US2712519A - Process for evaporating and drying chlorinated hydrocarbons used in the dewaxing of mineral oils - Google Patents

Description

July 5, 1955 r A; HQPPE 2,712,519

PROCESS FOR EVAPORATING AND DRYING CHLORINATED HYDROCARBONS USED IN THE DEWAXING OF MINERAL OILS Filed NOV. 3, 1953 [F I: I m i la 3 i & I l w L l m l l \NVENTOR L AT TORNEYS- United States Patent ()1 PROCESS FOR EVAPQRATING AND DRYING CHLORINATED HYDRGCARBQNS USED IN THE DEVVAXENG CF MINERAL OILS Alfred Hoppe, Frankfurt am I /Iain, Germany, assignor to Edeleanu Gesellschaft m. b. 52., Frankfurt am Main, Germany, a body corporate of Germany Application November 3, 1%3, Serial No. 390,044

Claims. (Cl. 20239) amounts of water are continuously drawn in, and that the water originates mainly from the oil to be treated. This water accumulates and leads to disturbances in operation owing to the resulting corrosion. As the risk of corrosion by water exists even at low concentrations, it is very necessary to remove the water thoroughly.

Therefore, the solvent serving for dewaxing or a part of it has been dried continuously, after its recovery from the evaporation plant used for the dewaxed products, by passing it through a drying plant in which drying takes place chemically, for example, by means of calcium chloride. This method has several disadvantages, for example, the fact that chemicals foreign to the process must be introduced into the dewaxing plant, which chemicals are continuously consumed and therefore constitute an economic burden.

A considerable improvement is brought about by carrying out the drying by rectification of the solvent in direct association with the evaporation of the solvent in the groups of evaporators which involve working in a plurality of evaporators at progressively decreasing pressures. The vapours from the first filtrate evaporator pass into a rectifying column and are divided into an aqueous top fraction. After the condensation of the top fraction the greater part of the water separates as a separate layer, and

the practically anhydrous layer can be re-used as solvent.

In this procedure the two groups of evaporators for the filtrate and for the slack wax are, as usual, operated with decreasing pressure, that is to say, a succeeding evaporator is operated at a lower pressure than the preceding evaporator, so that the first evaporator has been at the highest pressure and also at a relatively high temperature.

This method, which is especially advantageous from the standpoint of economy, is able quite satisfactorily to maintain the water content of the circulating solvent at a low value, for example, of 0.03%, but it has the great disadvantage that corrosion is not avoided. it is known that chlorinated hydrocarbons, for example, dichlorethane and methylene chloride, are not stable in the presence of water at high temperatures. In the process described above there is therefore an increased risk of corrosion in the first evaporator owing to the high temperatures and high concentrations prevailing therein.

The present invention is based on the observation that the evaporation of the solvent from the products of dewaxing can be carried out without any risk of corrosion if the first filtrate evaporator, from which the greater Patented July 5, 1955 ice part of the water contained in the solvent escapes in the form of vapour, is operated at a temperature below 100 C., and advantageously within the range of C. to C.

It has also been found advantageous, in contra-distinction to the method hitherto used of working under decreasing pressure from one evaporator to the next, to operate the second filtrate evaporator at a higher temperature and therefore at a higher pressure than the first evaporator. It has been unexpectedly found that under the conditions prevailing in the first evaporator in accordance with the present invention so extensive a dehydration takes place therein that the higher temperature in the second evaporator entails no risk of corrosion. For example, even at a working temperature of 8090 C. in the first evaporator the dehydration of the solvent circulating therethrough maintains a constant water content in the solvent below 0.03%.

In accordance with the invention, therefore, the first filtrate evaporator, the vapours from which are separated in a rectifying column connected thereto, is operated at a temperature below C., and advantageously at 8090 C., and the secondevaporator connected thereto is operated under a higher pressure and at a higher temperature than the first evaporator.

The temperature in the second evaporator may be about C. without corrosion taking place, which temperature corresponds to a pressure of 2 atmospheres. The subsequent evaporator or evaporators are operated at progressively decreasing pressures in known manner. It is of advantage to connect to the second evaporator a further evaporator which is operated at the same pressure as the first evaporator, but at a tempearture somewhat higher than that in the second evaporator.

In the apparatus for carrying out the process of the invention it is of advantage to insert in the conduit between the first and second evaporators a pump for feeding the residue of the evaporation.

The top product from the rectifying attachment of the first filtrate evaporator is passed either by way of condenser, or advantageously by way of a heat exchanger for the incoming cold filtrate or slack wax, into a receiver and thence to the water separator.

A plant consisting of two groups of evaporators is shown diagrammatically in the accompanying drawing.

In the drawing one of these groups of evaporators consists of three evaporators and serves for evaporating the filtrate, which has been obtained by dewaxing a mineral oil with the use of dichlorethane or a mixture of dichlorethane and methylene chloride as solvent. A further group of evaporators consisting of two evaporators serves for evaporating the solvent from the crude parafiin wax, which has been obtained in the dewaxing process. The operation or" the plant is described below by Way of example in connection with a process in which the dewaxing has been carried out with a mixture of dichlorethane and methylene chloride.

The dewaxed oil-solvent mixture (filtrate) enters the dewaxing plant through a conduit 1. It passes through a preheater 2 and conduit 3 into a heater land evaporator 5, where it is partially evaporated. The residue from the evaporation is fed by way of conduits 6 and S by means of a pump 7 into a heater 9 and an evaporator 10. The heater 9 is heated with steam. Here the filtrate is brought to a higher temperature than in the heater 4 and the evaporator 10 is under a higher pressure than the evaporator 5. The filtrate passes through conduit 11 and a steam-heated heater 12 into the next evaporator 13 operating at the same pressure as the evaporator 5. The working temperature here is about 115 C. In order to ensure this temperature being attained an additional heater 14 is provided. A pump 16 withdraws "39 into a receiver for the circulating solvent.

3 the filtrate freed from solvent from the evaporator through conduit and feeds it through conduit 17 to a storage tank.

In the evaporator 5 there are evaporated from the oil-solvent mixture, which has been preheated in the preheater 2 and heater 4 to about 89 to 90 C., a part of the solvent, principally methylene chloride, and the greater partof the water. In the rectifying column 5a connected to the evaporator 5 the vapours are separated into an aqueous top fraction and a practically anhydrous bottom fraction, which flows through conduit The top fraction leaving the column 5a is passed by way of con- .duit 20 in part through conduit 21 into the preheater 2,

and in part by way of conduit 22 into a condenser 23.

The condensatesare passed through the corresponding conduits 24,25 and 26, 25 to the receiver 27.

In the case of mixtures of dichlorethane and methylene chloride the evaporation is carried out at atmospheric pressure. In order to produce the necessary pressure conditions when dichlorethane is used alone, the system consisting of the filtrate evaporator 5, condenser 23, receiver 27 and preheater 2 (outer side) .is maintained under reduced pressure. For this purpose there is used a vacuum pump 29, which Withdraws the vapours from the receiver 27 through conduit 28 and passes then through conduit 30 into a condenser 31. flows through the conduit 32 back to the receiver 27.

The solvent is pumped from the receiver 27 by a pump 34 into a water separator 36 by way of conduits 33 and 35. The water deposited therein is removed through conduit 37, and the moist solvent forming the lower layer is delivered by way of conduit 38 to the upper part of the column for the purpose of irrigation.

The vapours evaporated in the filtrate evaporator 10 are passed through conduit 40 into the heater 4 of the evaporator 5, and condensed, and the condensate passes by way of conduit 41 to the solvent receiver.

The last residues of solvent are evaporated in the third evaporator 13, the vapours pass through the conduit 42 together with the vapours under the same pressure as the evaporator 5 through conduits 21 or 22 to the receiver 27 The parafiin wax containing solvent from the dewaxing process is fed through the conduits 61 and 63 to the evaporator plant consisting essentially of the evaporators and 68. The wax is preheated in the preheater 62 and heater 64 of the evaporator 65. vapours obtained from the evaporator 65 contain, in addition to the solvent, water which has accumulated in the paraffin wax cakes. They also pass into the water separator 36 by way of the receiver 27. They pass into the receiver 27 partially by way of conduits and 71 and the preheater 62 and conduit 75. They also pass in part through conduits 72 and 73 into the condenser 23 and thence through conduit 24 into the receiver 27.

The practically anhydrous vapours which are dissolved in the second paraffin wax evaporator 68 after preheating in the heater 67, are fed by way of conduit 74 into the heater 4, where, in the same manner as the vapours from the filtrate evaporator 10, they serve for preheating the mixture of filtrates and solvent. The wax freed from solvent passes through conduit 69 into the storage tank.

The following example illustrates the invention:

A light spindle oil distillate was split up into a waxfree filtrate and oil-free wax by means of a mixture of dichlorethane and methylene chloride in a dewaxing plant of the kind described above having a daily output of 250 metric tons. The distillate contained 0.02% of water. This water had been taken up by the solvent and must be separated in order to avoid corrosion.

The dewaxedoil (filtrate) was freed from solvent in the plant consisting of three evaporators 5, 10 and 13. It was heated in the preheater 2 by the hot vapours from The condensate Theevaporator 2 and in the heater 4 by the vapours leaving the evaporator 19 at C. The liquid passed into the evaporator 5 at a temperature of 76 C., which evaporator was maintained under a pressure of 1.15 atmospheres (absolute). In this evaporator the greater part of the water present in the filtrate was driven off with the methylene chloride. The vapours passed into the rectifying column 5a connected to the top of the evaporator 5, and the vapours were irrigated in the column 5a with methylene chloride from the Water separator 36 (by way of conduit 38). The ascending vapours contained less water than they could take up to the aforesaid temperature and pressure conditions. Enrichment or saturation with water of the vapours leaving the column was brought about by the water-saturated methylene chloride introduced as a reflux.

The methylene chloride introduced as a reflux thereby gave up water, flowed to the bottom of the column and was there withdrawn having a residual content of water of 0.02D.O3%. It was returned to the cycle through conduit 39. V

The aqueous vapours leaving the top of the column 5a were condensed in the cooler 23 and in the preheater 2. The condensates passed through the receiver 27 into the separator 36, where two layers formed, an upper aqueous layer, and a lower methylene chloride layer. The water was removed through the conduit 37. The liquefied methylene chloride contained only such a proportion of water as corresponded to the solubility of water in methylene chloride at the temperature of the water separator 36. It was returned to the column 5a as reflux.

From the water separator 36 about 2 litres of water were removed per hour.

In the sump of the evaporator 5 the filtrate freed from the greater part of the methylene chloride and Water collected. It still contained 160 parts by volume of solvent. The filtrate was fed from the evaporator 5 (by way of conduits 6 and 8) by means of the pump 7 into the evaporator 11 being heated on its way in the steamheated heater 9. In the latter evaporator the greater part of the dichlorethane was evaporated at a temperature of 110 C. The higher temperature corresponded to a higher pressure of 2 atmospheres (absolute), which necessitated the interposition of a pump to convey the filtrate from the evaporator 5 to the evaporator 10.

The vapours leaving the evaporator 10 were used to heat the fresh filtrate in the heater 4 before introducing it into the evaporator 5. The filtrate oil-solvent mixture remaining in the evaporator 10 still contained 23% by.

volume of solvent. After being heated in the steamheated heater 12 it was passed into the evaporator 13, in which the residual content of solvent was removed, until only traces remained, at a pressure of 1.15 atmospheres (absolute) and a temperatureof C. The solventfree filtrate oil was drawn through the conduit 15 by the filtrate-discharge pump 16 and fed to the storage tank. In the following table the foregoing working conditions of the filtrate evaporator plant are summarised:

I claim:

1. A continuous process for recovering low boiling chlorinated hydrocarbons used as solvents in dewaxing mineral oils by evaporating the solvent from the filtrate and the wax obtained in the dewaxing process in a m.ulti-' stage evaporating plant and drying a part of the solvent 5 before recycling it, which process comprises operating the first filtrate evaporator at a temperature below 100 C., rectifying the solvent v.-.pours obtained in the first filtrate evaporator, causing the resulting top fraction containing water to separate by cooling into an aqueous layer and a solvent layer, removing the aqueous layer, feeding the residue from the first evaporator to a second evaporator operated at a higher temperature and higher pressure than the first evaporator, and evaporating the residue from the second evaporator in an evaporator or evapor tors at increasing temperature and decreasing pressure.

2. A continuous process as claimed in claim 1, wherein the solvent is dichlorethane.

3. A continuous process as claimed in claim 1, wherein the solvent is a mixture of dichlorethane and methylene chloride.

4. A continuous process for recovering low boiling chlorinated hydrocarbons used as solvents in dewaxing mineral oils by evaporating the solvent from the filtrate and the wax obtained in the dewaxing process in a multistage evaporating plant and drying a part of the solvent before recycling it, which process comprises evaporating the solvent from the filtrate in three stages of pressure, the first evaporator being operated at a temperature below 100 (3., the second at a higher temperature and higher pressure and the third at the same pressure as the first evaporator and at a temperature somewhat higher than the temperature in the second evaporator, rectifying the solvent vapours obtained in the first filtrate evaporator,

causing the resulting top fraction containing water to separate by cooling into an aqueous layer and a solvent layer, and removing the aqueous layer.

5. A continuous process for recovering a mixture of dichlorethane and methylene chloride used as solvents in dcwaxing mineral oils by evaporating said solvent from the filtrate and the Wax obtained in the dewaxing process in a multi-stage evaporating plant and drying a part of the solvent before recycling it, which process comprises evaporating the solvent from the filtrate in three stages of pressure, the first evaporator being operated at a temperature of 80 to 90 C., the second at about 115 C. and the third at the same pressure as the first evaporator and at a temperature somewhat higher than the temperature of the second evaporator, rectifying the solvent vapours obtained in the first filterate evaporator, causing the resulting top fraction containing water to separate by cooling into an aqueous layer and a solvent layer, and removing the aqueous layer.

References Cited in the file of this patent UNITED STATES PATENTS 2,049,059 Goss et a1 July 28, 1936 2,276,089 Ragatz Mar. 10, 1942 2,589,212 Agapetus et al. Mar. 18, 1952 2,593,931 Stearns Apr. 22, 1952 FOREIGN PATENTS 493,999 Great Britain Oct. 18, 1938

Claims (1)

1. A CONTINUOUS PROCESS FOR RECOVERING LOW BOILING CHLORINATED HYDROCARBONS USED AS SOLVENTS IN DEWAXING MINERAL OILS BY EVAPORATING THE SOLVENT FROM THE FILTRATE AND THE WAX OBTAINED IN THE DEWAXING PROCESS IN A MULTISTAGE EVAPORATING PLANT AND DRYING A PART OF THE SOLVENT BEFORE RECYCLING IT, WHICH PROCESS COMPRISES OPERATING THE FIRST FILTRATE EVAPORATOR AT A TEMPERATURE BELOW 100* C., RECTIFYING THE SOLVENT VAPOURS OBTAINED IN THE FIRST FILTRATE EVAPORATOR, CAUSING THE RESULTING TOP FRACTION CONTAINING WATER TO SEPARATE BY COOLING INTO AN AQUEOUS LAYER AND A SOLVENT LAYER, REMOVING THE AQUEOUS LAYER, FEEDING THE RESIDUE FROM THE FIRST EVAPORATOR TO A SECOND EVAPORATOR OPERATED AT A HIGHER TEMPERATURE AND HIGHER PRESSURE THAN THE FIRST EVAPORATOR, AND EVAPORATING THE RESIDUE FROM THE SECOND EVAPORATOR IN AN EVAPORATOR OR EVAPORATORS AT INCREASING TEMPERATURE AND DECREASING PRESSURE.

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