Process for the Recovery of Hydrochloric Acid

Abstract

Hydrochloric acid is recovered from a lignin composition in a process, comprising providing a particulate lignin composition that comprises lignin, water and hydrochloric acid; contacting the particulate lignin composition with a stream of stripping gas comprising an aprotic gas to obtain an acidified vapor stream that comprises water vapor, hydrochloric acid and aprotic gas; and recovering hydrochloric acid from the acidified vapor stream.

Claims

1. A method for the recovery of hydrochloric acid from a lignin composition, comprising: providing a particulate lignin composition that comprises lignin, water, and hydrochloric acid; contacting the particulate lignin composition with a stream of stripping gas comprising an aprotic gas to obtain an acidified vapor stream that comprises water vapor, hydrochloric acid, and aprotic gas; and recovering the hydrochloric acid from the acidified vapor stream.

2. A method according to claim 1, wherein the particulate lignin composition has been obtained from a hydrolysis of lignocellulosic material with hydrochloric acid.

3. A method according to claim 1, wherein the particulate lignin composition is contacted with the stream of stripping gas at a temperature in the range of 150 to 280 C., preferably in the range of 180 to 250 C.

4. A method according to claim 1, wherein the stream of stripping gas is at a temperature in the range of 20 to 150 C. before it is contacted with the particulate lignin composition.

5. A method according to claim 1, wherein the stream of stripping gas is contacted counter-currently with the particulate lignin composition.

6. A method according to claim 1, wherein the aprotic gas is selected from the group consisting of air, nitrogen, carbon monoxide, carbon dioxide, noble gases and combinations thereof.

7. A method according to claim 6, wherein the aprotic gas is a combustion gas.

8. A method according to claim 1, wherein the aprotic gas comprises an organic vapor.

9. A method according to claim 8, wherein the organic vapor comprises a hydrocarbon having from 1 to 12 carbon atoms, preferably 1 to 4 carbon atoms.

10. A method according to claim 1, wherein the acidified vapor stream is subjected to absorption or adsorption to recover the hydrochloric acid.

11. A method according to claim 10, wherein the acidified vapor stream is subjected to absorption with an aqueous absorbent, to yield acid-loaded absorbent.

12. A method according to claim 11, wherein the aqueous absorbent substantially consists of water.

13. A method according to claim 11, wherein the acid-loaded absorbent is subjected to one or more distillation steps to yield a hydrochloric acid-rich fraction with a higher acid concentration than the acid-loaded absorbent.

14. A method according to claim 13, wherein at least a portion of the hydrochloric acid-rich fraction, optionally after further acid concentration, is recycled to a hydrolysis of lignocellulosic material.

15. A method Process for the production of a lignin product, comprising: hydrolyzing a particulate lignocellulosic material with hydrochloric acid to obtain a dissolved saccharides-containing hydrolysate and a particulate lignin composition that comprises lignin, hydrochloric acid and water; contacting at least part of the particulate lignin composition with a stream of stripping gas that comprises an aprotic gas to obtain an acidified vapor stream that comprises water vapor, hydrochloric acid, aprotic gas, and a hydrochloric acid-lean lignin composition; and recovering the hydrochloric acid-lean lignin composition as lignin product.

16. A particulate lignin composition, comprising: lignin, hydrochloric acid and water, wherein content of the hydrochloric acid is in a range of 100 to 10,000 parts by weight per million (ppmw), based on the weight of the particulate lignin composition and content of the water is in a range of 0.1 to 2% weight, based on the weight of the particulate lignin composition.

Description

EXAMPLE

[0031] A series of vessels were loaded with a lignin composition that comprised about 49.5% wt of lignin, on a dry basis, and about 50.5% wt of a concentrated hydrochloric acid solution, containing 37% wt of hydrochloric acid. The hydrochloric acid content in the lignin composition was therefore 18.7% wt.

[0032] Nitrogen gas was passed as stream of stripping gas along the bed of the lignin composition at a flow rate of 87.3 or 174.5 Nm.sup.3/kg/h. The nitrogen gas was supplied at ambient temperature, i.e. about 20 C., and pre-heated to the drying temperature before being contacted with the lignin composition. The lignin compositions were heated to various temperatures. At different periods of supply of the stripping gas the hydrochloric content of the lignin product then obtained was determined.

[0033] The results are shown in the Table below. The Table indicates the temperature at which the lignin composition is contacted with the stripping gas (T), the flow rate of the stream of stripping gas (Flow), the time during which the lignin composition was contacted with the stripping gas (t), the total amount of stripping gas supplied per weight unit of lignin composition when the lignin product was removed for determination of the hydrochloric acid content (Gas) and the content of hydrochloric acid on the lignin product, expressed as hydrochloric acid on the lignin product (HCl.sub.prod).

TABLE-US-00001 TABLE Exp. No. T, C. t, hr Flow, Nm.sup.3/kg/h Gas, Nm.sup.3/kg HCl.sub.prod, % wt 1 170 1.30 174.5 3.78 1.08 2 170 2.30 174.5 6.69 0.88 3 170 3.67 174.5 10.67 0.71 4 170 6.10 174.5 17.74 0.59 5 200 0.17 87.3 0.36 0.73 6 200 0.43 87.3 0.95 0.50 7 200 0.67 87.3 1.45 0.45 8 200 1.83 87.3 4.00 0.39 9 200 6.00 87.3 17.09 0.36 10 200 0.25 174.5 1.09 0.69 11 200 0.62 174.5 2.69 0.55 12 200 0.80 174.5 3.49 0.47 13 200 1.25 174.5 5.45 0.34 14 220 0.17 174.5 0.72 0.46 15 220 0.43 174.5 1.89 0.38 16 220 0.80 174.5 3.49 0.35 17 220 1.00 174.5 4.36 0.26 18 220 1.25 174.5 5.45 0.26
The results show that hydrochloric acid can be efficiently removed from hydrochloric acid-containing lignin compositions. Especially at elevated temperatures and at flow rates above 100 Nm.sup.3/kg/h, the level of hydrochloric acid that remains in the lignin product can be reduced to a low value within a short period and thus with the use of a limited amount of stripping gas. That has the advantage that a smaller amount of stripping gas has to be subjected to e.g. absorption to recover the hydrochloric acid entrained.