Integrated process for conversion of hydrocarbonaceous assets and photobiofuels production
The present invention is generally directed to procedures that incorporate CO.sub.2-producing conversions of hydrocarbonaceous resources with biofuels procedures that utilize CO.sub.2 in photosynthesis. In some embodiments, such procedures involve the absorption of CO.sub.2 in an absorption fluid. In some such embodiments, such absorption is carried out in an absorption tower. In some other such embodiments, there’s a subsequent desorption of this CO.sub.2. Generally, at least some of the CO.sub.2 seized by the absorption liquid can be used to grow microbes or diatom species.
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Carbon dioxide (CO.sub.2) is a famous greenhouse gas and attempts to reduce the emissions of the gas into the atmosphere are desirable. CO.sub.2 is commonly formed when hydrocarbonaceous resources are converted into hydrocarbonaceousproducts, e.g., hydrogen or electricity. As an example, a gas-to-liquids (GTL) process converts roughly two-thirds of the starting gas (methane or natural gasoline ) into hydrocarbonaceous liquid products with another one-third being emitted as CO.sub.2. Thecurrent high costs related to capturing and sequestering this CO.sub.2 utilizing conventional amine scrubbing technology coupled with sequestration of high pressure CO.sub.2 are such that doing so is normally not economically-viable. Accordingly, itis desirable to reduce both CO.sub.2 emissions as well as the costs associated with their sequestration. Toward this end, it has been suggested that CO.sub.2 be captured when electrical power is made from hydrocarbonaceous resources, such as for example in theintegrated-gasification-combined-cycle (IGCC) process. See, e.g., U.S. Pat. No. 5,666,800.
Approaches to capture and enhance the entrance of CO.sub.2 into the atmosphere have primarily focused on amine scrubbing from flue gas or super-atmospheric gas streams coupled with compression of the CO.sub.2 before sequestration underground.This presents difficulties. First, the costs to compress the CO.sub.2 can be significant. Secondly, there are questions regarding whether the (CO.sub.2 sequestered in underground reservoirs will in fact, stay there.
One approach to reduce greenhouse gas emissions would be to substitute a crop-based biofuel for a petroleum-derived gas. When preparing the crop-based biofuel, CO.sub.2 is consumed throughout the plant growth cycle. By way of example, there is curiosity inethanol generation from corn, and biodiesel from various grains. The issues with this crop-based approach include: (1) diversion of scarce farmland that’s engaged in developing food for manufacture of transport fuels; (2) use of scarce fresh waterfor the generation of biofuels (in the United States, the decline of the Ogallala aquifer because of agricultural use could restrict future agriculture); and (3) the energy used to make the finished biofuel (i.e., product) reduces the internet energyproduction, wherein related energy utilization steps include fertilization, planting, harvesting, drying, grinding, fermenting, extracting, distilling, transesterification and the like (some studies have indicated that there is no net energy productionfrom ethanol).
An alternate to crop-based biofuels is to utilize a photobiofuels procedure that transforms the CO.sub.2 to liquid hydrocarbonaceous goods by use of photosynthetically-responsive microbes (“microbes”). A photobiofuels procedure, in the context ofthis invention, is a biological process using microorganisms like algae (e.g., microalgae) or diatoms (e.g., phytoplankton) to convert carbon dioxide to liquid hydrocarbonaceous goods like triglycerides, alcohols, acids, mono-estersand other oxygenated compounds. By this way, the photobiofuels procedure utilizes sun as an energy source to produce lipids (triglycerides) and carbs (e.g., sugars and starches). The photobiofuels procedure can also produce oxygen as aby-product. Photobiofuels processes can be distinguished as open or closed, as described below.
An open photobiofuels process is one in which an aqueous liquid comprising the algae and/or diatoms is in direct contact with the air. This is generally done with ponds. An benefit I’m open photobiofuels process is its relativelylow price. Disadvantages have an inability to accumulate the generated O.sub.2, an inability to reduce contamination of the aqueous liquid using native microbes, and difficulty in controlling the temperature. A superb example of a photobiofuelsprocess are seen at”A Look Back at the U.S. Department of Energy’s Aquatic Species Program: Biodiesel from Algae” by Sheehan et al. (referred to herein as the”Sheehan report” or simply”Sheehan”). This document was prepared by the NationalRenewable Energy Laboratory as NREL/TP-580-24190.
A closed photobiofuels process is one where the aqueous liquid comprising the algae or diatoms isn’t in direct contact with the air, but is rather protected by a transparent structure that permits light to enter. Benefits ofthe closed photobiofuels process include the ability to collect generated O.sub.2, defense of the liquid out of introduction of native germs, and improved ability to control the temperature. The main disadvantage of the process is cost (seeSheehan, Technical Review pages 245-246). Examples of closed photobiofuels procedures can be found at the following U.S. Patent Application Publications from Berzin: US20050260553, US20050239182, and US20050064577–jointly known herein as the”Berzin patents” or just”Berzin”.
Taking a look at the open photobiofuels procedure described in Sheehan, many attractive features have been found: (1) CO.sub.2 from coal-fired power plants can be transformed into some photobiofuel (Executive Summary, page ); (2) that the CO.sub.2 fromthe coal-plants was a 13% concentration and bubbled into ponds comprising the microbes (Program summary page 4); (3) concentrated, high pressure CO.sub.2 sources in electricity plants, synthetic fuels plants, along with IGCC plants were found to function as mosteconomical sources (Technical Review, page 216); (4) >90% of injected CO.sub.2 is consumed (Executive Summary, page ii); (5) the procedure doesn’t use water that is fresh, but rather uses more abundant saline water that cannot be used in conventionalagriculture (Program Summary, page 10); (6) the yield per acre of biofuel is thirty times that which can be got for crop-based biofuels (Program Summary, page 3); (7) the consequent algae can comprise 60 wt% triglycerides–a photobiofuel pre-cursor(Program Summary, page 6); (8) oxygen is created as a by-product, but this can act to inhibit microbe development (Technical Review, page 181); (9) that the reagents needed to encourage growth of the microbe (minerals and nitrogen) can be recycled (Technical Review,page 145); (10) methane or ethanol can be made from fermentation of biomass that doesn’t yield triglycerides (Program Summary, page 6); and (11) the triglycerides can also be used as valuable specialty compounds (Technical Review, page 1).
Despite its allure, many problems are identified or associated with the above-described open photobiofuels process: (1) the microbes may only grow well under rather narrow conditions of salinity, pH, and temperature (TechnicalReview, page 16); (2) low nighttime temperatures may restrict productivity (Executive Summary, page ii); (3) yearly temperatures cycles (growing season) may also restrict productivity (Technical Review, page 213); (4) zooplankton can act as grazers and eat themicrobes that make the photobiofuel (Technical Review, page 152), and such grazers can be a particular issue at nighttime (Technical Review, page 180); (5) carbon dioxide is only consumed during the day when sunlight is accessible; (6) the cost of theproduced biodiesel was projected (in 1995 dollars) as being between $1.40 to $4.40/gallon; and despite carbon credits, this was thought to be double the cost of gas gas, and consequently not competitive (Program Summary, page 19; and ExecutiveSummary, page ii); (7) an analysis in the report concluded, that it will be tricky to come across many places where each of the resources necessary for microalgae farming (e.g., flatland, brackish or waste waters, and cheap CO.sub.2 supplies) are allavailable in juxtaposition (Technical Review, page 259).
One approach to improve upon the economics of such above-described processes would be to utilize a closed photobiofuels process. This leaves a better chance to control the temperature, salinity, pH and microbial species. Examples of this are shown theBerzin patents. However, an economic analysis of closed systems performed by Sheehan concluded that the prices of these systems were restrictive (Program Overview, page 5)
While the cost of petroleum gas has improved markedly since the above-described 1995 study and might now make this workable, efforts to improve the economics of these photobiofuels process continue to be desirable. The approach taken herein toimprove such economics would be to boost the integration of these processes for conversion of hydrocarbonaceous assets assist the photobiofuels process. Improved economics have been attained either by lower cost operations, improved productivity improved price of theproduct, and combinations thereof.
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