Utility selection


The Tradeoffs Between Process Changes, Utility Selection, Energy Cost, and Capital Cost  [c.323]

The ultimate reference in guiding process changes to reduce utility costs and utility waste is the plus/minus principle. However, process changes so identified prompt changes in the capital/energy tradeoff and utility selection. Using the total cost targeting techniques described in Chaps. 6 and 7, it is possible to effectively screen a wide range of options using relatively simple computation. In the next three chapters we shall focus in detail on heat integration of reactors and heat-driven separators.  [c.323]

Although the composite curves can be used to set energy targets, they are not a suitable tool for the selection of utilities. The grand composite curve is a more appropriate tool for understanding the interface between the process and the utility system. It is also, as is shown in later chapters, a useful tool for study of the interaction between heat-integrated reactors and separators and the rest of the process.  [c.185]

Under certain conditions it may be appropriate to focus on the modelling of a segment of a larger domain in order to obtain detailed results within that section, while maintaining computing economy. To develop such a model, first the entire flow domain is simulated using a relatively coarse finite element mesh. The results generated at the end of this stage are used to define the boundary conditions at the borders of the selected part. This section is then modelled utilizing a refined mesh to obtain detailed predictions about phenomena of interest in the flow field. The procedure can be repeated using a step-by-step approach in which the zooming on a segment witliin a very large domain is achieved through successive reduction of the size of the segments at each step of modelling.  [c.156]

Even after 30 years of research activity in the field, my personal experience encompasses only a fraction of the methodologies included in the book. I have selected the methods and examples on the basis of utility and reliability as judged by frequency of application in the literature or by indication that specific procedures are especially convenient. I will welcome comments from chemists whose experience, good or bad, will help in recognizing the best of the many methods that are available.  [c.182]

The utility of acid-base titrimetry improved when NaOH was first introduced as a strong base titrant in 1846. In addition, progress in synthesizing organic dyes led to the development of many new indicators. Phenolphthalein was first synthesized by Bayer in 1871 and used as a visual indicator for acid-base titrations in 1877. Other indicators, such as methyl orange, soon followed. Despite the increasing availability of indicators, the absence of a theory of acid-base reactivity made selecting a proper indicator difficult.  [c.278]

Spectroscopic Detectors The most popular HPLC detectors are based on spectroscopic measurements, including UV/Vis absorption, and fluorescence. These detectors range from simple designs, in which the analytical wavelength is selected using appropriate filters, to essentially a modified spectrophotometer equipped with a flow cell. When using a UV/Vis detector, the resulting chromatogram is a plot of absorbance as a function of elution time. Instruments utilizing a diode array spectrophotometer record entire spectra, giving a three-dimensional chromatogram showing absorbance as a function of wavelength and elution time. Figure 12.29a shows a typical flow cell for HPLC when using a UV/Vis spectrophotometer as a detector. The flow cell has a volume of 1-10 ftL and a path length of 0.2-1 cm. One limitation to using absorbance is that the mobile phase must not absorb strongly at  [c.584]

Another example of vims clearance is for IgM human antibodies derived from human B lymphocyte cell lines where the steps are precipitation, size exclusion using nucleases, and anion-exchange chromatography (24). A second sequence consists of cation-exchange, hydroxylapatite, and immunoaffinity chromatographies. Each three-step sequence utilizes steps based on different properties. The first sequence employs solubiUty, size, and anion selectivity the second sequence is based on cation selectivity, adsorption, and selective recognition based on an anti-u chain IgG (24).  [c.45]

The apparatus utilized to carry out size-exclusion (gel-permeation) chromatography is analogous to that used for isocratic operating conditions (see Fig. 4). The column is packed with a gel-filtration stationary phase, selected according to the molecular weight of the protein of interest (31). A variety of commercially available gel-filtration matrices faciUtates separations ranging from molecular weights of 50 to 10 (Fig- 6). However, a single gel having a porosity which is capable of sieving molecules over the entire separation range does not exist.  [c.49]

On-site purification of gaseous hydrogen is accompHshed using combinations of chemical conversion, cryogenic adsorption, and palladium membrane processes depending on the purity and throughput requirements (see Membrane TECHNOLOGY). For small hydrogen streams, stand-alone hydrogen purifiers based on selective permeation through palladium membranes are available. These units take advantage of the high permeabiHty of hydrogen through palladium metal. Generally, the membranes are heated to get higher processing capacity per unit area. However, provisions must then be made to remove hydrogen from the membrane prior to cool-down to prevent formation of small cracks which then allow impurities to leak through the membrane. Small to large hydrogen streams can be purified by adsorption carried out at cryogenic temperatures, usually near the boiling point of Hquid nitrogen. Activated charcoal and siHca gel are both effective adsorbents for purification. However, if any significant quantity of oxygen must be removed, activated charcoal should not be used because of the potential for an explosive chemical reaction with the adsorbed oxygen during regeneration. Regeneration of the adsorbent is accompHshed through a process of heating and reverse purging. Large hydrogen streams can be purified using a room-temperature palladium catalyst bed to convert oxygen impurity into water foUowed by cryogenic adsorption. Because the oxygen impurity has been removed, the higher adsorption capacity of activated charcoal can then be utilized without danger of explosion.  [c.88]

Combinatorial Chemistry. The development of stepwise methods of synthesis of polypeptides and polynucleotides has spawned a new methodology, combinatorial chemistry, for the production of new, functional molecules. Combinatorial chemistry is a way of rapidly generating a large number of closely-related compounds, followed by the screening of each of the compounds with respect to certain desired properties (eg, binding to a particular molecule) (151). A variety of methods of synthesis and screening utilize the combinatorial approach. These include parallel chemical synthesis and testing of multiple compounds (individually or in mixtures) in solution or on soHd supports and biotechnological or organism-based synthesis of biological oligomers coupled to methods of selection and amplification. In most appHcations, automated instmmentation has been developed that will produce a suite of compounds by covalent biochemical synthesis. These compounds may be small or large molecules (eg, oligopeptides and oligonucleotides of varying lengths) that are then screened by their abiUty to bind a biological molecule (eg, receptor or enzyme proteins). Once a compound that shows the desired binding properties is identified, a Hbrary of its variants can be produced, such that an optimized molecule can be obtained.  [c.206]

Single-reaction-step processes have been studied. However, higher selectivity is possible by optimizing catalyst composition and reaction conditions for each of these two steps (40,41). This more efficient utilization of raw material has led to two separate oxidation stages in all commercial faciUties. A two-step continuous process without isolation of the intermediate acrolein was first described by the Toyo Soda Company (42). A mixture of propylene, air, and steam is converted to acrolein in the first reactor. The effluent from the first reactor is then passed directiy to the second reactor where the acrolein is oxidized to acryUc acid. The products are absorbed in water to give about 30—60% aqueous acryUc acid in about 80—85% yield based on propylene.  [c.152]

Bag cleaning and control methods need to be selected. Eor cloth bags, shaking is weU-estabhshed, but pulse-jet cleaning is probably the most popular choice today whenever felted bags can be successfully utilized. Pulse-jet cleaning should be more desireable for appHcations handling heavy dust loads in continuous operation since it is always controlled by an automatic timing device. Automatic timing can also be appHed to shaker filters, but for apphcations of light dust loading or intermittent gas flow, remote manual control may be preferred.  [c.405]

The unusually high toxicity of fluoroacetic acid and of other monofluorinated organic compounds that can be metabolized to fluoroacetate has stimulated much research into the mechanism of this toxicity (8,19—23). Fluoroacetate mimics acetate by being incorporated into the tricarboxylic acid cycle of cellular respiration where it becomes converted into fluorocitric acid. This acid inhibits the enzyme, aconitate hydratase, which normally catalyzes the dehydration of citric acid. As a result, citric acid accumulates in the organism and the energy-producing cycle is intermpted. Because of the time it takes for the fluorocitrate to form and accumulate, there is usually a latent time of at least an hour before the appearance of symptoms of fluoroacetate poisoning, eg, ventricular fibnUation or convulsions. This is advantageous in its use as a pesticide. One characteristic of fluoroacetate toxicity is the wide range in lethal doses for different species ranging from (LD q, mg/kg) 0.06 in dogs, 0.2 in cats, 0.4 in sheep or rabbits, 2—10 in humans, 5 in rats, 7 in mice, to about 400 in toads (20,24). The only suggested antidotes for the poisoning are 1,2,3-propanetriol monoacetate (20,23), acetamide (20), and other acetate donors, but these only have an effect if adininistered before significant amounts of fluoroacetate have been converted to fluorocitrate. To determine if fluoroacetate poisoning has occurred, it is often desirable to detect the presence of small amounts of the poison in animal tissue. Although difficult, this can be done by spectrochemical methods (25), processes involving ion-selective fluoride electrodes (21,26), or gas chromatography often combined with mass spectrometry (27). A microbial detection of fluoroacetate utilizing DNA technology and bioluminescence has been reported (28).  [c.307]

Rubber. Fluorosihcone mbber is used successfully as O-rings for fuel lines containing gasoline and aviation fuels. Its insulative properties allow its use as spark-plug boots and plug wire in transportation vehicles. The effect of alternative fuels on fluorosihcone mbbers has generated the largest interest in this class of materials. The use of alcohol—gasoline mixtures has been selected because it is a key transportation vehicle fuel of the future. Fluorosihcone mbbers exhibit stable physical properties (10) over the entire range of methanol—fuel blends for periods up to six months at 60°C. They also return to their original physical properties after dryout following immersion. Immersion tests have utilized methanol—ASTM Reference Fuel C (RFC) blends and blends of methyl tert-huty ether (MTBE) with RFC. The greatest fuel swell (33%) is seen at a methanol—RFC ratio of 25 75. This behavior is identical to that shown by a fluorocarbon reference material. Similar resistant effects were seen using oxidized gasoline or "sour" gasoline as the immersion medium. Its low temperature properties are demonstrated as follows fluorosihcone mbbers can be formulated to show the smallest value for compression set after immersion in 25 75 methanol—RFC for 22 hours at 177°C and —30° C (38% vs fluorocarbon reference at 100%). MTBE is shown to have less effect on fluorosihcones than methanol.  [c.401]

Figure 2 shows the three yield levels in Table 2 together with the percentage of the U.S. area needed to supply SNG from biomass for any selected gas demand. Although relatively large areas are required, the use of land- or freshwater-based biomass for energy appHcations is stiU practical. The area distribution pattern of the United States (Table 3) shows selected areas or combinations of areas that might be utilized for biomass energy appHcations (9), ie, areas not used for productive purposes. It is possible that biomass for both energy and foodstuffs, or energy and forest products appHcations, can be grown simultaneously or sequentially in ways that would benefit both. Relatively small portions of the bordering oceans also might supply needed biomass growth areas, ie, marine plants would be grown and harvested. The steady-state carbon suppHes in marine ecosystems can conceivably be increased under controUed conditions over 1993 low levels by means of marine biomass energy plantations in areas of the ocean dedicated to this objective.  [c.11]

In 1955 the South African Coal, Oil, and Gas Corp. (Sasol) commercialized the production of Hquid fuels utilizing Fischer-Tropsch technology (35). This Sasol One complex has evolved into the streaming of second-generation plants, known as Sasol Two and Three. The Sasol One process, shown in Figure 2a (36), combines fixed-bed Ruhrchemie-Lurgi Arge reactor units with fluidized-bed Synthol process technology (37). For Sasol One, 16,000 t/d of coal is cmshed and gasified with steam and oxygen. After a number of gas purification steps in which by-products and gas impurities ate removed, the pure gas is processed in both fixed- and fluidized-bed units simultaneously. Table 1 gives product selectivity comparisons of fixed-bed and Synthol operations. Conversion to hydrocarbons is higher in the Synthol unit and the CO ratio is also higher. Because the fixed-bed Arge reactor favors the formation of straight-chain paraffins, there is greater production of diesel and wax fractions than the Synthol unit. The Arge reactor products have lower gasoline octane number but higher diesel cetane number relative to Synthol. The high wax production using the Arge reactor was disadvantageous at the time owing to market limitations of wax fuels. Sasol One produced a vast array of chemical and fuel products, including gasoline at 1.5 x 10 t/yr.  [c.80]

From 20 to 25 nonsystemic fungicides are utilized in agriculture, although use is declining. These are some of the oldest known fungicides and cover a wide range of chemistry from simple inorganic salts to highly complex organic stmctures. Selective accumulation by spores plays a dominant role in the toxicity of many of these compounds. The majority are regarded as general cell poisons and can be used only when they are not able to penetrate host plant tissue in appreciable amounts. The fungal pathogen is controlled before it infects the plant so that the resulting efficacy is primarily achieved through protecting the plant rather than curing the disease. The mode of action, ie, biochemical basis for activity, of most known nonsystemic fungicides is generally nonspecific, and inhibition at multiple sites results ultimately in interference with energy producing or transferring processes which dismpts fungal respkation and membranes (4).  [c.103]

Extrusion. This forming process is used extensively in metals and plastics industries, but infrequendy in glass manufacture. The main reason for the lack of acceptance is the inherent low rate of production when employed to shape glass. The maximum extmsion rate is tens of centimeters per minute (99). Depending on the type of glass being processed, temperatures of up to 950°C and pressures up to 1 MPa (1000 bars) are utilized. Through careful control of the processing parameters and the selection of nonwetting die materials, sharp edged compHcated rods and tubes can be made to close tolerances.  [c.311]

Comparison of Heat-Transfer Fluids. A large number of heat-transfer fluids are available for use at moderately high (100—300°C) temperatures. Several are utilized at temperatures up to, and sometimes exceeding, 400°C. A dozen fluids may fill fill the operating requirements of a specific appHcation. Fiaal fluid selection should be based on safety of the fluid duting service, heat-transfer rate, operating pressure drop, and system cost. Table 2 offers a comparison of Hquid-phase heat-transfer fluids on the basis of pumping rate, heat-transfer coefficient, frictional pressure drop, and minimum velocity required for turbulent flow. Table 2 shows the relative performance of each fluid as physical properties change with temperature.  [c.505]

Thermal Engine Cycles. Thermal engine cycles operating with organic refrigerants are employed to recover energy from waste heat streams at temperatures below 150°C. Recovery of such heat is justified only when recovery caimot be effected through process-oriented heat utilization. Typical systems employ the Rankine cycle to produce electrical or shaft power. Thermal efficiencies of Rankine cycles are low, but thermal engines are appHed when large quantities of waste heat are available. The most frequently used refrigerants are halocarbons and hydrocarbons. Mixed refrigerants that evaporate and condense over a selected temperature range are used when the available heat source undergoes a wide temperature change as heat is removed. Cascaded systems, ie, thermal engine cycles in series operating at different temperatures, sometimes are employed to increase thermal efficiencies. In such systems, each thermal engine cycle may employ a different refrigerant.  [c.509]

Pressure-Swing Adsorption Purification. In nearly all cases where high purity (>99%) hydrogen is needed, PSA is used in preference to cryogenic separation in the newer steam-reforming hydrogen plants and other hydrogen purification appHcations. Pressure-swing adsorption utilizes the fact that larger molecules such as CO, CO2, CH, and H2O, and also N2, C2H, and other light hydrocarbons, can be effectively separated from the smaller hydrogen gas by selective adsorption on high surface area materials such as molecular sieves (qv). Hydrogen has a very weak affinity for adsorption. The process of pressure-swing adsorption is capable of producing very pure (>99.9%) hydrogen at recoveries of 70—90%, depending on the number of  [c.419]

All fired equipment, whether process furnaces or utility boilers, is subject to federal, via the 1990 Amendment to the Clean Air Act (CCA), and often local regulation, usually in the form of sulfur and nitrogen oxide, NO, limitations (see Exhaust control, industrial). Use of low NO burners reduces the nitrous oxide in the flue gas. Flue gases can be suitably brought into regulation compliance by a combination of conventional control techniques including selective catalytic reduction and flue gas scmbbing. Effluents from other utility systems, such as blowdowns from steam dmms, cooling water systems and poHshers, can normally be handled by neutralization.  [c.429]

Ma.nua.1 Mixing Methods The most obvious procedure for measuring reaction rates is simply to mix reactants together and then monitor either the disappearance of a reactant or appearance of a product. Eor reactions that are slow enough, mixing can be as simple as pouring Hquid solutions into a flask or admitting gases into a reaction bulb. Aliquots may be removed from the mixture at selected time intervals, quenched, and the concentrations measured utilizing the same instmmentation used to measure static concentrations. The reaction vessel needs no special properties and may be inserted into a weU-thermostated temperature bath. Quenching is done by quickly plunging the aUquot into a low temperature bath or by diluting it with excess solvent. Concentrations may be determined by volumetric titration, a classical method that is usually precise and accurate, or by a host of other methods (see Analytical METHODS, survey). Quenched aUquots are also mandated when components must be separated by, for example, chromatography (qv), before being quantified. Eor gas-phase kinetics, measurement of total or partial pressures is a common strategy (see Pressure measurement).  [c.509]

Therefore the extent of extraction or back-extraction is governed by the concentration of X ia the aqueous phase, the distribution coefficients, and selectivities depending on the anion. In nitrate solutions, the distribution coefficient decreases as the atomic number of the REE increases, whereas ia thiocyanate solutions, the distribution coefficient roughly increases as the atomic number of the REE increases. The position of yttrium in the lanthanide series is not the same in nitrate and thiocyanate solutions, and this phenomenon has been used for high purity yttrium manufacture in the past. A combination of extraction by carboxyUc acids then by ammonium salts is also utilized for production of high purity yttrium.  [c.545]

The materials used in the epitaxial layers for LEDs depend on the desired wavelength of emission, performance, and cost. The emission wavelength is selected by choosing the appropriate semiconductor compound or alloy with the corresponding energy gap. In addition, the highest performance devices are obtained by utilizing direct gap semiconductors that are lattice matched. A plot of common III—V semiconductor compounds and their alloys as a function of lattice parameter is shown in Eigure 6a. A similar plot for the III—V nitride compounds, employed to fabricate bright blue and blue-green LEDs, is shown in Eigure 6b. The nitride alloys exhibit band gap energies that correspond to emission in the ultraviolet to red portions of the spectmm.  [c.118]

When NO destmction efficiencies approaching 90% are required, some form of post-combustion technology appHed downstream of the combustion 2one is needed to reduce the NO formed during the combustion process. Three post-combustion NO control technologies are utilized selective catalytic reduction (SCR) nonselective catalytic reduction (NSCR) and selective noncatalytic reduction (SNCR).  [c.510]

H. Skistad, Utilizing selective withdrawal in the ventilation of large spaces Select-Vent, in Proceedings of Spacevent 98, Stockholm 1998.  [c.640]

The slow oxidation of primary alcohols, particularly MeOH, is utilized for the oxidation of allylic or secondary alcohols with allyl methyl carbonate without forming carbonates of the alcohols to be oxidized. Allyl methyl carbonate (564) forms 7r-allylpalladium methoxide, then exchange of the methoxide with a secondary or allylic alcohol 563 present in the reaction medium takes place to form the 7r-allylpalladium alkoxide 565, which undergoes elimination of j3-hydrogen to give the ketone or aldehyde 566. The lactol 567 was oxidized selectively with diallyl carbonate to the lactone 568 without attacking the secondary alcohol in the synthesis of echinosporin[360].  [c.366]

ZnCl2 is essential. The reaction was utilized in the synthesis of strophanthidin. Only the q, /3-alkene in the a, fi- and 7, (5-unsaturated ketone 51 is reduced selectively[47], Triethoxysilane is another reducing agent of the enone 52 and simple alkenes[48].  [c.519]

I undertook the present task to give a birds-eye view of the broad field of palladium in organic synthesis. 1 have tried to accomplish this ttisk by citing many references these were selected from a much larger number which I have collected over the years. I tried to be as comprehensive as possible by selecting those references which reported original ideas and new reactions, or evident synthetic utility. Synthetic utility is clearly biased towards catalytic rather than stoichiometric reactions and this emphasis is apparent in the selection of the  [c.559]

A major disadvantage of the chlorination process is residual acetic acid and overchlorination to dichloroacetic acid. Although various inhibitors have been tried to reduce dichloroacetic acid formation, chloroacetic acid is usually purified by crystallization (15—17). Dichloroacetic acid can be selectively dechlorinated to chloroacetic acid with hydrogen and a catalyst such as palladium (18—20). Extractive distillation (21) and reaction with ketene (22) have also been suggested for removing dichloroacetic acid. Whereas the hydrolysis of trichloroethylene with sulfuric acid yields high purity chloroacetic acid, free of dichloracetic acid, it has the disadvantage of utilizing a relatively more expensive starting material and producing a sulfur containing waste stream.  [c.88]

SCR is a standard, commercially demonstrated process which has been appHed to large coal-fired power boilers in Germany and Japan. Many of the catalysts are preformed, supported catalysts impregnated with vanadium and tungsten oxides (see Catalysts, supported) that cataly2e the reduction of NO to N2 and O2 by reaction with NH at flue gas temperatures of 250—450°C. A catalyst charge is very expensive it constitutes as much as 45% of the capital cost of the SCR portion of boiler installation. Moreover, difficulties that have been encountered involving catalyst poisoning point to the need for careful selection of coal sources. Thermal Denox (122,118) destroys NO by gas-phase reduction with NH. It is limited to temperatures of 900—1100°C and an oxygen content below about 3% by volume. Developed by Exxon, it has been used appreciably in petroleum and process industry combustion gases, as well as in a few coal-fired boilers in Germany. Although less expensive than the SCR process, it has not received significant power industry attention, probably as a result of its limited temperature appHcation window and the need to use an appreciable excess of NH (unless a mixture of both NH and H2 can be employed). The urea reduction process (119), utilizing a urea-water solution sprayed into the boiler flue gases, has a somewhat wider operating window (800—1200°C, up to 7% O2) than Thermal Denox. The process is less well developed and has not been commercially demonstrated except for trials on a power boiler in Sweden. Another process undergoing research development destroys NO by the reaction of isocyanic acid obtained from cyanuric acid sublimation (120,121). This method appears to have good prospects for diesel engine exhaust NO removal.  [c.391]

The basic flow sheet for the flotation-concentration of nonsulfide minerals is essentially the same as that for treating sulfides but the family of reagents used is different. The reagents utilized for nonsulfide mineral concentrations by flotation are usually fatty acids or their salts (RCOOH, RCOOM), sulfonates (RSO M), sulfates (RSO M), where M is usually Na or K, and R represents a linear, branched, or cycHc hydrocarbon chain and amines [R2N(R)3]A where R and R are hydrocarbon chains and A is an anion such as Cl or Br . Collectors for most nonsulfides can be selected on the basis of their isoelectric points. Thus at pH > pH p cationic surfactants are suitable collectors whereas at lower pH values anion-type collectors are selected as illustrated in Figure 10 (28). Figure 13 shows an iron ore flotation flow sheet as a representative of high volume oxide flotation practice.  [c.50]

Oilseed nd Vegeta.ble Oil Fuels. Limited research has continued on the utilization of seed and vegetable oils as motor fuels, particularly as substitute diesel fuels and diesel fuel extenders (164). Work has focused on studies of the yields and properties of oils from oilseed and vegetable oil crops, the performance of neat oils and oil—diesel fuel blends as fuels for compression ignition engines, improvement of the transesterification process and the fuel characteristics of the resulting esters as diesel fuels, upgrading vegetable oils to gasolines and diesel fuels by hydrocracking processes, and field tests of the hquid fuels made from seed and vegetable oils in tmcks and buses. Although several operating problems have been observed, such as lubricating oil deterioration and crystal formation in cooler weather even with some of the lower viscosity seed oil esters, significant advances have been made. Esters of selected vegetable oils are very promising candidates for both indirect and direct fuel-injected engines.  [c.47]

Plasmid Vectors for Facile Introduction of Passenger DNA and Selection of Recombinants. The map of a commonly used plasmid vector, pUC19 (7), is shown in Figure 2. Three parts of the vector are key to its utility. The origin sequence, oh, allows the repHcation of plasmid DNA in high copy number relative to the chromosome. A gene, amp, encoding the enzyme beta-lactamase, which hydrolyzes penicillin compounds, allows  [c.229]

In the eady 1990s, many usehil natural products, eg, fragrances, davors, and potential natural pesticides, cannot be economically synthesized by chemical means (475). However, advances in biotechnology and fermentation technology, coupled with a desire for naturally derived compounds, show promise for the utilization of microorganisms in the commercial manufacture of natural products. A primary constraint in this approach is the limited avadabihty of microbial strains to produce commercially exploitable amounts of the desired compounds. Such strains often require mutagenesis and extensive selection before they can be used on a commercial scale. Although this is a costiy and primarily random process that may not yield a usehil result, enhanced understanding of microbial physiology and genetics can greatly expedite the development of usehil strains (475).  [c.55]

An additional approach to biological weed control is referred to as the inundative or augment approach to biological weed management. This approach utilizes pathogenic propagules formulated as a weed control agent, eg, mycoherbicides. The mass-inoculation of pathogenic propagules in an effective formulation can enhance the dissemination and survival of the pathogens, overwhelm target weed resistance, and produce results similar to those achieved with chemical herbicides. Mycoherbicides often contain native pathogens that are active against native weeds and are thus highly selective against the target weed species (483,484,491).  [c.56]

At one time, methane was widely used to produce acetylene (qv), by processes involving either electric arcs or partial oxidation. The so-called Reppe chemicals (ie, 1,4-butanediol and derivatives), once made solely from acetylene, can now be made from butane the outlook for continued acetylene demand from methane is poor. In 1993, in fact, acetylene production for chemicals was only about a third of that in 1970 (see Acetylene-DERIVED chemicals). Much interest has been shown in direct conversion of methane to higher hydrocarbons, notably ethylene. Development of such a process would allow utilization of natural gas from remote wells. Much gas is currently flared (burned) from such wells because the pipeline gathering systems needed for such gas tend to be prohibitively expensive. If the gas could be converted on-site to a condensable gas or pumpable Hquid, bringing those hydrocarbons to market would be faciHtated. In the early 1990s, partial oxidative coupling of methane to higher hydrocarbons (chiefly C2S) achieved by passing methane and an oxygen-containing gas over a basic oxide catalyst at high temperatures (600—700°C) and low pressures (<1 atm) has been the method of choice. However, despite enormous efforts, C2 yields higher than about 30% have not yet been realized. Direct methane conversion to other materials, such as methanol, has similarly not yielded commercially interesting results, mainly due to the extreme temperatures and very low throughput required for high selectivity to the desired products (7).  [c.400]


See pages that mention the term Utility selection : [c.6]    [c.184]    [c.96]    [c.576]    [c.125]    [c.327]    [c.610]    [c.319]   
See chapters in:

Chemical process design  -> Utility selection


Chemical process design (2000) -- [ c.184 , c.185 , c.186 , c.187 ]