Hydrochloric acid waste plastics

Hydrochloric acid Comhustion of coal or wastes containing chlorinated plastics Coal-fired boilers, incinerators Irritant to eyes and respiratory system... 

An account is given of the chemical recycling activities of BASF in a pilot plant at Ludwigshafen in Germany, where mixed plastics waste is processed to obtain hydrochloric acid, oil, gas, naphtha, aromatics and alpha-olefins. 

In the chemical industry chlorine is used for the production of various chemical compounds, such as hydrochloric acid, hypochlorites, chlorates, bleaching powder, aluminium chloride, corrosive sublimate, cupric chloride, carbon tetrachloride, tin recovery from used cans, sulphuryl chloride, for extraction of bromine from Stassfurt waste liquors, etc. In the organic chemical industry it is used for the chlorination of aliphatic and cyclic organic compounds, for the preparation of medicaments, the manufacture of plastics, insecticides, fungicides and herbicides. Monochloracetic acid, ethylene chlorhydrine, chloral, chlor-... 

Also, the impact on the environment in the pyrolysis of waste plastics must be taken into consideration. If a PVC material is contained in the reactant, the hydrochloric acid is evolved during decomposition of PVC which causes air pollution. Thus, a system is needed... 

First of all, the dechlorination of waste plastics is necessary. This is because chlorine (e.g. from PVC) in MWP causes contamination of all product streams with chlorinated organics, as well as corrosion problems. Dechlorination of MWP can be carried out in a twin screw at around 300°C, at which temperature other plastics do not start to degrade HCl gas envolved from degradation of PVC in MWP is recovered as a hydrochloric acid. Subsequently, the dechlorinated MWP in the melted form is liquefied using the above methods. 

As shown in Table 15.1, adding 1-2% of slaked lime enables the desired level of chlorine in recovered fuel to be achieved, thereby allowing the fuel to be suitable as a diesel fuel. However some chlorine still remains. There is always a small percentage of moisture existing in the waste plastic. It is later separated out and condensed as water. This water reacts with chlorine species in the fuel and produces hydrochloric acid. 

As mentioned above, the only wastes discharged from the plant are hydrochloric acid, pretreatment residue, and moisture contained in the waste plastics. Therefore, the recycling ratio is calculated as 99.0 wt% in the pyrolysis and distillation sections, and 91.1 wt% in the whole plant as shown in Table 26.13. The heat balance shown in the Table 26.15 indicates that the total heat recovery ratio is 72.6%. 

During the pyrolysis of mixed waste plastic, one of the main problems associated with the feedstock recycling is the presence of plastic containing hetroatoms, e.g. PVC, ABS, PVDC, etc. Efforts are made to remove the heteroatoms before pyrolysis. Chlorine can be removed either by thermal degradation or by using a catalyst. The HCl generated in the process can be used as industrial hydrochloric acid. 

For the pyrolysis of plastic waste with a high PVC content, it is probably better to first dehydrohalogenize it in a reactor with added sand. Tests have shown that hydrogen chloride gas can be produced from PVC at temperatures of between 350 and 400°C, which is up to 99 % pure and, after adsorption of the residual hydrocarbons, may be used to make very pure hydrochloric acid. After treating PVC for 20 minutes at a temperature of 350°C, more than 90 % of the bound chloride has split off. This time is reduced to less than 10 minutes if the temperature is increased to 400°C (13). ... 

Shioya, K. et al. (2005) Suppression of hydrochloric acid generated in recycling of waste plastics, (P 2005067196, (pn. Kokai Tokkyo Koho. 

PVC has a special position in the recycling of plastics [1]. As a result of the relatively weak bonding of chlorine to the polymer chain, the chlorine atom is split off at low temperatures of about 150 °C and hence complicates the material recycling of plastics wastes containing PVC. Corrosion, which could be initiated by the released chlorine or hydrochloric acid produced from it is less of a problem than the coal like polymer residue, which remains suspended in the machine or is distributed in the melt and further in the product. Many times it produces breakdown of the equipment and necessitates cleaning of the screw, barrel and dies. Therefore as a rule, PVC must be carefully removed from mixed plastic waste before most types of recycling - material or chemical. Because the significant difference between the density of PVC and that of other thermoplastics separation with one of the well known methods is possible. It is, however relatively expensive. 

In urban areas, chlorine emission originates mainly from the untreated smoke of household waste incineration plants burning plastic packaging, especially PVC-containing waste. In the atmosphere, chlorine in contact with moisture is transformed into hydrochloric acid. 

The waste containing hydrochloric acid was neutralized with saturated aqueous sodium hydrogen carbonate. Evaporated solvents and distillation waste were stored in a plastic container and treated at the chemical waste disposal facility of a university. 

Sugar cane waste is another raw material that can be treated in a hot solution of concentrated acetic acid in hydrochloric acid solution. After re-concentration, the lignin is then precipitated in warm water and finally recovered by dissolution in acetone. Due to all this complex chemistry, the major commercialised wood polymers are blends. These plastics contain wood powder, starch or lignin. The presence of lignin as a filler in other polymers improves the quahty of the biodegradation. Some of those products are reinforced with flax or hemp. 

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