FINE CHEMICALS HYDROGENATION

Fine chemical hydrogenations are sometimes still carried out in G/s processes ... 

STRs in the most recent fine chemical hydrogenations [26]. The L/S slurry is circulated back at high flow in a loop connected to a Venturi. The local underpressure in the neck causes gas to be sucked in the intense turbulence achieves a very large interfacial area between tiny bubbles and the slurry. An external heat exchanger on the loop enables an almost unlimited heat removal, convenient for extremely high exothermic reactions, and isothermal operations. On the other hand, JLRs are restricted to a batch mode and can only accommodate catalysts compatible with the pump (low hard ness, low attrition). 

AMMONIA METHANOL FINE CHEMICALS HYDROGEN PEROXIDE... 

Jet-loop reactors tend to replace stirred-tank reactors in recently built equipment for fine-chemical hydrogenation. The external heat exchanger on the liquid circu-... 

Fine chemicals hydrogenation of quinones, sugars, lactones, substimted aromatic compoimds. 

Rhenium catalysts are exceptionally resistant to poisoning from nitrogen, sulfur, and phosphorus, and are used for hydrogenation of fine chemicals. 

The 30% reagent-grade hydrogen peroxide is purer than the industrial grades, is covered by ACS reagent specification, and is used as a laboratory reagent and in some specialty uses (see Fine chemicals). Several grades are also marketed for electronics use and thus have exceptionally low impurity levels. Some of these latter contain very Httie or no stabilizers (see Electronic materials). 

Kuusisto, J., Tokarev, A.V., Murzina, E.V., Roslund, M.U., Mikkola, J.-P., Murzin, D., and Salmi, T. (2007) From renewable raw materials to high-value added fine chemicals - catalytic hydrogenation and oxidation of D-lactose. Catal. Today, 121, 92-99. 

Hydrogenation reactions, particularly for the manufacture of fine chemicals, prevail in the research of three-phase processes. Examples are hydrogenation of citral (selectivity > 80% [86-88]) and 2-butyne-l,4-diol (conversion > 80% and selectivity > 97% [89]). Eor Pt/ACE the yield to n-sorbitol in hydrogenation of D-glucose exceeded 99.5% [90]. Water denitrification via hydrogenation of nitrites and nitrates was extensively studied using fiber-based catalysts [91-95]. An attempt to use fiber-structured catalysts for wet air oxidation of organics (4-nitrophenol as a model compound) in water was successful. TOC removal up to 90% was achieved [96]. 

In recent years research of possible utility in the production of fine chemicals has increased substantially and in part consequent to government policy. This work has been too variegated to summarize briefly. A flurry of work in the hydrogenation of CO also originated in government policy. It led to the elaboration of our imderstanding of these reactions, but it is not clear that it led to major developments. 

TA-NaBr-MRNi was prepared by the reported method [3]. RNi (W-1 type) was prepared from 1.9 g of Raney nickel alloy (Kawaken Fine Chemical Co., Ni/Al = 42/58). To wash out the excess base and aluminum salts, a sufficient amount of deionized water was used with ultrasonic irradiation. The modifying solution was prepared by dissolving of (R,R)-tartaric acid (1 g) and NaBr (6 g to 10 g) in 100 ml of water and adjusting the pH to 3.2 with IN NaOH aqueous solution. RNi was heated in the modifying solution at 100 C for 1 hour, washed with water (50 ml), methanol (50 ml, twice), and THF (10 ml). The TA-NaBr-MRNi obtained by this method was immediately used for the hydrogenation. 

Many companies spiecialize in the production of chemicals grouped in chemical trees characterized by the same chemical roots (compounds) or the same/similar method of manufacturing. Examples are the Lonza trees based upon (I) hydrogen cyanide, (2) ketene (H2C=C=0) and diketene (4-methyleneoxetan-2-one), and (3) nitrogen heterocycles. A different t3q)e of tree is that of DSM Chemie Linz, which branches out from ozonolysis as the core technology (Stinson, 1996). Wacker Chemie has developed its chemical tree leading to acetoacetates, other acylacetates, and 2-ketones (Stinson, 1997). Table 1.1 shows examples of fine chemicals. 

The. selective hydrogenation of a nitro group in the presence of other reactive functionalities is a frequently encountered problem in fine chemicals manufacture. Ciba-Geigy (Novartis). scientists developed, in collaboration with a catalyst manufacturer, a new Pt/Pb on CaCO. catalyst that allows the chemoselective hydrogenation of an aromatic nitro group in the presence of C=C, C=0, C=N as well as Cl or Br substituents in selectivities > 95% (even C C groups react very slowly) (Bader et al., 1996). Eqn. (3) shows an example (Bader eJ a/., 1996). 

Hydrogenation of cinnamaldehyde Pt-Co/C or Pt-Ru/C Cinnamyl alcohol Fine chemicals, perfumery... 

Hydrogenation of benzaldchyde Ni Benzyl alcohol Fine chemicals... 

Hydrogenation of w-nitroanisole Pd/C f -Anisidine Dyes, fine chemicals... 

Hydrogenation of a,p-unsaturated Raney Ni Saturated esters Fine chemicals. 

When hydrogenation is carried out in a continuous process often so-called trickle-ttow reactors are used. Mass-tran.sfer limitations often occur. An elegant improvement is the application of extrudates with a noncircular cross section, which increa.ses the external surface without increasing the pressure drop. Trilohe and Quadrilohe shapes are generally used in oil-refinery processes and they might also be useful in fine chemicals production. 

Activated carbons Hydrogenation in fine chemical industry... 

Section 4.2.2 gives speeific examples of PTC. It is expected that the combination of PTC with a transition-metal cocatalyst and hydrogen peroxide or molecular oxygen will probably gain importance in fine chemicals applications. 

Hydrogenations involving consecutive reactions are common in the organic process industry and even in the hydrogenation of fats. In the fine chemicals industry we have examples of acetylenic (triple) bonds to be selectively converted to olefinic (double) bonds. Lange et al. (1998) have shown, for the comversion of the model substance 2-hexyne into cis-2-hexene, how catalytically active microporous thin-film membranes can accomplish 100% selectivity. This unusual selectivity is attributed to avoidance of backmixing. 

Liquid-liquid reactions occur between two or more liquid phases whereby a system consisting of an organic and an aqueous phase is applied most frequently. Usually reaction takes place in one phase only. Phase-transfer catalysts are sometimes used to make transfer of a reactant to the reacting phase easier. Among typical liquid-liquid reactions utilized in fine chemicals manufacture are nitrations with mixtures of nitric and sulphuric acid, conventional hydroxylations performed with hydrogen peroxide, esterifications, alkylations, brominations, and iodinations. 

---