 1-propynyl-
C
9
H
8
37
4.787 to 4.887
Benzyl nitrile
C
8
H
7
N
38
4.901 to 4.937
Benzene, (1-methyl-2-
C
10
H
10
cyclopropen-1-yl)-
39
4.937 to 4.969
2-Methylindene
C
10
H
10
40
5.078 to 5.110
Dodecane
C
12
H
26
41
5.110 to 5.160
Naphthalene
C
10
H
8
42
5.656 to 5.711
Naphthalene, 2-methyl-
C
11
H
10
43
6.311 to 6.343
Dodecane
C
12
H
26
44
6.470 to 6.493
Dodecane
C
12
H
26
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.
46
5.184 to 5.239
1,4:3,6-Dianhydro-.alpha.-d-glucopyranos
C
6
H
8
O
4
Benzofuran, 2,3-dihydro-
C
8
H
8
O
47
5.339 to 5.398
Benzenepropanenitrile
C
9
H
9
N
48
6.126 to 6.158
Amobarbital
C
11
H
18
N
2
O
3
49
6.176 to 6.212
Pentobarbital
C
11
H
18
N
2
O
3
50
6.444 to 6.467
1-Pentadecene
C
15
H
30
51
6.472 to 6.499
Dodecane
C
12
H
26
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
Table 14, shown below, shows changes in the character of the effluent from the preparatory scale reactor as the reaction temperature increases.
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 61176152 | May 2009 | US | |
| 61226244 | Jul 2009 | US |
