Two-step processes

Concerning solar-powered processes, two-step cycles are also under investigation, which require higher temperatures like the Zn/ZnO cycle or ferrite cycles. Most recently a closed ferrite cycle was demonstrated in the HYDROSOL-2 project in a 100 kW range on a solar test tower in Almeria (Roeb, 2008). 

If an ion possesses two excited states with approximately same energy separation, energy transfer can occm between two ions in the first excited state (Figme 4c). One ion returns uomadiatively to the ground state while the second is promoted to the second excited state, then decays with emission of a photon whose energy is about twice that of incident photons. There are other upconversion processes two-step absorption, cooperative sensitization, cooperative luminescence. Upconversion by energy transfer is the most efficient process. 

The liquid product from the lOO C reactor is countercurrently stripped with 90 C air to remove nitrogen oxide gases. The more volatile oxidation by-products such as valeric and butyric acids are removed by steam distillation and the liquors concentrated for adipic acid recovery. Adipic acid is crystallised from the liquors at about 40-50 C and is recovered by centrifugal separation. Mother liquor is then recycled to the process. Two-step crystallization may be used to improve recovery and reduce the proportion of succinic acid impurity in the recycle. 

In the metal plating industry, cyanides are frequently eliminated from waste discharges by treatment with chlorine at high pH (alkaline chlorination process). Two steps are involved (1) the oxidation of cyanide, CN , to cyanate, CNO , and (2) oxidation of CNO to Nj and CO2. 

Hexene reacts with borane to give a new product known as an alkylborane, which is listed as unknown for the moment. The alkylborane product is treated with NaOH and H2O2 in a second chemical reaction and the major product obtained after this two-reaction process (two-step process) is 1-hexanol (52), isolated in 81% yield. The second reaction with hydroxide and peroxide will be discussed later in this section, but for now focus attention on the new borane product of the first reaction. The remainder of the 100% is alcohol 53 as a minor product, and this will be explained later. 

Table 5.17). For example, PET needs to be spun at speeds of 5000 m/min and above in order to exhibit significant crystallinity (see Fig. 5.23). As mentioned at the beginning of this chapter, the lack of crystallinity during the conventional low-speed spinning process forced the industry to use an additional step (drawing) immediately after the spinning process (two-step process, TSP). In this way, the PET fibers exhibit a high degree of orientation, and they wq fully oriented yarns (FOY).

There is a two-step process to predict the detectable detail - object diameter diagram. The optimal data collection parameter settings to maximise SNRAproj for the defect to the surrounding material - Optimal... 

The first step involved massive testing at ANDREX laboratory to determine the optimal detection process. Two imaging methods were discussed, one using a linear detector array, the other using a high resolution image intensifier. 

Energy redistribution is the key primary process in chemical reaction systems, as well as in reaction systems quite generally (for instance, nuclear reactions). This is because many reactions can be separated into two steps ... 

Since the first formulation of the MO-LCAO finite basis approach to molecular Ilartree-Pock calculations, computer applications of the method have conventionally been implemented as a two-step process. In the first of these steps a (large) number of integrals — mostly two-electron integrals — arc calculated and stored on external storage. Th e second step then con sists of the iterative solution of the Roothaan equations, where the integrals from the first step arc read once for every iteration. 

The process whereby aldehydes are produced from arylmethyl (also alkyl and other) halides by the action of hexamine is known as the Sommelet reaction. The reaction is essentially the conversion of an amine into an aldehyde the hexamine serves the dual role of converting the halide into the amine and the amine into the aldehyde, but its function is different in the two steps. When starting from a halide, the reaction proceeds in three stages —... 

Ammonia (NH3) is the most important commercial compound of nitrogen. It is produced by the Haber Process. Natural gas (methane, CH4) is reacted with steam to produce carbon dioxide and hydrogen gas (H2) in a two step... 

The cases of pentamethylbenzene and anthracene reacting with nitronium tetrafluoroborate in sulpholan were mentioned above. Each compound forms a stable intermediate very rapidly, and the intermediate then decomposes slowly. It seems that here we have cases where the first stage of the two-step process is very rapid (reaction may even be occurring upon encounter), but the second stages are slow either because of steric factors or because of the feeble basicity of the solvent. The course of the subsequent slow decomposition of the intermediate from pentamethylbenzene is not yet fully understood, but it gives only a poor yield of pentamethylnitrobenzene. The intermediate from anthracene decomposes at a measurable speed to 9-nitroanthracene and the observations are compatible with a two-step mechanism in which k i k E and i[N02" ] > / i. There is a kinetic isotope effect (table 6.1), its value for the reaction in acetonitrile being near to the... 

Hydroboration-oxidation (Sections 6 11-6 13) This two step sequence achieves hydration of alkenes in a ste reospecific syn manner with a regiose lectivity opposite to Markovnikov s rule An organoborane is formed by electro philic addition of diborane to an alkene Oxidation of the organoborane inter mediate with hydrogen peroxide com pletes the process Rearrangements do not occur... 

IS a two step process m which the first step is rate determining In step 1 the nucleophilic hydroxide ion attacks the carbonyl group forming a bond to carbon An alkoxide ion is the product of step 1 This alkoxide ion abstracts a proton from water m step 2 yielding the gemmal diol The second step like all other proton transfers between oxygen that we have seen is fast... 

The Wittig reaction is one that IS still undergoing mech anistic investigation An other possibility is that the oxaphosphetane intermedi ate IS formed by a two step process rather than the one step process shown in Figure 17 13... 

Amides are sometimes prepared directly from carboxylic acids and amines by a two step process The first step is an acid-base reaction m which the acid and the amine combine to form an ammonium carboxylate salt On heating the ammonium carboxy late salt loses water to form an amide... 

Substitution nucleophilic unimolecular(SNl) mechanism (Sec tions 4 9 and 8 8) Mechanism for nucleophilic substitution charactenzed by a two step process The first step is rate determining and is the ionization of an alkyl halide to a carbocation and a halide ion... 

Historically these compounds have been made in two-step processes. Eor smaller volumes, reaction of an appropriate ketone or aldehyde with a cyanide salt followed by treatment with an ammonium salt proves satisfactory (Strecker synthesis). Eor larger volumes, treatment of the ketone or aldehyde with HCN to produce a cyanohydrin, followed by treatment with ammonia has been practiced. However, in 1990, DuPont began practicing a new one-step... 

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. 

Both oae-step and two-step oxidation processes are known. A number of catalyst systems are known most use a molybdenum compound as the main component. The acryhc acid is esterified with alcohol to the desired acryhc ester ia a separate process (63—66). 

A two-step process involving conventional nonoxidative dehydrogenation of propane to propylene in the presence of steam, followed by the catalytic ammoxidation to acrylonitrile of the propylene in the effluent stream without separation, is also disclosed (65). 

Emulsion Process. The emulsion (79,80) ABS process involves two steps, production of a mbber latex and subsequent polymerization of styrene and acrylonitrile in the presence of the mbber latex to produce an ABS latex. This latex is then processed to isolate the ABS resin (81,82). 

It has been known since the early 1950s that butadiene reacts with CO to form aldehydes and ketones that could be treated further to give adipic acid (131). Processes for producing adipic acid from butadiene and carbon monoxide [630-08-0] have been explored since around 1970 by a number of companies, especially ARCO, Asahi, BASF, British Petroleum, Du Pont, Monsanto, and Shell. BASF has developed a process sufficiendy advanced to consider commercialization (132). There are two main variations, one a carboalkoxylation and the other a hydrocarboxylation. These differ in whether an alcohol, such as methanol [67-56-1is used to produce intermediate pentenoates (133), or water is used for the production of intermediate pentenoic acids (134). The former is a two-step process which uses high pressure, >31 MPa (306 atm), and moderate temperatures (100—150°C) (132—135). Butadiene,... 

Adsorption. In the design of the adsorption step of gas-phase processes, two phenomena must be considered, equiUbrium and mass transfer. Sometimes adsorption equiUbrium can be regarded as that of a single component, but mote often several components and their interactions must be accounted for. Design techniques for each phenomenon exist as well as some combined models for dynamic performance. 

---