Removal of metal impurities of phosphoric acid by the method of separating parts by parts with foam

Petroleum Engineering

Master's Thesis

Abstract

Phosphoric acid is the second most consumed mineral acid in the world and is used as a raw material in the production of detergents, food and pharmaceutical products. In this sense, the purification of phosphoric acid is one of the essential needs of consuming industries. 95% of acid consumed in industries that need pure phosphoric acid is produced by thermal method and only 5% is produced by dry method. The acid prepared by thermal method has high purity, but its production cost is very high. Considering the annual increase of 3.2 to 2.5% in the need for pure phosphoric acid, reducing its production cost is considered one of the daily needs of the industry. To purify the phosphoric acid produced in a more efficient way, the extraction method is usually performed to remove major impurities and to increase its purity, methods such as ultrafiltration, surface absorption, crystallization and ion exchange are used. These methods face disadvantages such as the difficulty of performing the process, the high cost of providing and maintaining equipment, the high cost of resin and the need to revive it. Also, the processes of ion exchange and surface adsorption are more suitable at low concentrations of efficiency.

In this project, in order to remove metal impurities from phosphoric acid, the method of component-by-component separation with foam is used, which is considered a new method to perform this process. It removes impurities from the feed and leaves a pure product. In addition to high efficiency, this method has advantages such as ease of carrying out the process, low operating cost and low energy consumption. Also, it is considered a green process due to the absence of chemical solvents.

The ability of this process to remove phosphoric acid impurities, the effect of inlet air speed, time, concentration and selectivity of surfactants to each metal were investigated using KEN10, SDS and SFD surfactants. Also, all the experiments were performed in semi-continuous mode.

For KEN10 surfactant, the optimal inlet air speed was equal to 0.043 cm/min and the optimal concentration was equal to 1.2 CMC (CMC=0.229 mg/cc). In these conditions, the total removal percentage of metals is equal to 31.19%, the enrichment ratio is equal to 1.95, and the percentage of lost phosphoric acid is equal to 9%.

For SDS surfactant, the optimal inlet air velocity is equal to 0.020 cm/min and the optimal concentration is equal to 2CMC (CMC=0.35 mg/cc). In this condition, the total removal percentage of metals is equal to 70.20%, the enrichment ratio is equal to 4.39% and the percentage of lost phosphoric acid is equal to 8.26%.   

For SFD surfactant, the optimal inlet air speed equal to 0.014 cm/min and the optimal concentration equal to CMC (CMC=2.33 mg/cc) were obtained. In this condition, the total removal percentage of metals is equal to 59.93%, the enrichment ratio is equal to 4.28, and the percentage of lost phosphoric acid is equal to 4.71%.  

Also, by performing two test steps, the total metal removal percentage for SDS surfactant was 95.31% and for SFD surfactant it was 91.09%.  

Key words: phosphoric acid, fractionation of foam, removal of metals, nonylphenol ethoxylate, sodium dodecyl sulfate, disodium laureth 3 sulfosuccinate

1-1. Phosphoric acid

The discovery of phosphorus by Brant [1] in 1669 caused its combustion product, phosphorus pentaoxide (P2O5), to be known soon. In 1694, Boyle[2] was able to obtain phosphoric acid by dissolving P2O5 in water for the first time, and in 1769 they succeeded in separating calcium phosphate, which is one of the main components of bone. About 30 years later, they realized the beneficial role of calcium phosphate in agriculture and increasing plant growth. Over time, the importance and uses of phosphoric acid became known [1].

Phosphorus, in the form of various phosphates, is one of the main components of the structure of living organisms, and the use of natural phosphate fertilizers such as human bones, fish and bird droppings in agriculture has a long history.The modern phosphate industry started in the middle of the 19th century with the production of phosphate fertilizers, at that time, the effect of sulfuric acid on bone or phosphate mineral sources was used to concentrate and provide more accessible phosphorus. In parallel with the expansion of the use of phosphate fertilizers, the methods of making elemental phosphorus and phosphoric acid also varied [1, 2].

Phosphoric acid, which is also known as orthophosphoric acid, is a mineral, transparent, colorless and odorless acid with the chemical formula H3PO4.

Phosphoric acid is a trivalent acid and one of the organic acids Acetic acid, citric acid and lactic acid are stronger and weaker than inorganic acids such as nitric acid, sulfuric acid and hydrochloric acid. This acid easily reacts with bases and produces alkaline phosphates and is relatively activated at high temperature and reacts with metals and metal oxides. Phosphoric acid is the most expensive mineral acid available in the market, and it is also in second place after sulfuric acid in terms of consumption volume. The most important use of phosphoric acid is to convert it into phosphate salts in the production of chemical fertilizers [4]. Phosphoric acid has many applications in the chemical and food industries, and the physical properties and purity requirements of the acid are different in each of these applications. Phosphoric acid exists in 4 commercial [1], food [2], pharmaceutical [3] and laboratory [4] purities, the composition of the allowed percentage of its ingredients is given in table (1-2).

1-1. Applications of phosphoric acid

The need to make very pure phosphoric acid has increased greatly in recent decades, because this substance is used as a raw material for the production of detergents, food products for humans and animals, chemical fertilizers, etc. is used Due to the presence of various impurities in the acid prepared by this method, about 95% of the acid produced by this method is directly used as a chemical fertilizer, and it is prevented from being used in cases other than chemical fertilizers. The acid used in the food industry and cleaning products must be of high purity. B

ABSTRACT

Phosphoric acid is the second most used acid after sulfuric acid. A high purity is required for phosphoric acid in the food and detergent applications.

95% of pure phosphoric acid is produced by so-called thermal process and only 5% is produced by the wet process. This is mainly because much less impurities are introduced in the thermal process. However, its production is retarded by correspondingly high costs. Moreover, requirements for purified phosphoric acid are increased by 2.3 to 2.5 percent annually. Therefore, serious efforts to reduce the manufacturing costs are necessary.

There are many techniques for purification of phosphoric acid produced by the wet process. The most common method is extraction. Further purification can be accomplished by methods such as ultrafiltration, adsorption, crystallization, and ion exchange.

The above mentioned techniques suffer from problems such as making secondary pollutions, high cost, low selectivity, high energy consumption, and ineffectiveness at low concentration.

In this research for removal of trace metal impurities from phosphoric acid produced by the wet process, foam fractionation method have been applied.

Foam fractionation is based on selective adsorption or attachment of materials on the surface of gas bubbles rising through a solution. It offers many advantages such as high yield, low space and energy requirement, simple plant design, scaling up, and low capital and operating costs. The technique is particularly attractive for treating dilute solutions.

The ability of the process for removing trace metal ions from the phosphoric acid were evaluated.