(558a) Catalytic CO-Hydrogenation Co-Fed with Ammonia to Produce Fatty Amines and Nitriles

H.Karroum, V. Iablokov, N. Kruse

Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164

The global demand and market for fatty amines/nitriles is growing rapidly. Synthetic amines are extensively used in the chemical industry as solvents, agrochemicals, pharmaceuticals, detergents, polymers and fabric softeners. Industrially, amines are synthetized from nitriles, carboxylic acids, alkyl halides and carbonyl compounds. Amines can also be produced by the direct amination of alcohols. On the other hand, nitriles are produced by either ammoxidation or hydrocyanation using alkenes as target molecules. There are advantages and disadvantages (use of toxic reactants or formation of salt residues, for example) associated with these processes. In the present paper, we report on a “one-step one pot” synthesis of amines and nitriles using the Fischer Tropsch technology as a vehicle of hydrocarbon chain lengthening and ammonia as an agent to provide terminal nitrogen functionalization.

Catalysts used in the present study were Co-based (details will be communicated during the AIChE meeting once the patent application has been filed) and have been carefully characterized for their physico-chemical properties. They were activated “in-situ” in a high-pressure fixed-bed flow reactor and tested for their catalytic performance in terms of activity and selectivity (ex-CO₂, if not otherwise mentioned) after 12h time-on-stream using on-line GCMS. Catalysts were typically investigated to determine first their Fischer Tropsch chain lengthening properties in the absence of ammonia. H₂/CO ratios were varied at total pressures up to 20 bar and temperatures between 220 °C and 260 °C. At high H₂/CO ratios, mainly alkanes (91 %) and CO₂ (8 %) were formed, with no or little alkenes appearing in the product spectrum. Surprisingly, adding ammonia drastically increased the selectivity of alkenes to 37%, however, nitrogen-functionalized hydrocarbons were not detected at all under these conditions. The single-pass CO conversion (87%) in these experiments was only slightly decreased in the presence of NH₃. At moderate H₂/CO ratios (typical “methanation” conditions), CO hydrogenation led to the formation of alkanes (32%), alkenes (35 %) and alcohols (33%). Alcohols disappeared in the presence of ammonia and were replaced by fatty amines (both gaseous and liquid), the fraction of which attained 25%. The major amine product was found to be ethylamine. The CO conversion in these experiments dropped from 56% under pure Fischer Tropsch conditions to 31% in the presence of 15 vol% NH₃. At low H₂/CO ratios, the main compounds formed by CO hydrogenation were aldehydes (15%), alkenes (55%) and alkanes (23%). Aldehydes, disappeared quantitatively in the presence of 15 vol% ammonia in this case and were replaced by gaseous nitriles with a selectivity of 13%. Chain lengthened nitriles provided linear C₄₊ ASF characteristics with chain growth probabilities of about 0.5. Single-pass CO conversion decreased from 19% in the absence of NH₃ to 11% in the presence of NH₃. Remarkably, all experiments described above were completely reversible. i.e. the initial Fischer Tropsch catalytic performance, whatever H₂/CO ratio, was reproduced once ammonia was removed from the reactant feed.

All catalysts were characterized by XRD to demonstrate that cobalt carbide was formed even in the presence of ammonia. This conclusion was fully compatible with XPS results which clearly demonstrated the occurrence of carbidic carbon in the post-reaction C1s spectra. Present efforts are devoted to establishing mechanistic clues of the catalytic reaction networks using Chemical Transient Kinetics (CTK) in combination with Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS).