Acetylene black process

Acetylene and mixtures of acetylene with light hydrocarbons are the raw materials for a process that has been used since the beginning of the 20th century. Unlike other hydrocarbons, the decomposition of acetylene is highly exothermic (AH = — 230 kJ/mol). 

The discontinuous explosion process is the oldest technical process. It was mainly used for the production of color blacks. Continuous processes were later developed with production rates up to 500 kg/h [4.20], Acetylene or acetylene-containing gases are fed into a preheated, cylindrical reactor with a ceramic inner liner. Once ignited, the reaction is maintained by the decomposition heat that is evolved. The carbon black is collected in settling chambers and cyclones. Approximately 95-99% of the theoretical yield is obtained. 

The primary particles of acetylene black have different shapes than those of other carbon blacks (Fig. 58). As the increased order in the c direction of the crystalline regions indicates, folded sheets of carbon layers are the main structural component. Their application is limited to special uses, e.g., in dry cells, because of their relatively high price. Total worldwide production is ca. 40 000 t/a. 

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The increasing demand led to new production processes. The most important process today is the furnace black process. It was developed in the United States in the 1930s and substantially improved after World War II. It is a continuous process, which allows the production of a variety of carbon black types under carefully controlled conditions. Nearly all rubber grades and a significant part of pigment-grade carbon blacks are now manufactured by the furnace black process. Nevertheless, other production processes, such as gas black, lamp black, thermal black, and acetylene black processes, are still used for the production of specialties. 

Carbon black is produced by the partial combustion or thermal decomposition of hydrocarbons. Several methods are used, including the furnace black, thermal black, lamp black and acetylene black processes. The furnace black process is the most common. In this process, natural gas (or another fuel) is burned to form a hot gas stream that is directed into a timnel. An aromatic oil is sprayed in and the black forms as the gas moves down the tunnel. The reaction is quenched with the addition of water, and the product is collected as a low density powder (fluffy black) or is further processed into millimeter sized peUets. 

Thermal decomposition Thermal black process Acetylene black process Natural gas or mineral oils Acetylene... 

Acetylene black process operates continuously by exothermic pyrolysis of acetylene... 

In the acetylene black process the tubular reactor only has to be heated once to 800°C by the combustion of an acetylene/air mixture. The pyrolysis reaction is then carried out with pure acetylene, which proceeds strongly... 

The thermal black and acetylene black processes are based on thermal decomposition in the absence of oxygen in a closed system. In the former two refractory-lined reactors operate in parallel at around 1300 "C. One is heated by burning a mixture of fuel... 

The acetylene black process relies on the exothermic decomposition of acetylene into carbon and hydrogen at elevated temperatures, the heat released sustaining the reaction. Acetylene blacks have average particles sizes in the 30-40 pm range, but the particle shape is more branched than the spherical shape of thermal blacks. 

In the acetylene black process, acetylene is burned with air depleted of oxygen. This gives pure carbon blacks, but of large particle size. 

The production process or the feedstock is sometimes reflected ia the name of the product such as lamp black, acetylene black, bone black, furnace black, or thermal black. The reason for the variety of processes used to produce carbon blacks is that there exists a unique link between the manufactuting process and the performance features of carbon black. 

A number of processes have been used to produce carbon black including the oil-furnace, impingement (channel), lampblack, and the thermal decomposition of natural gas and acetjiene (3). These processes produce different grades of carbon and are referred to by the process by which they are made, eg, oil-furnace black, lampblack, thermal black, acetylene black, and channel-type impingement black. A small amount of by-product carbon from the manufacture of synthesis gas from Hquid hydrocarbons has found appHcations in electrically conductive compositions. The different grades from the various processes have certain unique characteristics, but it is now possible to produce reasonable approximations of most of these grades by the od-fumace process. Since over 95% of the total output of carbon black is produced by the od-fumace process, this article emphasizes this process. 

Acetylene Black A process for making carbon black from acetylene by thermal decomposition at 800 to 1,000°C in refractory-lined, water-cooled retorts. 

Channel Black Also called Gas Black. One of the processes used to make carbon black the others are the Acetylene Black, Fumace Black, Thermal Black, and Thermatomic processes. In the Channel Black process, natural gas was incompletely burnt in small flames, which impinged on cooled channel irons that were continuously moved and scraped. Invented by L. J. McNutt in 1892 and commercialized that year in Gallagher, PA. The last United States plant was closed in 1976. 

Lampblack The original process for making carbon black by the incomplete combustion of oils. Superseded by the Acetylene Black, Channel Black, Fumace Black, and Thermal processes. 

The cathode mix is a compressed mixture of electrolytic Mn02 (EMD) and synthetic graphite or acetylene black to provide electronic conductivity, in a ratio of 4—5 1, wetted with electrolyte. The cathode current collector is generally the external steel can, which may be nickel-plated or coated with conductive carbon. Reduction of Mn02 in alkaline conditions is a complex process and follows a number of steps which can be written formally as... 

Acetylene black is derived from feeding acetylene into high-lempcralure retorts whereupon the acetylene dissociates into carbon and hydrogen. This reaction is exothermic (other carbon black processes arc endothermic). Temperature control of the furnace is effected by throttling the acetylene feed. 

Kornienko et al. [32] have utilized wetproofed electrodes of acetylene black containing 40 wt.% PTFE to reduce CFC 113 to CTFE in 3 M LiCl at 35°C. The presence of tetraalkylammonium cations considerably facilitates the reduction process. It is assumed that CFC 113, like other halogenated compounds, forms a positively charged complex with the tetraalkylammonium cation, which is much more easily reduced than the CFC 113 itself. The largest effect was found for tetra-M-butylammonium ion (TBA+), giving a 96% yield of CTFE. The increase in CTFE current yield is explained by the shift of potential to less cathodic values and to the displacement of water molecules by organic cations in the layer next to the electrode because hydrogen evolution is slower. 

In 1968 Mantell (28) described several processes for the production of carbon black. He also lists 24 distinct grades of blacks identified by their respective particle diameters (average), surface area and oil absorption (structure). These include the then common grades of channel black, gas furnace blacks, oil furnace blacks, thermal blacks, lampblack, and acetylene blacks, in language sufficient for the manufacturer to identify each grade by these three variables. 

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