Alkali catalysts

Alkali catalysts are commonly used in transesterification reactions because of their relatively low cost and ease of handling (Atadashi et al., 2012). In addition, transesterification reactions can be performed at low temperatures and pressures with a very high conversion yield, reaching 98% in a short time (Fukuda et al., 2001). Sodium hydroxide (NaOH), potassium hydroxide (KOH), and sodium methoxide (CHjONa) are the most common homogeneous alkali catalysts employed (Demirbas, 2009a,b Helwani et al., 2009 Sharma et al., 2008). Many researchers have studied the use of these catalysts in transesterification reactions with oils of different FFAs content, ranging from 5 wt% to 15 wt%, as listed in Table 6.4. However, the use of 

Research Using Homogeneous Chemical Catalyzed Transesterification of Different Feedstocks for Biodiesel Production 

Feedstock Alcohol (°C) (AlcohohOil) Base Catalysts Time % Yield Reference 

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Phenol-formaldehyde (PF) resins were synthesized to manufacture non-flammable insulating foam. When alkali catalyst, for example, barium hydroxide (Ba(OH)2), was present, lesol resins are produced[l]. In the analj s of molecular species of resol, capillary GC-MS had been used to separate hemiformal-type compoimds(acetylated hydroxybenzylhaniformals)... 

To produce biodiesel, refined vegetable oils are reacted with methanol in the presence of alkali catalysts such as sodium hydroxide, potassium hydroxide, and sodium methylate. The overall base-catalyzed process has several problems that also... 

In the third step, the chemical structure is used to determine if the substance is compatible with materials which are common to the process unit, such as air, water, oxidizers and combustibles, acids, alkalies, catalysts, trace metals, and process utilities (see Section 2.2.4). Even if the substance is considered to be a non-explosion hazard (both nonenergetic and compatible with the... 

The cleavage of diacetone alcohol by alkali catalyst to form acetone was followed by a dilatometer (Akerlof, JACS 49 2955, 1927). Diacetone alcohol was 5% by volume, KOH in water was 2N and the temperature was 25°C. Find the rate equation. 

One example of a new class of compound in this area is dioctyl carbonate (1, Table 4.9). The product is synthesized by the trans-esterification reaction of octa-nol and dimethyl carbonate in the presence of alkali catalyst (Fig. 4.20). Dioctyl carbonate (Cetiol CC) is a dry emollient with excellent dermatological compatibility and a comprehensive and convincing performance profile for various appli-... 

Catalysts for low-temperature gasification include combinations of stable metals, such as rathenium or nickel bimetallics and stable supports, such as certain titania, zirconia, or carbon. Without catalyst the gasification is limited (Krase et al., 2000). Sodium carbonate is effective in increasing the gasification efficiency of cellulose (Minowa et al., 1997). Likewise, homogeneous, alkali catalysts have been employed for high-temperature supercritical water gasification. 

The partial synthesis of 4,5-dioxoaporphine has been achieved. Preparation of cepharadione B (43), 2,10-dimethoxy-4,5-dioxodehydroaporphine (84d), 4,5-dioxodehydronantenine (86d), and 4,5-dioxodehydrocrebanine (87d) was achieved in DMSO by air oxidation of the corresponding dehydroaporphines with an alkali catalyst as described above (Section V,A,1). Oxidation of nan-... 

In the saponification of an EVA copolymer, usually an alkali catalyst is used. The alkali catalyst acts as a catalyst for the transesterification between EVA and an alcohol. It is known that in a process where saponification proceeds mainly with this transesterification, when water is present in the reaction system, the alkali catalyst is consumed, and the reaction rate of the saponification decreases. 

This arises, because water accelerates the direct saponification reaction between the EVA and the alkali catalyst. Moreover, water also accelerates the reaction between an acetic acid ester formed as a byproduct in the transesterification and the alkali catalyst. 

The saponification is achieved by adding an alkali catalyst, such as sodium hydroxide, potassium hydroxide, or an alkali metal alco-holate. The saponification is carried out at 30-65°C for 1-6 h. The concentration of the copolymer solution is 10-50%, and the amount of the catalyst used is 0.02-1.0 equivalents with respect to the ester component (1). In presence of methanol, methyl acetate is formed as a by product. This can be removed by purging with nitrogen. 

The mechanism for the production of nylon-12 from the lactam is similar to that for nylon. However, in the case of nylon-12, the ring opening is more difficult and the rate of polymerization is slower, at least in part owing to the lower solubility of the lactam in water. A catalyst such as an acid, amino acid, or nylon salt can serve as a ring-opening agent. Nylon-12 can also be produced via anionic polymerization, ie, polymerization using an anhydrous alkali catalyst. This process can be quite fast even at low temperatures, eg, a few minutes at 130°C. 

Aerial oxidation of the dehydroaporphines (52)—(54) with alkali catalysts gives the corresponding oxoaporphines, 4,5-dioxoaporphines, and JV-methyl -aristolactams in low yields. The 4,5-dioxoaporphine (55) from the oxidation of (54) corresponds to 4,5-dioxodehydronantenine, which is found as a natural product in the dried fruits of Nandina domestica.34... 

Alkali metal alkoxides such as KOH, NaOH, and CH3ONa are the most effective catalysts in alkali-catalyst transesterification. When using KOH, NaOH, and CH3ONa alkali-catalyst for FAME conversion, the active catalytic species were the methoxide anion (CH 0 ), formed by the reaction between methanol and hydroxide ions of KOH and NaOH. In addition, the methoxide anion was formed by dissolution of sodium methoxide. Sodium methoxide causes the formation of several byproducts, mainly sodium salts, that have to be treated as waste and additionally require high-quality oil (16). However, KOH has an advantage because it can be converted into KOH by reaction with phosphoric acid, which can serve as a fertilizer. Since KOH is more economical than sodium methoxide, it is the preferred choice for large-scale FAME production process. 

Figure 4 compared the conversion yields of three different alkali catalysts at a molar ratio of 1 6, 60°C, and a reaction time of 20 min. All three alkali catalysts caused some difference in conversion yields. NaOH... 

For example, the traces of alkali dissolved from the glass of the container, catalyse the decomposition of hydrogen peroxide (H202). However, the addition of an acid would destroy the alkali catalyst and thus prevents decomposition. 

It can be assumed that two separate networks with no covalent bonds between the UPR and the cyanate-based triazine network are formed. The possible addition of terminal hydroxyls from the unsaturated polyester to the —C = N bonds in BPA/DC is rather improbable as the addition of alcohols to cyanates, leading to iminocarbonate derivatives (Scheme 8), only occurs in the presence of strong alkali catalysts [134], The cyanate cyclotrimerization has been evidenced from disappearance of the 2230 and 2270 cm-1 and the appearance of 1370 and 1560 cm-1 absorption bands in the infrared spectra of the crosslinked IPN. 

Hoechst and Henkel first attempted ethoxylation of these materials in 1989 with alkali/alkali earth and aluminium hydroxycarbonates respectively but these catalyst activities were too low for commercial application [24, 25]. Vista, in 1990, patented [26] the use of activated calcium and aluminium alkoxides and Lion Corporation, in 1994, filed a patent using magnesium oxide [27]. There was a flurry of activity in the 1990s and Michael Cox and his co-workers have written most of the literature [28-30]. The proprietary catalysts are more expensive than those for standard alcohol ethoxylates and generally have to be removed from the final product. They are more reactive than the standard alkali catalysts with the result that the reaction proceeds faster and at lower temperature and uses less catalyst. 

Miscellaneous Reactions. Sodium bisulfite adds to acetaldehyde to form a white crystalline addition compound, insoluble in ethyl alcohol and ether. This bisulfite addition compound is frequently used to isolate and purify acetaldehyde, which may be regenerated with dilute acid. Hydrocyanic acid adds to acetaldehyde in the presence of an alkali catalyst to form cyanohydrin the cyanohydrin may also be prepared from sodium cyanide and the bisulfite addition compound. Acrylonitrile [107-13-1] (qv) can be made from acetaldehyde and hydrocyanic acid by heating the cyanohydrin that is formed to 600—700°C (77). Alanine [302-72-7] can be prepared by the reaction of an ammonium salt and an alkali metal cyanide with acetaldehyde this is a general method for the preparation of a-amino acids called the Strecker amino acids synthesis. Giignard reagents add readily to acetaldehyde, the final product being a secondary alcohol. Thioacetaldehyde [2765-04-0] is formed by reaction of acetaldehyde with hydrogen sulfide thioacetaldehyde polymerizes readily to the trimer. 

It is known that low-molecular-weight esters of phosphorous acid react, in the presence of alkali catalysts, with formaldehyde to give the corresponding hydroxymethyl phosphonates. This reaction was used to synthesize cellulose hydroxymethylphosphonates (V). The structure of these compounds has been confirmed by hydrolysis to hydroxymethyl-phosphonic acid, which was identified by paper chromatography. 

The fate of other fatty acids and minor components during processing has not been investigated. The conditions used to conjugate linoleic acid have little or no effect on either monounsaturated or saturated fatty acids, however, any polyunsaturated fatty acids may be conjugated. The products of the reaction of alkali catalysts on these fatty acids are more complex than that discussed for linoleic acid (Reaction 4) and will not be discussed except to note that these reactions may produce undesirable products. 

As a result of the need for acid-resistant alloys and other equipment required for acid esterification, the process is typically more capital intensive than base trans-esterification. The higher capital costs associated with the use of acidic catalysts are usually offset by the ability of the process to accept lower cost feedstocks (1). Acidic catalysts may be used to recover soap byproducts of alkali-catalyst based tra i-esterification processes (3, 71). In these processes, acid is used to convert soap to free fatty acids and then to esters (see below). 

Many oil products are available that cannot be esterified directly using alkali catalysts as they have sufficient fatty acid content to neutralize an alkali catalyst, yet have high ester contents. An acid esterification step may be employed in advance of base catalyzed esterification. These pre-esterification methods need only provide sufficient acid and alcohol to esterify the fatty acids present (3, 68, 71), although... 

Mechanisms accompanying the alkali catalyst accumulation process... 

In another study on the same subject conducted by Jones et al. it was found that the extent of alkali vaporization with the subsequent improvement in catalyst stability can be decreased by addition of phosphoms compounds. It is speculated that the effect of phosphwus is related to the enhanced retention of the catalyst surface area. Kaminsky et al. reported that a i ysical mixture of the alkali catalysts with silica or alumina often helps to trap alkali vapors and consequently preserves catalyst activity. ... 

The NaOH in the mixture was thought to be formed by reaction between the alkali catalyst and traces of water. The higher alcohols (for example sec. and tert. butanol) were significantly more active than methanol in formate synthesis. It was proposed that the carbonylation reaction occurs by a two-stage mechanism in which an alcoholate ion reacts with CO to form a complex which, in turn, reacts with the alcohol to produce the formate and regenerate the ion. 

However, as the pressure is increased above about 10 to 15 atmospheres, especially when metallic oxide catalysts or metal-alkali catalysts are used, the product tends to become more and more oxygenated in character and exceedingly complex mixtures may be obtained. Such products, because of their complexity and difficulty of separation into components, are of little commercial value from the standpoint of being sources of valuable oxygenated organic compounds. 

The literature is not free from controversy on the subject of the iron-alkali catalysts, however. Audibert and Raineau claim that ferric oxide and not iron is the active catalyst for the formation of liquid products. It has been reported that iron oxide promoted with potassium hydroxide is not active as a catalyst toward this type of reaction.12 Whether these discrepancies are due to differences in methods and materials of catalyst preparation, differences in methods of operation, or in difference in gas mixtures it is difficult to say although it would seem probable that the trouble lies in the catalyst. 

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