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=Liquid carbon dioxide= Liquid carbon dioxide is a liquid state of carbon dioxide that is one of the most common substance in daily life.

General Properties
It is a type of liquid which is highly compressed and cooled from gas carbon dioxide. Under normal conditions, it does not form. It only exists when the pressure above 5.1 atm, under the temperature of critical point (31.1°C) and above the temperature of triple point (-56.6°C). The chemical symbol of it is same as carbon dioxide (CO₂). It is transparent and odorless and the density of it is 1101 kg/m³ when the liquid at saturation -37°C.

Introduction
The viscosity is a measure of a fluid substance that is the resistance of itself. It can be described as high viscosity or low viscosity. Before the study of viscosity of liquid, a scientist called van der Gulik has explained that how the viscosity of gas determines. He said that the increase of temperature can increase the viscosity of gas, but it is opposite to liquid. He also proposed the influence of the molecules exert on each other to viscosity. Another person called Brillouin also has mentioned that the concept of free path of molecules should be given up. After several ideas have been mentioned and proposed, the typical image of the viscosity of liquids is that the molecule is actively bouncing in a space that is formed by other molecules when the momentum is exchanged as collisions. Therefore, the viscosity coefficient is measured by the efficiency of exchange and by the number of collisions per unit of time and volume.

Method
The viscosity of liquid carbon dioxide is measured by using a vibrating-wire viscometer at temperatures of five levels 220K, 230K, 240K, 260K and 280K that are along isotherms between 217K (triple point temperature) and 304K (critical point temperature) over the complete liquid range. The accuracy of this measurement is estimated to 0.01. By using the vibrating-wire viscometer that including a wire, there is an alternating electrical current generates the Lorentz force and an electromagnet raises a magnetic field. After the electrical current stopping, an induction voltage is caused by the free damped oscillation of the wire when it has been in the magnetic field. The induction voltage has been enlarged, sampled and digitized and it is kept as a set of 2048 numbers on a computer disk and the data of this signal is a measure of the sample liquid for its viscosity.

Conclusion
After the common cleaning and filling process, the vessel should be pressurized at temperature firstly and then cooled down to the wanted temperature and depressurized to approximately 8 MPa. As a result, it has avoided the leakage of the liquid carbon dioxide sample and prevented the extra damping because the insufficient equilibrium. The next step is needed to satisfy the equilibrium. Under these circumstances, the first measurement is performed to determine the resonant frequency of the wire. The synthesizer delivers the electrical current that is adjusted to this frequency and measure it 5 to 7 times with various period of time. The resulting series of 2048 numbers needs to transfer following Fourier transformation. Hence, the width and the resonance frequency are determined by using the computed signal to match with Lorentz function. The resonant frequency is in a range of 765Hz at 280K,350MPa to 823Hz at 220K, 0.55MPa. The scientists have set 8 tables with various temperature to show the viscosity of liquid carbon dioxide.

How to Make It?
This is just a very simple way to make a few amounts of liquid carbon dioxide at home. The first step is that the purchasing of solid carbon dioxide (dry ice), which is available from some grocery stores or hardware stores. It is important that keeping a low temperature for dry ice by using certain cooler ice when taking it back home. Secondly, cutting dry ice into smaller pieces that may look like crushed ice by using a hammer. Next, using a pair of scissors to cut off the narrow portion of the tip that is end of a plastic pipette. Therefore, there is a big opening that can be used to collect some of the crushed dry ice. Then, the next step needs to crimp and close the opening of the plastic pipette with needle-nose pliers. After that, submerging the pipette in a clear container filled with warm tap ware by holding it with the pliers. With the dry ice starting melting, the plastic bulb (the closed large opening) will expand. When the pressure reaches to above 5.1 atm, liquid phase of carbon dioxide will appear. However, the bulb will crack quickly and the remaining will turn into gas and some will revert back to solid.

Carbon Capture and Storage
CCS is an important technology to help to reduce carbon dioxide emission. In this application, liquid carbon dioxide is the majority of the inventory.

Liquid carbon dioxide has no corrosion due to that there is no free water or impurities in it. The key point of CCS application is dissolving water in liquid carbon dioxide rather than dissolving carbon dioxide in water. The reason is that there is no loosely oxygen atom which will form oxides. Hence, the potential of corrosion does not exist. Besides, considering carefully the formation of hydrate when the application happens at low temperature as there may be corrosive potential of liquid carbon dioxide. The formation of hydrates depends on temperature, pressure, the gas pollution in carbon dioxides and the concentration of water. In CCS system, all of the water can be dissolved in liquid carbon dioxide at a range of 10°C to 25°C, but when the temperature is under an equilibrium temperature(4°C), it is possible that the corrosion will appear due to the hydrates has formed at some level of water content.

Extraction of Extra Virgin Olive Paste
Extra virgin olive oil (EVOO) is a type of olive oil that extracted from the fruit of Olea Europeae. To obtain the high quality of it, the application of compressed fluids has been experimented, like liquid carbon dioxide.

Firstly, the collecting of sample that is extracted from olive paste by liquid carbon dioxide. It is performed as two different ratios of solid-liquid, one is 1:5 and the another one is 1:10 and two different period for calculating the yield of olive oil, one is every 30 minutes and the another one is after 180 minutes. Therefore, there are three sets of experiments where the difference of ratio and time can be tested together. And the tests within every 30 minutes are called discontinuous process, another one within after 180 minutes is called continuous process.

After finishing each of the tests, the yield of olive oil extraction can be shown by using a diagram. It is clearly that the discontinuous process has extracted higher yield. The yield is 15.49% and 16.64% of the continuous extraction after 180 minutes, for 1:5 and 1:10, respectively. Compared with other classical physical applications, the advantages of extracting olive oil within liquid carbon dioxide includes the limit hydrolysis and oxidation reaction, the concentration of bisphenols is higher than classic methods, the presence of limonene and other aromatic compounds. The most important one is that there is no large amount of pollution requiring disposal due to the production of olive mill waste water. Hence, the liquid phase of liquid carbon dioxide.

Others
The other uses of liquid carbon dioxide include the preservation of food, fire extinguisher and softening drinks. For food preservation, the food industry is largely using liquid carbon dioxide to refrigerate, preserve, store and soften. For fire extinguisher, as the liquid carbon dioxide is anti-flammable. Besides, the use of liquid carbon dioxide also cools the burning surface to avoid further damage. For softening drinks, the liquid carbon dioxide is compressed by gas carbon dioxide under certain conditions. It has been largely used in the soft drinks production. What’s more, to remove caffeine from coffee, the liquid carbon oxide can also perform usefully as it is a flexible solvent.