Showing posts with label process refractometer. Show all posts
Showing posts with label process refractometer. Show all posts

Process Refractometers for Water Treatment Chemical Concentration Monitoring

Process Refractometers for Water Treatment


Pure water treatment removes undesirable chemicals, biological contaminants, suspended solids, and gases from raw water. Water purification aims to produce water for a specific purpose, such as human consumption and medical or industrial use.

Polyaluminium coagulants are increasing use in potable water treatment plants, particularly for soft, colored surface waters. Polyaluminium chloride (PACl) is gradually replacing Alum (aluminum sulfate), a commonly used coagulant in water treatment plants. Alum coagulates at a limited pH range (between 5.5 and 6.5) and often requires alkali to the raw water to achieve the optimum coagulation pH. Furthermore, the alum floc produced is particularly fragile, which is vital if a coagulant is required to maximize color removal in a microfiltration-based water treatment process.

K-Patents Teflon Body Refractometer PR-23-M from Miller Energy, Inc.


Water treatment by chemical precipitation is a complex process. It starts with adding flocculants, specifically, Polyaluminium Chloride (PACl) and Sodium Hydroxide (NaOH). PACl is a synthetic polymer dissolved in water. It precipitates in big volumetric flocs, which absorb suspended pollutants in the raw water. The turbidity of the raw water defines Polyaluminium Chloride quantity. PACl concentration must be higher than 10 % To keep the flocculation process smooth. Polyaluminium Chloride is stable in the storage tank; however, it tends to crystallize after some time. Vaisala K-PATENTS® refractometer monitors the concentration of PACl to inform about the need for tank or pipe cleaning, thus preventing blockage caused by the PACl crystals.

NaOH regulates pH level, increases alkalinity, and neutralizes acids in the water. In alkaline water, the coagulation and flocculation processes work more effectively. Moreover, sufficient alkalinity prevents dissolving the lead from pipes and pipe fittings and reduces the corrosive effect of the water to iron pipes.

Further, particles suspended in water start to precipitate and agglomerate to form larger particles, known as flocs. The flocs are then settled at the bottom, forming sludge, and then removed from the process. After separating most of the floc, the remaining suspended particles and unsettled floc get filtered to remove water.

In the filtration phase, the water goes through the layers of anthracite, sand, and gravel. As a result, organic compounds contributing to taste and odor get removed. Other remaining particles get trapped by adhering to the sand and gravel particles.

After harmful micro-organisms get removed through filtering, it is necessary to add disinfecting chemicals to the water to inactivate any remaining pathogens and potentially harmful micro-organisms. One of the disinfecting chemicals used is Sodium Hypochlorite (NaOCl). When dissolved in water, this chemical releases chlorine, which is an efficient and safe disinfectant if added in a sufficient amount. Apart from sodium hypochlorite, liquid chlorine and chlorine dioxide are also choices as disinfectants.

Fluoride may also be added to the water to reduce tooth decay and prevent chronic diseases. However, fluoride in the water must not exceed recommended levels. Excessive levels of fluoride can be toxic or cause undesirable cosmetic effects such as staining of teeth.

Sodium Hypochlorite is unstable and quickly decomposes. The stability of NaOCl solution is dependent on the following factors:

  • Hypochlorite concentration
  • The temperature of the solution
  • PH value of the solution
  • The concentration of the impurities during catalyzing decomposition
  • Exposure to light

With the process refractometer, it is possible to monitor NaOCl concentration and control the disinfection conditions.

The water purification disinfection stage happens in the disinfectant basin. Then, corrosion control assures the high quality of the purified water. Finally, the pure water gets stored for further consumption.


Vaisala K-PATENTS® Teflon Body Refractometer PR-23-M provides in-line measurements of Polyaluminium Chloride and Sodium Hydroxide at the initial stage of purification, ensuring the efficient flocculation of undesired particles. In addition, through the measurement of Sodium Hypochlorite and Fluoride at the water disinfection stage, high-quality purified water at the outlet is assured.

Refractometer installations happen in three different points in a by-pass loop between each chemical tank pump outlet and the treatment point. The refractometer allows monitoring the chemicals concentration at the exit from the storage tank to the pipe treatment point.

Typical measurement ranges are:

  • PACl is ca. 10-11 %
  • NaOH is ca. 40-45 %
  • NaOCl is ca. 8-12 %

Miller Energy, Inc.

Refractometry in Oil Refining and the Petrochemical Industry: Sulfuric Acid Alkylation

Refractometers Used in Sulfuric Acid Alkylation

Typical end products

  • Alkylate (premium higher-octane gasoline blending stock for motor fuel and aviation gasoline).
Chemical curve: Sulfuric acid 88-100 R.I. per Conc wt.-% at Ref. Temp. of 20 ̊C

Refractometers Used in Sulfuric Acid Alkylation


Motor fuel alkylation using sulfuric acid (H2SO4) or liquid hydrofluoric acid (HF) is one of the oldest catalytic processes used in petroleum refining. The purpose of the alkylation is to improve motor and aviation gasoline properties (higher octane) with up to 90 % lower emissions compared to conventional fuel usage.

The problem with HF is that the catalyst forms a hazardous air pollutant when released as a superheated liquid, while H2SO4 does not. Therefore nearly 90 % of all alky units built since 1990 have adopted the H2SO4 technology. 

The leading alkylation unit licensor, with a 90 % share of the market, is DuPont (Stratco®). Another licensor is EMRE (Exxon Mobile Research Engineering, formerly K.W. Kellogg).


In the process, isobutane is alkylated with low molecular weight olefins (propylene, butylene and pentylene) in the presence of a strong acid catalyst to form alkylate (the premium higher-octane gasoline blending stock). The catalyst (sulfuric acid) allows the two-phase reaction to be carried out at moderate temperatures. The phases separate spontaneously, so the acid phase is vigorously mixed with the hydrocarbon phase to form higher molecular weight isoparaffinic compounds.

After the reactor, the mixture enters a separation vessel where the acid and hydrocarbon separate. The acid is then recycled back to the reactor.

Instrumentation and installation

Refractometers Used in Sulfuric Acid AlkylationThe K-Patents Process Refractometer PR-43-GP is installed after the settlers to continuously monitor in real-time the concentration of acid in the process.

The concentration of sulfuric acid is critical to achieve the complete consumption of isobutane. A highly variable concentration of isobutane in the feedstock upsets the sulfuric acid content in the process.

It is important to determine the proper quantity of acid that will be fed into the process. This is achieved by combining routine sample titration analysis with continuous acid monitoring by the K-Patents Process Refractometer. Real-time measurements reduce the need for sampling and laboratory analyses that cause delay in the implementation of any necessary adjustments to the acid flow.

Continuous monitoring removes the uncertainty involved between titration measurements. The K-Patents refractometer will indicate any gradual fluctuations in the acid flow, allowing precise control over efficient acid consumption and resulting in cost savings. It is also useful in preventing acid runaway, an unwanted situation commonly described as wild acid.

Acid runaway may happen when the acid strength drops below 85-87 % H2SO4. As a result, the reactions between olefins and isobutane turn into reactions of olefins only, producing polymers known as acid sludge, ASO or red oil.

The K-Patents refractometer is not affected by acid soluble oil (ASO). The refractometer indicates actual acid strength regardless of the amount of hydrocarbons present, which is essential when transferring acid emulsion. It is also an extremely useful tool in real-time process acid strength measurement during agitated conditions.

The initial acid concentration is typically 85-100 % and the temperature is 15 °C (59 °F). The benefits of the K-Patents refractometer’s continuous monitoring system include substantial cost savings due to reduced acid consumption, and smooth alkylate production without acid runaways.

The K-Patents Process Refractometer System for Alkylation Acid Measurement Consists of:

  1. The K-Patents Process Refractometer PR-43 for hazardous locations in Zone 2. or The K-Patents PR-43 Intrinsically Safe model for installations in hazardous locations up to Zone 0.
  2. Optional parts:
    1. Different flow cell options for easy sensor installation
    2. EXd enclosure for easy isolator and transmitter mounting
    3. Parts for a start up
    4. Spare parts supplied for two years of operation
    5. Start-up and commissioning service
  3. User specified tests and documentation.

Alloy C-276/ASTM C276 should be considered as wetted parts material when the acid piping flow velocity is at a maximum of 6 m/s (20 ft/s). Alloy 20 can be considered when acid piping flow velocity is at a maximum of 1.8 m/s (6 ft/s). However, it is the responsibility of the end-user to specify the appropriate material, ensuring that it is satisfactory for the intended operating requirements.

Non-sparking incentive (Ex nA) and intrinsic safety (Ex ia) approvals are available for hazardous area installations.

Always consult an applications expert with any process-critical instrumentation application. By doing so, you will ensure a successful, safe, and efficient deployment.

Miller Energy, Inc.

Reprinted with permission from K-Patents.

Industrial Refractometers Used in Process Control

Refractometer Pharmaceutical Use
Refractometer for pharmaceutical use (K-Patents).
Part physics, part material science and part chemistry, refractometry is the process which measures the composition of known substances by means of calculating their respective refractive indexes (RI). RIs are evaluated via a refractometer, a device which measures the curve, or refraction, resulting when the wavelength of light moves from the air into and through a tested substance. The unitless number given by the refractometer, usually between 1.3000 and 1.7000, is the RI. The composition of substances is then determined when the RI is compared to a standard curve specific to the material of the substance.

Process refractometers provide the analysis to quickly, reliably, and very accurately identify a sample and determine it's concentration and purity levels. They measure the refractive index and temperature of flowing liquids, and apply mathematical functions to determine the concentration of dissolved solids.

Common industrial refractometer applications are:
  • Calculating beverages’ amount of sugar dissolved is water.
  • In commercial food applications such as juice production or tomato processing, refractometers are used to measure degrees Brix (Tthe Brix scale relates refractive index to sugar concentration, and is a key way to maintain consistency).
  • In the pharmaceutical industry, process refractometers are used to monitor and control concentration levels during supersaturation, a critical process in crystallization.
  • In pulp and paper production, process refractometers for measuring dissolved solids in black and green liquor during the chemical recovery process.
Equipment manufacturers have developed numerous refractometer configurations tailored to specific each use and application. Each has a set of features making it the advantageous choice for its intended application. Product specialists can be invaluable sources of information and assistance to potential refractometer users seeking to match the best equipment to their application or process.

For more information on industrial refractometers, contact Miller Energy by visiting or by calling 908-755-6700 in New Jersey or 610-363-6200 in Pennsylvania.