Complete conversion

Single irreversible reactions. An excess of one feed component can force another component toward complete conversion. As an... 

An excess of ethylene is used to ensure essentially complete conversion of the chlorine, which is thereby eliminated as a problem for the downstream separation system. 

In a single reaction (where selectivity is not a problem), the usual choice of excess reactant is to eliminate the component which is more difficult to separate in the downstream separation system. Alternatively, if one of the components is more hazardous (as is chlorine in this example), again we try to ensure complete conversion. 

This reaction can be forced to effective complete conversion by... 

Figure 2.4 Reaction and separation in sulfuric Eicid manufacture allow effectively complete conversion despite reversibility of the reaction.

Reactor conversion. In Chap. 2 an initial choice was made of reactor type, operating conditions, and conversion. Only in extreme cases would the reactor be operated close to complete conversion. The initial setting for the conversion varies according to whether there are single reactions or multiple reactions producing byproducts and whether reactions are reversible. 

Achieving complete conversion of FEED to PRODUCT in the reactor usually requires an extremely long residence time, which is normally uneconomic (at least in continuous processes). Thus, if there is no byproduct formation, the initial reactor conversion is set to be around 95 percent, as discussed in Chap. 2. The reactor effluent thus contains unreacted FEED and PRODUCT (Fig. 4.1a). 

Four possible arrangements can be considered a. Complete conversion of both feeds. Figure 4.7a shows the most desirable arrangement complete conversion of the decane and chlorine in the reactor. The absence of reactants in the reactor effluent means that no recycles are needed. 

Also, although there are no selectivity data for the reaction, the selectivity losses would be expected to increase with increasing conversion. Complete conversion would tend to produce unacceptable selectivity losses. Finally, the reactor volume required to give a complete conversion would be extremely large. 

Laboratory studies indicate that a hydrogen-toluene ratio of 5 at the reactor inlet is required to prevent excessive coke formation in the reactor. Even with a large excess of hydrogen, the toluene cannot be forced to complete conversion. The laboratory studies indicate that the selectivity (i.e., fraction of toluene reacted which is converted to benzene) is related to the conversion (i.e., fraction of toluene fed which is reacted) according to ... 

Solution The reversible nature of the reaction means that neither of the feed materials can be forced to complete conversion. The reactor design in Fig. 

If this reaction takes place in air, the evolved nitrogen monoxide is oxidised to the dioxide and this dissolves again as in equation (9.1) hence virtually complete conversion of nitrogen dioxide to nitric acid can occur (see nitric acid, below). With alkalis, a mixture of nitrite and nitrate is formed ... 

C,H5N,NHC,Hs+HC1 = C,H 5N C1+H,NC,H5- C H5N NC H NH +HC1 gen atom of the aniline molecule, giving aminoazobenzene. Since this reaction is irreversible, whilst the former is freely reversible, the final result is the complete conversion of the diazoaminobenzene into the aminoazobenzene. (The intermediate formation of the benzenediazonium chloride can be demonstrated by adding dimethylaniline, with which the diazonium chloride couples preferentially, giving dimethylaminoazobenzene, C6HsN NC6HiN(CH3)i.)... 

A condition of equilibrium is reached (70-90 per cent, of bisulphite compound with equivalent quantities of the reagents in 1 hour), but by using a large excess of bisulphite almost complete conversion into the... 

Note 4. Gas-liquid chromatography showed complete conversion into the bis-ether. 

Carboxylic acids react with butadiene as alkali metal carboxylates. A mixture of isomeric 1- and 3-acetoxyoctadienes (39 and 40) is formed by the reaction of acetic acid[13]. The reaction is very slow in acetic acid alone. It is accelerated by forming acetate by the addition of a base[40]. Addition of an equal amount of triethylamine achieved complete conversion at 80 C after 2 h. AcONa or AcOK also can be used as a base. Trimethylolpropane phosphite (TMPP) completely eliminates the formation of 1,3,7-octatriene, and the acetoxyocta-dienes 39 and 40 are obtained in 81% and 9% yields by using N.N.N M -tetramethyl-l,3-diaminobutane at 50 in a 2 h reaction. These two isomers undergo Pd-catalyzed allylic rearrangement with each other. 

The sulfuric acid hydrolysis may be performed as a batch or continuous operation. Acrylonitrile is converted to acrylamide sulfate by treatment with a small excess of 85% sulfuric acid at 80—100°C. A hold-time of about 1 h provides complete conversion of the acrylonitrile. The reaction mixture may be hydrolyzed and the aqueous acryhc acid recovered by extraction and purified as described under the propylene oxidation process prior to esterification. Alternatively, after reaction with excess alcohol, a mixture of acryhc ester and alcohol is distilled and excess alcohol is recovered by aqueous extractive distillation. The ester in both cases is purified by distillation. 

Tin reacts completely with fluorine above 190°C to form tin tetrafluoride [7783-62-2] SnF. Titanium reacts appreciably above 150°C at a rate dependent on the size of the particles the conversion to titanium tetrafluoride [7783-63-3] TiF, is complete above 200°C. Fluorine reacts with zirconium metal above 190°C. However, the formation of a coating of zirconium tetrafluoride [7783-64 ] ZrF, prevents complete conversion, the reaction reaching... 

Most of the world s commercial formaldehyde is manufactured from methanol and air either by a process using a silver catalyst or one using a metal oxide catalyst. Reactor feed to the former is on the methanol-rich side of a flammable mixture and virtually complete reaction of oxygen is obtained conversely, feed to the metal oxide catalyst is lean in methanol and almost complete conversion of methanol is achieved. 

Steam Reforming. When relatively light feedstocks, eg, naphthas having ca 180°C end boiling point and limited aromatic content, are available, high nickel content catalysts can be used to simultaneously conduct a variety of near-autothermic reactions. This results in the essentiaHy complete conversions of the feedstocks to methane ... 

Finally, selective hydrogenation of the olefinic bond in mesityl oxide is conducted over a fixed-bed catalyst in either the Hquid or vapor phase. In the hquid phase the reaction takes place at 150°C and 0.69 MPa, in the vapor phase the reaction can be conducted at atmospheric pressure and temperatures of 150—170°C. The reaction is highly exothermic and yields 8.37 kJ/mol (65). To prevent temperature mnaways and obtain high selectivity, the conversion per pass is limited in the Hquid phase, and in the vapor phase inert gases often are used to dilute the reactants. The catalysts employed in both vapor- and Hquid-phase processes include nickel (66—76), palladium (77—79), copper (80,81), and rhodium hydride complexes (82). Complete conversion of mesityl oxide can be obtained at selectivities of 95—98%. 

Anhydrous lithium hydroxide [1310-65-2], LiOH, is obtained by heating the monohydrate above 100°C. The salt melts at 462°C. Anhydrous lithium hydroxide is an extremely efficient absorbent for carbon dioxide (qv). The porous stmcture of the salt allows complete conversion to the carbonate with no efficiency loss in the absorption process. Thus LiOH has an important role in the removal of carbon dioxide from enclosed breathing areas such as on submarines or space vehicles. About 750 g of lithium hydroxide is required to absorb the carbon dioxide produced by an individual in a day. 

Propylene feed, fresh benzene feed, and recycle benzene are charged to the upflow reactor, which operates at 3—4 MPa (400—600 psig) and at 200—260°C. The SPA catalyst provides an essentially complete conversion of propylene [115-07-1] on a one-pass basis. A typical reactor effluent yield contains 94.8 wt % cumene and 3.1 wt % diisopropylbenzene [25321-09-9] (DIPB). The remaining 2.1% is primarily heavy aromatics. This high yield of cumene is achieved without transalkylation of DIPB and is unique to the SPA catalyst process. 

Relatively high concentrations of organic peroxide or azo initiators are needed to obtain complete polymerization. After the reaction peak exotherm, polymerization slows down. Initiator concentrations must be high enough to complete conversion. Polymerization is inhibited by oxygen and copper, lead, and sulfur compounds (11). 

Some nitrate is also formed, thus the HOCl/NH stoichiometry is greater than theoretical, ie, - 1.7. This reaction, commonly called breakpoint chlorination, involves intermediate formation of unstable dichloramine and has been modeled kinetically (28). Hypobromous acid also oxidizes ammonia via the breakpoint reaction (29). The reaction is virtually quantitative in the presence of excess HOBr. In the case of chlorine, Htde or no decomposition of NH occurs until essentially complete conversion to monochloramine. In contrast, oxidation of NH commences immediately with HOBr because equihbrium concentrations of NH2Br and NHBr2 are formed initially. As a result, the typical hump in the breakpoint curve is much lower than in the case of chlorine. 

Methanol. Methanol is produced by stoichiometric reaction of CO and H2. The syngas produced by coal gasification contains insufficient hydrogen for complete conversion to methanol, and partial CO shifting is required to obtain the desired concentrations of H2, CO, and CO2. These concentrations are expressed in terms of a stoichiometric number, ((H2 — CO)/(H2 + CO2), which has a desired value of 2. In some cases CO2 removal is required to achieve the stoichiometric number target. CO and H2 are then reacted to form methanol in a catalytic methanol synthesis reactor. 

The radicals and other reaction components are related by various equiUbria, and hence their decay by recombination reactions occurs in essence as one process on which the complete conversion of CO to CO2 depends. Therefore, the hot products of combustion of any lean hydrocarbon flame typically have a higher CO content than the equiUbrium value, slowly decreasing toward the equiUbrium concentration (CO afterburning) along with the radicals, so that the oxidation of CO is actually a radical recombination process. 

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